I read in a soil and plant nutrition book about Hood River Pear growers spraying boron in the Fall to increase fruit set the following Spring. Is this practice still being used, and what is the reason behind it? I am thinking about spray my Variegated Holly trees to help set fruit since they are somewhat fussy about fruiting. Thank you, Paul.
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Boron is needed in small quantities for plant growth and fruit development and is applied in orchards to correct deficiencies in the soil. Application of boron is commonly based on soil tests or tissue analysis that indicated deficiencies or observing symptoms of boron deficiency: yellow and stunted growth, curled leaves, curled growing tip. Boron is applied both to the soil and as a folliar spray. Here is more information about boron in general: http://www.cals.uidaho.edu/edcomm/pdf/CIS/CIS1085.pdf
Unless you are seeing signs of deficiency, you probably do not need to add boron, but adding a small amount will not hurt your plants and could help. It is possible to add too much boron and damage your plants too. Application rates of boron (borax) to soil are typically 1-2 pounds per acre, so just one tree will need very little. Also, solubor is a soluble product that can be folliar applied, in which case application rates will be provided with the product.
Please let me know if you have any further questions.