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Best Soil for Marijuana: A Quick Guide for Cannabis Growers

Like most plants, cannabis requires a strong base if it’s going to grow well. There has been a lot written about the best soil for marijuana and for the beginner all this information can be pretty confusing.

For some strains, too rich a soil can affect the growth adversely. Others need a heavier mix. A lot can depend on whether you are growing autoflower or photoperiod strains. If you’re looking to grow a great tasting cannabis, therefore, it’s a good idea to read up on everything and build your knowledge base for the particular seed strain that you’ve opted for.

A good soil could mean the difference between a bountiful harvest and one that comes in just below average or worse. While cannabis seeds will actually grow in practically any medium, your aim is to cultivate more buds from your crop. The good news is that there is plenty of help and advice online. Here at Seedsman, for instance, you’ll find plenty of helpful articles on soil types and the best conditions for growth.

There are several factors about your soil choice that are going to be important. Whether you are growing indoors or outdoors is one. Another is the PH of the soil (how acidic or alkaline it is). The first thing we’ll do here is take a look at how these individual factors fit together to make the best soil for marijuana.



What Does a Great Soil Look Like?

While it’s considered a weed by most horticulturists and can grow practically anywhere, that doesn’t mean you don’t have to worry about optimal conditions for your crop to thrive. You’re not just trying to produce any old plant here but one with the right level of THC, CBD or trichomes.

That takes a bit of skill, expertise built up over time and a good deal of knowledge. If you’re serious about growing cannabis you have to put in the research hours!

There are certain things about the area where you plant that can improve the success of your crop considerably:

  • Excellent drainage (this applies whether you are growing indoors or outdoors) is an absolute must.
  • You also need to have water retention, however, at least enough for the roots of the plants to draw up enough to feed on. This can be a difficult balance to achieve.
  • Too much fungus and not enough bacteria can be a problem to. Your soil needs to be in good health which can often depend on where you live if you are planting outside.
  • The compost you use has to have a good ratio of phosphorous to nitrogen.
  • A pH of around 6 is ideal, something which means the soil is just slightly acidic. pH plays an important role in all sorts of cultivation. If you want to create the best soil for marijuana, you need to understand a little about this.

Let’s start with a definition: pH is a scale of acidity, with numbers ranging from 0 (very acidic) to 14 (alkaline). Seven is neutral.

There’s a lot of thought that has gone into deciding the pH of soil for growing cannabis and most say that around 6 is optimal – slightly lower or higher is okay but anything less than 5.8, for example, will mean you won’t get the crop you are really looking for.

The next thing you need to find is some way to measure the pH of your soil. That’s okay as there are plenty of testing devices available and they don’t cost very much.

What Are Soil Types?

For cultivating outside, you’ll probably be faced with three different soil types. A lot will depend on where you live and they are called sandy, loamy or clay soils. The trouble is that different locations can have mixtures of each. So, you can get a sandy clay or a loamy sand, for example.

It can be very confusing and that’s why we suggest you dig up the area where you want to plant and put your own soil there, one that is specially designed to help with growing cannabis.

Of course, one option is to avoid the natural ground altogether and plant your seeds in pots. This has the added advantage that you are able to control things a lot better and move your plants around.

Autoflowering Seeds vs Photoperiod Varieties

Before we look at making your own soil for either outdoors or indoors, there is also a difference between autoflowering and photoperiod strains and the soil they like. The former prefers a light or non-fertilized soil and might well thrive in untreated ground. You will want to add a natural fiber like coco coir which is readily available from garden stores as well as some perlite which is there to help with drainage.

Photoperiod strains generally have specific soil requirements that you will need to read up on before you decide to plant. You may have heard the term super-soils which are essentially specially developed environments that are designed to improve crop yield. This can be a difficult balance to get right especially if you are planting outside or are a novice cannabis grower.

Homemade vs Store Bought Soil for Marijuana

A lot will depend on how much work you want to do yourself. There are plenty of store-bought soils that are perfectly suitable for growing a cannabis crop. In some cases, you can grow straight out of the bag if you want to. The only thing that you may need is to add is some extra perlite which is used to improve drainage. Cannabis tends to require better drainage than most other garden plants.

Homemade soils are a different thing altogether.

We’d suggest you avoid these if you are a beginner and concentrate on getting your first crop. There’s plenty of time to build up your knowledge later.

For more experienced cannabis growers, however, there’s a certain pride in developing one’s own soil. In truth, it’s a lot simpler than many think. You usually start off with a store-bought mix and then add your own ingredients to this. For example, some growers like to add bat guano as a fertilizer. Others put in time release pellets which makes sure that their plants get the right amount of nitrogen and phosphorous in a steady infusion.

A lot will depend on the strain that you have decided to plant so it’s worth bending the ear of a few experts before you start any real experimentation.

What’s added to the soil during the growth process is also important as you want to keep the nutrient levels up to the right amount. One popular recipe is 420 fertilizer which contains an array of ingredients including rock phosphate and Epsom salts as well as sweet lime and blood meal. You can find vendors that sell this ready made if you don’t want the hassle of doing it yourself but there are plenty of recipes online.

What is No-Till Cannabis?

You might have heard this phrase from experts who grow cannabis. It’s a soil that is developed naturally over a long period of time. You basically don’t want to do much to the ‘living’ soil at all if you can help it and it’s about promoting the natural bacteria that form around the roots.

Get it right and you’re supposed to be able to replant over and over again without much problem. It rarely happens for most people, unless you live in a great location, and you may find yourself adding a little extra fertilizer now and again to top things up.

Our advice, if you’re not really that bothered about your soil, is to give this a miss. It’s one for the serious cannabis cultivator and there’s no real evidence that it produces a more superior crop (at least not for the amount of work you have to put into it).

Dealing with Drought Conditions

Depending on where your crop is growing, you may have to contend with droughts from time to time. This can spell the death knell for any crop, autoflower or photoperiod. Putting some polymers that absorb water in the soil can help. These can be bought for a few bucks from any hydroponics store and can stop things drying out.

Best Soil for Marijuana: Adjusting the pH

Finally, it’s one thing to know the pH of your soil, another thing entirely to change it. What do you do, for example, if you find that your soil is too acidic?

The most common way to change the acidity is to add lime to the soil because it is alkaline. Always start by adding just little and then retesting the soil with your indicator and it helps to leave for a while before doing this.

If the soil is too alkaline you should add something like sulphur, aluminum sulfate or iron sulfate. Again, start with too little rather than too much and retest before you add more. This is something that you’ll begin to get a feel for the more you do it.

Creating a great soil doesn’t require a degree in horticulture and there’s plenty of advice here online. Get the planting environment right, however, can make a big difference to your overall yield and is well worth looking into.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.


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