Heavy Rains Can Lower Garden Fertility

The frequent movement of water through the soil carries away very soluble fertilizer elements, or moves them beyond plant root zones. Therefore during, or directly after prolonged wet periods, fertility levels may drop below those best for good plant growth. One of the most soluble, and therefore the most critical, is nitrogen. Low nitrogen in plants results in paler green leaf color. Older leaves may turn yellow, while new growth may be weaker and new leaves develop slightly smaller than normal.

Nitrogen added to rain water during lightning is often discussed, but does not provide adequate replacement for that washed away during a heavy rain. Another result of very wet soils and standing water is oxygen starvation of plant roots as water pushes out air and prevents air exchange. Plants in such conditions may be stunted, and pale green in color. If the condition persists long enough, they may yellow and die. If anything can be done to improve drainage, plants may improve. The root damage from excessively wet soils can lead to other deficiency symptoms that result because the limited roots can not absorb sufficient materials to support the existing top growth.

Reddish coloration of lower leaves, typical phosphorus deficiency symptom, is one that frequently appears. Unless the amount and duration of water has been sever, plants should recover as soil dries. A fertilization with a high nitrogen fertilizer can help boost growth. This is done by a technique known as sidedressing. Do not apply more than recommended amounts when sidedressing.

Weak plants in wet soils could again be damaged by applying too much. A high nitrogen material frequently used for sidedressing is ammonium nitrate. It, or any other fertilizer, should be applied along the row three to six inches from the base of plants. For individual plants, apply in a circle around the plant and at least six inches away. Scratch it lightly into the surface after application. Most ammonium nitrate sold for fertilizer has about 33% nitrogen, and should be applied at about one pound per 100 feet of row, or 100 square feet. Since a scale is not always handy, remember that a pound of ammonium nitrate in a volume measure is slightly more than a pint.

If you are treating an even smaller area, figure two cups to a pint or 32 tablespoons which could be interpreted as roughly one teaspoon per square foot or foot of row. If other fertilizers lower in nitrogen are used, slightly larger amounts will be needed. If in doubt, remember that frequent light fertilizations provide more benefit, and safer and more efficient use of fertilizer than infrequent heavier applications.

Lawns as well as vegetable and flower gardens may suffer because of low nitrogen levels. Warm season grasses, such as zoysia, have made slow growth because of the long, cool spring. Low nitrogen levels can also slow their development. An application of a high nitrogen lawn fertilizer at this time can provide a boost for the warm season lawn. Cool season grasses, such as bluegrass and fescue, have made good growth except where exceptionally wet soils caused yellowing.

Improving Your Garden Soil, by Barbara Perry Lawton.