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Sulphur and cannabis plants


Sulphur is a molecular building block in a number of proteins, hormones and vitamins, such as vitamin B1. It is also found in a number of important plant tissues, including seeds and cellular fluid. Sulphur, in the form of sulphate, also plays an important role in the water management not just of the plant, but also in the soil.

Sulphur is a chemical element that has been known of since ancient times. We can see its application in things such as (sulphurous) health spa baths, match heads, gunpowder and battery acid. Furthermore, sulphur is well known for its stinking hydrogen sulphide, given off by among other things, the decomposition of egg proteins.



Sulfur periodic system







At normal temperature and pressure, sulphur is an odourless yellow solid that is not very toxic. Pure sulphur is found in nature in the form of yellow deposits in and around the edges of some volcanoes. Furthermore, volcanic rocks such as those found in Iceland and Sicily can contain high concentrations of sulphur. It has been estimated that around 0.05% of the weight of the Earth’s crust consists of sulphur.

When growing in soil it is very rare to encounter a sulphur deficiency; pretty much all soils and standing water contain sulphates, some have considerable amounts. A lot of sulphur is released into the air by the burning of coal, petroleum, diesel and other fossil fuels. It is removed in the form of acid rain or particles that fall to earth. The amount added to the soil fro this source is so great in Western Europe that there is no chance of any soil being deficient in this element.

Sulphur-enriched fertilizer is largely found from the same sources as potassium and magnesium-enriched fertilizers (see cAnna’s info on Potassium deficiency). When growing on hydro all nutrients needed by the plant are supplied from the system’s feed water. The hydro fertilizers used tend to have high concentrations of calcium and sulphur. To avoid the calcium and sulphur reacting with each other (so that barely-soluble gypsum is formed), the substances are separated by nutrient manufacturers in to an A and a B component.

Sulphur in the plant


In the plant sulphur is incorporated in proteins and organic structures. Thanks to this, when there is a deficiency of it, it is difficult for the plant to move sulphur around to where it’s most needed - in young leaves - with the result that these become light green in colour. Theoretically the symptoms should therefore first be visible in these young shoots. But in practice it has been repeatedly shown that the symptoms are clearest in older leaves.

The progression in chronological order:

  • Looks a lot like nitrogen deficiency; light green colouration in one or more large / older leaves.
  • Strong purple colouration in the leaf steles (thanks to the production of anthocyanate pigment).
  • More leaves discolour and the light green changes in places in to deep yellow.
  • In cases of extreme shortage in the plant, more deep yellow leaves, with purple stalks and leaf steles, and the growth and bloom are halted





Sulfur deficiency

Sulphur deficiency

When growing outdoors in soil the chance of sulphur deficiency is very slim. It can occur when growing in compost, as can phosphate deficiency (see cAnna’s info on phosphorus deficiency), when the pH is too high and there is too much calcium. Furthermore, when growing in compost or with hydro there can be a sulphur deficiency if the nutrient mix was not well put together.

Causes for sulphur deficiency

  • As with phosphate, sulphate becomes more available for the plant at a low pH. Check the pH of the medium, lower it if necessary with sulphuric, nitric, phosphoric or ascorbic acid.
  • In the event of a shortage then you can best add sulphur from an inorganic source with the magnesium-rich fertilizer Epsom salt (for hydro growing) or Kieserite (on soil; see cAnna’s info on magnesium deficiency).
  • For an organic alternative, mushroom manure and the manure from most mammals are good sources of sulphur. It is absorbed by plant in the form of sulphate, which becomes available in soils by the breakdown of organic sulphur compounds. This takes time! So work preventatively and make sure you start a grow with a good helping of well-rotted manure.

Higher concentrations of sulphur are not especially damaging for cannabis, but because they raise the salt concentration of the feeding water they are detrimental to plant growth should they push the EC level above safe limits. Since plants in generally absorb very little sulphate, it can accumulate in the soil moisture. An excess of sulphate is manifested as salt damage; stunted growth and a darkly coloured plant. At higher levels (high EC) you’ll need to flush the system with pure water.

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