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Index : Soils and Fertilization
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- 3. Choose the Right Winter Fertilizer - Top
- Most fertilizers we use in our gardens and landscapes are formulated to work best during the warm weather. That’s because the majority of plants we grow, only need fertilization in the spring and summer months. However, there are some exceptions; namely winter growing flowers and vegetables and potted patio plants.
There are lots of flowers and vegetables that Tucsonans plant and grow in the fall and winter. Flowers like pansies, petunias, stock, calendula, alyssum and lobelia all tolerate freezing temperatures. Cool season vegetables also tolerant of the cold and include; lettuce, spinach, chard, beets, broccoli and cauliflower. Because these plants are actively growing, they need a continuous supply of nutrients. In addition, most potted patio plants also need some level of nutrients during the winter months to stay green.
When temperatures are cool, the most common form of nitrogen in fertilizers ‘ammonium’ doesn’t work well. It is slow to release it’s nitrogen to plants. The best form of nitrogen for winter fertilization is ‘nitrate’. This form of nitrogen isn’t dependent on soil temperatures and will release it’s nitrogen for easy uptake by plants. Even in the coldest months of winter - at least as cold as it get’s here in Tucson - nitrate is an effective source of nitrogen for plants.
So how do you determine if your plants need nitrogen? Well, all plants do, but those that need it the most are green leafy winter vegetables, and to a lesser extent, cool season flowers and potted plants growing outside on the patio.
If plants are nitrogen deficient, their leaves will be a lighter green than normal. They’ll look rather anemic. Leaves will be smaller, and over time, plants will not develop new growth and will become stunted. Nitrogen is termed a ‘mobile element’. That means plants cannot move nitrogen from existing leaves to new growth in order to cover any shortages. So, older leaves are first to begin turning pale and yellowing.
Fortunately, winter nitrogen deficiencies can be quickly corrected with nitrate. Several commonly available water soluble plant foods and timed-release fertilizers contain nitrate. Look on the ingredient listing of the fertilizer to see if nitrate is present and what it’s percentage is in the total mix. The range of nitrate in these products is as little as one-half percent and as great as 6 percent. Fertilizers that have the highest levels of nitrate are best for winter fertilization. Follow label directions as to the frequency of application and the amount to use per application.
Even with correct nitrogen fertilization, don’t expect plants to put on much new growth during the winter. In mid and late Fall when temperatures are still warm, cool season flowers and vegetables continue to grow. But as temperatures drop in December, even these plants will slow their development. Flowering will continue, but plants won’t grow much until temperatures begin warming in late February.
Lots of gardeners like using organic sources of nutrients. There are many organic fertilizers high in nitrogen. Some of them include; blood meal, feather meal, hoof meal and horn dust, bat guano, fish emulsion, poultry manure and sewage sludge. The problem with organic fertilizers is that they’re not effective in the winter months.
Organic materials must be broken down by soil microbes, primarily beneficial bacteria and fungi, to release their nutrient to plants. In the winter, when soil temperatures are cool, these microbes just aren’t active. So they can’t convert the organic material to useable forms of plant nutrients, such as nitrate.
Wait to use organic fertilizers until the soils have warmed sufficiently in the spring, usually in April. After application of an organic fertilizer, don’t expect to see immediate results. It may take several weeks for the nutrients to be converted for plant absorption.
Finally, on a related matter, Aleppo pine trees often develop a condition called Aleppo pine blight during the winter months. The condition isn’t a disease, but rather is more likely insufficient water and nutrient uptake in cold weather. Tips on scattered branches appear to die back, but when warm weather returns the tree puts on new growth and the condition disappears. Winter fertilization will not prevent this condition, but monthly, deep watering of large pines will keep them in better overall health.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161. - Updated: November 28, 2004
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