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best soil mix for growing cannabis outdoors

Silty soil is the ideal growing medium. It’s easy to work, warms quickly, holds moisture, has good drainage, and contains a lot of nutrients. The best silty soil is dark, crumbly loam—it’s fertile and probably won’t need any amending.

We recommend these organic fertilizers:

In hot climates, sandy soil should be mulched to help with water retention and to keep roots from getting too hot.

Silt soils

There are also commercially available soil blends that already contain the proper mix of these types of ingredients.

If you’re growing weed outdoors, it’s great to find a community of cannabis growers in your area to see how others are growing in your specific climate. Local climates vary, so it can be helpful to see what strains thrive where you are, and also when other growers are popping seeds, harvesting, and more. You can also join online forums or Social media groups, but a great place to start is your local grow shop.

Growing containers

However, plants grown in pots, buckets, or barrels will likely be smaller than those planted in the ground because their root growth is restricted to the size of the container. In a broad sense, the size of the pot will determine the size of the plant, although it’s possible to grow large plants in small containers if proper techniques are used.

Sustained temperatures above 85°F will cause your plants to stop growing, while continued temperatures below 55°F can cause damage and stunting to plants, even death.

Best soil mix for growing cannabis outdoors

On the other hand, digging holes in the ground and planting your young plants straight into the soil allows them to grow without constraint, and will allow roots to access the maximum amount of groundwater. Thus, they will achieve larger sizes and will require less vigilant maintenance, but may be at increased risk of exposure to soil pathogens and even contamination from agricultural run-off, for example.

Sterilizing your soil by exposing it to steam can kill off many harmful bacteria, fungi and insects, while allowing several beneficial bacteria to remain alive. If purchasing good-quality commercial soil intended for growing cannabis, it is usually unnecessary to sterilize soil. However, if using local, natural soil, it may be helpful to sterilize where possible. It may also bring the added advantage of killing off any unwanted weed seeds present in the soil.

If soil solarization is not possible due to time constraints, it may be possible to sterilize your soil by using steam. Large-scale agricultural operations make use of expensive, specialized equipment, but it is possible to use cheaper household sources of steam such as a pressure cooker to sterilize soil.

If you’re using natural local soil, you can mix extra sand, silt or clay into it to improve its soil draining or retaining capabilities as needed. Drainage and soil stability may also be improved by adding gravel, which in technical terms is rock and mineral particles measuring 2m-75mm in diameter. Larger rocks can be removed where possible to avoid causing obstruction to the roots of plants.

Sterilizing your outdoor soil

One method of determining soil composition involves shaking soil in a jar full of water and allowing the particles to settle; a more detailed explanation can be found here.

When growing outdoors, there are several options available: grow your plants in pots or planters, keep them in growing bags (which may be the plastic sack your commercial soil was purchased in, or may be specially-designed bags that are typically made of hessian or breathable plastic). You can also dig holes in the ground and plant directly into the soil. Outdoor soil can be optimized using the methods outlined above, or use without modification if testing shows it to be naturally optimized for growing cannabis.

The optimum pH range for cannabis is between 5.5 and 6.5, making it slightly acidic. If soils are more acidic or alkaline than this, a range of deficiencies or toxicities can result. Soil that is too acidic or too alkaline disturbs a plant’s ability to absorb and use nutrients. If nutrients are not taken up in optimum ratios and quantities, your plants will not achieve the maximum quality and yield, your final harvest will suffer as a result.

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If soil is poor, you may wish to consider buying good-quality commercial soil and mixing it into existing soil. You can also add manure, mulch, bloodmeal, bonemeal, or a range of other soil additives designed to improve nutrition release. You can even grow your plants entirely in bought commercial soil, in bags or pots so that they are not exposed to local soil.

The smaller the average particle size in soil, the harder it is for water to travel through it. You can think of it like a coffee machine. If you pack the coffee into the wand too tight, it’s near impossible for the water to come filtering through. By the same principle, sandy soils have very quick water drainage, while soils with high clay content become waterlogged easily.