Fertilizing Gardens

"Make hay while the sun still shines" is an adage that certainly pertains to spring gardening activities in this area of Texas.

Gardeners should take advantage of any current dry conditions to prepare planting sites. Rental stores do not have a tremendous demand for roto-tillers in early spring, so smart gardeners can beat the rush by acting now. This unpredictable Texas weather could also take a “wet” turn and make soil preparation at a later time unfeasible. This would be disastrous since crops such as beets, broccoli, cabbage, carrots, collards, corn, kohlrabi, lettuce, mustard, onions, parsley, sugar snap peas, potatoes, radish, spinach and turnips should be planted no later than February.

The first step in creating a productive garden is site evaluation. All vegetables are most productive in full sunlight conditions. If your garden site does not receive at least 8 hours of direct sunlight daily, you will not successfully produce those crops which have seed?bearing fruit. These include tomatoes, peppers and eggplant. By "successfully produce", I mean tomato plants which will yield at least 15 to 20 pounds of fruit per plant. Greens (lettuce, collards, mustard) and root crops (carrots, beets, radish) can tolerate shady conditions, but will not excel.

Another important factor of successful gardening is sufficient fertilization. However, you must use care not to use excessive amounts of fertilizer.

Through the years, I have advocated the use of ammonium sulfate (21?0?0) as a recommended nitrogen?only fertilizer for older gardens where complete-analysis fertilizers have been used year after year. Because of the abundance of potassium in the native soil of our area, and because of the build?up of phosphorus which occurs after several seasons of fertilizing with a complete fertilizer, a high nitrogen fertilizer can be recommended as the best selection for most growers.

To continuously use a balanced fertilizer in gardens promotes the occurrence of nutrient deficiencies of such minor elements as iron and zinc. However, ammonium sulfate (21-0-0) will release IMMEDIATELY release, and the majority of folks can and WILL burn their plants by adding too much! The recommended application is one pound per 100 square feet. Since one pound per hundred isn’t enough to show up white (with fertilizer) on the ground, most folks will add more!!!

I now recommend that a complete fertilizer with percentages of nitrogen, phosphorus, and potassium should be used in new gardens that are less than 2 years old. This includes the use of a 50% slow release fertilizer (our most common is 19?5?9 but anything close to a 3?1?2 ratio is OK???this is not a precise operation) during bed preparation for gardens or flowers at the rate of 3 pounds (3 cups full) per 100 square feet. For flowers and vegetables, I recommend one pound (one cup) per 100 square feet of the same slow release formulation every 3 weeks beginning after fruit-set or full bloom, and every 2 weeks for foliage crops. If un-decomposed organic material (including all materials sold as “compost”) is worked into the soil, these rates should be DOUBLED for the first 3 months to prevent nitrogen tie-up by micro-organisms trying to decompose the organic materials. Animal manures may be substituted for commercial fertilizer and used at a rate of 60 to 80 pounds per 100 square feet of garden area.

The most common problem during early spring, when plants are growing vigorously, is iron chlorosis-- or lack of iron. This irregularity is characterized by streaks of green through a predominately yellow leaf. In severe cases, brown margins or spots will develop, but this will occur after the leaf has been yellow for a period of time.

Plants which are extremely susceptible to iron chlorosis include okra, black-eyed peas, beans, azaleas, gardenias, peaches and pears. This lack of iron in a plant is not necessarily caused by insufficient iron in the soil. Because of the alkaline soil conditions of this area, iron can be present in the soil, but not available for plant uptake because of encapsulation by calcium or a strong adhesion to another soil mineral. So what can we do to make yellow plants green?

First of all, don't aggravate the condition with continuous applications of balanced fertilizers. Secondly, make sure that your plants have access to an available, note I say available, iron source. Iron sulfate sold as copperas can be used, as well as any product which has at least 16% iron as a component of the mix-- such as Ironnate or Iron Plus (16% iron plus nitrogen), or glauconite (Greensand with 18% iron -- use 10 pounds per 100 square feet). Iron sulfate can be applied as a foliar spray but be sure to use one teaspoon of liquid detergent per gallon of spray to insure uniform coverage.

For gardens, soil applications are recommended. One effective technique of application is to mix iron sulfate with organic material (leaves, grass clippings, etc.). Simply add 7 pounds of iron sulfate (copperas) to 400 pounds of organic matter (or one cup to a bushel of organic material). You can add more without danger of plant damage. As the organic matter decomposes, the iron that has "stained" the surfaces will be slowly released for plants to use. Such "fortified" organic material can be worked into the soil prior to planting and/or used as a mulching material for newly established seedlings and transplants. Another technique in avoiding iron chlorosis problems will be discussed later. It will be added after raised beds have been prepared.

Certain other ingredients should also be added to boost yields. The latest research indicates that the presence of available calcium prevents certain physiological disorders of vegetables as well as increases the efficiency of nitrogen uptake and stimulates growth. In the highly calcareous soil of Texas, it is difficult to imagine that plants need more calcium. However, research indicates that much of the calcium in the soil is not soluble or available for plant use. The best remedy for this situation is the addition of gypsum. Gypsum (calcium sulfate) is a neutral product that will not cause our soils to become more alkaline. We sure don't want that! Gypsum is sold as Sof?N?Soil or gypsum, and is recommended at the rate of 40 pounds per 100 square feet.

An additional step can be taken after beds have been prepared to avoid chlorosis problems later, as well as installing a cheap "starter solution" for seedlings and transplants. After planting beds have been firmed, make a 3-inch deep furrow for seed, or a 6-inch deep furrow for transplants. The furrow should be made down the center. Into this furrow, distribute evenly 1/2 pound (1/2 cup) of iron sulfate (copperas) and 1/2 pound (1/2 cup) of super phosphate (0?20?0) per 10 linear feet of bed. This band of iron and phosphorus will provide a concentrated source of available iron and available phosphorus for use as a "starter" solution on young and growing plants. Cover the band of iron and phosphorus with at least 2 inches of soil.