Q&A for Boron in Almond Orchards

Several articles have been posted on the importance of boron. These have highlighted the importance of boron for fruit set, reliance on hull sampling for tree boron status, and foliar applications.

In regards to these posts, I have received several good questions that I thought I would share.

Q. When should I apply boron to my field?

A. The hull serves as a sink for boron. Applications made after the fruit is removed will be more effective in increasing boron levels within the tree. The nutrient will require transpiration in order to move throughout the tree, and therefore ground applications made in the dormant season will have minimal effect on the coming year’s crop, but will impact the next, next year crop. In other words, an application made in January 2015 will provide the most benefit to the 2016 crop. I should add that an application in the 2015 dormant should increase boron applications in 2015 hull samples – it just will not be in the fruit bud of the tree until 2016.

Q. What about foliar sprays, and do I need them?

A.  A foliar spray made between post-harvest and pink bud has been shown to increase yields. This is an effective way to increase boron levels within the tree. Unless boron hull levels are over 150 PPM, foliar sprays are recommended. Low rates should be applied.

Q. What about if my water or soil contains boron?

A. Boron can be a toxic salt at too high of a level. If soil or water levels are too high, boron should not be applied. Again, hull analysis for boron should indicate if the tree is requiring boron. Boron levels within soil will eventually reduce if applications by irrigation water or fertilizer are eliminated.

Q. Does boron leach?

A. Yes. Boron will leach at different rates depending upon soil textures. Soils with lower exchange capacities should make smaller, more frequent soil applications (~10-15 lbs of solubor/acre), while soils with higher exchange capacities may suffice with larger applications (~15-20 lbs solubor) every other year.

Q. How much boron is used by the tree?

A. This is dependent upon hull concentration and crop load. Keep in mind that boron is in greatest concentration in the hull, and hull removal amounts are typically double that of kernel yields (e.g. a 2000 lb/acre crop removes 4000 lbs/acre of hulls). In regards to removal, the following table indicates rates of removal for 1000 kernel lbs for various hull boron levels:

Hull Boron Content (PPM) Lbs of Boron Removed per 1000/kernel lbs
75 0.15
100 0.2
125 0.25
150 0.3
200 0.4
300* 0.6
500* 1

*These levels are considered toxic within almond.

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10 thoughts on “Q&A for Boron in Almond Orchards

  1. Can the hulls be safely returned to the soil in order to recycle the boron and other nutrients? Alternatively, can they be cultivated into say Olives which also require reasonable boron levels?

    1. Yes, we believe they can. They are also a great source of potassium (~3% K). Within CA, hulls serve as a source of cattle feed – a byproduct in which they have considerable value (~$150-175/ton), which explains why it isn’t done in CA orchards.

  2. I applied boron during the fall of 2013, my hull samples for 2014 show a low level. Should I hold off on applying any more boron because it takes a year to see the results from the 2013 application ? Thanks

    1. Ernie,
      Good question. I made a bit of a mistake – what I meant to say is that boron applied in the dormant will not be present in the buds at bloom. It will, however, move into the hull in the season. I fixed the article to reflect this.

      This means that you should consider another boron application if tissue concentrations aren’t above 80-90 ppm.


  3. I would like to know when and almond is on the tree and into mid to late late stage will the outside skin smell like a peach. I am not sure I have a almond tree. Could you give me an answer thank you Lee

  4. Could you please provide some recommendations or references for foliar application. I am planning my routine late season foliar nutrient applications on my sandy-soil young-orchard.

    I would like to figure out how much and what form of Boron to add. And if I can add it to an existing foliar nutrient application or split it up..

    1. Paul,
      Generally, foliar applications are very low rates – typically around .2-.4 lbs of actual boron in 100 gallons of water. This is equivalent to 2-4 lbs of a 20% boron product (e.g. Solubor). More can be found in this earlier article. In regards to compatibility – that is not an easy question as it depends on formulations and other nutrients applied. I haven’t heard of many issues with compatibility with boron products, but if applying 3-4 products, a bottle test might be warranted.


  5. Can a grower spray multiple boron sprays in the fall, or one in the fall and one at pink bud, to further increase the boron levels in the flower bud in a boron deficient (65ppm 2014 hull test) orchard to benefit the 2015 crop. Would this create toxicity in the flower bud? We already sprayed once, applied boron through drip in the fall and were wondering if a pink bud spray would be beneficial? Thanks

    1. Josh,
      A single spray should do the trick. If possible, a lighter dose now and one at pink bud may be of benefit (0.2 lbs of actual boron/100 gallon of water per acre). If not possible to run the rigs through, I would apply the higher end of the application – 0.4 lbs of actual B/acre.

      You made the right call on applying boron to the soil this fall. It should be reflected in next year’s hull analysis.


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