Sunday, March 21, 2010

Broccoli, beets, and boron

In this area, when a garden’s soil test results come back from UGA, near the end of the report, in tiny print, is a note about adding boron to the soil for broccoli and beets. The recommendation is for 1 tablespoon of boron per 100 feet of row, or per 100 square feet.

Boron, an essential micronutrient for plant growth, tends to leach out of soils that receive a lot of rainfall, and the metro-Atlanta area usually (drought years excepted) gets at least 50 inches of rain each year. That counts as a lot.

The good news is that organic matter helps hold boron -- and other nutrients -- in the soil. This means that gardens to which organic matter has been added routinely are less likely to be deficient.

However, some plants need more Boron than others. Broccoli and beets are two that need more, but the Boron page of the Agronomic Library for Spectrum Analytics has a longer list of high-boron users, referred to as "high response crops," and the list includes other root vegetables in addition to home-garden staples like lettuce and corn. The page also includes a table of deficiency symptoms that might help a gardener figure out whether low boron is a problem in his or her garden.

I’m thinking about this now because I planted the carrot and beet seeds yesterday. Both are on the “high response crops” list, so I will be adding some to their space tomorrow (it is raining today).

Boron isn’t present in the usual NPK fertilizer formulations (which I will not be using again anyway), but it is available in the laundry-soap aisles of many grocery stores, as 20 Mule Team Borax. I never plant as much as 100 square feet of any one crop, so I adjust the amount of borax to match the approximate square footage that I’ve planted.

I usually add the borax to a full watering can and try to move the can smoothly over the planted area for even dispersal. It is also possible to just sprinkle the dry powder over the area, but any wind makes even distribution less likely.

I only add boron to the areas that are planted with “high response crops" each year, rather than the entire garden, because I don’t want to add too much. The problem with micronutrients is right in their category name, the prefix “micro.” They are useful only when present in very small amounts. Too much is as big a problem as too little, and getting rid of what’s already been added is much harder than adding more.


  1. Awesome post this - I need help with both my broccoli and beets and this might just be the secret - thank you - peace

  2. I wish I had time to get my soil just right for my veggie residents, but I know I would never get past the soil test, LOL!

  3. Ruralrose and Erin--Boron is a scarce nutrient in soils in many parts of the country, but I would check with a local extension office before adding any, just to make sure. (Erin's soil is probably fine, but I don't know anything about soil in BC.)

    The good news is that plants are pretty good at using what's available, so even when soils aren't perfect, most garden plants grow and produce! They just don't do it quite as well as they might with more ideal conditions.

    That said, people around here have trouble with broccoli and beets, too. Boron often helps, but sometimes it's a soil pH problem, instead.

  4. Thank you for your post about boron. I need to apply it to my garden per my soil test results and recommendations. BTW I live on the Eastern Shore of Maryland. Small world!

  5. Anonymous,

    Glad to know that the post was helpful. The soil where I lived on the Eastern Shore (the address was at Wallops Island) was wonderfully rich compared to the clay I am working with now.

    If the area you live in is at all similar, you probably have a great garden, but getting to it involves dodging a whole lot of biting flies!

  6. Your post made me look into Boron with much greater interest. Thanks!

    Here's something I found that may brighten your day. A young female scientist singing "The Boron Song":

  7. Perez,

    Thanks for the link. What a great school project! Right now, post-tsunami in Japan and with the nuclear reactor problems at Fukushima daichi, I am guessing that boron is on the minds of a lot more people than just gardeners.

  8. At what mixing rate are you using 20 mule team borax?

  9. Soil test reports from UGA recommend 1 tablespoon of borax per 100 feet of row, which I interpret in my own garden as "per 100 square feet." It seems to work. I don't add it to every bed every year - just to the crops that seem to need more boron (broccoli, beets). Hope that helps!


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