How to Grow Cannabis Indoors: A Step-by-Step Guide

Growing cannabis indoors is becoming a pastime for many green-fingered aficionados.

The reasons are varied. With the increased interest and experimentation in house plant cultivation, it was inevitable that people would apply their knowledge of plant care to growing cannabis. Many who occasionally like to light up a joint may find it challenging to locate a source or are hesitant to deal with a perhaps unsavoury element of society in procuring their grass.

If you grow cannabis indoors, it is something you can do in the privacy of your own home without having to deal with someone you don’t know or trust. The best reason for growing your own is the enjoyment you will get from watching those tiny little seeds you picked out of your stash sprout become some of the most lovely and lush of all house plants.

Anyone Can Grow Cannabis Indoors

Even if you haven’t had any prior experience growing plants in your home, you can have a successful crop of cannabis by following these simple directions. If you have had problems in the past with cannabis cultivation, you may find the solutions in the following chapters. To grow cannabis indoors involves four basic steps:

Get the seeds if you don’t already have some, head to, where you can select from a comprehensive library of the best strains from around the world.

Germinate the seeds. You can simply drop a seed into moist soil, but by germinating the seeds first, you can be sure that the seed will indeed produce a plant. To germinate seeds, place a group of them between about six moist paper towels or in the pores of a damp sponge. Leave the towels or sponge moist but not soaking wet. Some seeds will germinate in 24 hours, while others may take several days or even a week.

Plant the sprouts. As soon as a seed cracks open and begins to sprout, place it on some moist soil and sprinkle a little soil over the top of it.

Supply the plants with light. Fluorescent lights are the best. Hang the lights within two inches of the soil and after the plants appear above the ground, continue to keep the lights within two inches of the plants. It is as easy as that. If you follow those four steps, you will grow a cannabis plant. However, a few details are necessary to ensure prime quality and the highest yield in the shortest time.

Soil for Indoor Cannabis Grows

Your prime concern after choosing high-quality seeds is the soil. Use the best soil you can get. Scrimping on the soil doesn’t pay off in the long run. If you use unsterilized soil, you will almost certainly find parasites in it, probably after it is too late to transplant your cannabis. You can find excellent soil for sale at your local plant shop, nursery, K-Mart, Wal-Mart, and even some grocery stores. The soil you use should have these properties for the best possible results:

grow cannabis indoors
  • It should drain well. That is, it should have some sand in it and also some sponge rock or pear-lite.
  • The pH should be between 6.5 and 7.5 since cannabis does not do well in acidic soil. High acidity in soil encourages the plant to be predominantly male, an undesirable trait.
  • The soil should also contain humus for retaining moisture and nutrients.

If you want to make your own soil mixture, you can use this recipe:

  • Mix two parts moss with one part sand and one part pear-lite or sponge rock to every four gallons of soil.
  • Test your soil for ph with litmus paper or with a soil testing kit available at most plant stores.
  • To raise the PH of the soil, add 1/2 lb. lime to 1 cubic foot of soil to raise the PH one point.
  • If you absolutely insist on using dirt you dug up from your driveway, you must sterilize it by baking it in your oven for about an hour at 250 degrees. Be sure to moisten it thoroughly first, and also prepare yourself for a rapid evacuation of your kitchen because that hot soil will stink.
  • Now add about one tablespoon of fertilizer (like Rapid-Gro) per gallon of soil and blend it in thoroughly. Better yet, just skip the whole process and spend a few bucks on some soil.

Related post:

Organic Cannabis Soil – Making Your Own

Containers Needed to Grow Cannabis Inside 

After you have prepared your soil, you will have to come up with some kind of container to plant in. The container should also be sterilized, especially if they have been used previously for growing other plants. The container size has a great deal to do with the growth rate and the plant’s overall size.

It would be best if you planned on transplanting your plant not more than one time since the process of transplanting can be a shock to the plant, and it will have to undergo a recovery period in which growth is slowed or even stopped for a short while.

The first container you use should be no larger than six inches in diameter and can be made of clay or plastic. To transplant, simply prepare the larger pot by filling it with soil and scooping out a little hole about the size of the smaller pot that the plant is in. Turn the plant upside down, pot and all, and tap the pot’s rim sharply on a counter or the edge of the sink. The soil and root ball should come out of the pot cleanly, with the soil retaining the shape of the pot and with no disturbances to the root ball.

grow cannabis indoors

Another method that can bypass the transplanting problem is using a Jiffy-Pot. Jiffy pots are made of compressed peat moss and can be planted right into moist soil, where they decompose and allow the passage of the root system through their walls. The second container should have a volume of at least three gallons. Cannabis doesn’t like to have its roots bound or cramped for space, so always be sure that the container you use will be deep enough for your plant’s root system.

It is difficult to transplant a five-foot cannabis tree, so plan ahead. It is going to get bigger. The small plants should be ready to transplant into their permanent homes in about two weeks. Keep a close watch on them after the first week and avoid root binding at all costs since the plants never seem to do as well once the cramping of their roots has stunted them.

Related post:

A Pot For Your Pot: The Best Cannabis Growing Containers

Fertilizer Options

Cannabis likes lots of food, but you can damage the plants if you are too zealous. Some fertilizers can burn a plant and damage its roots if used in too high a concentration. Most commercial soil will have enough nutrients to sustain the plant for about three weeks of growth, so you don’t need to worry about feeding your plant until the end of the third week. The most important thing to remember is gradually introducing the fertilizer concentration to the plant. Start with a reasonably diluted fertilizer solution and gradually increase the dosage.

There are several good marijuana fertilizers on the commercial market, two of which are Rapid-Gro and Eco-Grow. Rapid-Gro has had widespread use in cannabis cultivation and is available in most parts of the United States. Eco-Grow is also especially good for cannabis since it contains an ingredient that keeps the soil from becoming acid. Most fertilizers cause a PH change in the soil. Adding fertilizer to the soil almost always results in a more acidic PH.

As time goes on, the amount of salts produced by the breakdown of fertilizers in the soil causes the soil to become increasingly acidic. Eventually, the concentration of these salts in the soil will stunt the plant and cause browning out of the foliage. Also, as the plant ages, its roots become less effective in bringing food to the leaves.

To avoid the accumulation of these salts in your soil and ensure that your plant is getting all of the nutrition it needs, you can begin leaf feeding your plant at about 1.5 months. Dissolve the fertilizer in worm water and spray the mixture directly onto the foliage. The leaves absorb the fertilizer into their veins. If you want to continue to put fertilizer into the soil and leaf feeding, be sure not to overdose your plants.

Remember to increase the amount of food your plant receives gradually. Cannabis seems to be able to take as much fertilizer as you want to give it as long as it is introduced over some time. During the first three months, fertilize your plants every few days. As the rate of foliage growth slows down in the plant’s preparation for blooming and seed production, the plant’s fertilizer intake should also be slowed down. Never fertilize the plant just before you are going to harvest it since the fertilizer will encourage foliage production and slow down resin production. A word here about the most organic of fertilizers: worm castings.

As you may know, worms are raised commercially for sale to gardeners. The breeders put the worms in organic compost mixtures, and while the worms are reproducing, they eat the organic matter and expel some of the best cannabis food around. After the worms have eaten all the organic matter in the compost, they are removed and sold, and the remains are then sold as worm castings. These castings are so rich that you can grow marijuana in straight worm castings. However, this isn’t necessary, and it is somewhat impractical since the castings are very expensive. If you can afford them, you can, however, blend them in with your soil, and they will make an excellent organic fertilizer.

Lighting Best Practices for Indoor Cannabis

Without light, the plants cannot grow. In the countries where cannabis grows best, the sun is the light source. The amount of light and the length of the growing season in these countries results in huge tree-like plants. In most parts of North America, however, the sun is not generally intense enough for long enough periods to produce the same size and quality of plants that grow easily in Latin America and other tropical countries.

The answer to the lack of sun, especially in the winter months, shortness of the growing season, and other problems, is to grow cannabis indoors under simulated conditions.

The rule of thumb seems to be the more light, the better. In one experiment we know of, eight eight-foot VHO Gro-Lux fixtures were used over eight plants. The plants grew at an astonishing rate. The lights had to be raised every day. There are many types of artificial light, and all of them do different things to your plants. The typical incandescent light bulb emits some of the frequencies of light the plant can use, but it also emits a high percentage of far red and infra-red light which cause the plant to concentrate its growth on the stem.

grow cannabis indoors

This results in the plant stretching toward the light bulb until it becomes so tall and spindly that it just weakly topples over. There are several brands of bulb types. One is the incandescent plant spot light which emits higher amounts of red and blue light than the typical light bulb. It is an improvement but has its drawbacks. It is hot, for example, and cannot be placed close to the plants.

Consequently, the plant has to stretch upwards again and is in danger of becoming elongated and falling over. The red bands of light seem to encourage stem growth which is not desirable in growing marijuana. The idea is to encourage foliage growth for obvious reasons. Gro-Lux lights are probably the most common fluorescent plant lights. In our experience with them, they have proven themselves to be highly effective. They range in size from one to eight feet in length so that you can set up a growing room in a closet or a warehouse.

There are two types of Gro-Lux lights: The standard and the wide spectrum. They can be used in conjunction with one another, but the wide range of lights is insufficient. The wide spectrum lights were designed as a supplementary light source and are cheaper than the standard lights.

Wide spectrum lights emit the same bands of light as the standard, but the standard emits higher concentrations of red and blue bands that the plants need to grow. The wide spectrum lights also emit infra-red, the effect of which on stem growth we have already discussed. If you are planning to grow on a large scale, you might be interested to know that regular fluorescent lamps and fixtures, the type used in commercial lighting, work well with standard Gro- Lux lights. These commercial lights are called cool whites and are the cheapest of the fluorescent lights we have mentioned. They emit as much blue light as the Gro-Lux standards, and the blue light is what the plants use in foliage growth.

Now we come to the question of intensity. The standard and wide spectrum lamps come in three intensities: regular output, high output, and very high output. You can grow an excellent crop of plants under the regular output lamps and probably be quite satisfied with our results. The difference in using the HO or VHO lamps is the time it takes to grow a crop. Under a VHO lamp, the plants grow at a rate that is about three times the rate at which they grow under the standard lamps. People have been known to get a plant that is four feet tall in two months under one of these lights. Under the VHO lights, one may have to raise the lights daily, which means a growth rate of at least two inches a day.

The only drawback is the expense of the VHO lamps and fixtures. The VHO lamps and fixtures are almost twice the price of the standard. If you are interested in our opinion, they are well worth it. Now that you have your lights up, you might be curious about the amount of light you give your plants daily.

grow cannabis indoors

The maturation date of your plants is dependent on how much light they receive per day. The longer the dark period per day, the sooner the plant will bloom. Generally speaking, the less dark per day, the better during the first six months of the plant’s life. The older the plant is before it blooms and goes to seed, the better the grass will be. After the plant is allowed to bloom, its metabolic rate is slowed so that its quality does not increase with age at the same rate it did before it bloomed. The idea, then, is to let the plant get as old as possible before allowing it to mature so that the potency will be as high as possible at the harvest time. One relatively sure way to keep your plants from blooming until you are ready for them is always to leave the lights on.

Occasionally a plant will go ahead and bloom anyway, but it is the exception rather than the rule. If your plants receive 12 hours of light per day, they will probably mature in 2 to 2.5 months. If they get 16 hours of light per day, they will likely be blooming in 3.5 to 4 months. With 18 hours of light per day, they will flower in 4.5 to 5 months. It is a good idea to put your lights on a timer to ensure that the amount of light received each day remains constant. A “vacation” timer, typically used to make it look like you are home while you are away, works nicely and can be found at most hardware or discount stores.

Related post:

How supplemental and side lighting can increase cannabis yields

Temperature and Humidity

The ideal temperature for the light hours is 68 to 78 degrees Fahrenheit, and there should be about a 15-degree drop in temperature for the dark hours. The growing room should be relatively dry if possible. You want a resinous coating on the leaves, and to get the plant to do this, you must convince it that it needs the resinous coating on its leaves to protect itself from drying out.

The plants develop broad leaves in an extremely humid room and do not produce as much resin. You must take care not to let the temperature in a dry room become too hot. However, since the plant cannot assimilate water fast enough through its roots, its foliage will begin to brown out.


Proper ventilation in your growing room is pretty important. The more plants you have in one room, the more important good ventilation becomes. Plants breathe through their leaves. They also rid themselves of poisons through their leaves. If proper ventilation is not maintained, the pores of the leaves will become clogged, and the leaves will die. If there is a free movement of air, the poisons can evaporate off the leaves, and the plant can breathe and remain healthy.

In a small closet with only a few plants, you can probably create enough air circulation just by opening the door to look at them. Although it is possible to grow healthy-looking plants in poorly ventilated rooms, they would be larger and healthier if they had a fresh supply of air coming in. If you spend a lot of time in your growing room, your plants will grow better because they will be using the carbon dioxide that you are exhaling around them. Getting a fresh supply of air into your growing room is sometimes tricky because your room is usually hidden away in a secret corner of your house, possibly in the attic or basement. In this case, a fan will create some movement of air.

grow cannabis indoors

It will also stimulate your plants into growing healthier and sturdier stalks. Often times in an indoor environment, the stems of plants fail to become rigid because they don’t have to cope with elements of wind and rain. However, this is an advantage because the plant puts most of its energy into producing leaves and resin instead of stems.

Dehumidify your Grow Room

Cannabis that grows in a hot, dry climate will have narrower leaves than cannabis grown in a humid atmosphere. The reason is that in a dry atmosphere, the plant can respirate more easily because the leaf moisture evaporates faster. In a humid atmosphere, the moisture cannot evaporate as fast. Consequently, the leaves have to be broader with more surface area to expel the plant’s wastes.

Since the broad leaves produce less resin per leaf than the narrow, there will be more resin in an ounce of narrow leaves than in one ounce of broad leaves. There may be more leaf mass in the broader leafed plants, but most people grow their own for quality rather than quantity.

Since the resin in the cannabis plant serves the purpose of keeping the leaves from drying out, there is more apt to be a lot of resin produced in a dry room than in a humid one. Dehumidifiers sometimes cost around $100.00 and are therefore a bit impractical for the “hobby grower.”

Watering Your Cannabis Plants Indoors

If you live near a clear mountain stream, you can skip this bit on water quality. Most of us are supplied water by the city, and some cities add more chemicals to the water than others. They all add chlorine, however, in varying quantities. Humans over the years have learned to either get rid of it somehow or to live with it, but your marijuana plants won’t have time to acquire a taste for it, so you had better see that they don’t have to. Chlorine will evaporate if you let the water stand for 24 hours in an open container. Letting the water stand for a day or two will serve a dual purpose: The water will come to room temperature during that period, and you can avoid the nasty shock your plants suffer when you drench them with cold water.

grow cannabis indoors

Always water at room temperature to lukewarm water. If your water has excessive chlorine in it, you may want to get some anti-chlorine drops at the local fish or pet store. The most important thing about watering is to do it thoroughly. You can water a plant in a three-gallon container with as much as three quarts of water. The idea is to get the soil evenly moist all the way to the bottom of the pot. If you use a little water, even if you do it often, it seeps just a short way down into the soil, and any roots below the moist soil will start to turn upwards toward the water.

The second most important thing about watering is to see to it that the pot has good drainage. There should be some holes in the bottom so that any excess water will run out. If the pot doesn’t drain, the excess water will accumulate in a pocket and rot the roots of the plant or make the soil sour or mildew. As we said earlier, the soil must allow the water to drain evenly through it and must not become hard or packed. If you have ensured that the soil contains sand and pearlite, you shouldn’t have drainage problems.

To discover when to water, feel the soil with your finger. If you feel moisture in the soil, you can wait a day or two to water. The soil near the top of the pot is always drier than the soil further down. You can drown your plant just as easily as you can let it get too dry, and it is more likely to survive a dry spell than it is to survive a torrential flood. Water the plants well when you water and don’t water them at all when they don’t need it.

Bugs and Pests

If you can avoid getting bugs in the first place, you will be much better off. Once your plants become infested, you will probably fight bugs for the rest of your plants’ lives. To avoid bugs, use sterilized soil and containers and don’t bring other plants from outside into your growing room. If you have pets, ensure they stay out of your growing space since they can bring in pests on their fur. Examine your plants regularly for signs of insects, spots, holes in the leaves, browning of the tips of the leaves, and droopy branches. If you find that despite all your precautions, you have a plant room full of bugs, you’ll have to spray your plants with some insecticide. You’ll want to use something that will kill the bugs and not you.

Spider mites are probably the bug that will do the most damage to cannabis plants. One of the reasons is that they are almost microscopic and tough to spot. They are called spider mites because they leave a web-like substance clinging to the leaves.

They also cause tiny little spots to appear on the leaves. Probably the first thing you’ll notice, however, is that your plants look sick and depressed. The mites suck enzymes from the leaves, and as a result, the leaves lose some of their green colour and glossiness. Sometimes the leaves look like they have some kind of fungus on them. The eggs are very tiny black dots. You might be wise to get a magnifying glass so that you can really scrutinize your plants closely. Be sure to examine the underside of the leaves too. The mites will often be found clinging to the bottom and the top of the leaves. The sooner you start fighting the bugs, the easier it will be to eliminate them.

One of the best insecticides for killing spider mites on cannabis is the “Fruit and Berry” spray made by Millers. Ortho also produces several insecticides that will kill mites. The ingredients to look for are Kelthane and Malathion. These poisons are lethal to humans, pets, and bugs, but they both detoxify in about ten days, so you can safely smoke the grass ten days after spraying. Fruit and Berry will only kill the adult mite, but you’ll have to spray every four days for about two weeks to be sure that you have killed all the adults before they have had a chance to lay eggs.

Keep a close watch on your plants because it only takes one egg-laying adult to re-infest them, and the chances are that one or two will escape your barrage of insecticides. If you see little bugs flying around your plants, they are probably white flies.

The adults are immune to almost all the commercial insecticides except Fruit and Berry, which will not kill the eggs or larva. It is the larval stage of this insect that does the most damage. They suck out enzymes too and kill your plants if they go unchecked. You will have to get on a spraying program, as explained in the spider mite section.

An organic method of bug control is using soap suds. Put Ivory flakes in some lukewarm water and work up the suds into a lather. Then put the suds over the plant. The obvious disadvantage is if you don’t rinse the soap off the plant, you’ll taste the soap when you smoke the leaves.

Related post:

The Best Bugs or Pests for a Cannabis Grow

Pruning Your Cannabis

We have found that pruning is not always necessary. One does it in the first place to encourage secondary growth and allow light to reach the immature leaves. Some strands of grass naturally grow thick and bushy, and if they are not clipped, the sap moves in an uninterrupted flow right to the top of the plant, where it produces flowers thick with resin. On the other hand, if your plants appear tall and spindly for their age at three weeks, they probably require a little trimming to ensure a nice full leafy plant. At three weeks of age, your plant should have at least two sets of branches or four leaf clusters and a top.

grow cannabis indoors

To prune the cannabis plant, simply slice the top off just about the place where two branches oppose each other. Use a razor blade in a straight cut. If you want to, you can root the top in some water and plant the top in moist soil when the roots appear, and it should grow into another plant. If you are going to root the top, you should cut the end again, this time with a diagonal cut to expose more surface to the water or rooting solution.

The advantage to taking cuttings from your plant is that it produces more tops. The tops have the resin, and that’s the name of the game. Every time you cut off a top, the plant seeds out two more top branches at the base of the existing branches. Pruning also encourages the branches underneath to grow faster than they usually would without cutting the top.

Harvesting and Curing

Well, now that you’ve grown your marijuana, you will want to cure it right so that it smokes clean and won’t bite. You can avoid that “homegrown” taste of chlorophyll that sometimes makes one’s fillings taste like they might be dissolving. We know of several methods of curing the marijuana so that it will have a mild flavour and a mellow rather than harsh smoke.

First, pull the plant up, roots and all and hang it upside down for 24 hours. Then put each plant in a paper grocery bag with the top open for three or four days or until the leaves feel dry to the touch. Now strip the leaves off the stem and put them in a glass jar with a lid. Don’t pack the leaves in tightly. You want air to reach all the leaves. The main danger in the curing process is mould. If the leaves are too damp when you put them into the jar, they will mould, and since the mould will destroy the resins, mould will ruin your marijuana.

You should check the jars every day by smelling them, and if you smell an acrid aroma, take the weed out of the jar and spread it out on newspaper so that it can dry quickly. Another method is to uproot the plants and hang them upside down. You get some burlap bags damp and slip them up over the plants. Keep the bags moist and leave them in the sun for at least a week. Now put the plants in a paper bag for a few days until the weed is dry enough to smoke.

Like many fine things in life, marijuana mellows out with age.

The post How to Grow Cannabis Indoors: A Step-by-Step Guide appeared first on Seedsman Blog.


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