TechnologyCultivating hemp: what's the best soil for growing cannabis?

Cultivating hemp: what’s the best soil for growing cannabis?


Growing cannabis is one of the most rewarding agricultural practices. This plant has a multitude of applications in various industries, from medicinal supplements to nutrition to textile production. Despite its dynamic nature, hemp is a surprisingly low-maintenance species. 

Its easy-growing tendencies make it one of the most sustainable crops in existence. To maintain its eco-friendliness, cannabis growers must be attentive to soil conditions. After all, a healthy environment ensures that your hemp can convert energy and nutrients into fiber, seeds, and oil as efficiently as possible. 

With that said, here are some critical points to keep in mind when preparing your soil for a hemp crop and how this plant can improve your soil condition overall. 

What to consider when preparing soil for growing cannabis

Hemp is not a picky plant. It can thrive in many types of soils. However, your best bet is to provide loose soil packed with an abundance of organic matter. More specifically, hemp does exceedingly well with fertile loams. 

“Loamy” soil contains particles of many different sizes. Typically, scientists split these various components into three categories:

  • Sand 
  • Silt 
  • Clay 

These different particle sizes – more commonly known as the soil’s “texture” – are critical to hemp’s ability to take up water. Notably, the soil’s texture influences the following factors and processes:

  • Aeration and drainage
  • Water retention capacity
  • How likely the soil is to erode
  • Content of organic matter
  • Chemical content and exchange

These elements are essential to hemp’s healthy growth. Since a loamy soil mix contains many textures, it has good drainage and storage capacities. The texture combination also enables the soil to provide comfortable aeration for the hemp plants’ root development. 

It’s also important to consider the acidity of the soil mix before you plant your hemp. Typically, the best range is between 6.0 (slightly acidic) to 7.5 (slightly alkaline). Many new hemp cultivators – and gardeners generally – tend to feel that they can brush off the soil’s pH. Unfortunately, this is far from true. 

The pH directly influences the soil’s nutrient availability. If it’s too acidic, your hemp’s health and growth rate may suffer. For example, undesirable acidity or basic levels could cause a shortage of minerals and nutrients, such as phosphorous, calcium, manganese, and more. This could stunt your hemp’s growth and reduce the fiber and other plant materials available for harvest. 

Distinguishing soil types from one another

Learning how to distinguish soil types from one another is essential to growing a successful hemp crop. For instance, you don’t want to accidentally purchase a cannabis soil mix that is too heavy in clay. Fortunately, it’s easy to learn how to tell them apart. 

For starters, sandy soil has the largest particle sizes, each being about 0.05-2.0 mm in diameter. Because of this, it feels gritty when you run your hands through it. On the other hand, clay has the smallest particles, making it feel sticky to the touch. Clay particles measure less than 0.002 mm. 

(Fun fact: If you were to arrange clay particles in a straight line, you’d need 12,000 of them to make a one-inch line. That’s how small they are!)

Silt falls in the middle of sand and clay. Each silt particle is about 0.002-0.05 in diameter. The particles’ sizes cause silt to feel somewhat like flour, having a smooth feeling in your hands.

If you’re making your own organic soil for cannabis, it’s best to get familiar with each of these. That way, you can achieve the perfect ratio for hemp-friendly loamy soil: 40% sand, 40% silt, and 20% clay.

Be wary of soils that are prone to compacting. This species is highly sensitive to flooding and compacted soil, which is why drainage is such a critical aspect of soil for cannabis. Heavy rains, too much surface water, and poor drainage are all factors that could lead to hemp’s demise. Such conditions are a death trap for cannabis plants. 

Fertilization practices for hemp crops

Choosing the right soil for cannabis isn’t just about the plant’s physical growth. Additionally, the soil’s nutrient availability is a crucial factor that determines the plant’s cannabinoid content. In 2019, researchers found that supplementing the plant with Nitrogen, Phosphorus, and Potassium changed the concentrations of CBG (cannabigerol) and CBN (cannabinol). Mainly, they discovered: 

  • The flowers’ CBG levels increased by 71%. 
  • CBN levels in the flowers fell by 38%. 
  • CBN concentrations in the leaves were lowered by 36%. 

Further, the scientists learned that different fertilization regimens resulted in varying effects on hemp’s many cannabinoids. 

For example, supplementing phosphorus alone didn’t cause any changes to the concentrations of THC (tetrahydrocannabinol), CBD, CBN, or CBG in any of the plant’s top flowers. However, there was a 16% reduction of THC in the leaves. 

The researchers also offered the plants a supplementation program with humic acid only. This specific treatment had the most interesting effect. Instead of merely increasing or decreasing the cannabinoid concentrations, humic acid changed the plant’s chemical compounds’ distribution. Specifically, the cannabinoids were spread more evenly between the leaves, flowers, and stalk. 

Additionally, the humic acid supplementation approach boosted cannabinoid levels only at the top of the hemp plant. However, overall, this fertilization method dropped THC concentrations by 37% and CBD by 39%. 

With all this said, fertilization is not something to take lightly when growing cannabis, especially if you’re cultivating industrial hemp. Supplementing your soil’s nutritional availability can have dramatic consequences for your plant’s cannabinoid concentrations. 

If you throw off your hemp’s delta-9-THC content too much, you might accidentally push the plant over the line to be legally considered as “marijuana.” (The cutoff for hemp is 0.3% THC.)

The main pointers to keep in mind when developing a fertilization routine for your hemp crop are as follows:

  • Hemp’s nitrogen uptake is the highest during the first six to eight weeks of growth. 
  • The flowering and seeding stages require more potassium and phosphorus. 
  • Industrial hemp typically requires the following mineral quantities:
    • Nitrogen: 80-100 lbs/ac (pounds per acre) 
    • Phosphate: 52-70 lbs/ac
    • Potash: 52-70 lbs/ac

Not all cannabis growers can cultivate on a large scale. For example, someone might have state permission to grow their own cannabis through the state’s medical marijuana program. 

If you’re growing cannabis at home, using high-quality potting soil or custom organic potting mix, your plants will do just fine with organic sources of nutrients like:

  • Bone meal
  • Earthworm castings
  • A balanced NPK fertilizer 

What is the best climate for hemp? 

Part of providing the optimal growing conditions and soil for cannabis is knowing what makes the best climate. An atmosphere that’s too dry can dehydrate your plants, sucking up the moisture shortly after watering. On the other hand, too much humidity can lead to mold growth and wet soil. Neither of these things is suitable for hemp plants and may inhibit their productivity. 

Plus, the growing climate directly affects the soil temperature. Areas prone to sweltering temperatures will cause the soil to heat up, which can quite literally fry the root systems or the leaves. 

(Fortunately, this is easily mitigated. Insulating the soil with a layer of mulch can keep the roots comfortable throughout the day, protecting them from severe weather fluctuations.) 

Researchers have investigated hemp’s ideal climate conditions for decades. Here’s what most of that research has taught cultivators so far:

  • Generally, a mild, humid climate is the best for growing hemp. 
  • Hemp does best in areas with at least 25-30” of rainfall per year. 
  • Northern locations at high elevation, particularly those with cold climates, have lower yields than warmer regions at lower elevations.
  • Cannabis plants will flourish in full sun. 

Sustainability and hemp cultivation

Hemp is one of the most sustainable crops that agriculturalists could ever dream of growing. It can improve the soil quality in which the plants grow and don’t need any harmful pesticides to resist attacks from insects. Plus, some of hemp’s chemical residue can be used to develop botanical substances to repel unwanted bugs organically. 

Cultivating hemp is an essential part of improving Earth’s ability to resist environmental degradation if planted on a large scale. Here are some of the most critical advantages this plant has to offer the weakening planet. 

Hemp’s role in soil remediation

Hemp is a deep-rooting plant, extending far down into the earth. (The plant’s roots can grow to about 0.5 m, or 1.6 ft, long.) This far-reaching root system is central to its ability to heal the soil by merely existing and allowing its normal physiological behaviors to play out. 

Scientists have determined that you can expect hemp to consistently remove heavy metals from contaminated soils, particularly, Cadmium (Cd) and Nitrogen (Ni). Over time, hemp removes heavy metals from deeper layers of soil. 

This means that cultivators can use their hemp crops to improve soil quality, thereby strengthening land-use efficiency. This practice is known as “phytoremediation,” and hemp is known worldwide to excel at it. In total, hemp can extract:

  • Metals
  • Pesticides
  • Solvents
  • Explosives
  • Petroleum 

In fact, a 2019 study yielded a fascinating discovery. For one, the scientists confirmed that hemp’s ability to remove contaminants from soil extends to various heavy metals outside Cd and Ni. 

They planted six hemp plant varieties in two different contaminated soil types, Miracle-Gro Potting Mix, and PRO-MIX HP Mycorrhizae High Porosity Grower Mix. The plants were split into two groups, placing each type of soil in two different environments: in a greenhouse or outdoors. 

The researchers found that all the hemp generally grew to the same height and experienced the same seed germination rates. Although all hemp plants have some capacity to uptake contaminants like heavy metals, the scientists noted that the outdoor cannabis removed more than twice as much from the soil. 

That’s not all. The contaminated soil seemed to boost cannabinoid concentrations. Plants grown in the poor-quality soil had 2.16-2.58% increase in cannabidiol. Additionally, they showed an 18-fold increase in cannabidiolic acid synthase gene levels. 

(Cannabidiolic acid synthase is an enzyme that contributes to the formation of cannabidiol.)

This means that growing cannabis might function as a positive feedback loop. As hemp removes harmful materials from the soil, it improves the substrate quality, and further strengthens itself, and boosts its medicinal value in the increased production of CBD. 

Growing hemp could improve your monoculture

Even farmers who aren’t exclusively interested in hemp cultivation would do well to add this plant to their crop rotation. Hemp or not, rotating crops is an essential practice in reducing your plants’ vulnerability to pests and diseases. Plus, this practice increases organic carbon and the amount of organic matter available in the soil. 

However, adding hemp into your lineup can significantly improve the advantages you yield from crop rotations. For example, hemp cultivated for fiber can produce 25 tons of aboveground biomass per hectare (about 2.5 acres). Plus, it can create far more root biomass that is distributed much more deeply in the soil than wheat or corn. 

Ultimately, two-thirds of all this organic matter can replenish the soil, improving conditions for other plants. Hemp biomass can also improve soil porosity and friability (the soil’s ability to crumble easily), and mend soil structure altogether. 

This plant’s ability to thrive in the absence of harmful pesticides can benefit your other crops, too. Research has shown that hemp can decrease nematode populations and reduce the presence of pathogenic fungi in soil. 

These advantages have been demonstrated repeatedly. For example, a team of scientists found that hemp cultivation boosted wheat yields in two out of three growing seasons when grown in rotation with a monoculture. Yet another study reported a 10-20% increase in wheat yield following hemp growth. These successes have also been observed in soybean and alfalfa. 

Many ongoing studies are focused on hemp’s ability to improve cultivation results for other plants. For example, the Rodale Institute pitted the herb against yellow foxtail (Setaria pumila) and redroot pigweed (Amaranthus retroflexus) to determine which cover crop is best. 

They found that growing hemp as a summer cover crop suppressed weed growth and did so for a longer period, helping to establish the winter cover crop. However, different seed varieties should be planted at varying times to ensure these benefits are consistent year-round. 

Growing Cannabis

Hemp is an incredible plant that offers a broad range of advantages to sustainable agriculture. From natural weed suppression to the removal of heavy metal contaminants, hemp’s repertoire of ecosystem services just keeps on giving. 

As you prepare for your upcoming crop, make sure to provide your plants with the best-quality soil to initiate a feedback loop that will benefit even your conventional monocrops. 

Jazmin Murphy
Jazmin Murphy is a trained science writer & reporter who has covered a breadth of topics. She is also a strong supporter and advocate of cannabis for recreational, wellness, and medical purposes.


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