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The Best Soil For Growing Autoflowering Cannabis

Autoflowering cannabis strains are known to be hardy and easy to grow. Despite their low-maintenance and photo-independent nature, they can still benefit from optimised soil and nutrients to reach maximum yield and quality.

Autoflowering cannabis strains are known as the easy option when it comes to cultivating the herb. Their hardy nature, fast growth, and ability to flower without a change in photoperiod make them a prime choice for both beginner and advanced growers alike. These sturdy strains often require little maintenance and allow sufficient room for error; however, when chasing the optimal yield and bud quality, a few boxes need to be checked. One such box is adequate soil.

Autoflowering strains contain genetics from Cannabis ruderalis, a subspecies that evolved and adapted to extreme weather and light cycles far into the Northern Hemisphere. Such adaptations and the resulting hardy nature of autoflowering strains mean that they aren’t too picky about soil. However, to encourage them to reach their true potential, an optimal soil mix should be applied.

LIGHT AND AIRY SOIL

Autoflowering strains favour light and airy soil with less nutrients than photoperiod strains would prefer. It’s best to make your own soil mix as opposed to purchasing a ready-made mix from stores, as they may be too high in nutrients like nitrogen.

Heavy potting soil will stress autoflowering varieties, preventing their roots from accessing adequate amounts of air. Roots may also have a difficult time penetrating and growing through a heavy medium.

This basic recipe offers a soil mix that contains adequate nutrients, as well as materials that will help to boost the aeration of the soil medium.

  • 3 parts peat moss
  • 3 parts compost
  • 2 parts perlite, pre-wet
  • 1 part vermiculite, pre-wet

GO EASY ON THE FERTILISER

Autoflowering strains are usually short and compact, a genetic trait stemming from the ruderalis subspecies. This characteristic, along with their rapid growth times, means that autoflowering strains don’t actually need that many additional nutrients.

Most autos will only stay in the vegetative phase for a short period of time, meaning they won’t require a huge amount of veg nutrients like nitrogen. Adding too much can actually burn autoflowering strains, so feed them conservatively.

During the seedling phase, your autoflowering plants won’t need any nutrients. Growers can start supplementing with nutrients about 2 weeks into the grow, but should do so lightly to avoid damaging the crop.

Even during the flowering phase, autoflowering varieties don’t need a huge amount of extra food. Bloom nutrients and boosters can still be applied, but with a less-is-more approach. Pay close attention to your crop and apply when you deem necessary.

SOIL PH

The pH scale is a measurement of how acidic or alkaline a substance is. The scale features 14 readings, with 7 being neutral, numbers lower than 7 being acidic, and numbers over 7 being alkaline. Soil can vary in pH, with differents plants thriving in varying levels. Autoflowering strains are similar to photoperiod varieties in that they prefer a slightly acidic soil medium.

Growers should try to keep their soil within an optimal pH range of 6.2–6.5. If purchasing soil, make sure the product is suitable in terms of acidity. If you need to regulate the pH of your soil, there are numerous products available to achieve this.

MICROORGANISMS

The soil that your autoflowering plants are growing in isn’t merely a medium that the roots sit in while the plant grows—it’s much more than this. The soil is a diverse and thriving web of life that includes symbiotic organisms and pests alike.

Whether you are cultivating your plants indoors within a grow room or tent, or outdoors within greenhouses or garden beds, your soil can be supplemented with beneficial microorganisms.

As all growers will know, especially those who raise their crop in the great outdoors, there are many pests out there with an appetite for fresh cannabis leaves, roots, stems, and flowers. These critters take many forms, and lots of them reside within the soil. Parasitic nematodes can be a problem, eating cannabis roots from both the insides and outsides.

Autoflowering cannabis strains have different soil requirements in comparison to their photoperiod counterparts, preferring light and airy media.

Which Soil Is Best For Autoflowering Cannabis?

When growing autoflowering Cannabis plants, it is very important to keep them supplied with nutrients in the form of hard foods, or liquid feeds. Knowing which medium to use and the quality of soil required can really set you on your way to bountiful harvests.

So if you’re wondering what soil is best for growing weed, below we’ll explain what to know, the signs of good and bad soil quality, as well as what you should consider when it comes to planting this year.

1. The Benefits of Organic Soil

Soil consists of organic material that is in a permanent state of decomposition. Teaming with beneficial microorganisms that are responsible for converting nutrients to the plant’s roots, living soil is Mother Nature’s way of allowing plants to work in a symbiotic relationship.

As the tiny microorganisms decomposing the organic matter, they make the nutrients available for the roots, which are now able to access all the available nutrients and minerals found within the soil web.

Once this symbiosis occurs, then the only real requirement is for the soil to be adequately watered. This is basically the most simple form of organic growing that is perfect for those new to growing, it requires very little maintenance, and labor, as well as allowing the grower to work with a slow buffering organic process.

2. Other Additives That Improve Soil Quality

Some of the downsides to using soil found in the ground is that it can be very dense once watered. Restricting root growth during the early stages of a Cannabis plant’s life is never advised, so adding other substrates into your living soil can be very advantageous.

Coco

By simply adding a 25-50% ratio of coco coir to your soil, the quality of the mix will become very airy and lightweight. Adding coco will enhance the air pockets present, the wicking action of the medium, as well as encourage a mass expansion in the rhizosphere. Coco is very user friendly and is well associated with large yields.

The best thing about adding coco is the fact it is an inert growing medium, so does not have any nutritional value in terms of Nitrogen, Phosphorus, or Potassium, including trace elements.

Pros

1. Increases aeration and holds water better: Due to its characteristics, coco fiber can increase aeration in the soil and can absorb up to 10x its own weight in water, making it vital for growers living in dry weather.

2. Cheap: Coco fiber is relatively cheap and comes in various forms. You can find it compressed into a brick or already washed and ready to use out the bag, the price may change a bit depending on your preference but it won’t be absurdly expensive.

3. Easy to use: Coco is a sterile medium so fungus and other bugs avoid it, making it perfect for growing cannabis. Also, because of its neutral pH, you can use it with soil amendments without worrying.

Cons

1. Sterile: Because this type of medium is sterile, it won’t contain any of the nutrients your plant needs, even though you can mix it with soil or even amend it, you will have to provide all the nutrients your plant needs if you’re only using coco.

2. Needs to be washed: The quality can vary from brand to brand, so depending on the brand, you will have to soak it and wash it a couple of times to remove impurities before using it.

3. Hard to find good quality: Even though it’s relatively easy to find coco coir, it can be hard to find good quality coco fiber. This doesn’t mean you can’t use it but you will have to wash it thoroughly and experiment with a couple of brands before you’re 100% satisfied.

Biochar

An incredible organic addictive that has amazing water-holding capabilities, an enormous surface area, and is a source of pure carbon. Biochar is made by heating wood to such temperatures that the end result is a tiny, charcoal-black crystalline substrate.

Due to the fact it is 100% carbon and has a shelf life of thousands of years, organic farmers use biochar with their soil to improve water retention allowing for less watering times, feeding the beneficial microorganisms a rich source of carbon, and helping save the planet.

Pros

1. Increases soil fertility: Biochar can boost soil fertility when used in combination with amended soil because it prevents nutrients from leaking out and provides carbon which increases the availability of nutrients in the medium.

2. Holds nutrients and moisture: Thanks to its porous surface, biochar can absorb a lot of water and draws in minerals which are essential for plant development.

3. Reduces the need for fertilizers: Because biochar is carbon-rich, it accelerates the decomposition of organic matter which results in more nutrients being available in the medium, a perfect choice for organic growers.

Cons

1. Can affect yields: Due to the porous characteristic, biochar can absorb too much water and nutrients when used in excess and can end up stressing your plants which will show signs of deficiencies .

2. Can be contaminated: The quality of biochar is influenced by the material it is made of, so it can come contaminated with heavy metals or harmful compounds that are bad for your plants.

3. Harmful to humans: If not dealt with caution, you can end up breathing ash which is a concern if exposed to daily, also, it can irritate you if it comes in contact with your eyes or skin for a long period of time.

Perlite

Perlite is usually used in soil mixes to increase aeration and improve the soil’s texture, by using perlite in the proper amounts you will not only improve drainage but also avoid compaction, making it a better medium for the roots to grow in.

Usually, perlite is used in combination with coco fiber and soil to provide the best medium for the roots, while perlite improves aeration, coco fiber absorbs water, balancing those two elements in the best ratio possible.

Perlite can also be used to plant clones in, when you place your cuttings in perlite, the roots usually grow stronger and faster because they need oxygen to thrive and perlite helps provide it.

Pros

1. Increased aeration: Perlite creates small air pockets in the soil so if used properly, it can improve the growth rate.

2. Sterile medium: Because it’s a sterile medium, perlite won’t affect the pH of your medium or increase the amount of minerals in it.

3. Avoids soil compaction: Perlite needs to be thoroughly mixed in the soil before using, this will create several air pockets that make the soil fluffier, avoiding compaction.

Cons

1. Can dry the medium faster: You will need to check your plants closely because with more oxygen in the soil you will have to water more often.

2. Needs to be washed first: If the brand you’re using does not pre-wash the perlite, it may come with a fine dust that can be harmful if inhaled so we recommend washing your perlite before using.

3. Needs to be watered more often: Because the medium will dry faster, you will need to water more and this means you will need to check on your plants at least 2 times per day to make sure everything goes accordingly.

Vermiculite

Vermiculite can be used to improve the quality of your soil, just like perlite, vermiculite has several qualities that will make your plants grow better and faster. This mineral helps aerate the soil, holds water and nutrients while not being toxic or changing the pH.

If your soil is compact or does not drain water properly, you can add vermiculite to provide the roots a better medium to grow in, just make sure you’re using the proper ratio because too much can hold a lot of nutrients and water and end up harming your plants.

Pros

1. Neutral pH: Because it’s a sterile medium, vermiculite will not alter your soil’s pH so there’s no need to worry about checking the runoff every day.

2. Can prevent mold: When used in the proper ratio, vermiculite will absorb the excess water, preventing mold and fungus in the soil.

3. Improves soil quality: Just like perlite, vermiculite improves the soil’s texture and makes it fluffier, preventing soil compaction.

Cons

1. Can be expensive: Depending on where you live, vermiculite can be relatively hard to find and a bit expensive because it’s not usually found in regular grow shops.

2. Can affect plants if used in excess: Because perlite holds nutrients and water, using it in excess can ultimately result in overwatering and overfeeding .

3. It’s said to be harmful: When buying low-quality vermiculite, it can contain asbestos and can cause lung problems. Inhaling these tiny fibers can cause asbestosis, mesothelioma, and lung cancer if exposed for a long time so it’s essential to buy the best quality possible and wash it before using it.

3. Signs of Good Soil

Due to the process in which soil is naturally produced, there are a few factors to consider if you are going to prepare your own. If buying soil from a well-known brand, or your local garden center’s cheap and cheerful products then there are some things to consider.

✔️ Check the packaging to see the nutritional value of the soil. A good brand will take the time to display a soil nutrient analysis displaying-N-P-K values, amount of perlite, vermiculite, compost, trace elements, and the bacterial and fungi count present.

✔️ Worms aerate the soil as they crawl through eating up organic matter. If you see your soil full of worms then do not worry. Not only will these little helpers aerate the soil but will release beneficial bacteria from their gut as they do.

✔️ Good store-bought soil will have perlite or coco added allowing for the ideal balance of air to water retention. Avoid soils that do not have any perlite unless you are purposely buying pure worm castings.

4. Signs of Bad Soil

✔️ Bad soil will have an unpleasant smell which is a red flag bad bacteria are present, causing the medium to be in an unfavorable acidic state.

✔️ Drainage will be poor, causing the soil to become dense and heavy. This weight can restrict root growth and slow plant development down dramatically. The ratio of water retention, drainage, and wicking capabilities will all be out of balance.

5. How to make your own soil

To make your own soil mix you need to have in mind the conditions that you will have during your growing cycle, things like temperature and humidity may have an influence in the best mix, so make sure you know the conditions before mixing your soil.

Best nutrients for soil

We recommend always using organic nutrients when growing in soil because soil it’s organic matter and contains microorganisms that can greatly benefit your plants if taken care of properly.

We cannot recommend a certain brand or organic nutrients line but as long as you’re using high-quality organic nutrients and use them appropriately, you’ll be fine.

Just make sure the nutrients are 100% organic and keep an eye on the pH level because a drastic increase or decrease can ultimately kill the microorganisms present in your soil.

Cheap mix for DIY soil

Even though you can find organic nutrients in your local grow shops, they can be quite expensive so if you’re on a budget there are good alternatives that are relatively cheap.

There are several other methods to make your own organic nutrients such as KNF and Bokashi.

Depending on the space you have available, you can try composting or vermicomposting, these methods allow you to make your own tailored organic soil that will provide everything you need without spending too much.

Best soil for beginners

If you’re a beginner grower and don’t know exactly how things work, here is a general soil recipe that will work fantastically in almost all types of weathers, just remember that as time passes and you get more experienced, it’s ideal you adjust it to your specific needs.

General DIY soil recipe mix:

  • 80% organic soil
  • 10% perlite
  • 10% coco fiber

Remember that you can and should tweak it to your needs, but as long as you maintain a similar ratio your plants will grow exceptionally.

PH too high or pH too low

If the pH of your medium is too high or too low, you should check the nutrient solution you’re feeding, have in mind that most additives are sterile and neutral so if you’re experiencing pH problems you should check the water source and nutrient solution.

Best soil for marijuana

The best soil mix will depend on the weather you have throughout your grow cycle, by following the table you can easily choose the one that better suits you.

Additive When to use Advantages
Coco fiber Use in dry environments or to improve soil quality. Holds water and helps avoid soil compaction.
Biochar Use in dry climates or when growing in organic soil. Improve water retention and helps decompose nutrients faster.
Perlite Used to help aerate the soil in humid environments. Helps dry the soil faster and increases aeration.
Vermiculite Used in dry environments, helps keep the soil moist. Improves soil quality and helps keep it moist.

As a general rule, you should always use 70-80% of organic soil mixed with the additive of your choice, always have in mind to use additives with different properties, for example, vermiculite shouldn’t be used with coco fiber because both absorb a lot of water and can cause overwatering.

  • 70% organic soil
  • 15% perlite
  • 15% coco fiber or 15% biochar or 15% vermiculite

We recommend using 70-80% organic soil mixed with 15% perlite and 15% coco fiber, or substituting coco for vermiculite or biochar, always respecting their properties to avoid having oxygen or water in excess.

Remember you should be on the lookout for the tips your plants give you and adjust the ratio if needed.

6. In conclusion

Having all of the nutrients covered is one-half of a top-quality soil for marijuana, however, it should also have the ideal ratio of drainage, air pockets, and wicking action.

Once you have found the ultimate balance, you can now confidently re-use your organic growing medium for multiple crops with the understanding the more time the living soil food web has to develop, the greater the results in terms of plant performance and yields.

EXTERNAL REFERENCES

This post was most recently updated on September 7th, 2020.

Additives that will help you improve soil quality, resulting in better root growth and what to consider when it comes to growing in organic soil.