Seasons of the Garden
How to boost foliar feeds, also includes research briefs and gleanings.
May/June 1987
By Greg and Pat William's
Boost Your Foliar Feeds
RELATED CONTENT
Many gardeners spray the leaves of their crops with foliar fertilizers as a way of supplying the plants with micronutrients such as zinc and boron. There is also a more controversial practice that uses the leaf sprays to provide macronutrients such as nitrogen and phosphorus. Results of this type of foliar feeding have varied considerably. In fact, in some tests macronutrient-sprayed crops have produced worse yields than unsprayed ones. To improve such fertilizers' effectiveness, growers sometimes add surfactants (which keep the liquid from beading up on the leaves) or humectants (which lengthen drying times).
Researchers at Texas A and M University recently tested more than 40 such aids, or adjuvants, to determine whether any of them actually enhanced the uptake of foliarapplied nitrogen and phosphorus by soybeans. The results? Glycerol, an inexpensive alcohol available at drugstores, was the only adjuvant that had a significant positive effect. When just 0.05% glycerol was added to the foliar solution, sprayed leaves contained 8.9% more nitrogen and 34.2% more phosphorus.
Furthermore, while some of the adjuvants that were tested damaged leaves, though concentrations were less than 1%, glycerol caused negligible harm even at 10% concentrations. More research is needed to confirm the Texas findings, but it certainly looks as if gylcerol is the adjuvant of choice for those who want to try macronutrient sprays on their plants.
Research Briefs
Garlic oil works. Garlic makes a good insecticide as well as a repellent. A senior-citizen horticulture class in Reedley, California, experimented with a garlic oil spray concocted as follows: Lots of finely minced garlic was soaked in mineral oil for at least 24 hours. About two teaspoons of the oil were added to a pint of water in which 1/4 ounce of Palmolive soap had been dissolved. This was thoroughly stirred, then strained into a glass container for storage. When used as a spray, one or two tablespoons of oil mix was blended into a pint of water.
The results reported by the Reedley class were astonishing! Cabbage moths, cabbage loopers, earwigs, leafhoppers, mosquitoes (including larvae), whiteflies and sonic aphids were killed on contact. Houseflies. June bugs and squash bugs died within a minute after being sprayed. Cockroaches, lygus bugs, slugs and hornworms were killed more slowly. Ladybugs, Colorado potato beetles, grasshoppers, grape leaf skeletonizers, red ants and sow bugs were not affected.
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