Physiological Disorders and Nutrient Deficiencies

foliar spray to treat a physiological disorder associated with calcium uptake.”20 Unless your fields or garden beds suffer from severe soil calcium deficiency, it does not make much sense to spray calcium chloride on tomato or pepper foliage (see “Calcium Deficiency” below).

Boron Deficiency

Some vegetables, such as brassicas, are heavy boron feeders. You can correct a deficiency with the careful addition of borax to the soil in liquid form (1 tablespoon per 100 square feet [9.3 m2] in 1 gallon [4 L] water) or 1 tablespoon Solubor in 1 gallon water. Or add boron more slowly by adding kelp (10 pounds per 100 square feet [49 kg/100 m2]) or wood ashes (note that wood ashes also increase soil pH and soil potassium, sometimes excessively). Foliar seaweed sprays as soon as transplants are set, and repeated several times until head or fruit formation, may help to prevent deficiency problems. While boron is essential for root growth and fruit development, it can become toxic if overapplied. Always test the soil and apply only the recommended amount.

Calcium Deficiency

Add gypsum if your pH is above 6.2, or calcitic lime if your soil pH is below 6.2 and a soil test shows that soil calcium is low.

Iron Deficiency

In high-pH soils, iron forms chemical compounds that are unavailable for uptake by most plants. High pH-induced iron deficiency is common in high-pH western US soils. You can lower soil pH by adding sulfur. For an emergency intervention, apply a root drench or spray leaves with iron chelate. Iron that has been treated with lignin derived from woody plants is usually allowed by organic certification, but check with your certifier first. Iron that has been chelated with synthetic materials, such as EDTA, is not allowed. Apply 1 tablespoon of chelated iron in 1 gallon (4 L) of water as a soil drench or as a spray on new foliage, in the evening when humidity levels are high.

Nitrogen Deficiency

Nitrogen is the most commonly found nutrient deficiency in vegetable crops. Be careful not to overdo nitrogen, though, because too much nitrogen causes rapid leaf tissue growth with little or no root growth as well as low flower and fruit production. Apply liquid nitrogen sources as a root drench, such as 1/4 pound (113 g) of alfalfa meal plus