Harvest is here. This is a good time to pull a a bag of almond hulls for a boron analysis. In making this recommendation, there are questions that are consistently asked.
I already know my leaf tissue levels, so why do I need to perform a hull analysis for boron?
Leaf sampling is not effective in determining the levels of boron as there are no obvious foliar symptoms of moderate boron deficiency. Furthermore, leaf levels may appear adequate while the actual levels within the tree are too low or high. Since the hull of the almond is a “sink” for boron, the analysis of mature almond hulls is a better indicator of boron status.
When should I collect samples for a hull analysis?
Boron will continue to accumulate in the hull until harvest. The best time to collect a hull sample is anytime after shaking the nuts. Varieties within the orchard may have differing boron levels due to different yields; it may be useful to pull a sample from the other varieties.
How do I interpret the results?
Trees with hull boron levels of less than 120 ppm may benefit from a postharvest boron spray (1-2 lb of a 21% B product in 100 gallons of water per acre). This will help with pollen germ tube growth in the flowers next spring but will not improve overall boron status of the tree. Boron applied earlier in the season as foliar spray is not a substitute for this timing because it is sequestered into the hull and is unavailable for the developing fruit bud.
Hull boron of less than 80 ppm indicates the need for a ground application. Fertilize with 2-4 pounds of actual boron per acre. This is equivalent to 10-20 pounds of a 21% soluble boron product (i.e. Solubor). Boron can be applied through the irrigation system, broadcast or sprayed on the ground, or included in a herbicide spray. Herbicide sprays containing glyphosate may need to be buffered to prevent reduction of
If hull levels are over 200 PPM indicate excessive boron. In these cases, it is important to perform soil and water analysis to determine strategies for boron management.