Types of soil can vary from loamy to sandy or silty. Can cannabis be grown in all types of soil?
From the tropics to the desert, cannabis grows in almost every corner of the globe. But, growing cannabis outdoors is a very different prospect to growing it indoors. With indoor grows, cultivators can control almost every variable, including humidity, temperature, lighting, and soil chemistry. With outdoor grows, there are many more variables to contend with, and one of the most influential of these is soil. Where indoor growers often buy a ready-made soil blend specially developed for cannabis, many outdoor growers use the native soil.
The Five Main Types of Natural Soil
Soil consists of decomposed organic matter broken down by worms, fungi, and other microorganisms. The quality of soil varies widely across the globe and is dependent on climate, exposure to pollutants, and the vegetation that grew on the land in times gone by.
Soil consists of three key ingredients – sand, clay, and silt. These can then be further subdivided into five main types, of which native soil comprises of some variation.
- Sandy soil is gritty with rapid drainage and struggles to hold nutrient content.
- Silty soil is fertile, with small smooth particles that retain water exceptionally well but exhibits poor drainage.
- Clay soil consists of small compact particles that exhibit a sticky texture and has poor aeration, but holds water well.
- Peat soil is acidic and full of organic matter.
- Saline soil is high in salt content and is commonly found in more arid regions around the world.
The Best Types of Soil For Cannabis
The ideal soil for outdoor cannabis is one that’s loamy, dark, and rich in nutrients with a light, fluffy texture. The soil should have the ability to retain water (less sandy) while also allowing for excess water to drain quickly (less silty). Loamy soils consist of a mixture of sand, silt, and clay, with the ideal ratio between each being roughly 40:40:20.
Aside from texture, the best soil for outdoor cannabis also has strict requirements around pH, and the ratios and quantities of pathogens and pests in the soil. All of which can be tested with specialized equipment.
Many growers choose to create their own soil blends in order to obtain full control over pH, nutrient content, and texture. But, for those who wish to work with mother nature without manipulating the soil excessively, one easy check to determine the soil composition is to place a few handfuls in a glass jar, before covering it with water and shaking it.
Once the particles settle, it will provide a reasonably clear indication as to the composition of the soil.
The loamy soil that outdoor cannabis cultivators desire will result in a layer of clear water at the top with gradually more dense bands of particles in layers down to the bottom. The depth of each layer will provide an indication of the ratios between the different compounds.
Sand will usually form the bottom layer, while peaty soil will result in small particles floating up top. Silty soil will result in a thin layer of particles towards the bottom, where the top layer may take a long time to clear.
The Importance of Testing pH
Soil pH is extremely important when it comes to growing cannabis. Ideally, it should be slightly acidic, in the range of 5.5 and 6.5. When soil pH drifts outside of this window, nutrient toxicity and deficiency often result. Soil that’s too acidic or alkaline means that plants struggle to uptake nutrients correctly. While plants may still grow in excessively acidic or alkaline soils, they are unlikely to yield anywhere close to capacity.
The easiest way to measure pH is with a pH meter. These are widely available in most garden stores for a reasonable price. If you need to adjust the pH, then there are several compounds that you can add to bring it back into the required range. For soil that’s too alkaline, then the addition of sulfur can help acidify the soil. While to increase pH, lime is the most commonly used compound.
Sterilizing Native Soil
Sterilizing native soil is a process of killing off harmful microorganisms and insects while allowing the beneficial ones to remain. Those who purchase a commercial soil blend don’t have to worry about sterilizing soil, but for anyone considering planting in native soil outdoors, then it may be worthwhile.
There are several ways to sterilize soil, most of which are time-consuming. Solarization is one popular method where growers till the soil and break it into fine pieces before watering it and covering it with a transparent sheet of plastic. When exposed to the sun, the temperatures rise and kill off harmful microorganisms. To ensure effective sterilization, the temperature must reach 114°F (46°C), and the sterilization process ideally lasts for four to six weeks.
Those with time constraints can use steam to sterilize the soil. Small-scale growers can use a pressure cooker, while those with a larger grow operation can avail of the commercial solutions offered by large agricultural operations.
For those who prefer to take a more holistic approach, there are also ways to introduce beneficial microbes and insects into the native soil to help bring it into a state of balance. While less labor-intensive than sterilization, this process does require a certain degree of expertise and knowhow.
The Relationship Between Native Soil and Chemovar
Among beginner growers, autoflower strains are particularly popular. With a time-based flowering cycle as opposed to a reliance on photoperiod, they exhibit many favorable qualities. Outdoor growers should be aware that the soil requirements for autoflowers differ from their photoperiod cousins. They prefer aerated and loose soil that isn’t overly high in nutrients. As a result, growers may wish to add perlite or coco coir to the existing soil in a 1:1 ratio.
Growing outdoor cannabis is rewarding, fun, and a much cheaper alternative when compared to indoor growing. With fewer overheads and less maintenance, it’s an attractive option for many. But, while the advantages are clear, a little knowhow still goes a long way. After all, growing cannabis outdoors places the grower at the mercy of the elements, and the chemistry and composition of the very soil beneath their feet!