Last summer Dee Blair, a veteran southern Indiana gardener, was having problems with her pepper plants, which refused to set fruit after blossoming. Then Dee sprayed the leaves, stems, and blossoms of her struggling peppers with a solution of fish emulsion, seaweed, and Epsom slats dissolved in water. A few days later she repeated the spray -- and the plants began setting fruit.
''Foliar feeding made the biggest differnce,'' she says. ''I could almost see the change overnight.''
Dee is inclined to believe that the extra minerals, especially magnesium, present in the leaf spray was the key to helping the peppers set fruit. A pepper plant's need for magnesium increases substantially when it begins developing fruit.
No one will argue with the idea that a fertile soil is the best way of providing all the nutrients a plant needs. However, under certain conditions -- during drought, soil deficiencies, insect attack, and the time when a plant's growth pattern is changing -- a plant not be getting all the nutrients it needs from the soil.
At these stressful times you may want to give your plants a boost with a foliar spray.
A foliar spray is a good way of applying missing nutrients right where the plant need them to begin building healthy tissue. Research has shown that it is eight times more efficient for plants to absorb aplied fertilizers through their leaves than through their roots.
All three of the major nutrients (nitrogen, phosphorus, and potassium), as well as a host of trace minerals, can be absorbed through a plant's leaves.
No one knows exactly how nutrients are absorbed through a plant's leaves, however.
Some think that the nutrients enter through the stomata (the openings on the bottom of a leaf through which plants breathe). Others think that the nutrients pass directly though the leaf's surface cells by diffusion. In any case, they do agree that plants can and do absorb nutrients through their leaves.
Foliar sprays can be made from any fertilizer that is soluble in water. The four most-often-used leaf sprays are fish emulsion, seaweed, manure tea, and compost tea. Unfortunately none of these leaf sprays provides a balanced diet for plants.
Liquid seaweed, for instance, contains very little of the major nutrients. However, liquid seaweed does contain traces of the 70 elements found in the oceans. Many of these minerals are vital to plant growth. Therefore, seaweed leaf sprays are an excellent way to correct minor mineral deficiencies during times of stress.
Fish emulsion, manure tea, and compost tea are more often used to supply the major nutrients. These solutions also contain many trace elements, but not as many as liquid seaweed.
To make a fish emulstion or seaweed spray, mix one or two tablespoons of the fertilizer in a gallon of water and add a squirt of biodegradable soap to help the solution stick to the plant leaves. Spray the solution on your plants early in the morning when the stomata are open. Absorption is also aided by sunlight.
To make compost or manure tea, hang a bag of either material in a bucket of water overnight. Strain the solution through fine-mesh cloth so it does not clog your sprayer. Dilute the tea with water until it has the color of pale tea. Spray on your plants.
Do not wait until the leaves show signs of stress or deficiency before applying foliar sprays. By then it will be too late to help prevent all of the stress-related damage. A better idea is to give plants a dose of leaf spray each time they change their growing pattern, such as when a vine starts sending out runners, forming flowers, setting fruit, or enduring heavy attack by insects.
Midsummer is the best time to consider foliar spryaing.
Foliar spraying may also help enhance the flavor of some fruits. Cantaloupe, for example, tastes flat when cultivated in soils that are low in magnesium. A foliar spray of seaweed or Epsom salts (magnesium sulfate) immediately after fruit begins to set and again when the fruits are two inches in diameter will make the fruits sweeter.
Vegetables are not the only plants that will benefit from periodic foliar feedings. Fruit trees, especially apples, and grapes are also helped by foliar feedings. As an added side effect, seaweed acts as a mild insecticide on these and other plants.
Despite all the good things to be said about the foliar feeding of plants, don't depend on it to provide substantial nourishment for your crops. Build up a rich soil to do that.