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Index : Soils and Fertilization
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- 9. Correct Nutrient Deficiencies of Plants Before Winter - Top
It's hard to imagine now, but our first frosty autumn weather is just around the corner. Cold sensitive plants such as citrus, bougainvillea, hibiscus and others are always subject to cold injury. But you can help minimize the adverse effects of cold by making sure plants have an adequate supply of nutrients going into winter.
Probably the most common nutrient deficiency of plants is that of nitrogen. Plants lacking in nitrogen will have an overall anemic appearance. Leaves will not be as green as they should be. If the deficiency is severe, leaves, especially the older ones will be yellowed.
You can easily correct a nitrogen deficiency by applying any fertilizer that contains nitrogen. Nitrogen is the first of the three numbers that appear on the fertilizer label. When using a granular fertilizer, it's important to water the fertilizer into the soil around the plant. You can also use a liquid, or water soluble fertilizer containing nitrogen.
Be careful not to apply too much nitrogen. Use only enough to green the plant up but not enough to stimulate a burst of new growth. Soft, new growth is very susceptible to freeze damage, even on plants that are generally considered cold hardy. If the fertilizer label calls for a certain amount to be used per plant of for a given area, then use only half that amount.
Along with nitrogen, iron is the nutrient most commonly deficient in many of our landscape plants. Unlike nitrogen, Iron deficiency shows up first on the youngest leaves. Areas between the leaf veins turn yellow, while the leaf veins remain green. This creates a fish- bone like pattern on the leaf. As the deficiency becomes more severe, newer leaves may turn completely white. Iron deficiency is common on citrus, rose, gardenia, nandina, bougainvillea, photinia, privet, magnolia and a host of other non-desert type plants.
Iron deficiencies can be corrected by applying water soluble iron, called "chelated" iron.
Garden centers, nurseries, and horticulture supply stores all carry chelated iron products. The most commonly available brands include; Sequestrene 138, Ferrione 138, Ferriplus, and Sequestar. These products are packaged in smaller sizes for the home gardener. Don't waste money buying non-chelated forms of iron such as iron sulfate or ferrous sulfate. Only chelated iron works in our highly alkaline desert soils. Unlike nitrogen, iron will not promote tender new growth in the fall. Apply it to the soil full strength, according to label directions.
Yellowing of plant leaves does not necessarily mean a nutrient deficiency. Many plant, such as roses and citrus, come out of the summer with some yellowed and or browned leaves. This is natural. Some plants such as grapes, deciduous fruit trees, ash, sycamore and crape myrtle go into winter dormancy. Their leaves are beginning to yellow in preparation for autumn leaf drop.
Plants should continue to be watered frequently enough to meet their moisture requirements. Plants stressed for moisture going into late fall and early winter will be more prone to cold injury. The exception to this are grapes and other deciduous fruits such as peach, apple and plum trees. They should be watered less in the fall to encourage them to go into their normal fall and winter dormancy.
Finally, if you have plants that are cold sensitive, add some potassium to the soil. Potassium is the element most responsible for promoting cold hardiness. It is the third number on the fertilizer container and is available in all "complete" fertilizers. Choose a product that is low in nitrogen and high in potassium. General purpose fertilizers with equal parts nitrogen and potassium can also be used. Remember, apply at half-strength so as not to encourage a new flush of growth.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
- Updated: September 30, 2001
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