March 24, 2011

What is the Best Soil for Growing Marijuana?

March 24, 2011
The best soil for weed utilizes several components.

While cultivating cannabis, there are a surplus of variables that can lead to your plant’s success or failure. There’s the grow space, the light source, the air circulation, the climate control, the nutrients used, the growing vessels chosen – and all of it is essential in getting the high-quality harvest every grower is looking for. And while $1200 dryer tents and full spectrum grow lights might be essential for your setup, there’s another key ingredient that can’t be overlooked: What is the best soil for marijuana?

The subject of soil usually doesn’t command much thought, but any roadside ditch dirt won’t do your marijuana plants any favors. If you’re choosing soil over your other growing options, it’s imperative that your cannabis soil mix provides enough stability for your weed to plant its roots, while also providing the levels of drainage, water retention, and nutrients that your cannabis needs to thrive. 

The Best Soil for Growing Marijuana

Just as there are variables that can lead to your grow’s overall success, there are a set of traits that lead you to getting the best soil to grow pot too.

What’s the Best Soil Mix for Cannabis?

When choosing and mixing soil, texture is the most apparent attribute. Generally divided into three key categories – sandy, silty, or clay – it’s the texture that determines the overall structure of the (cannabis soil). 

Sandy Soils

Sandy soils are composed of large granules, making for a coarse structure. This coarseness provides good water drainage and aeration, on top of it being easy to work with. However, sandy soil’s poor water retention leads to quick drying and frequent watering. That headache is in addition to sand not carrying any helpful nutrients for your cannabis plants. Sandy soil alone is definitely not the best soil for growing cannabis.

Silty Soils

Silty soils have a slightly finer texture due to their medium granular size. This leads to better water retention, while still being able to stabilize your marijuana plants for growth. Silt’s richness in minerals and organic substances also make it a nutritious, fertile soil for your weed – but still not as beneficial as some other options. And while those positives are glowing, they come along with less efficient drainage.

Clay Soils 

Clay has an even finer texture than silty soil, with granules measuring less than 0.002 millimeters. It also packs a plethora of minerals and nutrients for your marijuana plants, making it an extremely fertile soil choice. However, clay’s composition is heavy and hard to manage, and its draining abilities are abysmal. 

While sandy, silty, and clay soils all have their own benefits individually, the best soil mix for cannabis can be reached by combining all three:

Loamy Soils

A 40:40:20 mixture of sand, silt, and clay is the best direction to go for your marijuana’s potting. This mixture ensures the final product incorporates the best traits of each soil: the sand’s drainage and air flow, the silt’s optimal water retention, and the clay’s minerals and nutrients. All in all, it makes it a good soil for growing weed.

If you’re looking for loam, you won’t have to look for long. Most potting soils found in any store’s garden section are considered loam. It’s unmistakable by its rich composition and recognizable texture – while clay can be tightly compressed and sand often fails to compress at all – loam can compress and hold its form momentarily before breaking back down into its diverse crumbles. In those crumbles can be a variety of amendments that offer a great nutritional structure for your cannabis plants.

Amendments to Improve Your Marijuana’s Soil

Even once you have the structure of your soil sorted out, it can be easy to get overwhelmed. Every single choice in front of you is a loam soil, but the variety remains vast, and your senses are overtaken by an unfamiliar array of gardening jargon: perlite, worm castings, bone meal . . . 

It can be a confusing process, but just take the nutrients and microorganisms in stride. Various amendments are added to a variety of soils, and these store-bought soils act as a wonderful base for your weed’s growth. Still, it’s your responsibility to fill in the gaps to make your soil the best soil for cannabis that it can be. 


In gardening circles, perlite is quickly growing to be one of the most widely utilised soil amendments. Made from volcanic gas, perlite works to improve soil’s drainage and air circulation. Many commercial soils come pre-added with perlite, but if you’re working with natural soil, adding 10-15% of perlite could get you its desired effects.


Vermiculite has a very similar composition and use to perlite. However, rather than improving water drainage, it works to reach your desired level of water retention. A good balance of perlite and vermiculite can lead to more controlled moisture and aeration, resulting in some darn good soil for weed. 

Worm Castings

While a farm of worms can easily result in an endless supply of worm castings, the squeamish grower can still buy bags of the stuff at many nurseries or online. Worm castings provide a constant release of nitrogen into the soil, promoting soil health and plant growth. Nitrogen is a central component of the chlorophyll molecule, which is responsible for creating ‘food’ during the plant’s photosynthesis process.

Coco Coir

Coconut isn’t just for pina coladas and Almond Joys – coco coir, or the recycled natural fibres from coconut husks, is a fantastic soil amendment to improve your harvest. Adding it to your mixture can lead to better water retention without making your (cannabis soil) heavy or difficult to work with. If your soil base isn’t already using coco coir, you can add up to 30% to your mixture to gain the desired effects. 

Additional Nutrients

Many first-time growers are eager to load in extra nutrients for their little weedlings, adding vegetable scraps or manure to their cannabis soil mix. This, however, could have adverse effects. A lot of DIY and store-bought soils are already packed with organic material, and loose food scraps can actually hurt your plants’ development. If you want to add these elements to your grow, compost is the way to go. 

Considered “black gold” among gardeners and farmers alike, compost is a great way to reduce waste while also supplying your plants with much-needed nutrients. Though specifics vary from sample to sample, compost carries the full array of plant nutrients – primarily nitrogen, phosphorus, and potassium. The best part of it all is that you get out of it what you put into it. If your weed needs calcium, throw some egg shells into your compost. If it needs potassium, toss in some fruit rinds to take your marijuana’s soil to the next level!

There is a huge array of soil amendment options out there that can help your cannabis plants grow healthy, hefty buds. It’s all a matter of doing your research and equipping your soil with the right amendments at the right intervals. Just be sure to not get over zealous too early – later on, it’s always easier to add than subtract. 

Some other soil amendments that people have found to help attain the best soil for weed are:

  • EM-1: Nutrients to help improve the health and yield of your plants.
  • Bat Guano: Contains more nitrogen and phosphorus than any other soil amendment. 
  • Bone Meal: Great source of phosphorus, and a surefire way to keep your pH level in check. However, be wary when using bone/blood meal for outdoor grows – they attract animals!
  • Blood Meal: Can also help lower soil’s pH level, as well as supply your plants with nitrogen. 
  • Crustacean Meal: Enriches the soil with calcium, phosphorus and chitin. Made from ground-up seafood shells. 
  • Kelp Meal: Adds potassium, as well as 60+ other essential nutrients to support your soil. 
  • Humic/Fulvic Acid: Helps support root intake, allowing the plant to absorb nutrients more easily. 
  • Mulch: Assists your soil in retaining moisture and supporting helpful microbes. 

But if you don’t want to go through the trouble, you can buy bottled nutrient mixtures to aid each phase of your cannabis plant’s growth. 

What is the Best Soil for Growing Weed Indoors?

The tenets of cannabis soil selection remain similar whether you’re cultivating indoors or outdoors. Texture is still very important, with a loamy soil mixture of clay, sand, and silt supporting cannabis growth the best. In addition, it’s still smart to give your plants the nutrients they need to prosper, and the best way to deliver those nutrients is through soil amendments.

The key difference when you move your grow indoors is the level of control. You no longer have to worry about environmental interference or weather disrupting the quality of the soil or the plant itself. This also extends to your choice of amendments. In outdoor grows, using soil additives like blood meal or bone meal could prove difficult, as they attract wildlife that could harm your marijuana. Unless you’re Snow White or Dr. Doolittle, that won’t be an issue for indoor cultivation. 

However, if you’re still overwhelmed with your choices, here are some of the best potting soils for cannabis that you can buy in stores or online:

The Best Potting Soils for Marijuana

  • Foxfarm, Happy Frog Potting Soil
  • Black Gold, Natural & Organic Potting Mix Plus Fertilizer
  • Mother Earth, Coco + Perlite Mix
  • Nature’s Living Soil, Super Soil Organic Concentrate
  • Big Rootz, All Purpose Potting Soil – pH Adjust and Enriched

Even when you’re purchasing bagged potting soil, be sure to pay attention to any amendments that have been included in the mixture. An attentive grower is a good grower!

So . . . What Soil to Use for Weed?

At the end of the day, good cannabis soil comes down to a couple factors:

  1. Mix: The ideal texture for maximum growth support can be achieved with a 40:40:20 mixture of sandy soil, silty soil, and clay soil – resulting in a loamy soil. This mix allows for the levels of water retention, drainage, aeration, and structure that your cannabis plants need.
  2. Soil Amendments: You need to make sure you’re supplying your cannabis plants with the nutrients they need to thrive. This can be done with rich soil amendments like perlite and coco coir.

While cultivating cannabis, you’re bound to come across an issue or two. A way to set yourself up for success, though, is by starting off with a strong base. A well-composed, nutrient-rich soil can be the difference between a disappointing yield and a high-worthy harvest. Or, if you don’t want to go through the trouble of soil altogether, check out your options with hydroponic growing! In either case, to continue setting your grow up for success, check out these other articles from the Weed Blog:


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