Soil Nutrition

It’s Spring! Time to Feed the Plants!

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By Dawn Pettinelli, UConn Home & Garden Education Center

Plants need nutrients to grow and develop just like we need vitamins and minerals. They get most of their nutrients dissolved in the water they take up with their roots. When we add fertilizer to the soil around our garden plants, we are adding vital plant nutrients.

Native Connecticut soils are typically low in pH and low in nutrients. Our native plants have adapted to our native soils but most of our garden plants are not from around here. Zinnias and tomatoes are from South America, bluegrass lawns and lilacs hail from Europe and rhododendrons from Asia. Our native soils may not supply the nutrients they need so it is up to us to do so.

Of course, the best way to know which nutrients and how much to add is with a soil test. April is a very busy month at the UConn Soil Nutrient Analysis Lab (www.soiltesting.cahnr.uconn.edu) but there is still time to get your soil tested before planting.

Without soil test recommendations, always follow the directions on the fertilizer package. Applying too much can injure your plants plus excessive nitrogen and phosphorus can wind up in our waterways. Before fertilizing, calculate out the square footage of your garden or lawn. You don’t need to measure exactly; you can measure a pace and then walk down the length and across the width of your gardens to get a rough estimate of area. For odd-shaped beds or lawns, break them down into more square, oval or rectangular areas and add them up.

All fertilizers come with 3 numbers on the package denoting the percent, on a dry weight basis, of nitrogen, phosphorus and potassium. Nitogen promotes green, leafy growth, phosphorus encourages fruits and roots, and potassium is for all round health and tolerance to stresses like drought, cold and disease. So, fertilizers with a higher nitrogen number would be most appropriate for turf grasses, trees and shrubs, while ones higher in phosphorus are generally used in vegetable and flower gardens.

Adding fertilizer to perennials with a watering can and a hand rake.
Fertilizer spread around a perennial. Photo by dmp2024

Whether you select a synthetic or natural organic fertilizer is a matter of personal choice. Both are beneficial to plants. For annual plantings, whether vegetable or flowers, it would be ideal to mix the fertilizer into the top 6 inches of soil. That’s where most of the roots will be so it makes sense that the nutrients they need are there too. Put down the fertilizer, as well as any limestone or other amendments shortly before planting. Long season annuals, like tomatoes, pumpkins and marigolds would appreciate a second application of fertilizer, referred to as side dressing, about 2 months after the first one.

As you are cleaning up your perennial beds and see the new shoots popping through the soil, add some fertilizer around plants and carefully scratch it in. Do the same for bulbs. It is harder to fertilize if the beds are heavily mulched. Not much fertilizer spread on top of mulch will make it to the plant roots. Rake or pull away the mulch, sprinkle some fertilizer directly to the soil around your plants and replace the mulch.

For trees and shrubs, fertilizer should be spread under the whole canopy as a healthy root system will grow at least as wide as the branches and perhaps even more so. Do your best to remove the mulch before fertilizing. Typically trees and shrubs are fertilized once a year in the spring. Once they have reached their mature size, often the fertilizer is cut down to half rate as woody plants can recycle many of the nutrients they need.

Lawns can be fertilized now but pay attention to the moisture level of the soil. With all the rain that we have been experiencing, the soil is pretty soggy in spots. Stay off wet soils as they will become compacted. Most lawns do well with just a spring and fall application of fertilizer. If the clippings are left down, they supply nutrients plus add organic matter to the soil. Be sure to set your spreader on the proper setting.

If you have questions about fertilizing or if you have any other gardening questions, contact the UConn Home & Garden Education at (877) 486-6271 or www.homegarden.cahnr,uconn.edu or your local Cooperative Extension Center.

Watch Out for These Nutrient Deficiency Symptoms

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Watch Out for These Nutrient Deficiency Symptoms
By Haiying Tao, Ph.D., UConn Home & Garden Education Center

Plants need at least seventeen essential nutrients to complete their life cycles. Scientists group these essential nutrients into macronutrients (carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulfur, calcium and magnesium), which are required in large quantities and micronutrients (zinc, iron, copper, boron, manganese, chlorine, molybdenum and nickel) which are required in small quantities. Sufficient amounts of these nutrients are required in order for plants to produce well. If there is a deficiency of any essential element, yield and quality can be reduced. Alternatively, too much of a nutrient can be toxic to plants. Diagnosing nutrient deficiencies and toxicities is important for both growers and gardeners to ensure optimum harvests.

When low in an essential nutrient, plants exhibit distinct visual symptoms, which often allows us to distinguish which nutrient is deficient. A first step in diagnosing nutrient deficiencies is to describe what the symptoms look like. Symptoms caused by nutrient deficiencies are generally grouped into five categories: 1) stunted growth; 2) chlorosis or yellowing; 3) leaf spots; 4) purplish-red coloring; and 5) necrosis or death of plant parts.

The next step is to identify whether the deficiency symptoms appear on older (lower) leaves or younger (upper) leaves first. If the deficiency symptoms appear on older leaves first, then the deficiency symptoms are possibly caused by one of the nutrients that are mobile in plants, such as nitrogen, phosphorus, potassium, magnesium, chlorine, or molybdenum. In contrast, deficiency of nutrients that are immobile (calcium, sulfur, boron, copper, iron, zinc, manganese, nickel), the symptoms first appear on younger or upper leaves.

Nitrogen deficiency on corn leaf.
Nitrogen deficiency on corn leaf. Photo by Dr. Haiying Tao

Nitrogen deficiency symptoms include yellowing of the lower leaves (chlorosis), stunted and slow growth, and death of older leaves in severe cases. Nitrogen deficient plants will mature early, and the crop quality and yield are often reduced.

Phosphorus deficiency symptoms occur in the older leaves first and typical deficiency symptoms are purpling of leaves and leaf margins and stunted growth. Plants that are deficient in phosphorus are generally weak and maturity is delayed.

Potassium deficiency symptoms first appear on older leaves. Typical deficiency symptoms are yellowing and necrosis of the leaf margins. When potassium deficiency is severe, older leaves turn yellow with brown dead tissue around the edges, but the upper new leaves may stay green. Sometimes one may confuse potassium and nitrogen deficiency because both show yellowing on older (lower) leaves first. The difference is that the chlorosis starts from the tip and progresses along the ribs of the leaf if nitrogen is deficient, but the chlorosis starts from the tip and progresses along the edge of the leaf if potassium is deficient.

Blossom End Rot on Tomato
Blossom End Rot on Tomato. Photo by dmp2024

Another nutrient that is commonly found deficient is calcium. Typical calcium deficiency symptoms are poor leaf expansion, curling followed by necrotic patches in the young leaves. Calcium deficiency can cause misshapen fruit and aborted buds. If you find the tip of tomatoes or peppers rotting, cavity spot in carrots, and black heart in peanuts and celery, it’s likely the plants are calcium deficient. However, don’t hurry to apply calcium fertilizers. Check on other stresses such as drought because lack of moisture in the soil can lead to insufficient uptake and transportation of calcium within plants, which leads to symptoms similar to calcium deficiency.

In sandy and low organic matter soils, sulfur deficiency can occur. Typical sulfur deficiency symptoms are reduced growth rate with plants becoming stunted and thin stemmed. In cole crops (such as cabbage, broccoli, etc.), discoloration appears in younger leaves first. Symptoms may include light green or yellow leaves, a reddish coloration on the undersides of leaves as well as leaves that are cupped inward.

Sulfur deficiency in cabbage.
Sulfur deficiency in cabbage. Photo by Dr. Haiying Tao

It is not always easy to identify nutrient deficiencies just by looking at a plant because the symptoms of several deficiencies are similar in appearance. Also, more than one nutrient may be deficient. It is not uncommon for other stresses such as disease, drought, excess water, genetic abnormalities, herbicide and pesticide residue injury, insects or salt injury may cause symptoms that are similar to nutrient deficiency. The best way to confirm if you have nutrient deficiency is to test your soil and plant tissue.

For questions on nutrient management in the garden or farm, feel free to contact the UConn Soil Lab at (860) 486-4271. For all your other gardening questions, contact the UConn Home & Garden Education at (877) 486-6271 or www.homegarden.cahnr,uconn.edu or your local Cooperative Extension Center.

Dr. Tao is an Assistant Professor and Soil Fertility Specialist in the UConn Department of Plant Science & Landscape Architecture.