Soil & Fertilizer

We start first with soil and fertilizer, as, whether you grow indoors or outdoors, it is the one thing you will need to fully understand.

What Makes a Good Soil?

When it comes to growing cannabis, a good starting soil can be a variety of grow mediums that when combined, provide a similar set of benefits: insulation to protect the roots from temperature spikes, anchor to provide plant and root stability, high water retention to feed the plant over time, and lightweight enough for proper aeration. A good soil should have some trace elements that your plants might need, and it should also be hospitable to microbes that can break down organic matter over time to feed the plants organically if desired. As for how to obtain a good soil to start with, there are two ways: getting it from the ground and getting it commercially from a store.

Ground Soil

A good way to tell if the ground soil you have access to is suitable for cannabis is to see how everything else grows in it. If taken from an area with a lot of vegetation already growing, then there is a good chance the soil is good for cannabis. There should be a decent amount of natural, organic nutrients already in the soil to support the first few weeks of plant growth. However, if the soil seems too firm (clay) or too soft (sand), with a lack of vegetation growing around it, then it might not be suitable for growing, although adding a thick layer of compost with either the clay or sandy soil might help amend it enough to make it suitable for  growing.

The risks with starting from a ground soil is that it has a higher chance of containing weed seeds, insects, and diseases when compared with commercially sold soil. Ground soil is also very compact and dense, which works great in a large open area but not so much in a small container, so to provide more aeration and drainage you will want to at least mix it with perlite, a lightweight rocklike material, at a 1:1 soil to perlite ratio before use.

Fertilizer Amendments

Each type of soil can either include or not include fertilizer, and depending on the fertilizer type, it can be great or terrible for growing cannabis.

 

Unfertilized soil is easy to spot because on the packaging, it will tell you to include fertilizers right away, and these soils are really easy to work with because as a blank canvas, you can go any direction you want when choosing a fertilizer to pair it with.

Organically fertilized soil mixes in compost, manure, bone meal, and other organic materials that slowly decompose over time to feed a plant with a constant supply of nutrients. While the organic matter in the soil will not feed a plant as fast as a liquid fertilizer, it also will not over-fertilize a plant with large nutrient spikes, making this a great choice for an easy-to-manage grow. The main drawback with an organic soil is that over time, the organic matter in the soil will slowly deplete typically halfway through a grow, and it will need to be replenished by mixing in more organic matter with the soil or you can switch to a liquid fertilizer instead for the latter part of the grow.

Synthetically fertilized soil mixes are easy to spot, as these typically state "feeds for up to X months" on the packaging. The slow-release fertilizers used in these soils come in the form of small pellets that release their nutrients at a slow rate over a specific period of time. The problem here is that most of these are designed to boost vegetative growth and will be high in nitrogen. While this is great for the vegetative stage, it could negatively impact your plants in the flowering stage. Because of this, we do not recommend starting with a synthetically fertilized soil, although it may be unavoidable as these are the most common bag soils on the market, so if you do start with this soil type, find one with the least amount of feed included so that after a month or two, when the built-in fertilizer has been depleted, you can replace it with something more suitable for your plant’s grow cycle.

Aeration Amendments

No matter what type of soil you are starting with, we always recommend mixing in some perlite (at a minimum 5:1 soil to perlite ratio and up to a 1:1 ratio) to give your soil additional aeration at the cost of having to water more often. Since cannabis can easily recover from under-watering but has a ton of issues if overwatered, this is a great simple amendment to help prevent that from happening.

Bag Soil Types

Commercial bag soil comes in a variety of brands and types, but they all generally follow a similar naming structure. To start, let’s differentiate the mixes available, starting with a potting mix.

Potting mix is typically the “fluffiest” type of bag soil available, made specifically for use with small pots, and most contain no dirt at all but instead opt for lighter-weight organic materials, such as peat moss, bark, and compost, to provide most of the same benefits as a soil blend while allowing for more airflow and room for easier root development.

Potting soil is similar to a potting mix blend but includes dirt as well, so generally, it will be little heavier and less expensive when compared with potting mixes. However, potting soils are still blended with a lot of lightweight material, making it a good economical option when used for potted grows.

 

Gardening soil, which is similar to that of potting soil but more dense and compact, usually has a lot more dirt included along with some other beneficial materials like peat moss and perlite to give it a little more aeration, or compost and manure to give it some nutrients. These are made for larger outdoor grow areas, like raised beds, and should be mixed with some perlite to give it more aeration if used in pots.

Topsoil is basic ground soil with nothing else included, and while it is generally the cheapest option available, you are better off trying to find a good ground soil yourself for free from a fertile area as the composition in topsoil varies greatly based on where it was taken from. There is no guarantee that the topsoil you find is able to grow cannabis well.

How to Feed Your Plants

There are 2 different blends of fertilizers you will need to switch between depending on the life cycle of the plant. From a seedling all the way to the vegetative stage, you will want to use a grow fertilizer that is high in nitrogen for plant growth and healthy leaves. When the plant starts the flowering stage, you will want to switch the fertilizer type to a bloom fertilizer that is high in phosphorus for flower and bud growth.

If you are going with generic fertilizers, you will want to use ones that are recommended for general plants and vegetables. The easiest way to identify a grow fertilizer is by the packaging; there will always be 3 numbers — each pertaining to how much percent of the fertilizer product is made up of each of the main 3 nutrients. As long as the first number — nitrogen — is at least the same as, if not higher than, the other numbers, then this will probably work as a grow fertilizer. If the second number is higher than the other 2 numbers, then it will probably work as a bloom fertilizer. As for dosage, follow the instructions on the fertilizer packaging, but instead of using a full dose, start with 25% of the dosage when the plant is a seedling up until the vegetative stage. From here, up the nutrients to 50% of the recommended dosage for the rest of the grow, unless the plant shows signs of malnutrition. Finally, when switching from the grow to bloom fertilizer, stay with 50% of the recommended dosage until the final flush or harvest.

Fertilizer Types

There are two options when it comes to fertilizers: solid fertilizers that slowly release nutrients over time and liquid fertilizers that can easily be taken in by the plant but will need to be repeatedly applied.

Organic solid fertilizers can either come in a mix of different organic matter to provide a balanced nutrient solution or as individual ingredients to boost specific nutrients, so unless you are trying to correct a specific nutrient deficiency, be sure to get the mixed versions. Typically, this fertilizer type require you to mix it in with the soil, and can be used early on with a basic soil or to recharge an organic fertilized soil that has run out of organic matter. Organic solid fertilizers are a great way to continuously feed a plant, but they will need to be replenished every month or two when the plant shows signs that the nutrients have been depleted.

Synthetic solid fertilizers come in multiple forms, although the two most common types are either small pellets or sticks that need to be staked into the soil. Both types release fertilizer at a slow pace and usually last for 2-6 months. Due to the long feed time, these fertilizers are the easiest to work with; however, the problem here is that in a typical 3-4 month grow, you will want to switch from a grow to a bloom fertilizer before the second month, and with this fertilizer type, it is very hard to remove or flush out the with water, making it hard to control.

Liquid fertilizers come in both organic and synthetic forms, but both work similarly; once the liquid fertilizer reaches the roots, the nutrients in the fertilizer are available to the plant right away. This makes liquid fertilizers great at giving the plants exactly what it wants at all stages of the grow cycle but makes it easier to over-fertilize a plant if not careful.

Note That Fertilizer Is Not Food. Nutrients from fertilizers are often thought of as food for the plant, but that is not the case, as plants make their own food with light and carbon dioxide through the process of photosynthesis. What fertilizer is to a plant is more like a multivitamin, providing health benefits when taken in the correct amounts but could be harmful if given too much or too little at a time.

Soil & Fertilizer Recommendations

The best potting soils are usually found locally, so if you have one available check your nearest plant nursery to ask what they recommend. As for national brands, for organic growing, we like FoxFarm Ocean Forest Potting Soil, which contains everything you need to jumpstart your grow, and in our experience, it requires no additional fertilizers for at least a month into the grow. For a more economical option, Miracle-Gro Nature's Care Organic Potting Mix works well out of the bag. In our experience, it has enough organic matter to last for the first few weeks before needing additional feed.

The General Hydroponics MaxiGro (grow fertilizer) and MaxiBloom (bloom fertilizer) line of water-soluble fertilizers are a good all-in-one starting point for those on a budget, and these liquid fertilizers have the added benefit of also being usable in hydroponic setups as well. For a higher quality customizable option, the General Organics Go Box comes with both a grow and bloom liquid fertilizer, which is enough to feed multiple grows as well as a number of supplemental nutrient bottles that will boost growth and help with different nutrient deficiencies should they arise. As for an organic solid fertilizer option, Dr. Earth Life Organic All Purpose Fertilizer is a great starting feed to convert a normal soil into an organic matter-rich soil and then when your plants are in flower you can recharge the soil by mixing in some Dr. Earth Flower Girl Bud and Bloom Booster to give the flowers the extra phosphorus it needs.

Did this guide help? This article was taken directly from The Absolute Beginner's Guide to Growing Cannabis book, so if you like the advice above you'll love the rest of the book, which includes a lot of exclusive content not found anywhere else. You can find both the e-book and paperback copy on Amazon, and it's free with a Kindle Unlimited subscription!