Plant Health

Plectosporium – Not as Spooky As it Sounds!

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By Emily Leahy, UConn Plant Diagnostic Lab

White blister like spots on an orange pumpkin
Raised white lesions, indicative of Plectosporium blight, on a pumpkin. William Nesmith, University of Kentucky.

A chill in the air, football playing on the TV, and a certain kind of latte in your hand – there is only one season which encapsulates all three. Autumn is at our doorstep, bringing with it vibrant colors to paint the trees and an abundant harvest to use in all the season’s culinary endeavors. Many of the crops most representative of fall are cucurbits – the most relevant of which being various varieties of squash and pumpkins. Although the season is associated with comfort, danger lurks for these plants in the form of a fungal disease – Plectosporium blight.  

As the disease name suggests, the fungal pathogen Plectosporium tabacinum is responsible for its occurrence. Following a typical cycle of disease in infected hosts, fungal reproductive structures overwinter on crop residue. The pathogen even has the ability to dwell in soil for up to three years, much overstaying its welcome. As the growing season progresses, fungal spores will enter hosts through natural openings like cuticles and stomata. Plectosporium tabacinum prefers a cool and rainy environment, as windy and wet weather can assist in the spread of fungal spores and therefore the disease itself.  

White lesions on a pumpkin stem
Squash host exhibiting tissue desiccation in late stages of infection. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Plectosporium blight has a few key symptoms which are easy to spot. White or cream-colored patches of various sizes will be present on stem tissue and can also spread to leaf petioles – the stalk which connects the leaf to its stem or branch. In severe cases of infection with Plectosporium tabacinum, hosts can become entirely defoliated as these lesions deplete petioles of their strength. Raised circular lesions in colors including white, tan, and gray, will appear on the body of the fruit and possibly leaves. As the disease progresses, infected tissue will become increasingly brittle and dry, forming tan abrasions that detract from the plant’s vigor.  

Up close image of white spots
Symptom of Plectosporium tabacinum – white pathces on a squash stem. Virginia Tech Learning Resources Center , Virginia Polytechnic Institute and State University, Bugwood.org

Fear not – all hope is not lost for the unofficial mascots of autumn. There are management strategies readily available to deter Plectosporium tabacinum. Due to the pathogen’s ability to dwell in plant residue and soil for long periods of time, crop rotations are beneficial to position potential hosts away from areas where the disease was observed in the past. In addition, assuring that plants have ample space between each other and therefore promoting air circulation. This leaves fungal pathogens without a suitable place to dwell, reducing infection of plants in the area. Control can also be achieved by fungicides, including Chlorothalonil and strobilurin based compounds. Always read the label in full before using any chemical product on your plants. 

The number of management strategies available for Plectosporium blight is a comforting indicator that this disease is easily controlled. As you are outside admiring the fall foliage and enjoying a reprieve from the harsh heat of summer, peruse your fall cucurbit harvest for the aforementioned symptoms. Stay curious and enjoy the dynamics of the season – it'll slip away in the blink of an eye!  

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations. 

This article was published in the Hartford Courant September 13, 2025

Extreme Sports for Plants: Temperature Tolerance

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By Dr. Matthew Lisy, UConn Adjunct Faculty

Spathiphyllum wallisii in a pot wilting indoors

This Spathiphyllum wallisii is forty years old. In the fall of 2024, it wilted due to an extreme negative temperature change. (photo by M. Lisy)

Spathiphyllum wallisii outside, lush and healthy

This is the same Spathiphyllum wallisii showing a lot of new growth during the warm, humid summer of 2025. (photo by M. Lisy)

Plants, like humans, have an ideal temperature preference.  In general, we like to have temperatures between 60 to 80 degrees Fahrenheit.  Temperatures outside this range cause us stress.  Our plants have very similar temperature requirements, only they have no ability to shiver or move!  This past winter, I had a 40-year-old houseplant near my bedroom window.  Our fall weather hit, and we dropped about 30 degrees in a day.  My plant wilted and looked like it was going to die.  After a long process of investigation and discussions with my fellow plant professionals, I can only conclude it was the rapid temperature change.  The good news is that it made a full recovery once it adapted to the cooler weather.

This past winter, I had some Sansevieria that were under my windowsill.  They get beautiful light in the later part of the day.  The house is heated to 55 degrees, which is above their lower temperature tolerance, but the plants were not looking good.  This spring, I found out that the storm window had fallen out of place.  This set up a cold draft that negatively affected the plants, causing some formerly unexplained rot over the winter.

Not all plants have the same susceptibility to temperature.  Cacti and succulents are usually from hot, arid climates.  These plants are used to seeing temperatures soaring in the day, and then getting comparatively cold at night.  As long as they are given proper light, most of these plants can tolerate life very easily in our homes.  Even cold, unheated basements or outdoor greenhouses are just fine as long as temperatures stay above freezing.

Many of our plants come from the tropical forest floor where they are used to similar temperatures during the day and the night, all year long.  While there is some adaptation to life in our homes, they have a preferred temperature and humidity range.  There are some really neat “new” Philodendron species being offered for sale.  Many of them have minimum temperatures of 60 or even 65.  This can be difficult to do in an era where our smart thermostats are programed to turn down while we are not home, and up when we return in the evening.  These temperature swings may be intolerable to our plants.

Be careful watering plants when the sun is shining.  Those little water droplets can end up capturing the sun’s rays just like a greenhouse would.  The droplets heat up and can actually burn a spot in the plant leaf.  Remember, each drop can do this, so many times, the whole plant can look like a spotted mess!

Temperature can many times mark the difference between success and failure to keep some of the more difficult species of houseplants.  Changes should be done slowly to avoid stress.  If houseplants are kept outside in the summer, waiting too long can see the loss of some plants with lower temperature tolerances.  Placing plants closer to the house or inside a simple greenhouse can help during the first cool nights of early fall.  Especially sensitive plants should be brought in before any threat of cool weather.  I learned this lesson the hard way with my prized Philodendron squamiferum.  Its ideal temperature range is 65-85 degrees Fahrenheit.  I had it in the basement and was planning on moving it to the first floor, but left it down there as the light was nice.  While this plant technically can tolerate temperatures in the 50s for a short duration, it got too cold for too long and it dropped all its leaves one night (it died).  As a general rule of thumb, if it is too cold for people, it will be too cold for our houseplants!

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations.

This article was published in the Hartford Courant August 2, 2025

Put an End to Blossom-End Rot: Water and Nutrient Management is Key

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By Nora Doonan, UConn Soil Science Graduate Student, Department of Plant Science & Landscape Architecture

5 ripe tomatoes
Photo by Julie-Ann Adorno, Soil Science Graduate Student, UConn Plant Science & Landscape Architecture

It can be frustrating to put time and energy into growing tomatoes, only to find that your tomatoes have developed blossom-end rot. Blossom-end rot is a physiological disorder that commonly affects tomato plants, characterized by a black, sunken spot on the fruit. This disorder is caused by insufficient calcium as a result of nutrient and water management challenges. Blossom-end rot can also affect peppers, eggplants, squash, and watermelons. In tomatoes, it is commonly seen on larger and elongated varieties, which can have a greater demand for calcium. Calcium is an essential plant nutrient that is required for proper growth, especially for the development of cell walls in the tomato fruit. When a fruiting tomato plant experiences calcium deficiency, the cell wall can collapse and show the appearance of blossom-end rot. Soil tests can reveal if your soil has sufficient levels of calcium and can determine if your soil pH is optimal for nutrient availability.  

Oftentimes, the soil is sufficient in calcium levels, but blossom-end rot still occurs. Blossom-end rot can be closely associated with soil moisture that is too wet or too dry. The soil should never dry out completely. It is important to water regularly to ensure that plants receive 1 to 2 inches of water a week. A cycle of dryness followed by overwatering is only promoting calcium deficiency in the plant. If soil is too saturated, there may be insufficient oxygen levels in the soil that can affect the roots’ ability to take up water and nutrients.  

One method of maintaining optimal soil moisture is to mulch tomato plants with an organic mulch, such as wood chips or straw, after the soil has warmed up. This will help to prevent excessive evaporation and drying of the soil. Another method is to plant tomatoes in a mound of soil that is high in organic matter or compost. Organic matter can retain soil moisture and provide adequate drainage.  

There are other factors that can affect calcium uptake by the plant, such as high concentrations of ammonium, potassium, and magnesium in the soil. This can be caused by over fertilization. Specifically, over fertilizing with nitrogen can promote excessive production of leaves in the tomato plant, which can preferentially distribute calcium to the leaves rather than the fruit.  

Calcium movement in the plant is dependent on transpiration, which is the loss of water to the atmosphere from plant leaves, stems, and flowers. Calcium is taken up through the roots and relies on water flow through the xylem for transport through the plant. This movement of water through the xylem is driven by the process of transpiration. Calcium is not redistributed from the leaves to the fruit. In addition, the overfertilization of ammonium, potassium, and magnesium can allow for competition in root uptake of calcium because they are all positive cations. Damages to roots, caused by fertilizer burns or cultivation, can also be a factor in impairing nutrient and water uptake. To prevent blossom-end rot through fertilization practices, apply fertilizer as recommended by a soil test and apply nitrogen fertilizers in the form of nitrate, rather than ammonium.   

Any affected fruits can be removed from the plant, as they will continue to drain moisture and calcium for development from other fruits. A foliar application of calcium can be made to the leaves when the fruit is young, but it is not the most effective method, since calcium in the leaves is relatively immobile. The goal is to prevent the need for foliar application through water and nutrient management across the tomato plant growth stages. Hopefully these methods will allow you to prevent blossom-end rot starting at beginning stages of growth, so that you can enjoy a bounty of beautiful, red tomatoes.  

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations. 

This article was published in the Hartford Courant June 14, 2025

Put in the Work Now for Lasting Garden Beauty 

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By Heather Zidack, UConn Home & Garden Education Center 

If you’re planning to do some landscape renovations this summer, you will often hear the suggestion of doing certain tasks “until the plant is established.” If you’ve heard this phrase and wondered what the pros mean, you’re not alone. It’s crucial to understand that the first year of growth is one of the most critical to ensure the success of trees, shrubs and perennials in the landscape.  

The “establishment period” is when a newly transplanted plant pushes roots beyond the original root ball to anchor itself into the surrounding soil and adapt to its new environment. Establishment happens in as little as 2-4 weeks for your veggie starts and other annuals. However, if you are installing woody ornamentals or perennials, it is recommended to provide support for their first year in the landscape. Some species, especially fruiting plants may need longer attention to ensure establishment and landscape success. 

Keeping the plants properly hydrated is going to be your first line of defense in preventing transplant shock. Using sprinkler systems for supplemental water can be problematic for trees, shrubs and perennials. These systems, especially those designed for lawns, maintain moisture in the top 1-2 inches of soil. Our non-turf plants need much more.  Providing adequate water will help new plants acclimate by providing sufficient hydration, but it will also encourage the root system to expand. Roots pull moisture and nutrients from the soil but also act as an anchor to keep the plants upright. Keeping only the top few inches of soil moist will encourage roots to stay in that shallow layer instead of expanding deeper into the soil, hindering the development of that anchoring system. Additionally, watering demand tends to be more frequent with shallow root systems, as the first few inches of soil are more susceptible to drying out on sunny days. Lastly, the shallow roots need to compete with established turf for resources at a 1-2-inch depth. 

While in this establishment period, the standard watering recommendation is 1-2 inches per week, depending on the species of plant. An inch of water is equivalent to 0.62 gallons per square foot of garden area. Watering the plant at this rate encourages it to stretch its roots downward into the soil.  With deeper roots, plants can find moisture even during times of temporary drought deep below ground. This is a huge contribution to drought tolerance, as opposed to the common belief that the plant will just “live longer without water.”  

If the forecast does not predict an inch of rain within the week, gardeners should be out checking the soil for moisture a few inches down and providing supplemental water if necessary. Always check the soil before watering, especially if you are new to gardening. Squeeze the soil in your hand. If the soil particles stick together easily, it is likely that there is enough moisture. If soil clumps fall apart between your fingers or the texture is dusty, the soil is too dry and more water is needed. If you can squeeze water out of the soil like a sponge, there is too much moisture, and you should come back and check in a day or two. Overwatering can lead to root rot and other diseases and finding the balance is a fine-tuned skill developed over time.  

Monitor your new plantings for the first year and watch for signs of transplant shock, pests and disease so that you can adjust quickly and keep your plants healthy during this time. While transplant shock is a normal response to being planted in a new location, the symptoms can be startling to gardeners.  Remember that the UConn Home & Garden Education Center is here to help you determine if you are looking at transplant shock, disease, or possible pest damage. It’s easier to catch and treat issues earlier than it is to react at the end of the season. If you’re vigilant, we can help you find your way to solutions much more quickly! 

Staking should only be done as a temporary measure for young trees where the environment or the species of tree requires extra support. In most cases, trees should be perfectly capable of supporting themselves. Exposure to the elements, like the occasional strong breeze, can help to strengthen them as they adjust. However, temporary staking can help take some of the stress off the young trees if they are establishing in harsher environments. While there are many situations that may be appropriate, consider staking newly planted trees when they are in open areas, have high wind exposure, or are in an area that risks mechanical or physical damage. Staking may also be appropriate if the root ball is significantly smaller in relation to the tree’s size, or if the tree has a top-heavy canopy. 

Once your plants are well anchored into your landscape, they will be able to find water and nutrients on their own while standing tall in the face of our New England climate. Putting in the attention and care to help plants establish in their first year or two in the landscape will reward you with many years of enjoyment to come.  

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations. 

 

 

This article was published in the Hartford Courant June 7, 2025

Spring Showers Bring Flooded Gardens

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By Amelia Martin, UConn Plant Science Graduate Student 

Rain gauge showing half an inch of rain on a cloudy day
Photo by H. Zidack, UConn HGEC

You may have noticed the heavy rains and chilly temperatures last week’s nor ’easter brought to Connecticut. Maybe you were one of many who checked their back window to see their gardens had flooded and their plants are looking worse for the wear. If this sounds familiar and you are curious what garden flooding means for your plants and want to know how to protect them- you found the right article! 

A flooded garden is not a unique problem, especially during periods of heavy rainfall, but there are some factors that may contribute to the severity of flooding. Having minimal or poor drainage can amplify the problem, especially if planting in garden boxes with closed bottoms. Soil compaction can contribute to flooding if you are planting directly in the ground. Compacted soil can happen if there has been too much tillage, if wheels or machinery have been over the area, or even from excess foot traffic. Lastly, the layout and landscaping of a yard can contribute to flooding as well. If you placed your garden at the bottom of a hill or there are minimal drainage angles surrounding your garden, water may be pooling up faster than it can drain.  

To prevent flooding, check your gutters and make sure they are free from debris and directed to a drain or storm barrel. Put down gravel and mulch to help prevent surface flooding. Avoid cutting your grass too short to maintain strong roots which help to absorb water. Maintain healthy soil to allow for the best water absorption. Dig out a shallow drainage channel if you have the space for it. Consider switching to raised beds with drainage rather than in-ground gardens in easily flooded areas. Try adding native plants to your garden. Native plants have deep roots which helps them absorb excess water and prevent runoff. While handling these issues would be preventative measures, let’s talk about what to do if your garden has already flooded.  

Assess the drainage situation and take note of where the water is pooling the most. If flooding is unusual in your garden- there may be something blocking the normal drainage route, which may be a quick fix. If not, knowing where water is likely to pool may help in future garden planning, or help you determine where to make improvements.  

Stay off your garden beds.  If you step on your soil while it is saturated, it will compact it, ruining the soil’s tilth. Instead, if you need to access your garden beds consider putting a wooden board down to walk on to distribute your weight better. 

Re-fertilize your plants. Heavy rain can wash away nutrients out of the soil through a process called leaching. Check the forecast to make sure no more extreme weather is immediately approaching before fertilizing- or you may have to do it again. 

Add supports to your plants. The wind and rain may have led to plants falling over. Add in some additional supports to get them upright again and give them a better chance for the next time heavy rain comes.  

While having a flooded garden may be a bummer, there are some gardening activities that are actually easier to do in saturated soil! Once the rain stops and the ground is still wet, use this time to weed. The soft ground will make weeds especially easy to pull up- just try not to step on the garden beds. After a rain or a flood, re-mulching is always a good idea. The rain might wash away some previously placed mulch, use this as an opportunity to locate any spots barren of mulch and in need of a re-fill. After a couple days when the soil is soft but not sodden, the ground will be the perfect consistency to dig and put stakes.  

Lastly, check for any young plants that didn’t survive the water or any seeds that haven’t come up. Take this as an opportunity to plant new seeds, as seeds do better in already moist soil where they have less chance of being displaced when watered.  

At the end of the day, while having a flooded garden may not be the best for your plants, it is not the end of the world. There are a handful of preventative measures that can be taken ranging from backyard renovations to quick fixes- it is about finding what works best for you and your garden.  

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations. 

This article was published in the Hartford Courant May 31, 2025

Spring Landscape and Garden Issues in 2025

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By Pamm Cooper, UConn Home & Garden Education Center This spring has been a dramatic one as ornamental trees and shrubs are putting on quite a colorful floral display. Many deciduous ornamentals including redbuds, forsythia, crabapples, fruit trees, quince azaleas and many others were not adversely affected by last summer’s drought and the cold, windy winter and frozen soils that followed. A lesser noticed but significant drama is the negative effect these same environmental conditions had on ornamental and native evergreens. 

Rhododendrons and ‘Green Giant’ arborvitae seemed to suffer the most damage followed by cherry laurels and hollies. Last year’s drought conditions that extended into late fall combined with very windy winter conditions and frozen soils were tough for some evergreens. Winter desiccation injury on broadleaved and needled evergreens causes foliage browning when plants cannot take up the water needed to keep foliage healthy. Damage to many rhododendrons and some azaleas could be seen during the winter and is still evident this spring. Buds may provide new leaves by June if branches are still alive.  

In contrast, 'Green Giant’ arborvitaes suddenly showed symptoms after warm weather began this spring. This was evident especially in trees on windy sites. Needles are brown or off color and time will tell if they are able to recover. If branch tips are flexible and show new buds, growth may resume. Prune any dead branches that show no signs of recovery. 

Large tent like structures with little caterpillars inside them in the crotch of a tree branch.
Eastern Tent Caterpillars in a Black Cherry Tree. Photo by Pamm Cooper

Eastern tent caterpillars have hatched from overwintering egg masses on native black cherries. Silken nests are evident located in crotches of these trees. Caterpillars feed outside the tents at night and hide in them during the day. There is only one generation, and feeding is generally finished by late June. Trees have time to leaf out again to remain healthy during the growing season. Birds like cuckoos and vireos will rip tents apart to feed on the caterpillars. 

If you have Oriental lilies, be alert for the lily leaf beetle. This bright red insect can severely defoliate these lilies. Adults overwinter in soil close to the plants they were feeding on the previous season. They appear as soon as lilies begin new growth above the ground. Leaf undersides should be checked for eggs and larvae and crushed when found. Leaves can be treated if needed with a product that larvae will ingest as they feed on the treated leaves. Never spray flowers with any insect control product and always follow directions as written on the product label. 

Snowball aphid feeding damage is noticeable on the new leaves of European cranberry bush and snowball viburnums. As the aphids feed on the new leaves and twigs, leaves curl and twigs twist in response to aphid feeding on the sap. Aphids can be found by uncurling the leaves. Treatment is difficult as they are not out in the open where contact control products can reach them. Feeding should end within two months of egg hatch. These aphids overwinter as eggs laid on the branches of host viburnums. 

Viburnum leaf beetles, Pyrrhalta viburni, are another significant pest of ornamental and native viburnums. They’re active soon after viburnums leaf out. Damage will be seen as larval populations grow and they skeletonize leaves. Some viburnums may suffer complete defoliation. This pest prefers arrowwood, European cranberry bush or American cranberry bush viburnums. Try switching to resistant varieties such as V. plicatum and Korean spicebush viburnum V. calesii if leaf beetles are a chronic pest. 

If anyone has small St John’s wort shrubs or certain weigela cultivars that seem to be dead, wait and see if new growth resumes as it gets warmer and sunnier. The smaller St. Johns’ wort shrubs die back in fall, leaving brown stems with withered fruit. Prune these back almost to the ground as basal growth appears. Some weigela cultivars are just slowly getting started, while others are already full of leaves. Do not give up these plants but wait and see what happens in May. 

As always, our UConn Home and Garden Education Center office staff welcomes any questions gardeners may have concerning landscape and garden plants problems. Across the New England region, people are having much the same problems as we are having in Connecticut from the winter weather, but we can hope that plant recovery be swift and complete. Enjoy the growing season and stay alert- scout for pests and other problems before they get out of hand.  

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations. 

 

 

This article was published in the Hartford Courant May 10, 2025

A Gardener’s Guide to Planting by Hardiness Zones

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By Marie Woodward, UConn Home & Garden Education Center

Map of Connecticut USDA Hardiness zones as of 2023. Most zones in the state are either zone 6 or zone 7.
USDA Hardiness Zone Map for Connecticut, 2023

If you are wondering whether that shrub, flower, or tree that you saw in a magazine or catalog will grow well in your garden, using a hardiness zone map is your best bet to ensure success.   

A hardiness zone map is a tool that divides a geographical area into distinct zones based on average annual minimum winter temperatures. These maps are used by gardeners and farmers around the world to determine which plants are most likely to thrive in a particular region. Each country has its own hardiness map that correlates to their climate. In the United States, the USDA publishes a hardiness zone map, which covers all fifty states and includes Puerto Rico, Guam, American Samoa, and the U.S. Virgin Islands. It uses climate data collected over many years from weather stations throughout a specific region. Then the data is analyzed to determine average minimum winter temperatures from different areas.  

The concept of hardiness zones was first introduced in 1927 by Dr. Alfred Rehder. Rehder worked at Harvard's Arnold Arboretum as a botanical taxonomist. He wanted to address the challenges gardeners and growers faced in selecting plants suited to their local climate. Prior to Rehder’s map, there was no standardized system for categorizing plants based on their ability to survive winter temperatures. His hand-drawn map featured eight hardiness zones and was based on the lowest winter temperatures recorded in various regions across the country. Rehder aimed to provide a practical tool for gardeners and growers. His map made it easier for them to choose plants with the best chances of survival in their region, ultimately contributing to more successful gardens and agricultural endeavors. Rehder’s innovative approach recognized the importance of adapting agricultural practices to local climates. In the 1960s, the USDA adopted and adapted Rehder's concept, creating the first official USDA Plant Hardiness Zone Map.  

Since its initial release, the USDA Plant Hardiness Zone Map has been updated several times to reflect changes in climate and the availability of more accurate data. The latest update of the USDA hardiness map was released in November 2023, jointly developed by the USDA's Agricultural Research Service (ARS) and Oregon State University's PRISM Climate Group. This update incorporates data from 1991 to 2020, covering a broader range of weather stations than previous versions. One of the key findings from this update is that the contiguous United States has become approximately 2.5 degrees Fahrenheit warmer on average compared to the previous map. As a result, around half of the country has shifted into the next warmer half zone, while the other half has remained unchanged. The updated map still consists of 13 zones, but now offers more detailed information on temperature ranges within each zone, including 10-degree zones and 5-degree half zones. Connecticut has two hardiness zones each of which is divided into half zones; (6a,6b); (7a,7b), to better reflect the temperatures in the state over the past few decades.   

The importance of hardiness zones lies in their ability to help gardeners and farmers choose plants that will thrive in their specific region. By selecting plants appropriate for their zone, growers can reduce the risk of frost damage and increase their chances of a successful growing season. However, due to unexpected temperatures outside the average range, there is no guarantee that a plant won’t suffer but it does reduce the risk of plant damage. In addition to gardeners, researchers use hardiness zones to study the spread of insects and exotic weeds, while the USDA Risk Management Agency uses the map to help determine crop insurance rates for commercial growers.  

While the USDA Plant Hardiness Zone Map is an invaluable tool, it is important to note that it is not the only factor gardeners and farmers should consider when selecting plants. Other factors, such as soil type, precipitation, and local microclimates, can also impact plant growth and survival. Gardeners should use the map as a starting point and supplement it with local knowledge and research to make the best plant selections for their specific needs. 

The development of the USDA Plant Hardiness Zone Map is a testament to the importance of adapting agricultural practices to local climates. Since its inception nearly a century ago, the map has evolved to reflect changes in climate and incorporate more accurate data. Today, the map remains an essential resource for gardeners and researchers alike, helping them to better understand and navigate the complexities of plant growth in the diverse regions of the United States. Knowing a plant’s hardiness zone when selecting that shrub, tree or flower will help you grow the garden of your dreams. 

 The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations. 

USDA Hardiness Zone Map 2023

A map of the united states color coded to display the USDA Hardiness zones across the country as of 2023. Lower numbered zones are colder and each increment is based on 5 degrees Farenheit.

National USDA Hardiness Zone Map, 2023

USDA Hardiness Zone Map 2012

A map of the united states color coded to display the USDA Hardiness zones across the country as of 2012. Lower numbered zones are colder and each increment is based on 5 degrees Farenheit.

National USDA Hardiness Zone Map, 2012

USDA Hardiness Zone Map 1990

A map of the united states color coded to display the USDA Hardiness zones across the country as of 1990. Lower numbered zones are colder and each increment is based on 5 degrees Farenheit.

National USDA Hardiness Zone Map, 1990

This article was published in the Hartford Courant May 3 2025

Rocky Start for Rhododendron’s This Spring

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By Heather Zidack, UConn Home & Garden Education Center

Two Rhododendron shrubs. Shrub in the foreground showing leaf curl while shrub behind it looks healthy and is not displaying any signs of stress.
Rhododendrons are showing a varying degree of stress responses to winter conditions in the landscape. Photo by Heather Zidack

Rhododendrons are looking rough this spring. You’ve probably seen it in your yard or in your neighborhood. The UConn Home & Garden Education Center has been seeing an increase in the number of calls regarding injury or damage to rhododendrons.  In most cases, we are finding these reports to be winter injury. This is an environmental type of damage, caused by a perfect storm of conditions that we have seen throughout the state. So, let’s take a closer look into why this is happening.

Plants lose water through their leaves. During active growth, that water is constantly replenished from the roots. When the temperatures drop and the ground freezes in the winter, available water becomes limited. Plants have adapted to this in many ways. Dormancy is triggered by multiple factors, but water conservation is certainly one of those. Deciduous trees shed their leaves completely. Evergreens have developed various leaf adaptations to help with survival, too.

As broadleaf evergreens, rhododendrons have developed a waxy coat on their leaves to help prevent water loss. They also have a physiological mechanism to help defend themselves further. Just as you’d clasp your hands together on a cold winter day to shield them from the elements, rhododendron leaves curl themselves into cigar-shaped cylinders. The leading theory is that this happens to protect the leaves from further water loss. This natural defense mechanism has grabbed our attention this spring, since our weather patterns have lent a hand in amplifying a natural phenomenon.

At the end of last summer, CT started to see a moderate drought in much of the state. These conditions have persisted through this spring. Water availability was limited as plants went into the winter and remained limited throughout the season. Add in frozen soil and harsh winter winds and the environmental stress increased even more. When water is unavailable to the roots – through either freezing or drought conditions, plants lose their ability to return water to the living tissues. This drying out, referred to as desiccation, leads to winter injury or winter kill depending on the severity of damage. While we are finally seeing rain, these plants need time to recover and may not be ready to unfurl just yet.

Many have noted that some plants are faring better than others even within the same bed. This is also normal to some extent. It can be easy to forget that plants are living things in our landscapes. There is going to be variance in their ability to withstand environmental pressures and their recovery rates.

If you are seeing this in your rhododendrons, be patient this spring and monitor over the next month or so. With an increase of rain in the forecast, the extra hydration should help plants recover - or at least push out new growth. These shrubs will shed any leaves that are damaged beyond repair on their own. Do not prune or fertilize shrubs until the end of May to avoid further injury.  If we go a week without rain, consider watering your shrubs to help speed up recovery – but only water if the soil feels dry to the touch! If by mid-late May you are seeing absolutely no improvement, we start to consider other factors that may contribute to the plant’s health. For now, they just need a little more time.

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations.

This article was published in the Hartford Courant Apr. 12 2025

Potted Plant Paradise

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By Dr. Matthew Lisy, UConn Adjunct Faculty
UConn Home & Garden Education Center

Finally, spring is here! It will soon be time to repot all our houseplants as soon as the cold weather completely stops.  Many of the plants purchased over the winter, as well as the ones sitting around for years should be repotted.  This does not imply that the pot size needs to be increased.  Many times, the plant can be left in the same size pot.  If it is rootbound, and the plant is known to get large, it’s good to go one pot size up.  Increasing the pot size when it is not needed just leads to root rot as the soil will not dry out properly.  Alternatively, if the plant is getting big, another option is to divide it into numerous smaller plants, each requiring a smaller pot.

Different varieties of Sansevieria in separate pots
Various Sansevieria species waiting for spring to be repotted – the three in front need bigger pots, and the rear one needs to be split. It’s best to repot during the growing season in order to avoid root rot. (photo by M. Lisy).

Many people think that if the pot size does not need to increase, then there is no need to repot.  This could not be further from the truth.  The plant is in a fixed medium.  The soilless mix will quickly run out of nutrients, even with regular fertilization.  Also, salts tend to build up in the soil, which harms the plant over the long run.  This is a natural consequence of plants in pots.  Soil can also get compacted too much over time and interfere with proper aeration of the root zone.  Tease away the loose soil from the root ball being careful not to break the roots.  Add the new soil and watch the plant grow!

This is also a great time to change out the pot.  Most of our houseplants come in plastic pots.  These are usually not very attractive.  Plastic pots are good for plants that like to be kept moist.  I prefer a clay pot in most cases.  This allows the soil to breathe and makes it harder to over water.  What I do not care for or recommend are the automatic watering pots.  I have found that these have a tendency to keep the soil too moist, and do not allow for a drying out period between waterings.  Stores use them as they require no maintenance from their staff, and the plants cannot wither and die due to lack of water.  Long term, these types of pots lead to root rot.

Different plants have different soil needs.  Cacti and succulents like it dry and fast draining.  Orchids like it airy and chunky.  Most houseplants prefer a mix that holds moisture but drains.  Try and match the plant to the right soil type.  There are great commercial mixes available for purchase, and prices on these have come down some lately.  Take some time to research the proper soil type for each plant.  Many of the plants take a typical houseplant mix, but some require additional drainage.  In this case, add perlite and/or sand.  To enable to soil to hold moisture for a longer period of time, add some vermiculite.

In all honesty, almost any soil can work for almost any plant provided that the watering is controlled.  Most of the time, houseplants get overwatered which leads to fungal problems.  People want to water at some magical interval, like every Friday, for example.  In reality, the weather greatly influences how quickly or slowly our plants dry out.  Sometimes they need water sooner, and sometimes they do not need water at all.  Let the plants determine the watering schedule.  If all these suggestions are followed, our plants will be living in a potted paradise, as will we!

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations.

The Challenges of Boxwood: Pests, Diseases, and Alternatives

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By Marie Woodward, UConn Home & Garden Education Center

Boxwood, a classic choice for formal gardens and hedges, has faced increasing threats in recent years. As gardeners grapple with these challenges, it is crucial to understand the issues at hand and explore alternative plants for our landscapes.

Boxwood Blight is an aggressive fungal disease that affects various Boxwood species and causes rapid defoliation and potential plant death. First identified in the United Kingdom in the mid-1990s, this disease has since spread across North America. Early symptoms include stem cankers, sunken lesions, and eventual dieback. To mitigate the risk of Boxwood Blight, choose resistant cultivars, practice good garden hygiene, and monitor your plants for early signs of infection.

The Box Tree Moth is an invasive pest native to Asia that feeds on Boxwood plants. Since its arrival in North America, this moth has wreaked havoc on Boxwood populations, leading to defoliation and plant stress. Symptoms of infestation include see-through plants, "stick shrubs," and stem cankers. Regular monitoring and integrated pest management strategies are essential for controlling this destructive insect.

As Boxwood plants continue to face challenges from pests and diseases, it is wise to consider alternative options for our gardens. Ilex crenata (Japanese Holly) is a versatile, broadleaf evergreen that can be shaped into hedges or topiaries. Its small, glossy leaves provide a neat appearance, and its adaptability to various soil types and sun exposure makes it a low-maintenance choice.

Row of Gem Box Ilex shrubs for sale
Gem Box Ilex is one of many fantastic substitutes for Boxwood shrubs. Photo by H. Zidack

Euonymus japonicus (Japanese Euonymus), an evergreen shrub with small, glossy leaves and tolerance for a range of growing conditions is another possible substitution. Its compact growth habit and easy maintenance make it an excellent choice for hedges or screens.

Ilex glabra (Inkberry), is a slow-growing evergreen native to North America, featuring dark green leaves and red berries in the fall. Its low, spreading habit makes it ideal for low hedges or mass plantings.

Privets (Ligustrum), are fast-growing, low-maintenance evergreen shrubs with small, glossy leaves. They can be used for hedges, screens, or as stand-alone specimens. However, keep in mind that three cultivars, border privet, (Ligustrum obtusifolium Sieb. & Zucc), California privet, (Ligustrum ovalifolium Hassk.) and European privet (Ligustrum vulgare L.) are listed on UConn’s invasive plant database.  If you decide to plant privets, look for seedless cultivars such as Golden Ticket privet (Ligustrum x vicaryi "KCLX1") at your local nursery.  

The Boxwood Blight and Box Tree Moth present ongoing challenges for gardeners and landscapers. By understanding these threats and adopting appropriate management strategies, we can mitigate the damage they cause. Additionally, exploring alternative plants can help create more resilient and sustainable gardens in the face of these challenges. With careful planning and thoughtful plant selection, our landscapes can continue to thrive in the face of adversity.

The UConn Home & Garden Education Center supports UConn Extension’s mission by providing answers you can trust with research-based information and resources. For questions about your boxwoods or other gardening questions, contact us toll-free at (877) 486-6271, visit our website at homegarden.cahnr.uconn.edu, or reach out to your local UConn Extension center at cahnr.uconn.edu/extension/locations.

This article was published in the Hartford Courant Feb. 22, 2025
It was been updated from its original publishing on Feb. 27, 2025