Best Soil for Hemp: Testing and Amending Soil
Few things in life are as fulfilling as growing your own crops in the soil of the Earth. Soil is the oldest and most commonly used medium for growing hemp. It offers many advantages over other growing media. Growing in soil is an easy and dirt-cheap way for farmers to cultivate healthy, potent, and flavorful hemp buds.
A high-quality soil mix provides plants with a wide array of nutrients and beneficial bacteria, fungi, and other microorganisms. It also may help to regulate pH and protect the plants from harmful pathogens.
Although soil is an excellent medium for growing hemp, farmers must choose the right soil type and maintain it to ensure a successful harvest. This article will describe the components a soil mix should have and how to test and amend soil to maintain its effectiveness.
The Best Soil for Hemp Includes Airflow and Drainage
One of the most critical considerations for hemp farmers is choosing a soil that offers adequate airflow and drainage. Hemp thrives in soil that has a light and loose consistency. Light, fluffy soil contains multiple air pockets that supply oxygen to both the roots and the microorganisms living in the ground.
Light soil also allows for adequate drainage, which helps regulate the amount of water the plants receive. Overwatering may lead to a variety of diseases and nutrient deficiencies in hemp. Soils that do not allow for sufficient drainage may prevent respiration in the roots. Further, if the roots remain wet for an extended period, they may rot.
Although soil should allow for adequate draining, it also should retain some water. Farmers must water their crops frequently if they use soil that does not hold water well. As with overwatering, underwatering hemp plants may also damage the roots and inhibit healthy plant growth. Striking a balance between water retention and drainage is crucial.
Best Soil for Hemp; Types of Soil
Sandy soil tends to be coarse, with large granules of sand. This type of soil is easy to work with, provides excellent drainage, does not easily become compacted, and provides enough space for oxygen to reach the plants’ roots. However, it is not ideal for hemp because it generally has a low pH and does not retain water or nutrients. Farmers using sandy soil likely will have to water and fertilize their plants frequently. This process can become expensive, as fertilizers and water are not always cheap, and applying them can be time-consuming.
Silty soil is somewhat coarse, with medium-size granules. This type of soil tends to be highly fertile, containing abundant minerals and organic nutrients. Notably, silty soil provides excellent water retention. However, it is easily compacted and does not drain easily. Hemp plants may develop root rot if they grow wet, compacted soil.
Clay soil consists of fine particles and is rich in minerals. Due to its density, clay soil retains water easily and provides a strong foundation to anchor plants into the ground. However, this type of soil tends to have a high pH, becomes easily compacted, and does not drain well.
Loam soil is the best soil for growing hemp. This type of soil comprises a mixture of sand, silt, and clay. This type of soil not only allows for adequate drainage and airflow, but it also can retain water. Loam soil is rich in minerals and organic nutrients and does not easily compact. The only downside to loam soil is that it may be more expensive than other soil types.
Hemp Plant Nutrients
Hemp plants need nutrients to thrive. Most soil mixes contain an array of nutrients, providing plants with a rich and varied diet. Specifically, hemp plants require large amounts of primary macronutrients, notably nitrogen, phosphorous, and potassium. They require somewhat lesser amounts of secondary macronutrients, such as calcium, magnesium, and sulfur. Finally, hemp plants need trace amounts of micronutrients, like boron, iron, and zinc. A good soil mix will contain an ample supply of macronutrients as well as healthy levels of micronutrients.
Plants use nitrogen more than they use any other nutrient, particularly during the vegetative growth period. Nitrogen is necessary for chlorophyll production, a pigment that supports photosynthesis in hemp and other plants. Nitrogen also increases resistance to diseases and environmental stresses.
A good soil mix contains organic sources of nitrogen. These may come from alfalfa meal, blood meal, compost, manures such as bat guano and worm castings, and other sources. As a rule, farmers will need approximately 150 pounds of nitrogen to produce 1,500 pounds of hemp buds.
Phosphorous is another macronutrient required for healthy hemp plants. It promotes nutrient uptake and facilitates energy metabolism and photosynthesis in hemp. This macronutrient also can enhance root growth, strengthen plant stalks, increase resistance to pests, diseases, and environmental stresses, and increase the quality and yield of hemp flowers.
Because all plants require phosphorous, most commercially available soil mixes will be rich in this macronutrient. Importantly, phosphorous comes from bone meal, rock phosphate, compost, and certain manures, among other sources. In most cases, 50 to 80 pounds of phosphorous per acre are adequate for the production of healthy hemp plants.
Potassium is the third primary macronutrient hemp plants require. This indispensable nutrient fortifies plant tissues, fuels plant growth, increases resistance to environmental stresses, and increases the yield and density of hemp flowers.
Like nitrogen and phosphorous, potassium is a common ingredient in most commercially available high-quality soils. Organic sources of this macronutrient include rock powders, wood ash, kelp meal, compost, and certain manures.
Although hemp requires calcium in smaller amounts than nitrogen, phosphorous, and potassium, it is still essential for healthy plant growth. Calcium improves nutrient uptake, fortifies cell walls, and regulates hormone and enzyme activity in hemp plants, among many other functions.
The best soil for hemp must contain calcium, although some strains of hemp may require an additional calcium amendment. Calcium often comes from gypsum, dolomite lime, wood ash, clamshell, oyster shell, eggshell, and other sources.
Magnesium is another secondary macronutrient essential for hemp plant growth. It is a critical component for chlorophyll production, and its presence enhances a plants’ ability to convert light into energy. This macronutrient also helps plants utilize iron and phosphorous and controls the production of enzymes.
Magnesium is present in most commercially available soil mixes, but some hemp strains may require additional magnesium amendment. Magnesium is present in dolomite lime, Epsom salt, soybean meal, and sulfate of potash magnesia, among other materials.
Sulfur is the final secondary macronutrient that hemp plants require. This chemical element allows for the production of chlorophyll, amino acids, plant proteins, and enzymes. An abundant supply of sulfur may stimulate root growth, boost plant metabolism, and increase disease resistance.
Most mineral-rich soils contain enough sulfur for healthy plant growth, including all of the best soil for hemp. Sulfur is a dominant element in Epsom salt, gypsum, potassium sulfate, and animal manures.
In addition to primary and secondary macronutrients, micronutrients are also important for the vitality of hemp plants. Chlorine, molybdenum, copper, iron, manganese, zinc, and boron are all necessary for healthy plant growth. Although these nutrients are needed only in trace amounts, all strains of hemp require them.
Most high-quality commercial soil mixes contain enough micronutrients for hemp plants. Growers source micronutrients from guano, kelp, molasses, worm castings, and other organic fertilizers to make the best soil for hemp in their garden.
Nutrient-rich soil is not, by itself, enough to ensure that plants will grow properly. One reason is that hemp plants cannot readily absorb most of the nutrients from the soil. To break down organic nutrients and make them absorbable, plants rely on certain bacteria, fungi, and other microorganisms in the soil.
The roots of hemp plants secrete exudates such as sugars, amino acids, and organic acids. The exudates attract and feed microbes that, in turn, break down organic compounds and make them bioavailable for the hemp plants. This symbiotic relationship benefits both the plants and the microorganisms.
In addition to making nutrients bioavailable, microbes also act as an “immune system” for plants. Soil that is teeming with beneficial microbes does not have enough space to accommodate colonies of harmful bacteria and other pathogens. Additionally, certain microbes may release compounds that destroy pathogens. Indeed, microbes are an essential component of the best soil for hemp.
Microorganisms such as mycorrhizal fungus, rhizobacteria, and predatory nematodes, can serve multiple vital functions: enriching soil; increasing the plants’ resistance to pests, diseases, and environmental stresses; stimulating root growth, and improving the overall health of hemp plants. Most high-quality commercial soil mixes contain these beneficial microorganisms; however, some low-quality soils contain harmful microbes that can infect both plants and humans.
Some soil mixes may contain too many nutrients for seedlings, clones, and young hemp plants to utilize. These are referred to as “hot” soils because they may cause nutrient burn in young plants. Nutrient burn may damage the roots of hemp plants and cause leaf tips to turn yellow or brown and appear burnt.
To avoid overfertilization, farmers should use a seed-starting soil mix when planting seedlings or clones. Worm castings are an excellent fertilizer for young plants, as they do not cause nutrient burn. Notably, soil mixes that contain fertilizers such as bat guano or chicken manure may be too strong for young hemp plants.
Best Soil for Hemp; Soil pH
Another important factor to consider when choosing a soil mix is pH. Hemp plants can absorb only those nutrients that lie within a certain pH range. A pH value of between six and seven is ideal for hemp grown in soil because it allows maximum nutrient uptake. Most high-quality soil mixes fall within the ideal pH range. However, some lower-quality mixes may be too acidic or alkaline for hemp plants.
How to Test Soil
The best soil for hemp will have a well-balanced pH. As such, farmers should test their soil before planting crops to ensure that it falls within the recommended pH range. Over time, even a soil mix that is already pH-adjusted may prove to be too acidic or alkaline. In addition to testing for pH, farmers should test their soil’s nutrient levels, especially if they plan on recycling or amending the soil. The best time to conduct such testing is several months before planting the crops to give farmers adequate time to correct any pH or nutrient imbalances.
The easiest way to test soil pH is to use a soil test kit, which growers can purchase online or at most garden centers. Some test kits also measure the levels of nitrogen, phosphorous, and potassium in the soil.
The most accurate way to test soil is to collect a soil sample and send it to a lab. Soil testing labs can precisely measure soil pH and levels of salts, heavy metals, and macro and micronutrients. However, it may take several weeks for a lab to analyze the soil and submit results to the grower. The lab’s services also may be far more expensive than a home test kit.
Most states recommend using the U.S. Department of Agriculture lab test to obtain an accurate and comprehensive scientific report on the soil. Farmers should check with local authorities regarding state industrial hemp growing programs and resources before choosing the best soil for hemp in their garden.
Adding Nutrients to Create the Best Soil for Hemp
Nutrients deplete quickly, even in the best soil for hemp. In fact, most soil mixes contain only enough nutrients to feed hemp plants for only three to four weeks for container gardens.
Generally, by the time the hemp plants begin flowering, they will have depleted many of the soil’s nutrients, at which point farmers may need to add fertilizers. The best way to accomplish this is by feeding the plants with liquid fertilizers or top dressing the ground with dry fertilizers such as compost or manure.
Farmers should closely monitor their plants for signs of deficiencies or toxicities to determine how to amend their soil correctly. For example, if the plants show nitrogen deficiency signs, amending the soil with nitrogen-rich fertilizers is advisable.
Typically, hemp requires more nitrogen during the vegetative growth phase and more phosphorous and potassium during the flowering stage. As the plants enter the flowering phase, farmers may need to amend the soil with phosphorous and potassium-rich fertilizers such as bone meal, kelp meal, and wood ash. Compost also provides an excellent soil amendment because it usually contains a variety of macro and micronutrients. However, because compost can vary significantly in its composition, farmers should test its nutrient levels before using it to fertilize crops.
Amending Soil to Increase Nutrient Uptake
Although most of the best soil for hemp falls within the ideal pH range, this may change as other amendments join the soil. If farmers find that their soil is too acidic, they can raise the pH level by amending it with dolomite lime, which will provide calcium and magnesium to the plants. Conversely, if the soil has become too alkaline, farmers can amend it with sphagnum peat, elemental sulfur, or aluminum sulfate, among other products. Correcting the soil pH will optimize nutrient uptake for hemp plants.
Nutrient uptake is also affected by microbes. Although most high-quality soils contain beneficial microbes, farmers may wish to add microbes to enhance these soil mixes. To achieve this, farmers can top dress the soil with compost, manure, or other organic matter. Farmers can also add unsulfured molasses to the water to feed the microbes in the ground.
Some farmers choose to inoculate the soil with microbes by feeding it with compost teas. Although this has become a prevalent practice, it is generally not advisable. Researchers have not determined whether compost tea is more beneficial than ordinary compost as a top dressing. Further, the tea may contain pathogens that can cause diseases in plants and animals if not properly brewed. Farmers may expose themselves to E.coli and other harmful bacteria in the process of brewing compost tea.
Amending Soil to Improve Texture
Farmers who do not have access to high-quality loam soil can use amendments to improve the existing ground’s texture. For heavy, compacted soils, adding coco coir may lighten the soil and increase water retention. For soils with poor drainage, growers can add perlite to improve airflow and drainage. Finally, for soils with poor water retention, farmers can amend it with vermiculite to lighten the soil and improve its water retention capacity. Farmers can get creative with amendments to make the most of their soil mixes.
Using cover crops is a great way to maintain the best soil for hemp. Farmers can plant cover crops in the off-season or during the winter to manage soil erosion, quality, fertility, and structure.
Recreating the Best Soil for Hemp
Many container gardeners throw away the soil after they have harvested their hemp plants. Because the soil no longer contains most of its nutrients. Instead, they buy a whole new bag of the best soil for hemp and start the process over again. Although this ensures that the new plants will receive proper nutrition, it is not very sustainable.
Growers who know how to test and amend soil can recycle their potting soil, using it for many seasons. The first step in recycling soil is to remove the hemp roots and other plant matter from the soil, and then mix it up to make it light and fluffy again. After the soil is mixed, growers should flush it with boiling water to kill any pathogens or insects and to remove excess salts. Next, they should pasteurize the soil by putting it in a plastic bag and letting it bake in the sun for two to three weeks. This process will kill any remaining pathogens and insects. Finally, growers should test the soil pH and nutrient levels, amend it with compost and other fertilizers and, if necessary, add dolomite lime or elemental sulfur to raise or lower the pH of the soil. Notably, some soil will inevitably be lost in the recycling process. As such, adding some fresh soil to the mix may also be necessary.
Hiring an Agronomist
For large-scale hemp farmers, hiring an agronomist may be the ideal way to improve soil conditions. A professional agronomist can provide accurate soil testing, recommend specific soil amendments, and develop an irrigation and fertilization plan to ensure optimum plant health and yield.
Closing Thoughts About the Best Soil for Hemp
Nothing is rewarding as growing healthy plants in healthy soil. Soil is one of the most influential media for growing hemp. A good soil mix can provide many macro and micronutrients and act as an “immune system” for plants. To ensure a successful harvest, farmers should choose a soil mix that offers sufficient airflow, drainage, and water retention and is rich in minerals, organic compounds, and microbes. They should also know how to test their soil and amend it to maintain its effectiveness. These practices will allow farmers to cultivate top-shelf hemp buds that are potent and flavorful.
In addition to choosing high-quality soil, farmers who hope to enjoy a successful harvest must select hemp seeds that possess potent and reliable genetics. Fortuna Hemp offers a wide selection of premium hemp seeds, bred to withstand harsh environmental conditions and imperfect soil conditions.
If you have any questions or comments about the best soil for hemp, let us know in the comment section below.