12/5/2019 – When reading this blog post about cabbages I noted her adding boron to the soil. Looked at my soil test reports and found they recommend 2 lbs of boron per acre–even though it is not cited in the table.
In the blog post, she uses “two tablespoons of household borax diluted in a gallon of water for about eight plants.” So, 1/4 cup (4 Tbsp) in the 2-gallon watering cans will provide 1 pint each for 16 cabbage plants.
Alternative application from Gardening Know How: Boron In Soil: The Affects Of Boron On Plants
“If you suspect a boron deficiency problem with your plants, using a small amount of boric acid (1/2 tsp. per gallon of water) as a foliar spray will do the job. Be careful as you use boron on plants. Again, heavy boron soil concentrations are toxic. Turnips, broccoli, cauliflower, cabbage, and Brussels sprouts are all heavy boron users and will benefit from a light yearly spray. Apples, pears and grapes will also benefit.“
[Based on common info boron is not mobile in plants and so you have to spray regularly to get it into the new growth. One source said to spray 6 times per year.]
By 20-Mule Team
Boron in Vegetables – Includes a table of typical application rates by vegetable. Here.
Boron application from Michigan State Univ.
- Boron may be blended into dry fertilizers such as 0-0-60 or 0-14-42.
- Boron fertilizers include borax (11 percent boron) and borate granular (14 percent boron). Solubor (20 percent boron liquid) is foliar applied and must be applied at recommended rate for specific crops.
- Application of 9 pounds borax per acre will supply 1 pound boron per acre.
- For gardeners, about 4 teaspoons borax per 1,000 square feet is equivalent to 1 pound boron per acre.
- Dry boron fertilizers should be broadcast along with other fertilizers and worked into soil.
- Boron fertilizer should not be applied if grasses including hay, pasture, turf, small grains or corn are sown immediately following application.
- Manure generally contains 0.03–0.08 pounds boron per ton, more if composted.
Crop Requirements: From Boron Deficiencies and Toxicities in Vegetable Crops by Gordon Johnson, Extension Vegetable & Fruit Specialist, University of Delaware Cooperative Extension
- Crops with high boron requirements (3 lbs/A): Broccoli, cabbage, cauliflower, rutabaga, turnips, beets, and swiss card, spinach
- Crops with medium boron requirements – (2lbs/A): Asparagus, carrots, cucurbits, eggplants, leeks, okra, onions, parsnips, radishes, strawberries, sweet corn, tomatoes, potatoes
- Crops with low boron requirements (1 lb/A): Peppers, sweet potatoes
- Crops with very low boron requirements (no application): Beans, peas
Soils deficient in boron can be amended with boron fertilizer such as Borax, boric acid, and Solubor, based on soil tests and crop requirements. In high pH soils, foliar applications are preferred. Once symptoms of boron deficiency are observed, it is usually too late to apply boron. Different cultivars vary in their susceptibility to boron deficiency.
If boron supplementation is indicated, a convenient source of boron for your garden is 20 Mule Team Borax. Here’s the formula to mix and apply to achieve about 0.8 ppm additional boron in the soil. Per 100 sq. ft. dissolve 1 1/2 TBL Borax in warm water and drench soil. Adjust the quantity of Borax depending on the area you want to treat. Quantity of water is not important as long as you have enough to evenly cover the intended area. One gallon is about right for 100 sq. ft. Water is just the vehicle for the Borax. Avoid contact with leaves of your plants. The concentration of this soil treatment may result in leaf scorch.