Soils in the region where I live are short on the mineral boron, an essential plant micronutrient. The University of Georgia soil lab doesn’t measure boron levels in its routine test for garden soil, but it does include a recommendation to add some to a home vegetable garden. This is the recommendation:
“Apply 1 tablespoon of borax per 100 feet of row to broccoli and root crops such as turnips and beets. This can be applied by mixing the borax thoroughly with approximately 1 quart of soil in a container and then applying the mixture along the row; or it can be mixed with a quart of water and applied to the soil in solution.”
University of Georgia, Soil Test Report, basic soil test for Home Vegetable Garden, 2018
What is a micronutrient?
The micronutrients are needed in tiny amounts, but they are essential for plant growth. Boron is one of several micronutrients that plants need. Other micronutrients include copper, iron, and nickel, among others.
For boron, the difference between not-enough and too-much is a pretty narrow range, according to K. Kelling at the University of Wisconsin and Ron Goldy at Michigan State Univ. Extension. This means that great care must be taken to not use too much.
How does boron help plants?
UMass Extension, Amherst, says that boron “is required for many different aspects of plant cell functioning, including protein synthesis, development of cell walls, carbohydrate metabolism and sugar transport, pollen growth, fruit set, and seed production.”
Sounds important, to me!
What happens when plants don’t get enough boron?
The UMass information about boron deficiency lists these possible effects of too-little boron:
- “stunting and distortion of the growing tip”
- “brittle foliage and yellowing of lower leaf tips”
- reduced flowering
- reduced fruiting
- distorted fruit
- “brown heart” (mushy brown centers) in root crops like turnips and rutabagas
- hollow stems in broccoli and cauliflower
- brown or otherwise discolored curds on cauliflower
Kelling’s Soil and Applied Boron publication adds that cabbages that are low on boron may show an “internal breakdown of head”.
Which plants need the most boron?
Some vegetable crops need more boron than others.
Ron Goldy’s U Michigan publication lists crops and their relative need for boron. The high-need vegetables for boron he includes are these:
- broccoli
- cauliflower
- celery
- table beets
- turnips
How can I provide boron to my garden?
One way to add boron is to follow the instructions on the UGA soil test report, to mix a tablespoon of borax in water or with soil and to spread that across a 100-foot row of garden, especially in areas where higher-need vegetables are growing. If your garden is not in rows, or is smaller, it will need less borax.
The borax you will need is in the laundry section of your grocery store, in the box of 20 Mule Team Borax. This should be fine for organic gardens, because it is a mined mineral.
You will need to be careful with this product, though, because it is easy to use too much. Do not apply the boron every year without having the boron levels tested at a reliable soil lab.
If you prefer to use another product, one that contains many micronutrients, including boron, to safely fill any gaps, try kelp meal. It is much more difficult to use too much boron when using kelp meal, because it is a much less concentrated source of the micronutrient. There is enough, though, to help your plants. Just follow package directions for safe use in your organic home garden.
Georgia isn’t the only state with low-boron soils
The 20 Mule Team Borax company notes that boron will be at low levels in soils that are sandy, or acidic, or that are low in organic matter (like Georgia clay!), or that are in areas of high humidity.
The company has found that low-boron levels are a common problem in soils east of the Rockies and in the Pacific Northwest. The middle of the country and the Southwestern region mostly have sufficient boron.
To learn more about soil fertility in organic home gardens, read my posts about potassium sources, soil pH, building good garden soil, and side-dressing your garden crops.