Down with dirt

Growth medium

Soil is required, except for cannabis grown with hydroponics or aeroponics

Sufficient nutrients—commercial potting soils usually indicate this as “N-P-K = x%-y%-z%” the percentages of the fundamental nutritional elements, i.e., nitrogen, phosphorus and potassium. Nutrients are often provided to the soil via fertilizers but such practice requires caution.
pH between 5.9 and 6.5. This value can be adjusted – see soil pH. Commercial fertilizers (even organic) tend to make the soil more acidic (decrease its pH).


The optimal day temperature range for cannabis is 24 to 30 °C (75 to 86 °F). Temperatures above 31 °C and below 15.5 °C seem to decrease THC potency and slow growth. At 13 °C the plant undergoes a mild shock, though some strains withstand frost temporarily. Frost occurs when air temperatures dip below 0 °C (32 °F) and ice crystals form.

Light can be natural (outdoor growing) or artificial (indoor growing).

Under artificial light, the plant typically remains under a regime of 16–20 hours of light and 4–8 hours of darkness from the germination until flowering, although the plant can use a full 24 hours of light without harm. There is an ongoing debate over the importance of the “dark period”. It has been shown that, when subjected to a regimen of constant light without a dark period, most types of flora, including Cannabis, will begin to show signs of decreased photosynthetic response, lack of vigor, and an overall decrease in vascular development. There is no defined flowering “stage”, unless you are discussing an auto-flowering variety (Cannabis Ruderalis). Typically, flowering is induced by changing the light schedule to 12 hours of light and 12 hours of darkness. Flowering in cannabis is triggered by a hormonal reaction within the plant that is initiated by an increase in its dark cycle, i.e. the plant needs sufficient prolonged darkness for bract/bracteole (flowering) to begin. Some Indica varieties require as little as 8 hours of dark to begin flowering, whereas some Sativa varieties require up to 13 hours.

Watering frequency and amount is determined by many factors, including temperature and light, the age, size and stage of growth of the plant and the medium’s ability to retain water. A conspicuous sign of water problems is the downward wilting of leaves. Too much water can kill young cannabis plants.

The additives in municipal water can reduce plant growth and can be removed with reverse osmosis filtration but is expensive and produces poorer results than well or spring water.

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