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Phosphorus and growing weed

PhosphorusPhosphorus plays an important role in all living organisms and forms an essential component in the nutrition of both plants and animals. It holds a key position in cell metabolism and in the total energy transfer of the plant. It is also a building block of the cell walls, DNA, and all kinds of protein and enzymes.

Phosphate is indispensible for young plants; around 3/4 of the total phosphate uptake occurs before the plant has lived a quarter of her lifecycle! The biggest concentrations of phosphate are also found in the developing parts of the plant such as the roots, growth shoots and vascular tissue.

Introduction

Phosphorus is a chemical element that belongs to the non-metals and that is not found in pure form in nature because it is highly reactive. It was discovered in 1669 by an alchemist from the evaporation of urine (in an attempt to make gold).

Phosphorus in the cannabis plant

Phosphate compounds in a form which plants can make use of are rarely found in nature. In days gone by, people used ground bones (bone meal) as a fertilizer, and later used sulphuric acid thanks to which the phosphates were made considerably more available. In the second half of the 19th Century, guano, a natural phosphate fertilizer made from accumulated seabird droppings, was quarried on a huge scale for use in agriculture.

These days the basic materials are extracted from natural phosphates, primarily these are phosphate-rich ores extracted from places such as Morocco, Algeria, North and South America. In order to make natural phosphates suitable for agriculture and horticulture they are first acidified and then purified. In alternative agriculture they are finely ground or heated and are available as expanded granules in stores.

Phosphate deficiency

Phosphorus deficiencyCertain symptoms of phosphate deficiency described in the literature should not be confused with nitrogen deficiency. A phosphate deficiency is characterised in cannabis not by a noticeable purple colouration in the stems and leaf veins, but by a small plant with purple-black necrotic leaves that warp and eventually crinkle the leaf.

Its progression in chronological order:

  • In the beginning the plant turns dark green, a different kind of dark-green (blue-green) than found with a potassium shortage.
  • The growth in height and the development of side shoots is retarded.
  • After 2 to 3 weeks there will be dark purple/black necrotic patches on the medium-young and older leaves, thanks to which the leaf is deformed.
  • The purple/black necrosis extends in to the leaf stalk. The leaf twists, crinkles and dies.

Causes for Phosphate deficiency

  • Having too high a pH in the grow medium (>pH7); means the plant has reduced capacity to take up phosphate, and in the soil there will be an accumulation of insoluble phosphate compounds
  • Soil that is iron or zinc-rich, or too acidic
  • By soil fixation

What to do

Inorganic phosphates, in ion form, are very easily taken up. As far as is known, plants take up no phosphorus in organic form. However, inorganic phosphates can be released in the decay of organic soil particles. Thanks to the residue effect of phosphates it holds that the older the soil the more phosphate rich it tends to be.

Enriching the soil with phosphate-containing fertilizers after a deficit has been discovered often has very little effect: thanks to precipitation or absorption phosphate hardly penetrates the soil and the disturbances in growth when the plant is young are hard to recover from. For this reason phosphate-fertilizers need to be well worked into the soil.

  • Prevention is better than cure, use good soil and/or a good fertilizer, go to a specialist shop for professional advice
  • With a high pH the best way you can acidify the medium with a dilute solution of phosphoric acid (safe pH value for hydro: 5.2 – 6.2, for clay soils: 6 - 7, for compost: 5.5 – 6.5).

pH

  • Alternative phosphate-containing fertilizers include: guano, blood meal, bone meal, natural phosphates, slag, and liquid manure. The drawback is that they contain a wide variety of levels of phosphate, which furthermore is relatively unavailable to the plant. The fineness of the phosphate source’s grinding and acidifying before using it improves the solubility of natural phosphates. The best solution is to choose products on the packaging of which is stated a guaranteed percentage.

An excess of phosphate is damaging to the environment and can trigger all kinds of side effects, including zinc, copper or magnesium deficiency.

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