By Jon Frank
All Minerals are important. But the most important mineral is the one you are missing.
As we start this foliar feeding course I am going to jump right in and discuss an important trace mineral that can easily be foliar fed.
Boron is a well-recognized trace mineral. Chemically it is neither metal nor is it a nonmetal. Therefore it is a metalloid--just like silicon. Here is one scientists' view on boron.
"The role of boron in plant nutrition is still the least understood of all the mineral nutrients and what is known of boron requirements arises mainly from studies of what happens when boron is withheld or resupplied after deficiency. This poor knowledge is surprising because on a molar basis the requirement for boron in higher than that for any other micronutrient."
What this really means is that the role of boron in plants is significant even in ways we don't fully understand. What we do know about the role of boron proves that it is absolutely critical for healthy plants. It is involved in the transport of sugar within the plant and the synthesis and structure of cell walls. It would seem that the role boron plays is structural rather than being used as an enzymatic trigger.
I believe one of the most important functions of boron in plants is the way boron assists calcium in building cell walls. Imagine building a shed with 2 X 4 studs. At the top there is another 2 X 4 where the wall studs are joined to the frame. Right at the intersection there is a need for a nail or screw to join them. In plants the studs would correspond to chains of pectic polysaccharide. Joining them together is the tag team effort of boron and calcium.
Boron and calcium work together to help build and structure the cell walls. When one or the other is deficient plants suffer. When calcium is deficient you can see bitter pit in apples and blossom end rot in tomatoes. When boron is deficient you see hollow heart in potatoes and brassicas.
There is a wide variable in how much boron should be present in plants. Some plants require only moderate amounts, others more, and some need quite a lot. Yet all plants need boron. Without boron cells die.
Boron plays a critical role in plant reproduction. Viable pollen must have an adequate supply of boron. It this is not supplied, the pollen is less viable. In corn the silks must have a bare minimum of 3 ppm of boron for pollen germination and fertilization. In other plants such as almonds the pollen tube may not properly elongate. When deficient in boron, the pollen tubes are so short that bees cannot trigger fertilization and yield is lost.
Lastly, in both corn and beans the concentration of boron in the root tips directly impacts the root's ability to take up phosphorous from the soil. Since phosphorous is the key component in ATP, which runs the plants' energy cycle, this is a big deal. When boron was adequately supplied the phosphorous uptake was more than double.
In the marketplace you can find multiple forms of boron including:
- Borax - 11% - water soluble powder
- Solubor - Sodium borate - 20.5% - water soluble powder
- Poly Borates - 10% - liquid
- Boric Acid - 17.4% water soluble powder
As a side note you need to be testing your soil for boron and keeping the level between 1.4-2.0 ppm. In soil any of the forms above are good. Plants pick up boron as boric acid B(OH)3. Therefore in foliar feeding this is the form to use. Don't use Solubor or Borax or liquid 10% Boron. Instead use boric acid.
Here is an important rule in foliar feeding regularly taught by Wendell Owens, my partner in International Ag Labs.
"When foliar feeding plants you must present nutrients to the plant in the form they can use it."
Another reason to use boric acid is that it mixes well with other low pH foliar sprays and it doesn't contain any sodium.
Boric acid has been used anywhere from 1 oz. to 3 lbs. per acre. I generally prefer rates of 2 oz. to 1 lb. per acre. If you need more than the top rate split the application.
When to Use
- Ahead of flower development
- When boron is low on the tissue test
- Use at low doses just to cover your bases
- Use regularly on high boron requirement crops
Here are a few sample applications.
Trace Mineral Spray for Grain Crops - Sprayed early season per acre
1 quart WayAhead 7X
2 lbs. Dextrose
2 oz. Boric Acid
Water as needed
Start with the water in the spray tank and then dissolve in the dextrose and boric acid. Once dissolved add other liquid foliar sprays. Note: If this spray is for corn just prior to tasselling then increase boric acid to 4 oz.
For gardens just add ¼ teaspoon of boric acid per gallon of regular spray solution. Shake until the boric acid is fully dissolved. Repeat late season.
Lastly a word of caution. With boron there is a fine line between deficient and toxic. Higher rates from 1-3 lbs. per acre should only be sprayed on crops with greater boron demand that actually need it. This is best determined by a plant tissue analysis.
