Everyone knows that different cannabis cultivars naturally contain different combinations of cannabinoids, but if you’re growing your own marijuana then it’s important to understand that the levels of THC, CBD and other compounds in your bud won’t be determined solely by genetics. Environmental conditions like soil nutrients also play a huge role, so if you want to maximise the cannabinoid content of your plants then it’s well worth taking the time to optimise your soil.
In a previous post we explained the basics of how to choose the right type of soil for your cannabis, so if you’re new to the subject then you might want to give that a read first. Here, we’re going to get a little more advanced and look at how you can add specific elements to your soil in order to influence the production of individual cannabinoids.
As with pretty much all plants, there are certain elements that marijuana needs in order to grow, photosynthesise and flower. These include nitrogen, potassium, calcium and phosphorus, and you’ll always want all of these in your soil. Yet as your crop moves through its growth cycle, you may need to tinker with the levels of each of these nutrients.
Getting the Balance Right
Nitrogen, for example, is essential for the production of healthy green foliage, so it’s really important during the vegetative stage. However, too much nitrogen during the flowering stage will encourage your plants to keep on generating new leaves without producing much bud, so you’ll end up with pretty weak cannabis.
To get around this, it’s a good idea to add nitrogen to your soil early on, when your plants are still young. Fertilisers like worm meal, bat guano and nettle tea are great for this, but time-release fertilisers should be avoided as they can overload your plants with nitrogen during the flowering phase.
Managing calcium levels can also make a huge difference to the potency of your bud. Research has shown that the concentration of THC in cannabis plants is directly correlated with the ratio of calcium to magnesium in the soil that they are grown in[i]. The more calcium there is relative to magnesium, the more THC you get, so if you’re trying to grow really strong weed then you may want to consider adding calcium in the form of dolomite lime. Additionally, it’s worth ensuring that the acidity of your soil is optimised to allow maximum calcium absorption by the roots of your plants, which means maintaining a pH of between 6.2 and 7.0.
Phosphorous is another element that is vital to the healthy growth of plants, although too much of this nutrient during the flowering stage can stunt the production of CBD. This is because excessive phosphorous causes a ‘nutrient lockout’, whereby the plant becomes unable to absorb other key elements like calcium and iron.
Likewise, an excess of potassium has been found to limit the production of THC[ii], so if you do decide to add phosphates or potassium to your soil, it’s a good idea to ensure you don’t overdo it during the flowering phase. So if you do decide to add phosphates to your soil, it’s a good idea to ensure you don’t overdo it during the flowering phase.
Is There A Soil That Contains The Perfect Balance?
Because each cultivar has its own nutrient requirements, the optimal soil type is always going to differ slightly between cannabis varieties. However, with a bit of experimenting it’s perfectly possible to find a soil that contains the right balance of nutrients for your plants.
To prove the point, a group of researchers once tried growing cannabis seeds of Afghan origin on 11 different soils, in order to determine which one supported the highest cannabinoid levels. Interestingly, they found that plants grown in soils containing low amounts of magnesium had the highest THC content. To be more specific, they discovered that a gilpin loam soil made of grey shales, and a manor loam soil made of mica schist, were optimal for maximising THC levels[iii].
Of course, there are many different types of soil and experienced growers will all have their own preferences regarding which ones to use. Some even choose to bypass the issue of soil altogether and opt for hydroponics or coco coir as a growing medium for their plants.
There are many other factors that will also influence the strength and quality of your plants, with temperature, light and humidity all being significant. However, soil is something that is well worth optimising as it provides your plants with the basic ingredients they need to biosynthesise those precious cannabinoids.
[i] Pate DW. Chemical ecology of Cannabis. Journal of the International Hemp Association. 1994;2(29):32-7. – http://www.internationalhempassociation.org/jiha/iha01201.html
[ii] Haney A, Kutscheid BB. Quantitative variation in the chemical constituents of marihuana from stands of naturalizedCannabis sativa L. in East-Central Illinois. Economic Botany. 1973 Apr 1;27(2):193-20 – https://link.springer.com/article/10.1007/BF02872989
[iii] Coffman CB, Gentner WA. Cannabinoid profile and elemental uptake of Cannabis sativa L. as influenced by soil characteristics 1. Agronomy journal. 1975 Jul;67(4):491-7. – https://pdfs.semanticscholar.org/ea21/7ed3883885abe6c385199e76ac3d3551fcb2.pdf