Boron is required by plants for cell division and formation of the plant’s growing points, also called grower’s tips. It is best if it is continuously supplied.

Deficiency of boron can be seen in the oldest leaves on the lower half of the plant becoming brittle and yellowed, and the grower’s tips dying back. Older leaves will be cupped upwards and stiff. Young leaves will be malformed and have prominent veins. Fruits are shortened and have cracks in their skins. Roots will have enlarged tips and will be black. Symptoms will appear around the first harvest.

To correct a deficiency of Boron
  • raise the ratio of organic matter to sand
  • lower the soil pH by adding Sulfur
  • add borax to the soil

Too much boron will show up in the oldest leaves with them cupping downwards and turning yellow and eventually expanding into dead spots between veins. The leaves can also become more circular shaped. If this condition is not corrected then the plant’s growth will be stunted with very few female flowers developing.

To offset excessive Boron
  • Heavy leaching can be used to remove some boron
  • add lime if the soil is acidic

Soil testing is an important activity for a successful garden. Soil stewardship is an ongoing process, where you test and amend, grow some stuff, then test, amend and grow some stuff….and so on. Focus on building soil tilth so it can really hold and make available to the plants all the important nutrients. You do this in part by adding compost, manure, rock dust, bone meal, kelp & fish emulsions. Read this article series to learn more about each of the 13 key nutrients for your garden.