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How To Grow Hemp Indoors?

Created by
JoshuaHolt JoshuaHolt
Added 6 October 2021

Hemp is a species of the Cannabis Sativa cultivar. Grown for various industrial and medicinal uses, it's one of the oldest plants known to man. However, there’s a lot of misunderstanding and speculation about the plant. While one type is cultivated for industrial purposes, the other is used to extract CBD, making it slightly confusing for beginners.

This will help you understand more about hemp. Plus, we will show you how to grow hemp indoors using artificial grow lights. 

What is hemp?

Photo by <a href=Image credit - Photo by Diyahna Lewis on Unsplash 

To keep it simple, scientists recognize only a single species of hemp or cannabis — Cannabis Sativa. So although you’ll hear a lot of terminologies, including Ruderalis, Indica, Sativa, etc., they are all the same. 

Cannabis plants are classified as hemp depending on the levels of cannabinoids (THC, in particular) produced by the plant. 

Hemp grown for industrial purposes is fibrous with large stalks and minimal cannabinoids, whereas hemp grown for medicinal uses contains large amounts of cannabinoids. In this article, we will focus on hemp that's grown to produce CBD.

Hemp has been legal in the USA ever since the introduction of the Farm Bill in 2018. As long as it contains less than 0.3% THC, it's considered hemp. Any strain higher than the specified level is not hemp. For example, strains containing 20% CBD and 1% THC are also referred to as marijuana and NOT hemp.

How does hemp grow?

hemp plant

Image Source - Photo by Diyahna Lewis on Unsplash 

Now you know that hemp and cannabis are the same, except for a difference in the THC levels, meaning they grow similarly. If you’re an experienced grower, it should be a breeze. If not, it might take a while to understand how hemp grows. 

Cannabis plants are dioecious in nature. For instance, tomato plants are monoecious, producing both male and female flowers on the same plant. However, cannabis male and female plants grow separately. While both female and male plants are used for industrial purposes, only female plants produce flowers containing cannabinoids.

Photoperiod

hemp in greenhouse

Image Credit - Photo by Richard T on Unsplash 

Cannabis plants are photoperiodic, which means they react to different phases of light. As a result, they need more light in the vegetative or growing stage than the flowering stage. 

Growers cultivating hemp or marijuana plants indoors must adjust their grow lights to provide at least 16-18 hours of light during the vegetative stage and 12 hours of light when it’s flowering. Growers usually refer to this as the 18/6 period where the plants receive 18 hours of light and 6 hours of darkness. 

Seed banks sell three types of seeds — regular, feminized, and autoflowering seeds. Regular and feminized seeds are usually photoperiod plants. However, “autoflowering” refers to another cannabis subspecies — C.ruderalis. 

Autoflowering seeds flower automatically without any assistance. They don’t need the grower to manipulate the cycles. In simple terms, they will flower whether they grow in an 18/6 or 12/12 cycle. 

No matter what type you grow, it’s easier to control the environment, including temperature and light indoors. You can use grow tents or convert a room into a grow room. The next step is to buy lights

Admittedly, all this sounds complicated, but it’s not. When the plants grow outdoors, they begin flowering when the days get shorter. You just have to mimic the same cycle indoors. 

pH 

pH is one of the most important factors to remember when growing cannabis or hemp plants. If Chemistry is not your strong suit, just remember that it’s a measure of how basic or acidic a substance is. 

The pH scale ranges from 0 to 14, and you will need a pH meter to measure the soil’s pH. Although you will find strips and other ways to measure the pH, it’s usually a waste of time. So instead, invest in a digital pH meter, so it’s accurate and easy to read. 

For hemp plants, optimum pH levels vary from 5.5 to 6.5. This means that the plants can better intake the nutrients you’re feeding them when they remain in this range. If you go above this range, the plants will not be able to absorb the nutrients. 

Similarly, going below 5.5 will damage the plants as well. As you can understand by the range, cannabis and hemp plants prefer slightly acidic soils. 

Hemp undergoes four phases from growth to harvest: germination, seedling, vegetative, and flowering. The first step involves purchasing high-grade hemp seeds. 

Purchase good seeds

hemp seeds

Purchasing hemp seeds online or in local shops can get you a combination of both male and female plants. Known as “Regular seeds,” these seeds will grow just like any other cannabis or hemp plant. 

However, you could waste a lot of time trying to weed out male plants. Therefore, it’s best to go for feminized seeds that guarantee female plants. 

What happens if you grow both male and female plants in the same room? The male plant will eventually pollinate the female plants, leaving you with plants containing very few buds and loads of seeds. 

Since the goal is to get hemp buds filled with CBD, you will have to eliminate the male plants before they pollinate the females. 

Germination

hemp seedling

The next step is to germinate the seeds. There are many ways to germinate them quickly, but it’s not much different than germinating tomato seeds. You can plant the seeds in a medium of your choice (soil, coco peat, etc.), or you could use a few extra measures to ensure they germinate as fast as possible.

  • Soak the seeds in water for 12 hours. 
  • Place the seeds in a wet paper towel for 24 hours.
  • Plant the seeds in small containers filled with soil mixes meant for seedlings.
  • The warmer the environment, the better the chances of germination, so you can use heating pads to assist the seeds in germinating quickly. However, do not exceed 80 to 80°F as you risk killing the seeds. 
  • Wait until germination occurs and grow to at least 2-3 inches.

Seedling stage

hemp seedlings

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The seedlings develop a few nodes within two weeks of the seedling stage. Here are a few things to keep in mind when the plants are in the seedling stage. 

  • Water — Make sure that you do not overwater or underwater the seedlings. The key is to keep the soil moist. Water only when the surface dries.
  • Light — Hemp plants need lots of light, but the seedlings will do well with low-intensity lights. Many people begin with florescent lights during the seedlings stage. But, it’s also okay to use LED lights as long as they don’t burn the plants. Also, do not position the lights too close to the tips of the plants. 

That said, the lights cannot be too far away either since the seedlings may begin stretching. You can maintain an appropriate distance by adjusting the lights now and then depending on the growth. Start with a distance of 18-20 inches for LED lights. You can keep them closer if you’re using lights with less intensity, like CFLs and other fluorescent lights. 

  • Nutrients — You can use various fertilizers to grow hemp plants, but it’s best not to feed any nutrients when the plants are in the seedling stage. After two weeks, you can begin feeding them with nitrogen-based fertilizer at half strength. NPK fertilizers will have specific numbers like 1:2:3 etc., but the seedling stage requires more nitrogen or N nutrients. 
  • Photoperiod — As explained earlier, the seedlings will need more light as they grow. Therefore, you can begin with the 18/6 light/dark cycle that will remain constant until the plants are ready to progress to the flowering stage. 
  • Humidity — Hemp plants need different levels of humidity based on their growth levels. During the seedling stage, they thrive when the humidity is limited to 60-70%. You can increase the moisture by creating a dome until they develop a few nodes. 
  • Temperature — Hemp does well in temperatures ranging from 65 to 82°F. Although mature plants can manage in higher temperatures, the same is not valid for seedlings. 

By the 2nd or 3rd week, the plants are likely to develop at least 2-3 nodes. When they grow at least 4-5 inches, it’s time to transplant them from small pots to bigger containers. There’s no need to transplant if you’ve used bigger containers from the very beginning. 

Typically, hemp plants do well when you transplant them at least twice in their life cycle. You can transplant them when you see roots coming out of the bottom. However, you can skip this step if you’re a beginner and don’t want to go through the trouble of handling the plants repeatedly. After the 3rd week, the plants are officially in their vegetative stage. 

Vegetative stage

hemp vegetative stage

Image Credit - Photo by CRYSTALWEED cannabis on Unsplash 

Hemp plants thrive like marijuana plants. However, the final yields depend on the way they grow during the vegetative stage. For this reason, it’s essential to take care of the plants during the vegetative stage. 

The vegetative stage also allows you to train the plants according to your liking. Interestingly, cannabis and hemp plants tend to do well when they are stressed. However, you should never train them during the flowering stage. 

Again, here are the factors you should keep in mind during the vegetative stage. 

  • Water — Water the plants only after the surface dries. However, since the plants require more water during the vegetative stage, you will see that the soil dries faster, meaning you may have to water at least 2-3 times a week. 
  • Light — You can now increase the intensity of the lights. If you’re using LED lights or other high-intensity lights from the very beginning, you can adjust the position of the lights to accelerate the growth. For example, if the lights are about 22 inches away, you can decrease the distance to 18-20 inches, depending on how the plants react. 
  • Nutrients — You can start feeding full-strength nutrients by the fourth week if your plants react well. Again, stick to nutrients with higher amounts of nitrogen compared to potassium and phosphorus. In simple terms, make sure that the first number or N in NPK is greater than P and K. 

If you’re growing organic hemp, fertilizers like horse manure, cow manure, and even chicken manure will work most of the time. Feeding nitrogen-rich fertilizers will enhance the growth of the plants, including the leaves and stems. As a result, the plants grow stronger and taller. However, fix a schedule at the very beginning and stick to it. Feed only when you’re watering the plants or according to the instructions mentioned on the label. If you go overboard, you’ll end up with plants producing only leaves with very few flowers. 

  • Photoperiod — As the plants are in the vegetative stage, they will need more light compared to darkness. Thus, continue with the 18/6 cycle. As mentioned earlier, you can continue up to 8-10 weeks. However, going beyond that will be problematic if your grow room isn’t large vertically and horizontally. 
  • Humidity — Many people ignore the importance of humidity when growing cannabis. They maintain the same levels from the seedling to the flowering stage. However, humidity is one of the most critical factors that affect the growth of hemp and cannabis plants. It’s good to start with high levels and decrease as the plants grow further. Many growers aim for 40-50% levels during the vegetative stage. Anything above 65-70% can damage the plants. 
  • Temperature — Tee plants will now be able to handle slightly higher temps ranging from 65 to 82°F.
  • Training — Many experienced growers train their hemp plants. Typically, hemp plants produce one main cola filled with flowers, while the remaining flowers on other stems do not grow much due to a shortage of light. To increase the number of colas, growers train the plants using several methods, including LST, HST, Topping, and FIMming. 

Here’s a quick rundown on training methods so you know what to choose:

  1. Topping — Topping is one of the best methods to force the plants to produce more than a few colas. As the plants grow more than 3-4 inches, snip off the tip to distribute the light evenly to other parts of the plant.
  2. FIMming — Fimming is similar to topping, except the tip is cut slightly. As a result, the tips will look uneven, unlike topping that appears clean. Also, while topping, growers remove the entire tip, whereas fimming requires you to cut off only a part of it.
  3. LST — Known as Low-Stress Training, LST is one of the most common methods. Perfect for both photoperiod and autoflowering varieties, it involves pulling the top of the main stem to the sides of the containers. LST works even better if you pair it with topping or fimming.
  4. Defoliation — Defoliation is a method that refers to removing leaves from the plant. The lower parts of the plant turn yellow as the plant ages, and you can remove them. However, defoliation involves removing even healthy leaves to encourage lush growth. Beginners can try this too, but make sure that you don’t pull too many leaves, or the plants will not be able to feed themselves. 

Many other training techniques involve cutting off the branches or inducing extreme stress to force the plants to grow more resin. However, it’s not recommended for beginners. 

By the 5th week, the plants should be bigger and similar to:

hemp in vegetative stage

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By the 8th week, the plants will be similar to this:

vegetative stage

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When they grow several colas, they are ready to be switched to the flowering phase. Complete all your training methods during this phase as you cannot stress the plants during the flowering stage. Check for pests, nutrient deficiencies, and other problems before flipping them. 

Flowering Stage

flowering

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Once you decide to switch to the flowering phase, you just need to reduce the light hours, which mimics nature for the hemp plants. In short, the new cycle would be 12/12 hours with equal light and dark hours. If you have constructed your own grow tent, you can expect more than a few leaks that can be patched using duct tapes. 

Once you switch the cycle, there's no going back. In addition, it's important to create a grow room or purchase a grow tent that doesn't allow light to filter inside. 

Why? Because you don't want to confuse your plants. The flowering cycle is smooth if there's total darkness for at least 12 hours. It's best to use timers compared to manual interference because you may see unwanted changes in the plant if the cycles are not regular.

If you cannot maintain this, it's best to use autoflowering hemp varieties instead. Since autoflowering strains flower automatically based on a specific time period, you don't have to worry too much about light leaks. 

As always, there are a few things to consider: 

  • Temperature — Lower the temperature by at least 5°F at this point. The lower the temperature, the more the resin production. However, keep in mind that lower temperatures prevent the development of new buds. Since we are not looking for new buds and just want the buds to fatten up, lowering the temperature is best during the flowering phase. If you cannot reduce the temperature, increase the airflow. Installing small fans will help to reduce the heat to a great extent.
  • Humidity — Again, lower the humidity and stick to 40-50% during the flowering stage.  Low humidity or dry conditions will force the plants to produce more resin and pistils. 
  • Water — Reduce the watering during the flowering stage to stress the plants slightly. For instance, if you watered thrice a week during the vegetative stage, watering twice a week will be just fine. However, there's a catch here. Some strains are hungrier and require more water. So if the container feels light, it's time to water the plants. The key is not to let them dry out frequently, as it will stress the plants much more than you intended. 
  • Nutrients — Things change in this department a little more during the flowering stage. Remember how you're supposed to use nitrogen-rich fertilizers during the vegetative stage? Well, the flowering phase requires less nitrogen and more potassium and phosphorus. Phosphorus and potassium help the buds develop. Therefore, the ratio needs to be something similar to 1:2:3 during the flowering stage.

At this point, the plants develop as many pistils as possible. Pistils are nothing but fine hair the plants develop when they begin flowering. It also helps you differentiate between male and female plants since only female plants produce pistils. The male plants will develop small round or tear-drop structures with pollen in them. 

Coming to the female plants, you'll see white pistils at first. Within 2-3 weeks in the flowering stage, the color changes from white to amber, which means that you will have to harvest the buds soon. 

Harvest

harvest

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After a long wait, you finally get to harvest the buds. As always, you will have to consider a few factors. 

  • Temperature — The temps should be as low as possible to increase the CBD and resin production. Most hemp plants will do well, even if it’s about 66°F. Do not go lower than this, or you may encounter a few issues. 
  • Water — Many growers stop feeding nutrients when they are two weeks away from harvesting the buds. You can also flush the soil with water to remove the additional buildup of nutrients. 
  • Color — Even if you do not have a microscope or a loupe to watch the color of the trichomes, you can harvest when at least 50% of the buds turn amber in color. Doing so will ensure that you’re harvesting the buds right when the cannabinoid levels are at their peak. 

Finally, you can harvest the buds using a pair of clean scissors or any tool that does the job. The last step is to dry the buds. 

Drying

Spread the harvested buds on a clean surface and allow them to dry for a few days. Remember not to let the buds be too dry or moist. Again, you need to maintain a balance here. If the stems of the buds snap when you break them, it’s time to cure them. 

Curing

buds

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Curing the buds is essential. Pretty much everything is for naught if you skip this step because uncured buds are harsh and don’t taste well either. You need dank buds that can be used for a variety of purposes. 

To cure the buds, use glass containers or mason jars. Fill the containers to at least half of their capacity. Do not overwhelm the containers, or you’ll have fungus issues. 

Cure the buds for at least 6-8 weeks to ensure that you get great buds. Do not lose patience at this point because you want buds that are full of cannabinoids. Allow the buds to breathe for a few hours every day by removing the tops of the containers. 

Finally, after six weeks, you’re ready to use the buds. We hope this guide helps you grow as many hemp plants as you can!




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