Choosing The Best Soil For Cannabis: A Home Grower’s Guide
Growing cannabis in soil is a great way to crop fat, flavoursome buds. Moreover, soil is one of the most forgiving substrates. What are the best soils for growing cannabis? What do you need to know if you want to make your own soil? Our guide answers these questions and more!
Home grower’s guide to the best soil for cannabis.
When growing cannabis, using the right soil is crucial. Unfortunately, sourcing the best soil isn’t always straightforward. From cannabis-specific soils to bargain universal substrates and pre-fertilised types, the sheer amount of options can be overwhelming to novices. And what if you want to make your own soil from scratch?
Let’s talk about the best soil for growing cannabis.
WHAT’S THE BEST SOIL FOR GROWING WEED?
Not every soil is suitable for growing cannabis, and not all cannabis requires the same type of soil. Picking the optimal soil depends on the type of cannabis you’re growing, your climate, whether you’re growing at home or in the wild, etc.
Aside from these factors, there are some common traits among all cannabis soils. Let’s take a look at them:
Cannabis prefers a light and loose soil texture. A light texture promotes root development, and it ensures more oxygen reaches the roots for optimal growth and health.
• Drainage ability
Cannabis soil needs to have excellent drainage. When you water your plants, it shouldn’t pool on top of the soil. If the soil has poor drainage, your plants will get sick and turn out subpar yields, or die.
• Water retention
Just as important as good drainage is water retention, which is the soil’s ability to hold water. Good cannabis soil has an optimal balance of water retention and drainage.
• pH value
pH is a chemical scale that indicates how acidic or alkaline something is. This is important, as cannabis only does well within a small pH range. A good soil for weed has a pH of about 6.0. A pH of 5.8–6.3 will be fine, but if it fluctuates too far outside of this range, you will get diminished yields. If the pH is seriously off, your plants will die.
Cannabis soil needs to contain nutrients so your plants can grow. Fortunately, almost all soils you can buy already feature them. Know, however, that these nutrients will often last only 3–4 weeks. Around the time your plants start to flower, the nutrients in commercial soils will likely be depleted. This is when you should begin to add nutrients.
If you’re growing without additional nutrients, your soil needs to contain organic substances such as humus, compost, worm castings, guano, etc. Microorganisms in the soil will turn these substances into nutrients for your plants to access on demand.
TRAITS OF QUALITY CANNABIS SOIL
If you’re using store-bought potting mixes, these are already optimally “tuned” for growing. Different story if you’re growing organically, though. Natural soil comes in four varieties: sandy, silty, loamy, and clay. But know that most soils consist of varying ratios of these soil types.
For example, a soil may be clay and loamy, or sandy and silty.
Sandy soil is coarse with good drainage, but has poor water retention. When watered, nutrients such as nitrogen will also quickly get washed away. Sandy soil is easy to work with and is a viable choice for cannabis growers.
• Coarse structure
• Low pH
• Pros: Good drainage, keeps soil airy, high oxygen levels, easy to work with
• Cons: Poor water retention, needs frequent watering
Silty soil is a medium-coarse soil type that’s rich in minerals and organic particles. Its water retention is good, yet it has adequate drainage. Silty soils are very easy to work with. The minerals and organic substances within make it one of the most fertile soil types.
• Pros: Contains minerals and nutrients, retains water well
• Cons: Fair drainage
Loamy soil is a combination of sand, silt, and clay soils with added organic compounds. It is one of the best soil types for growing cannabis as it offers optimal water retention and drainage, and it’s rich in nutrients and oxygen. Downside: This type of soil can be expensive.
• Mixture of sand, silt, and clay
• Pros: Excellent water retention and drainage, contains nutrients, high oxygen levels
• Cons: Expensive
Clay soils consist of fine mineral particles. This type of soil is heavy and not easy to work with. It is very rich in nutrients and minerals, which makes it a good option to include in organic grows. Clay soil retains water well, but has poor drainage.
• Fine particle size
• High pH
• Pros: Rich in nutrients, retains water
• Cons: Poor drainage, heavy and compact, hard to work with
AMENDMENTS TO IMPROVE SOIL QUALITY
If you’re working with natural soil, chances are it won’t be perfect for growing cannabis—not from the start, at least. The texture may not be optimal or it may have poor drainage, for example. But you can improve any type of soil by adding amendments, most of which can be found in your local grow shop.
Coco coir (coco fibre) is made from coconut husks. These light fibres provide excellent water retention and can lighten compact soils. Some use a pure coco substrate with special nutrients to cultivate their weed. But to amend existing soil, it’s a good idea to add anywhere up to 30% coco coir, depending on the composition of your base soil.
Perlite is the most widely used soil amendment. Perlite consists of very light, bright-white rocks that greatly improve the drainage and airiness of the soil. Perlite also has decent water retention. To amend your soil with it, add 10–15% of perlite. You can add more, but then your soil may become too light and nutrients may leach out. Good-quality commercial soils often come with added perlite.
Most cannabis growers are familiar with using clay pebbles as part of a hydroponic setup. But did you know they can also be used to enhance soil structure? Adding clay pebbles to the bottom of your raised beds and containers will assist with drainage and prevent water from pooling at the base—a large risk factor when it comes to root rot.
Growers can also add clay pebbles to the top of containers and beds to serve as a mulch. Here, they help to trap moisture in the growing medium by preventing excess evaporation. Clay pebble mulch also casts shade over the top layer of soil, suppressing weeds and keeping beneficial microbes sheltered from the hot rays of the sun.
Vermiculite, just like perlite, is a heat-treated mineral you can use to make your soil lighter.It is also excellent at retaining water. Although vermiculite shares some characteristics with perlite, the two have opposite uses: Use perlite to increase drainage and airiness, and use vermiculite to increase water retention. Luckily, you can use both, as perlite and vermiculite work well together. Around 10% vermiculite is beneficial.
Worm castings are normally seen more as a nutritional soil amendment as they contain a plethora of useful microorganisms that benefit growth. But worm castings will also improve the texture, drainage, and water retention of your soil. When amending your soil with worm castings, use about 25–30%.
If your DIY cannabis soil is rich in organic material, you will likely not need to add nutrients to it. As a matter of fact, some growers make the mistake of adding manure and vegetable scraps to their soil to “fertilise” it. This results in soil getting “too hot” for the plants, hurting their development in turn. If you want to put your vegetable scraps to good use in your garden, you first need to compost them.
If you think you need to amend your cannabis soil with nutrients, you can easily purchase bottled solutions tailored to a plant’s phase of growth.
PHOTOPERIOD VS AUTOFLOWERING
One factor to consider when choosing the right soil for your weed is whether you’re growing photoperiod or autoflowering plants. Autoflowers prefer a light mix with fewer added nutrients. A great substrate for your autoflowering ladies is a 50:50 mix of coco coir and a light, peat-based soil with some added perlite for drainage.
When growing autoflowers, stay away from heavily fertilised soils and certain amendments like bat guano, as these will be too hot and overload your plants with nutrients. The same is true for cannabis seedlings, which do not like high levels of nutrients.
Plant autoflowers in their final growing container in a cup-sized hole in the centre of the soil. Fill the hole with seedling/starter soil with no nutrients and place your seed in it. This way, your seedling can grow without being surrounded by the hot soil, which would otherwise burn it.
For photoperiod plants, start them out in small seedling pots/cups with soil that has little to no nutrients. Replant after a few weeks. More mature plants will tolerate higher nutrient levels much better than seedlings.
STORE-BOUGHT VS HOMEMADE
If you’ve just started growing cannabis, it may be best to simply get ready-made soil from the grow store. The reason for this is that good-quality cannabis soil normally contains everything your plants need for healthy growth, in the optimal ratios. If you want, you can further improve your store-bought soil with a handful of perlite for increased drainage, but otherwise you should be good.
BASIC CANNABIS SOIL RECIPE
On the other hand, there may come a time when you want to make your own soil. After all, why spend good money on soil if your homemade version is even better? Here is a recipe for a basic homemade cannabis soil.
• 1 part vermiculite
• 1 part coco coir peat
• 2 parts compost
• ½–1 cup worm castings (or humus)
1. Sieve the compost to remove larger chunks.
2. Soak the coco coir peat in warm water. Check the directions of the product to see what kind of volume you will be getting.
3. Use a bucket and mix the coco coir peat with the vermiculite.
4. Add the compost.
Done! Double-check the pH value of your homemade soil. It should be in the range of 5.8–6.3.
The above is a basic soil recipe that will serve you well for most grows, indoors and outdoors. But you can further enhance your soil mix by adding organic fertilisers.
Bat guano is an excellent and inexpensive organic fertiliser for flowering marijuana. You can add it to a soil mix or spread it on the topsoil and water in later. You can also look into time-release nutrients such as Easy Boost Organic Nutrition pellets. Add a cup of these to your soil to feed your plants for their whole life cycle—100g is enough for 2–3 cannabis plants. All that’s left to do is water!
No-till cultivation is a gardening method that allows the soil to remain undisturbed (no digging, stirring, overturning, etc.). This way, microorganisms in the soil can create a thriving ecosystem that replenishes the soil with good bacteria, helpful fungi, and other living organisms. No-till cultivation promotes organic matter retention and water absorption because nutrients are constantly being recycled throughout the soil.
To learn about no-till cultivation and its benefits, check out this article!
AMENDMENTS FOR ARID/DROUGHT CONDITIONS
If you’re growing outdoors in a hot climate such as Southern Spain or a similar location, you don’t want to “cook” the root zone of your plants. If you’re using pots, choose white plastic containers, as these help to keep the soil temperature at a reasonable level under the beating sun. You can also look to air pots or smart pots to keep the roots of your cannabis plants cool. As an additional measure to protect the soil from fluctuating temperatures, you can add layers of dry straw onto the topsoil.
If you’re growing in drought conditions where your plants may at times go weeks without rain, or if you can’t make daily trips to your guerrilla grow location, use water-absorbent polymers to keep them hydrated! You can get these from hydroponic grow stores or can cut them out of diapers.
For a guerrilla grow in dry conditions, dig a hole about 60cm deep and 30cm in diameter. Add a few cups of polymer crystals to the bottom of the soil mix and fill up with the remaining soil. Place your plant into the soil and water liberally. As your plant grows, the roots will soon reach the polymers so it can drink even during drought. Tip: Soak the polymers in a light nutrient solution for a double benefit!
Soil is the medium of choice for most cannabis cultivators. Here is what you need to know to get the most out of your soil grow!
How to Grow Cannabis in Soil
First-time growers often start by growing cannabis in soil. If you’ve grown other plants in soil and/or have maintained a soil garden, this may be the best choice for you because you will already be familiar with a lot of what you need to understand to grow cannabis in soil.
Avoid Miracle-Gro! Do not use “Miracle-Gro” soil or any soil that has “extended-release” nutrients for growing cannabis. These types of soil will continue to release nitrogen to your plant roots for up to 6 months. This can cause deficiencies or burn your cannabis plants in the flowering/budding stage, reducing your overall yields. I have seen growers successively grow cannabis in Miracle-Gro, but many of them struggled with nutrient problems in the flowering stage.
Soil Pros for Growing Cannabis
Many Already Have Soil Experience – Growing cannabis in soil is similar to growing plants like tomatoes or corn – soil growing may be the most intuitive option for you, especially if you already have gardening experience.
Simple – hand-water your plants in containers
Outdoor Growing – most outdoor growers choose to grow with soil. In the wild, cannabis grows in soil, so growing outdoors in soil is most like a cannabis plant’s natural environment. Many people find that when growing cannabis outdoors, soil is the simplest and most intuitive way to grow. Growing with composted “super soil” gives the grower the ability to grow outside without needing to add synthetic bottled nutrients or manage the pH of the soil.
Option 1: Store-Bought Soil + Nutrients – Growers can buy soil online or at a store, and simply add nutrients throughout their grow while watering for thriving, happy cannabis plants.
Option 2: Compost or Purchase “Super Soil” – For those who don’t want to worry about soil pH or adding nutrients throughout the grow, there is the option of amending and composting your own super soil (or buying it already composted) specifically made for cannabis plants. While this option takes more time before you start growing, it can be somewhat simpler especially for those who have composted soil in the past.
Note: Some growers believe growing in organic composted super soil with a rich microbial life can actually improve the taste and smell of cannabis by causing a plant to produce higher levels of terpenes and terpenoids.
Soil Cons for Growing Cannabis
Pests – Soil is an organic material, and there are many types of bugs that can live in soil. Often, soil-growers seem to suffer more often from pests attacking their plants than hydroponic growers.
Slower Growth – Growing in soil is not as fast as growing in a soilless or hydroponic setup – hydroponic plants tend to get better growth rates, especially in the vegetative stage.
Get Soil and a Container for Your Cannabis Plants
- Common cannabis soil mixes include Fox Farms Happy Frog and Fox Farms Ocean Forest. Any high-quality organic soil mix will do in a pinch.
- Avoid Miracle-Gro soil or anything with “extended-release” nutrients!
- To improve drainage, it can be beneficial to add 30% perlite to aerate and loosen soil.
- Common cannabis containers include classic plastic pots, terracotta pots, smart pots (fabric pots) and air-pots. Learn more about different types of containers
Soil growing probably requires the least effort of any growing method (especially if growing in super soil). Your main effort will be spent watering your plants.
Not sure which soil should you start with? I recommend starting with Fox Farms Happy Frog soil and mixing the soil with about 30-40% perlite for a perfect cannabis soil starting mix. For the easiest soil growing, get a smart pot (a growing container made out of fabric – they work perfectly for growing cannabis).
Don’t want to use nutrients? Learn how to mix up your own super soil so it has all the nutrients your cannabis plants will need! Bonus: With composted super soil made using the recipe in the link above, you don’t need to worry about maintaining your pH! your super soil will automatically manage the pH for you.
Maintenance Cost – After setup, the main maintenance will be replacing your soil every grow (highly recommended – reused soil often does not get great results even with added nutrients). Occasionally you will have to replace used containers that crack or break. You also need to think about the cost of electricity and replacing nutrients every few grows.
Maintenance Effort – Watering your plants, providing nutrients and managing the pH to prevent deficiencies (composted super soil has microorganisms in it to help manage pH and make nutrients available to your plant roots).
How long until harvest? Soil has relatively slower growth rates than hydroponic methods, but a tuned-in soil grow can achieve impressive growth rates if given a great environment and plenty of bright light. Most soil grows require 1-3 months of vegetative time (depending on how big you want your plants) plus 2-3 months of flowering/budding (depending on your strain).
Many growers feel that cannabis grown in organic super soil has the best smell/taste profile, though this is highly disputed among hydroponic growers 🙂
How long can grower be away? It’s important for a grower to always remain close by for their first grow, especially for inexperienced growers. Experienced growers can safely spend more time away from the garden.
Bigger containers hold more water and therefore give growers more time away, since constant watering isn’t needed. In the best-case scenario, it is always best to check on your plants at least once a day. You never know when a pest infestation will take hold, a plant will fall over, or some other unexpected event will happen.
Most Common Soil Mistake: Overwatering
The most common mistake made by beginners growing cannabis in soil is they water their plants too often. Overwatering is almost never a case of giving your plants too much water at once. Instead, overwatering cannabis in soil is almost always caused by giving the plant water too often.
How to water cannabis plants in soil
Wait until the top of your soil feels dry up to your first knuckle (about an inch deep)
Add nutrients to your water (if needed), then adjust the pH. The most common reason growers get nutrient deficiencies is because they don’t adjust the pH of their water. Most soil growers only add nutrients every other watering (or even less often), but even when giving just plain water you still need to adjust the pH of your water to prevent deficiencies.
Start watering your plants and continue to add water until you see at least 20% extra runoff water drain out the bottom of your pot. Go back to step 1.
Cannabis-Friendly Soil Nutrient Suggestions
For new nutrients you haven’t grown with before, always start at half-strength and raise the amount slowly. Do not use nutrients with every watering! Most growers will add nutrients every other watering or even less frequently. Remember, a little bit goes a long way. You can always add more nutrients later, but it’s a lot more difficult to take them back from the soil.
An easy and simple nutrient system for beginning cannabis soil growers is the Fox Farms Nutrient Trio for Soil.
The Fox Farms trio works great for growing any cannabis strain, without needing any additional supplements.
There are three different bottles that you will need to grow cannabis, “Grow Big,” “Big Bloom,” and “Tiger Bloom.” They are often sold together. Simply follow the included nutrient schedule (here’s a PDF, here’s a JPG) from Fox Farms.
Be aware there is a soil version because Fox Farms offers a hydroponic version of the same nutrient line. Though in my experience the hydroponic version also works just as well in soil 🙂
Nutrient Picks for Growing in Soil
HydroOrganics Earth Juice Nutrients (Grow, Bloom) with the following supplements: Earth Juice Catalyst, Meta-K, MicroBlast & Hygrozyme (use as needed for roots)
This nutrient schedule was used to grow the following buds under a 250W LED.
Don’t Use Miracle-Gro or Other “Slow Release” Soils!
Say “No” to Miracle-Gro soil for growing cannabis!
Many of us have seen Miracle-Gro used around our homes, so we know that it works for ‘regular houseplants’. Cannabis is just a tough weed, so Miracle-Gro nutrients should work great for it, too… right?
No. Not really. Well kinda.
Standard Miracle-Gro nutrients (their all-purpose plant food) will work “just okay” for the vegetative stage of your plant’s growth, but anything with Miracle-Gro in it is a terrible choice for the flowering stage due to its high levels of Nitrogen. Using standard Miracle-Gro nutrients in the flowering stage will cause your buds to grow smaller than they could have, and they may possibly have a chemical taste from nutrient buildup in the plant tissue.
However, the real problem is Miracle-Gro’s “time-released” soil (or any type of extended-release spikes or soils that aren’t organic) which slowly release Miracle-Gro nutrients over the course of several months. These types of soil continue providing Nitrogen slowly throughout your plant’s life. That means your plant won’t be able to use up all the Nitrogen in the vegetative stage as it would with regular soil, again giving you the problem of too much Nitrogen in the flowering stage.
Basically, avoid giving your plants a lot of Nitrogen in the flowering stage! Anything that does that is not a good idea 🙂
General overview of soil growing. Get the pros and cons!