History & Culture

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

Narcissi and the Reflections of Spring

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By Abigayle Ward – Soil Science Graduate Student, UConn Department of Plant Science & Landscape Architecture

Daffodils in bloom
Photo by: Rebekah D. Wallace, University of Georgia, Bugwood.org

According to an ancient Greek myth, all those who had fallen in love with the young man Narcissus were met with contemptuous rejection. On a hunting trip, Narcissus stopped to drink from a pond and became enamored with his own reflection. Cursed to never experience a requited love of his own, he stared at himself until his death, and his place was taken by a flower.

While it remains disputed whether the character was named after the flower or vice versa, the enduring significance of the narcissus as a harbinger of spring is uncontested. With a native range spanning throughout most of Europe, northern Africa, and parts of Asia, legends describing this culturally significant early-season perennial have been told since antiquity. In China, daffodils are carefully grown to bloom for the Lunar New Year, which began this year on January 29th. Their Mandarin name, shuixianhua, literally translates as “immortal water flower”, attesting to their resilience throughout the early season cold.

The Royal Horticultural Society in the United Kingdom describes 13 different types of narcissi based primarily on morphological appearance and when they bloom. Some have long trumpets, while others have multiple flowers to one stem. Others have small trumpets and many petals, called ‘double daffodils’, while others still have few petals dwarfed by large, bowl-shaped trumpets. Daffodils also come in many interesting color combinations – while most of us are familiar with the classic yellow petals and orange trumpets, they also come with white petals, white trumpets, and some even have shades of salmon pink. As one of the earliest-blooming flowers in your garden, they add a lovely splash of color to an otherwise brown landscape. In beds, they go well with red or pink tulips. By themselves, daffodils make good borders, particularly if different color combinations are intermixed to create visual intrigue.

While it is too late now to plant daffodil bulbs with the guarantee of blooms, they can still be safely planted. If you have some bulbs and want to give them a try, be sure to plant them in a sunny spot with well-drained soil at least 6 to 8 inches below the surface. They may sprout, but not form a flower. Do not fear: Daffodils are quite resilient and will likely flower the next spring. If you want to wait, the ideal time to plant daffodils for blooms in the spring is November.

If you find an already-blooming daffodil at your local garden center, it can be planted in the ground any time after the blooms themselves have faded. Both the bulbs and the foliage are frost-hardy well into sub-zero temperatures, making them well-suited for growing in the unpredictable winter weather of Connecticut.

After the flowers have bloomed, you may wish to cut the flower stems and bring them indoors for some bright colors. If you leave the flowers on the plants, be sure to deadhead them as soon as the flowers begin to wilt. If daffodils are allowed to go to seed, the plant will divert precious nutrients and energy away from the bulb. Once the plant has finished flowering, only the foliage remains. While it is tempting to remove the foliage, the leaves are collecting energy and creating food for the bulb via photosynthesis. If the leaves are removed too early, the daffodil may not flower the following spring. Some gardeners like to tie up the leaves in rubber bands or braid them to keep them out of the way, although it is generally best practice to leave them alone until they turn brown by themselves. Damage to the leaves could introduce pathogens or attract pests, which could impact the ability of the plant to flower next year.

With proper care, daffodil bulbs can multiply, ensuring many blooms come back year after year. As we move forward into the season of renewal for ourselves and our gardens, consider planting some daffodils to add a bit of sunshine to your home landscape.

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 spring bulbs like daffodils 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 Mar. 8 2025

I Want My Mum: A Fall Classic Through the Ages

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By Abigayle Ward, UConn Department of Plant Science & Landscape Architecture Graduate Student

A group of fall flowers mixed with mums in a container.
Orange, purple, and white mums used as “filler” in a potted arrangement at Wickham Park in Manchester, CT. Photo by Abigayle Ward.

With the arrival of fall, one popular bloom brings the brilliant colors of forest foliage to our doorstep: With flower colors coming in purple, red, orange, yellow, and more, chrysanthemums, or more simply, mums, have been a favorite for centuries. First domesticated in China over 3,000 years ago, mum roots, seedlings, and flower pedals were used as herbal remedies in traditional Chinese medicine.

For nearly 2,000 years, mums have been the symbol of fall in Chinese culture: The Double Ninth Festival, celebrated on the ninth day of the ninth lunar month, celebrates harvest, ancestors, and the beauty of autumn, with mums taking center stage as both decorations, accessories, and a floral wine.

First introduced to Europeans in the 1600s, mums quickly became a fall favorite. By the mid-1800s, the Victorians had written extensive literature on the interpretation and meaning of the color of each bloom. While some colors have carried the same meaning for thousands of years – such as white blooms symbolizing mourning – others took on entirely different meanings. While in China, a red mum represents fortune and luck, a Victorian would interpret this as a declaration of love.

Luckily, it seems many home gardeners in the United States nowadays are more concerned with the aesthetic appeal of their blooms than the meanings, so major misunderstandings are avoided. With several thousand cultivars available, mums come in many color combinations and growth habits. The National Chrysanthemum Society of the USA recognizes 13 different flower classes, ranging from 6-inch diameter flower balls with many layers of florets to smaller, 2-inch diameter flowers with only a single layer of a few petals. Some mums bloom early, in August, while others will bloom in October.

A row of potted mums for sale on a bench
Mums can be found for sale at garden centers starting in late summer. Photo by dmp2024

Further, some mums are annuals regardless of USDA hardiness zone, while others are perennials in zones 5-9. While so-called “florist mums” or “pot mums” are generally grown as annuals and will not survive winter frost, “garden mums” can survive winter frost if planted early enough in the growing season. If you wish to purchase a garden mum, but the mums are unmarked, a good way to tell the difference between florist and garden mums is to check for stolons near the base of the plant. Stolons, also known as “runners”, are shoots that grow out from the base of the mother plant. A daughter plant may have roots growing from the end of a stolon. If you want to purchase a perennial mum, check around the base of the stem for stolons – they will most likely be quite short but are a good sign that the plants may overwinter successfully. Alternatively, if you want to be sure you grow a permanent mum installation that comes back year-after-year, you can start some varieties of hardy garden mums from seed in late winter prior to planting out in spring. Get any mums you want to try overwintering in the ground as soon as possible. You can plant mums next year in spring or summertime to give them plenty of sunny weather to grow hearty root systems prior to the first winter frost of 2025. Mulch around your fall planted mums to help insulate their roots from frost.

Both annual and perennial mums benefit from at least 6 hours of direct sunlight per day. In Connecticut, a sunny spot to the south of your home would be ideal. Water mums thoroughly once the topsoil is dry but try not to wet the leaves or the flowers. Water left on the leaves or flowers can make mums prone to fungal diseases, which can make them unsightly or even kill them in severe cases. Towards the end of the season, especially between October and November, consider leaving the blooms on as long as possible to allow late-season pollinators to collect nectar.

Whether planted in a permanent flower garden or kept in a pot on the porch for fall, mums are an excellent addition of rich fall colors to any home gardener’s flower collection. Consider picking some up this season at your local garden center or plan on purchasing plants or seeds next year.

If you have a question on caring for your mums or for other gardening questions, contact the UCONN Home & Garden Education Center, toll-free, at (877) 486-6271, visit their web site at www.homegarden.cahnr.uconn.edu or contact your local Cooperative Extension Center.