Boron toxicity at Christmas star.
29 OCTOber 2018
This month in ‘Focus on nutritional elements’ everything about boron. In crops the trace element boron plays a role in a proper cell division, functioning of growth substances and the transportation of carbohydrates.
Boron has a function when it comes to cell division in the plant. It makes sure that the growth substances function properly and it plays a part in the transportation of carbohydrates. A plant takes up boron mainly as boric acid (H3BO3-), but also in the shape of B(OH)4-. Boron is immobile in the plant, therefore a continuous supply is important during the growth of plants. The level of boron in the dry matter of the plant can differ strongly. In many crops the level of boron is between 0.002 and 0.008 % of the dry matter.
Boron is added to most potting soil base fertilizers. Boron can be rinsed out of a culture because of repeated ample irrigation without extra fertilization of this trace element. This is visible in the analysis results of a substrate sample. When it comes to trace elements, boron is a so-called ‘non-metal’. Therefore chemical processes in growing media in which metals can sometimes play a part, have no influence on the present boron.
A deficiency of boron expresses itself in poorly developed roots and dying growth tips. Leaves can look dried out and in fruit crops the fruit set diminishes. For example, cauliflower develops big holes in the way of flowering. Carnations become brittle and the calyx and petals develop poorly, which looks like crop damage by the insect thrips. In potted roses a deficiency of boron will lead to poorly developed growth tips which causes the plant to look deformed. An excess of boron also often happens. This will cause the tips of the leaves to turn yellow and die. The leaf nerves can also get clogged and the leaves may turn convex. Usually a strongly stunted growth precedes this. Strawberries, for example, are sensitive to a boron toxicity. In this crop reddening precedes burning of the leaf edges. As a tree nursery crop the Clematis is sensitive to sometimes very sensitive to boron toxicity. The level of sensitivity varies per variety.
Boron is added to most potting soil base fertilizers. Among others, the boron level of RHP certified products is checked before application in a substrate. There is a maximum level of boron for growing media with the RHP Horticulture quality mark. Within that norm, the substrate producer and the grower decide together what the level of boron needs to be, suitable to the culture.