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10 Tips for Growing Indoor Hemp

Indoor hemp growers face challenges that don’t impact outdoor growers. While some of the same problems befall both types of cultivators, the solutions can differ significantly. Indoor growers face unique problems from a closed environment.

Any grow room should have sufficient space for the number of mature plants that will occupy it. The room should have adequate vertical space, because some strains will stretch upward rapidly and crowd the lights if allowed to get too tall. An indoor grower will have to monitor the distance between the lights and plants and adjust the distance accordingly throughout the grow.

A good grow room should be fairly stark, not filled with other items that don’t relate to the grow. The walls should have a reflective surface like mylar, although a bright white will work well, too. Carpeting can be a big nuisance for any grow room, and if the room has carpeting, the grower would be wise to employ judicious use of thick plastic sheeting below the pots, which should use saucers and trays, because spills are inevitable.

With these basic parameters of a basic grow room outlined, let’s explore in greater detail 10 specific problems to remain aware of that many new indoor growers experience. Heed the tips for proper practices when it comes to these 10 areas of concern, and your grow will most likely be a success.

1. Humidity

A grow room that’s overly humid opens itself up to a host of problems, including powdery mildew and mold. High humidity during flowering can even cause your plants to produce more THC as a response to stress. Plants will grow much better in rooms with low humidity levels than in rooms with excessively high humidity. Obviously, the best levels fall within a specific range. For seedlings and young clones, 60- to 70-percent humidity is best.

For the vegetative phase, humidity should fall between 40 and 65 percent, for flowering it should be 40 to 50 percent, and for pre-harvest it should fall between 30 and 40 percent. A humidity meter placed in a central area of the room will determine if the levels need a boost from a humidifier, or if the levels need to reduce by more thorough ventilation and air circulation.

2. Temperature

For the most part, hemp plants enjoy moderate temperatures that aren’t too hot or too cold. Temperatures below 60 degrees Fahrenheit will cause plants to grow slower and fail to develop at an optimum rate, while temperatures above 90 degrees Fahrenheit can cause a similar situation, with less than optimum growth. While plants that are flowering will not achieve optimum cannabinoid production at less than ideal temperatures, hemp plants can be stressed into producing too much THC from temperatures higher than ideal. To achieve a high CBD to THC ratio temperatures during flowering should be monitored very closely.

Temperatures that are too hot or cold can also result in a higher incidence of mold, white powdery mildew, spider mite infestation, and a host of other problems. Strive to maintain a temperature range of 70 to 85 degrees Fahrenheit throughout the growing period. Use a thermometer to monitor temperature and adjust if necessary. If temperatures are prone to getting too low, use a heater with a thermostat control to promote stable temperatures.

3. Water Quality

All indoor growers should evaluate their water quality for pH and adjust if necessary. Regardless of the source, correct water pH is very important. Testing water pH should be a standard procedure for every hemp grower. Water pH test kits are readily available and easy to use. Hemp does best with a pH reading between 6 and 7. A level of 6.5 is perfect—even lower for hydroponic grows. For hydroponic cultivation, a level between 5 and 6 is best, with 5.5 being ideal. Most likely, your water won’t be right on target.

While you can likely grow hemp with it, your plants won’t grow with the same vigor that they will with pH in the proper range. Most likely, you will need to decrease your taps water’s pH rather than increase it. Using a reliable pH test, collect some tap water and take a reading. High pH means the water is too alkaline, and low pH means the water is too acidic. Neither extreme is desirable. You want to be somewhere in the middle.

Water transports vital nutrients throughout a hemp plant’s structure to help it grow. Improper pH prevents water from delivering these important building blocks. If your water pH is outside of the desirable range, don’t despair. There are easily obtainable products that will adjust it to a good level. Hemp growers should have some standard items in their cultivation arsenal that go beyond the most obvious ones.

A pH booster and a pH reducer should be at your disposal in the event you need them. These products are easy to locate at your local nursery or grow center. Test your tap water and follow the directions on your booster or reducer to adjust your pH to the optimum level. Most likely, the pH reducer will be the product most often used, since a lot of water straight from the tap tends to run a little high in pH.

4. Proper Soil

Most hemp growers and consumers prefer organically grown hemp, which requires growing in organic soil mixes. If you haven’t grown organically in the past but now recognize it as a superior method, there are some basic steps and products to get you up to speed.

One option is to purchase premixed organic soil. Several commercial soil companies sell their own prepared organic soil mixes that are ideal for hemp cultivation. This eliminates much of the work necessary in the early stages of plant growth, although supplemental soil additives will be necessary once the organic fertilizers in the soil are used up by the rapidly growing plants. Bat guano, kelp, fishmeal, and earthworm castings are common components of high-quality organic soil mixes. Sources such as Fox Farms—a company that has served the needs of hemp growers and other gardeners for many years—sell a range of organic soils and additives.

Fox Farms Ocean Forest and Happy Fog organic mixes both work well. If you’d prefer to make your own organic soil mix, the process is simple. Start with a good-quality basic potting soil—sans fertilizers. To this, you can add compost, perlite, coco fiber, pumice, peat moss, coco fiber, and other ingredients to create your own personal mix (be sure to do your research and combine ingredients at the recommended ratios). If you’re able to create your own compost to supplement your organic soil, by all means do so. This organic and nutrient-packed approach will pay dividends when harvest time arrives.

5. Soil Additives

Consistent with organic soils, remain true to organic practices when it comes to soil additives and fertilizers. A number of cultivation companies—some of them catering specifically to the hemp community—market plant nutrients and fertilizers. Fox Farms’ Big Bloom bottled formula is a great soil additive that’s organic, promotes growth, and keeps plants lush and healthy. Used in combination with Fox Farms’ Grow Big and Tiger Bloom, you will provide your plants with an almost completely organic (as organic as you can get from a bottle) growing regimen.

Fox Farms and other companies will also provide a schedule for feeding the plants these additives; Big Bloom, Grow Big, and Tiger Bloom are fed in various combinations and quantities of the growth cycles, since hemp has different nutritional needs during different stages of growth. Plants want nitrogen in the vegetative stage, and less nitrogen and more phosphorus during the flowering stage.

Hemp also enjoys a soil that’s very slightly acidic, thus appreciating a bit more fungus in the bacteria-to-fungus ratio than some other soils. Most experienced growers agree that the required dosages on the labels of these products are a bit high, so they feed at one half to three quarters of that amount with outstanding results.

6. Pot Selection

To grow hemp well, the pots in which they’re grown must be the appropriate size to accommodate the size of the plants. Large plants obviously need large pots so the roots have adequate room to develop and fully nourish and hydrate the plants and their rapidly growing flowers. The pots must have numerous holes at their base to allow for the rapid and thorough flushing of excess water. Smart pots and air pots can make great choices for growing hemp, because they make overwatering nearly impossible. Overwatering is a problem that impacts many novice growers. Pot saucers or trays will capture excessive water runoff—which is an invariable part of watering hemp—so invest in them and use them if you need to prevent water damage to your grow room floor.

7. Strain Selection

Few things are more important in a grow than the genetics that went into them. Growing stabilized strains from a well-known source will insure that, as long as you followed all of the other proper indoor cultivation tips listed here, you will harvest a hefty and cannabinoid rich batch of outstanding, sticky hemp flowers. Seeds and clones—if you have access to clones–are expensive these days, so choose your strains wisely and practice sound germination procedures to ensure your seeds soon become healthy seedlings. If you choose to grow more than one strain, ensure that they all grow to similar heights as well as have similar finishing times.

8. Appropriate Lighting

Don’t skimp on lighting. Make sure the lamps you buy are able to fully illuminate the square footage of the grow area. High-pressure sodium (HPS), metal halide (MH), and light-emitting diode (LED) all come in a wide variety of wattages and equipped with a range of hood designs. High-pressure sodium is the most widely used grow light, but LED is catching up in popularity. Many grows include two or more lamps, and more than one light can be useful if plants within the garden vary in height. Clustering plants with similar heights under the same lamp will accommodate the height variances. Lamp height will require adjustment throughout the plants’ growth cycle to ensure they receive optimum illumination. Be sure to provide the appropriate distance between the lamps and the plants based on the type of lamps you use.

9. Air Flow and Ventilation

Good airflow within the grow is important for circulating air throughout the room. Fans also help reduce humidity and help plant stalks grow stronger from regular movement. They will keep the grow room cooler during hot weather, too. Because many types of grow lights emit heat, grow rooms can become hot during the summer.

Hemp plants should have access to fresh air, so it’s important that the room be well-ventilated. Install vents and/or ducts if necessary. Ducts equipped with fans and forced-air technology are worth investing in for large grows because complete air replacement on a regular basis provides the plants with fresh air and keeps humidity and temperature levels in check.

10. Disease and Pest Prevention

Indoors, spider mites are the most common pest that will impact a grow. They can be a persistent and serious nuisance, and a challenge to eradicate. Spider mites have a detrimental effect on plants because they ingest liquid from the leaves and other areas of the plants they prey on, weakening the plants and lowering yields.

The second most common disease and pest problem for indoor growers, powdery mildew, can strike a number of plant species and results from various fungi species. There are several causes for powdery mildew, but the most common is high humidity. This is one of the reasons why proper humidity and air circulation are so vital to successful hemp cultivation. Be sure to space plants a proper distance from each other to promote adequate air flow between them.

Be sure to quarantine any plants you bring into your grow, or better yet, avoid the practice of adding plants altogether. One outside plant with a problem like spider mites can seriously impact an entire harvest, so for many people it’s not worth the risk.


Indoor growers face many unique challenges that could result in serious problems—and that differ quite a bit from the challenges outdoor growers face. Each has to work with different environmental factors. Because the indoor cultivation environment is manmade, an indoor grower must have a sound and proven strategy for success, as well as all the necessary equipment to detect, regulate, and treat unacceptable variances. Be smart and don’t let your challenges become problems that could impact your harvest!

Written By: Phil Samuelson

Edited By: Joseph Jackson

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