When it comes to growing cannabis, soil might just be the most important part of the whole setup. As the medium for root development, nutrient absorption, and overall plant health, your soil is the very foundation of your grow. As such, taking the time to properly learn how to manage soil and nutrients is an essential skill for any grower.
By ensuring the proper balance of essential nutrients, maintaining a healthy pH balance, and providing adequate drainage, growers can give their plants everything they need to optimize plant growth, maximize yield, and create the best final product.
What Makes Good Cannabis Soil?
Not all soil is created equally. With enough dedication, it’s possible to grow cannabis just about anywhere, but if you want to give your plants the best odds, you’ll need to prepare a proper patch for planting.
Soil Types
Broadly speaking, there are three main types of soil: sand, silt, and clay. Each has its own strengths and weaknesses and play a key role in healthy cannabis soil.
- Sand is large, coarse, and provides good drainage and aeration. However, sandy soil typically has a relatively low ability to hold water which can lead to faster nutrient leaching.
- Silt is finer than sand and has moderate water retention capabilities. Silty soil contributes to fertility as it contains several key nutrients. Lastly, it helps to solidify soil and retain moisture.
- Clay is the finest type of soil and has the highest water-holding capacity. Clay soils are nutrient-rich but often dense and compacted, giving them poor drainage and minimal aeration.
The ideal cannabis soil has a balanced texture with a mixture of sand, silt, and clay: loamy soil. This combination allows for maximum drainage, water retention, and nutrient availability to create the ideal environment for cannabis roots to grow, absorb nutrients, and support healthy plant growth.
Cannabis Soil pH
Maintaining the proper pH balance in your soil is absolutely vital for ensuring proper nutrient absorption in your plants. The pH level of the soil determines a plant’s ability to absorb any nutrients present adequately. Different nutrients have different solubility at different pH levels, and cannabis plants do their best growing in slightly acidic soil with a pH of 5.8-6.2.
Testing soil pH is quick and easy. If you don’t mind getting your hands dirty, just collect soil samples, mix them with distilled water, and test the solution using a pH testing kit. If you’re a bit more hands-off, then a soil pH meter is an easy alternative.
Adjusting pH levels is as easy as watering your plants. Mix up your nutrients and water like normal and add in any commercially available pH up or down additive. Stir thoroughly and water your plants. Be sure to check the soil pH about an hour after watering to get an idea of the new level.
When adjusting the pH of cannabis soil, it’s important to be gradual and test constantly to avoid drastic swings.
What Nutrients Does Cannabis Soil Need?
Just like any other organism, cannabis plants require a wide range of primary, secondary, and micro nutrients to reach their full potential.
Primary Nutrients
The primary cannabis nutrients are nitrogen (N), phosphorous (P), and potassium (K). These three form what’s known as an NPK ratio and this appears on almost any cannabis nutrients label. For example, if a nutrient formula is labeled as 3:1:1, it has three parts nitrogen for every one part of phosphorous and potassium.
- Nitrogen is the key element for the vegetative state and promotes lush foliage growth. It is a building block of many crucial amino acids, proteins, and chlorophyll, which are all needed for photosynthesis.
- Phosphorus is a driving force behind root development and flowering. Proper phosphorus levels encourage strong roots, early flowering, and improved flower growth, leading to higher yields.
- Potassium plays a role in overall plant health, stress tolerance, and nutrient uptake. Potassium enhances a plant's ability to fend off diseases and pests while improving the quality of flowers.
There is no single best NPK ratio. During the vegetative stage, a high-nitrogen ratio of 3:1:1 is usually ideal. By the time your plants are in full bloom, though, they should be on something more like 1:2:4 to promote flower development.
Secondary Nutrients
While nitrogen, phosphorous, and potassium are all that you absolutely need, there are several secondary cannabis nutrients that can benefit any plant. Three of the most important are calcium (Ca), magnesium (Mg), and sulfur (S). Calcium is useful for cell wall structure and leads to a more durable plant, magnesium is required for the creation of chlorophyll, and sulfur plays a role in disease resistance.
Micronutrients
Aside from primary and secondary nutrients, cannabis plants can benefit from a wide range of micronutrients including Iron (Fe), Boron (B), and Manganese (Mn). While these all play smaller roles in a plant’s health, they are certainly worth adding. Most lines of nutrients sell a specific micronutrient blend to take all of the guesswork out of measuring.
Organic vs. Inorganic Cannabis Soil Fertilizers
In general terms, all fertilizers can be said to be either organic or inorganic. This refers to the source of the nutrients in the fertilizer.
Organic Fertilizers
These tend to derive their nutrients from natural sources like compost, manure, or plant matter. Organic fertilizers offer several advantages such as improving soil structure, enhancing microbial activity, and increasing organic matter content to promote long-term soil health. Typically, organic fertilizers release nutrients slowly to provide a sustained and gradual nutrient supply. They also help to promote soil fertility and overall quality.
On the downside, organic fertilizers tend to have lower nutrient concentrations meaning that they require more to get the same effect, and nutrient uptake by plants may be slower compared to inorganic fertilizers.
Inorganic Fertilizers
Also known as synthetic or chemical fertilizers, inorganic fertilizers are manufactured through industrial processes. On the whole, this means that they have higher nutrient concentrations and provide nutrients more quickly to plants. This often leads to rapid growth and precise nutrient control.
However, inorganic fertilizers do come with environmental concerns such as nutrient runoff and the potential for water pollution. They have also been shown to disrupt soil microbial activity and reduce long-term soil health.
Final Thoughts on Cannabis Soil and Nutrients
Proper nutrient management of soil is an essential part of any successful grow. By using well-balanced, loamy soil, monitoring and adjusting soil pH levels, and paying close attention to the NPK ratios of your fertilizers, you can make sure that your plants have the best chances to thrive.
But preparing and monitoring your cannabis soil is just the beginning. If you want to learn all the best tips and tricks for cannabis cultivation, check out some podcasts from our list of the best cannabiz podcasts.
