Finding the Perfect Loamy Soil for Indoor Cannabis Growing

If you have farming experience, you’re probably familiar with loamy soils and why they work best for most crops. While loam soils are good, they are not all created equal. This is especially true when it comes to soil for indoor cannabis growing. This article will show you how to create the perfect loamy soil that will provide the perfect base for dense and frosty canopies 8-12 weeks down the line. 

Because cannabis plants are highly adaptable, they are easy to grow and can thrive in a wide range of climatic conditions. But when it comes to indoor growing, you need to start off with the right kind of growth medium. It is no surprise that some indoor growers are opting out of soil and into hydroponic systems, but we shall discuss that in a later article.  

For many, soil is easy to come by and definitely easier to work with. The tips that I will give you below will help you move your soil from ordinary loam soil to the perfect soil for growing cannabis indoors. Once you get it right with the soil, you can expect to have some sparkling heavily frosted nugs in no time.

Just in case I lost you at the start with loam soil, here is what it is.


What is Loam Soil?

Plants typically need three things to thrive—water, sunlight, and soil. Soil is a form of growth medium that holds nutrients, water, and air that the plants need. It ensures adequate drainage for the plant, helps in maintaining moisture, and offers support for growing plants. Soil is composed of mineral particles, decomposing matter, microorganisms, water, and air.

The mineral particles are what classify the different kinds of soil, of which there are three—sandy soils, silt and clay soil. Loam soil is a combination of all three in ratios that make it perfect for the growth of plants, including cannabis.

Ideally, loam soil should contain 40% sand, 40% silt, and 20% clay. But don’t worry, you will not need to measure the percentage of each of these to determine if you have the perfect loam soil for you cannabis. What you’re looking for is a soil that can:

  • Hold in moisture
  • Drain adequately
  • Is easy to work with

How to Determine the Perfect Loam Soil for an Indoor Canopy

There are five things that you must look out for when considering the perfect loam soil for growing cannabis indoors. They include:

  1. The texture of the soil
  2. Drainage ability
  3. Water retention
  4. pH
  5. Nutrients

With time, you’ll be able to identify most of these things just by looking at the soil. But before you get there, here is some help.


Texture, Drainage & Water Retention

The texture of the soil, how well the soil drains, and how much water the soil can hold are intertwined. Loam soils with too much sand will have a coarse texture because sand has large particles. This means that water will seep through the soil very fast and may wash away any nutrients in the process. This soil will be well aerated but will not hold in adequate moisture.

With that said, loam soils with too much clay have very fine texture as clay has small particles. When wet, the soil will clump together making the drainage very poor. Plants grown in this type of soil will lack oxygen and will get droopy from being overwatered. 

The ideal loam soil for growing cannabis should have light texture, drain well, and have moderate water retention abilities. Here are a few indicators for what good loam soil looks and feels like:

  • The soil is dark-colored and rich. 
  • It has loose texture.
  • It drains well. To check this, pour some water on the soil and see how it drains. The water should only pool on the surface for a few seconds before disappearing into the soil. It should also take a few minutes before the water starts seeping out on the other side. 
  • It retains air and moisture. When you squeeze the particles together the soil should still remain airy. Soil that clumps together will not be able to hold in moisture and air.

Soil pH

pH is the acidity or alkalinity of the soil. Soil that has been over-fertilized is likely to be very acidic. That’s why it is important to stick to organic soils. For best results, cannabis plants need a slightly acidic pH of about 6.5 pH. pH needs to be tested at a soil lab, but you can also get some home testing pH kits online. Fortunately, you can alter pH to make it ideal. 


Good loam soil for cannabis should have a sufficient amount of nutrients; this is what makes the difference between a shriveled canopy and a robust resinous canopy.

Cannabis plants will need macro and micro nutrients. The macro nutrients that should be obtained from the soil include nitrogen, phosphorous, sulfur, calcium, magnesium, and potassium.  Unlike hydroponic (nutrient-infused water) systems, soil contains non-inert matter that offers additional macro and micro nutrients. It is advisable to avoid non-organic nutrients as they build up in the soil over time causing toxicity over time. For example, an overload of nitrogen will result in excessive foliage that has low yield and poor quality buds.

Organic fertilizers are better tolerated by the soil as they contain elements that are beneficial for microbial life. It is advisable to start and stick to organic fertilizers if you are to enjoy your cannabis growing experience for a long time.

How To Create The Perfect Loam Soil For Indoor Cannabis Farming

Now that you know what to look out for, here’s how to control the texture, drainage, water retention, pH, and nutrients in your soil.


Improve texture, drainage, and water retention.

How do you improve the texture of your loam soil to ensure that it is just perfect for growing your coveted strain of cannabis? This can be achieved by adding some particles to the soil, it’s actually as simple as that. These particles can also be obtained easily from your local garden store:

  • Perlite: If your soil is leaning more towards clay, adding perlite rocks will help to improve drainage. Remember that you are aiming for only 20% clay in your soil.
  • Coco coir: This is made from coconut husks and will help to improve water retention without making the soil heavy. It helps to improve soil that is leaning heavily towards sandy soil.
  • Worm casting: worm casting is basically worm poop. It helps to improve the aeration of the soil, moisture retention, and drainage. 

Get your soil pH tested.

The first thing is to get your soil pH tested. However, you should do this after making all the other adjustments that you need to make on the soil as this will affect pH as well. If the soil is too acidic, adding an alkaline base such as agricultural lime will help. If the soil is too alkaline, adding an acidic base such as sulfur will help.

Stick to organic natural additives. 

It is pretty difficult to come by soil for indoor cannabis growing that already has the perfect blend of nutrients at the first instance. So, this is an area that constantly needs to be worked on. It is advisable that you stick to natural organic additives that will sustain a healthy soil life. A few things that you may need to add include:

  • Blood meal and fish meal to boost nitrogen 
  • Bone meal and bat guano for phosphorous 
  • Wood ash and kelp meal for potassium 
  • Dolomite lime for calcium and magnesium 
  • Epsom salts for sulfur

Your local garden store should have these items. But if you are a beginner, you may want to try premixed soil blends that contain the proper mix of all these ingredients. They may be slightly more expensive, but the investment will be worthwhile in the long run.

A Final Note

Now that you know what the perfect soil for growing cannabis indoors is, there are two things that you should look out for. The first is finding the right supplier for soil or soil additives. Is your supplier offering you products that are compatible with your growing technique and medium?

Secondly, consider what extra benefits you can derive from the soil products that you are buying, be it the actual soil or soil nutrients and particles to create the perfect loam soil for growing cannabis indoors. For example, if you are buying fresh soil, make sure you go for the type that is pre-inoculated with micro organisms that will boost the health of the soil. 

Ultimately, settle only for suppliers who go the extra mile to create forward thinking products, like Grove Bags. This can save you a lot of embarrassment and potential losses. Doing a little research before you embark on your cannabis growing endeavor is a very necessary step in the right direction. Cheers to a successful cannabis harvest!

Related: Cannabis Humidity Control Is Vital For Quality Buds and Here’s Why

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