The Indoor Cannabis Grow

There are many ways to grow your cannabis plant indoors. The two core methods of indoor growing are soil growing and hydroponics. There is a separate chapter for hydroponics, and so this chapter will deal with soil growing.

Indoor Grow Rooms
Figure 5.1 - Indoor Grow room. Picture by RealHigh.

There are many ways to grow an indoor soil garden. The most common indoor set-ups are:

l.Bench growing, 2.SOG growing, 3.ScrOG growing 4.Cabinet growing.

We will discuss these methods in a moment but let us first see what they all have in common.


Lights come in all shapes, sizes, wattage and type. A full indoor grow lighting kit should contain the following items. Bulb, reflector, ballast, timer and electrical inputs/outputs.

Figure 5.2 - Regular Bulb.

Figure 5.2 - Regular Bulb.

Figure 5.4 - This is a picture of a timer.

Most lighting kits are open, meaning that no hood or glass will cover the bulb. It hangs directly under the reflector. The bulb is fixed into a socket that is attached to the inside of the reflector. That socket is connected to the ballast. The ballast can be internal or external. If external there will be a cord leading to the ballast from the bulb's socket. The ballast plugs into a domestic light socket like the one you have in your home. Some ballast types even have a built-in timer.

When buying a lighting system it is recommend that you buy a complete system and an extra bulb. Check to make sure that the lighting system meets safety regulations and has some sort of guarantee with it.

Figure 5.5 - This is an example of what an external ballast looks like. You might be able to see the timer on top of it.

Figure 5.5 - This is an example of what an external ballast looks like. You might be able to see the timer on top of it.


Light can be separated into a spectrum, which form the colours of the rainbow. Red, Orange, Yellow, Green, Blue, Indigo, Violet. Each of these lights mix down to give white light. Artificial lights, because of their nature, tend to lean towards a tint of one of these colours when they mix down to form white light.

The electro-magnetic spectrum is a term used in lighting to describe the distribution of electro-magnetic radiation by reference to energy. This table roughly gives wavelengths, frequencies, and energies for parts of the spectrum. You may find it useful.

Spectrum of Electromagn etic Radiation


Wavelength (Angstroms)

Wavelength (Centimetres)

Frequency (Hz)

Energy (EV)


> 109

> 10

< 3 x 109

< 10-5


109 - 106

10 - 0.01

3 x 109 - 3 x 1012

10-5 -0.01</sup>


106 - 7000

0.01 - 7 x 10-5

3 x 1012 - 4.3 x 1014

0.01 -2</sup>


7000 - 4000

7 x 10-5 - 4 x 10-5

4.3 x 1014 - 7.5 x 1014

2 - 3


4000 - 10

4 x 10-5 - 10-7

7.5 x 1014 - 3 x 1017

3 - 103


10 - 0.1

10-7 - 10-9

3 x 1017 - 3 x 1019

103 - 105

Gamma Rays

< 0.1

< 10-9

>3 x1019

> 105

Here is the visible part of the spectrum.

Plants are green, which means that Plants absorb light at the middle of the spectrum (Orange to Indigo). Cannabis plants need this part of the light spectrum to reach full growing potential. The intensity of the light is also important. A light that feeds the full bandwidth with all light spectrums will work very well - like sunlight. When dealing with artificial lights it is better to choose a light that concentrates its intensity on the top part of the spectrum. The most common indoor light systems are called HID lights. We will discuss the full range of lights that you may come across in some grow rooms.


Domestic Lights:

Figure 5.6 - A domestic bulb. Also called an incandescent light source.

These are the lights you find in use around your house. These lights come in all sizes and wattage - 30 watts to 150 watt. These lights are not suitable for growing because of their low light intensity and bad colour spectrum.


Figure 5.7 and 5.8 - These are examples of some fluro fixtures and bulbs that can be bought in most hardware stores.

These lights are the long industrial lights that are found in many a school and work place. These lights come in nearly all lengths and sizes. 2 to 10 feet are the main sizes that are out there. They also run between 10 watts and 300 watts. These lights are okay for growing but they provide little light and are hard to set up properly. They also are not in best light spectrum for Cannabis plants to grow in.

Halogen Lights:

Halogen Grow

Halogen lights are the small lights that can be seen on the outside of factories for flood lighting the grounds during the night. They are usually small and black. These lights can range anywhere between 75watts and 4000watts.

Halogens get extremely hot and can provide an unsuitable condition for growing Cannabis under. They are not recommended because they are dangerous to use indoors for growing. They are also not in the best light spectrum for growing Cannabis.

Fluorescent White Tube Lights:

These are not in use much and are very similar to the Fluorescent lights except they are in the correct growing spectrum. These lights are not very strong and do not range much above 200watts. They are only recommend for growers who do not want to grow full flowering cannabis plants.

Figure 5.10 - White Tube Light.

BEST LIGHTING SYSTEMS Horticultural Lights:

These lights are professional horticultural lights. They are developed by horticultural lighting companies and are tested to suit growing plants indoors. These lights are commonly called HID (High Intensity Discharge). Like the former lights these also come in kits with bulb, reflector, ballast and timer. They also come in different wattage and different shapes and sizes. If you want to grow good bud then you need a HID. A HID is the second most important purchase you will make next to choosing your strain.

Metal Halide (MH) and Mercury Vapour (MV):

The lights are HID lights and are used for the seedling and vegetative growth stages of your plant. They can also be used for flowering and are quite good too. They come in all shapes and sizes and range from 75W - 4000watts. These lights are very common and are a good kit for the indoor Cannabis grower.

Mercury Vapour is not as common as it used to be. It has almost been replaced by Metal Halide now. If you have a choice between the two it is best to stay with the new MH kits. MV also has a tendency to be slightly out of the optimal spectrum range.

High Pressure Sodium (HPS):

This is the lighting choice of many a Cannabis Cultivator. These lights come in all shapes and sizes and have a range of 75watts -4000watts. These lights are in the perfect spectrum for growing cannabis and come highly recommended.

Figure 5.11 - This is an example of a HPS and also a MH Light system. There is nothing at face value to indicate that the light is a HPS or a MH. To check this out we need to look at the ballast and the bulb and read what is says about the type of light system that it is. MH lights tend to give off a blue tone, while HPS tend to give off an orange tone.

Figure 5.11 - This is an example of a HPS and also a MH Light system. There is nothing at face value to indicate that the light is a HPS or a MH. To check this out we need to look at the ballast and the bulb and read what is says about the type of light system that it is. MH lights tend to give off a blue tone, while HPS tend to give off an orange tone.


The first thing to say is that some growers have a MH set-up for seedlings and vegetative growth and a HPS for flowering. The HPS is a better flowering lamp, while the MH is a better veg lamp. If we can only afford one we should get a HPS. Both MH and HPS can be used for vegetative growth and flowering. However since we are growing for bud, we should try to get the best HPS we can.

The next thing they look for is the light kit itself. Check to see that the light is certified and is in good shape. Then check to see if the light is air-cooled. Some of these lights have a fan built in which keeps the light cool. If you see this then you know that you are going to need somewhere to vent your air. This may mean that you need to adjust a wall in your grow area so that the air is extracted from the light.

Duct Work For Growing Marijuana
Figure 5.12 - This picture shows two air-cooled hoods attached to their respective air ducts. This photograph is by Chimera.

Lights that are air-cooled (Figure 5.12) tend to last longer and do not heat up your grow area that much. Most expert growers like to keep a room at a stable controllable temperature and use these air-cooled lights to achieve that. If your light is not air-cooled then you will have to build an air vent and fan in your grow room wall to keep the temperatures under control. Cannabis leaves will burn if placed too close to a HID light.

Figure 5.13 - This is a water-cooled light system. These inventions have been around for awhile but have not caught on that much because they require a good bit of work. A constant pump of cool water must be circulated into and out of the light system.

The next thing to check is how the light is supported. Does it require a light stand or does it require to be hung from the ceiling. In most cases you will be able to make your own stand if you feel that you are not willing to fasten a few hooks and chains to your ceiling. Also check to see if the electrical fittings suit your needs. Will they plug straight into your system at home or do you need an adapter? Maybe you might require an extension cord with your purchase. Most HID kits can only take a specific wattage of bulb and a certain type of bulb. If you have a 600W HPS system, then you should only use 600W HPS bulbs. Some lighting kits have something called a 'switchable ballast' (Figure 5.14). This means that you use both MH and HPS lights with the system. Check your kit for further details.

Ballast Switch

Figure 5.14 - This is a picture of what the switch looks like on a ballast that can take 2 HID types.

Ballast Switch

Figure 5.14 - This is a picture of what the switch looks like on a ballast that can take 2 HID types.

The next thing to look for is the guarantee. Check to see what the manufacturer has said about this light and how long the guarantee is for. Last but not least is the most important part of your light. The wattage and lumens.


HID Lights can range anywhere between 75W and 4000W. In general the stronger the wattage the more light that bulb will produce. However we must also consider another factor and that factor is called Lumens. Lumens are the correct way of measuring how much light per square foot a bulb emits. Lumens and wattage do go hand in hand but can vary a large amount between systems. The better the lighting kit, the better the lumens it will cast. Lumens have more to do with the design of the light than the wattage of the light itself. Some 600W lights may give the same lumens as a 400W light. Have a look at this chart:
















This is interesting because we have two types of HPS lights using the same bulb wattage and one of the types is casting more Lumens than the other. The reason for this is that the higher lumens kit is better quality than the other. So we now know that some lighting kits produce better Lumens than others. Check through HID lighting kits and look at how many lumens they cast. This is a good indicator of how professional that light is. Also a 4000W HID is too much for one single plant. A 1K bulb is the maximum limit per light you should use. Use several 1K bulbs if you need more light. A 4K bulb will bleach Cannabis and is very hot.


Now for the big question. How many Lumens do I need? Well this depends on three things. (1) How much do you want to spend? (2) How many plants do you have? (3) How big is your grow area.

You do not want to go less than 2500 Lumens, even for one plant. You want to get the best so you need to hit the 45000 mark or more. In general one light that casts 45000 lumens is enough to cover a workspace of about 3 feet by 3 feet. This is quite an average space and you will probably get anything between 6 - 9 plants in that area. Again we must keep in mind the strain that we are growing. One large sativa plant can cover a 9 square foot grow area in no time. Short indica plants are different. You can get maybe 12 plants into a 9 square foot grow area. If you really want to pump up your plants then you may consider a lamp that casts 100,000 Lumens or more. If you want a bigger grow area then you may consider 2 lamps that cast 100,000 Lumens each. All is relative to how much you want to grow and the size of your grow room.

Let's say for the record that we would like to grow 4 plants. Then what we should aim for is a light that casts 45000 Lumens. This means we should buy a 600-Watt HID system. Let's say we want to pump up our available light to around 60,000 Lumens. This means we should buy a 1000-Watt HID system. If our area is bigger we might need 2 or more 1000-watt HID lights to achieve this. It all very respective to the 3 elements we mentioned above.

There is nothing wrong if you want to use a 1000-watt HID light on 2 plants. They will grow bigger and better. The only thing is, do we really want to spend all that money on the light and the electricity bill? HID lights range anywhere between $220/£200 and $700/£670 for a full kit. You may be able to buy the parts and build your own, but this is only recommended if you have some experience with lights first. A 600W HPS kit should cost about $250/£230. This is money well spent if you want great plants with big buds.

Over time you will understand more about grow rooms and how to light them properly. With experience you should be able to tell what light suits your needs. As a general rule, when in doubt buy a 400W HPS or better.



The reflector part of the lighting kit can also cause a difference in lumens cast between two different systems using the same bulb. The reflector does it exactly what is says. It reflects light. The other thing to consider is that when the light bounces off the reflector it is going to fall down on your plant. When it does your plants will absorb this light. Not all of the available light is picked up by the plant and some of the light will escape and reflect off your workbench. Your bench may even absorb some of the light. This is your light that you are spending money on so why not try and do something about saving this escaping light. Some reflectors are very good and some are very poor. Reflectors should not be any colour other than white or polished metal. Some reflectors may have a small green film of plastic covering their insides. Remove this if you can. It should just pull off like a piece of tape.

Many people get mirrors or tin foil and line their grow area with it. This is NOT good.

MIRRORS ABSORB LIGHT. This means that only a small amount of your light is reflected back towards your plant. What you need is something white. White is the best colour for reflecting light, period. Not shiny glossy white, just plain flat' white. A white wall will reflect more light that a mirror will. Many growers like to paint the walls of their grow flat' white. This helps a lot. Other people like to line their grow area with the back end of tin foil wrapping (the white side). This is okay, but make sure that you use the white side and not the shiny side.

A substance which looks like a tin foil sheet, called Mylar (Fig. 5.15), is very popular in cannabis grow rooms. Instead of using white walls you can use this reflective alternative. Most DIY and hardware stores will sell it in roles.

Figure 5.15 - Mylar comes in roles like this.
Mylar Grow Cannabis
Figure 5.16 - Mylar in the grow room by Shipperke

It is also recommend that you keep a spare bulb at all times in case your other bulb dies. It is no good going down to the local hardware store only to find that they are out of the bulb type that you need. This could leave your plants without light for along time.

It is also wise to remember that plants need water and lights use electricity. Both these factors when mixed are extremely dangerous. Be safe and wise and keep all electrical outlets away from your plant and liquids that you use.

Okay so you have your grow area set-up with all your security arrangements met. You have your lights set up and hanging down over your grow area. You also have some form of light reflection around your plants to help conserve your light. Your seed-bank has sent you your seeds and you have germinated them. They are on a tray next to you and you are preparing to transplant them into larger pots. The larger pot will stay with the plant throughout its life cycle and you need to provide the best medium possible in which your plant will grow.

Growing Marijuana Indoors Drug
Figure 5.17 - Nice Indica plant from BushyOlderGrower.


Soil comes in many types and varieties. What you will find as you go along is that you will add various ingredients to your soil to improve plant growth.

The Cannabis plant will grow long and winding roots into the soil. These roots absorb water and other minerals from the soil to help it grow. The soil also goes through dry periods when you do not water your plant or when the plant has absorbed most of the water. During these dry periods air is allowed to creep in between the soil particles, allowing the roots to breathe.

There are 3 main factors to look at when buying soil. (1) pH, (2) Nutrients and (3) Structure.

pH is a way of measuring how much acid and alkaline is in the soil. The pH scale runs from 1 - 14. 7 is neutral, 0 is very acidic and 14 is very alkaline. Cannabis plants in soil like a pH of 7. When choosing your soil you should be looking for a pH of 7. It should tell you this on the bag. Going above or below this mark can cause your plant problems during growth. Small pH meters (Figure 5.18) can be bought in most gardening shops and can be used to measure the overall pH of your soil.

Figure 5.18 - This is a picture of two cheap pH meters that can be purchased from most grow shops.

The three major nutrients that are found in soil are Nitrogen, Phosphorous and Potassium or NPK for short. NPK can come in two forms - with the soil or as a stand-alone fertilizer (usually in a bottle). When you look at the bag

Figure 5.18 - This is a picture of two cheap pH meters that can be purchased from most grow shops.


you will see that the % of each part is stated. Such as 20:20:20. This means 20% N, 20% P, 20% K. The remaining 40% is just other elements that make-up the soil. In liquid it would usually be water. This ratio can change between different types of nutrient and soil brands so we need to understand what Cannabis likes.

Cannabis plants like good levels of N and a normal level of P and K during vegetative growth. You need to pick a bag that has all three, not just 10:20:0. When looking at chemical fertilizers you need a mixture that has the first number higher or equal to the rest. 12-12-12 is fine, 20-20-20 is fine, 12-66 is fine and 18-4-5 is fine. The 12-12-12 and 20-20-20 are the best ones to find. Something like 8-20-20 is not suitable for vegetative growth. Bags with higher P are for flowering plants. As a grower we do not transplant to new soil for flowering. We simply use plant feeds to bring up the P levels during flowering.


Try to find a soil that is not too moist. In other words try to find a soil that dries out well and does not hold water like mud. It should say on the packet whether the soil is a wet or dry one. Try to find a balance between the two. Wet soil will sometimes cause plant damage because your roots need air to breathe. Dry soil may also dry out too quickly and needs to be watered more often. Try to find a soil that is loose and feels fine but slightly heavy in your hands.

Basically the soil structure is up to you. Do not buy anything that is hard and bulky or too soft and weightless. Medium Soft and heavy is what you want.


There are many more types of soil mediums out there and here we will briefly go through a few. Marijuana can be grown in most of these soil types but you will see that there may be some problems with a few of them.

Sand and Silts:



Sand soils can be pure sand or a mixture of sand and soil. The problem with sandy soil is that it drains water and minerals out too quickly. This means that it is a very dry soil and not suitable for our needs. These soils can waste our time and money.

Silt soils are nearly the same as sand soil except they are more clay-like and of a darker colour. Silts hold nutrients well but do not hold water very well. Like sands they are prone to quick drainage. Sands and Silts are rarely used on their own to grow cannabis. Mostly it is mixed with other soil types.


Figure 5.20 - Clay

Is a stiff tenacious fine-grained earth consisting of hydrated aluminosilicates that become flexible when water is added. Marijuana roots do not really like clay. Clay can rarely be used on its own to grow Cannabis. Mostly it is mixed with other soil types.


Figure 5.21 - Loam

Loams tend to be a mix of all of the above. The combination of the mix is always stated on the bag. In fact, in most cases normal soil that you buy in the shops has sand, silt and clay mixed in with it. When you encounter a bag of soil it is nearly always going to be a Loam. Loams are very fertile soil composed chiefly of clay, sand, and humus. They are highly recommended. It must be noted at this point that you do not want to bring natural outdoor soil in. This is because the soil may not be sterile and it may contain bugs and pests. Always buy soil from a gardening shop. Soil is the cheapest part of your grow.


Figure 5.21 - Humus

Is the organic constituent of soil, formed by the decomposition of plant materials and can be bought in bags at the local gardening shop. Most of these products try to eliminate bugs and other living matter from the soil but sometimes this is not 100% successful. Don't be too surprised if you find a worm or green fly in the package. Humus is also sometimes known as compost, but compost is the final mixture of manure (which is of organic origin), loam soil and some other mediums with added organic matter. Humus is that added organic matter stuff.


Figure 5.22 - Pots

Basically pots come in all shapes and sizes. Marijuana plants are best kept in pots that are somewhat large (1.5 - 3 gallon pots) because cannabis does grow long roots.

Also you are better off buying a pot that has some form of perforations (holes) at the bottom. The perforated pot sits on a small dish (you should be able to buy these at the same time you buy your pots). When you water your plant some of the water may drain down through the soil and come out through the perforations and into the dish. The dish should be emptied if this happens to avoid water spills.

More advanced growers use pots that do not contain perforations at the bottom. This is because advanced growers never water or feed their plants too much. If you over-water your plant, these perforated pots will drain some of the water through to the dish. What happens is that the water may also leech down some of the nutrients that you have added to your soil. Over-watering can cost you time, wasted nutrients and even kill your plant.

Before you use a pot make sure that you clean it thoroughly before use to get rid of any unwanted chemicals or dust that may have gathered in the shop or factory.

Pots are very cheap to buy. It is always best that you only use one pot per plant. If there is a problem with the soil, watering or nutrients then only one plant will feel the effects.

Cannabis Lower Classifications

Figure 5.24 - This is a great picture of a method known as double-potting which helps create a thicker stem. During vegetative growth the bottom of the top pot is cut away and is placed on top of a new pot with fresh soil. The roots grow right on down into the next pot. Look at the size of the cola in this picture by GIYO.

Figure 5.24 - This is a great picture of a method known as double-potting which helps create a thicker stem. During vegetative growth the bottom of the top pot is cut away and is placed on top of a new pot with fresh soil. The roots grow right on down into the next pot. Look at the size of the cola in this picture by GIYO.


So at this stage you now have the best soil that you can get your hands on. You take the seedling and make the transplant. You fill in the empty areas of the new pot with more soil. You pat down the top of soil lightly and you apply the stake if needed to support your plant. You also add a small amount of water to your plant and you place the pot on the bench under the light. You will leave the light on 24 hours a day and watch as your plant grows over the weeks from its seedling cycle to its vegetative state.

Cannabis Vegetative Growth

Figure 5.25 - A Picture of seedlings finishing their seedling stage and going into vegetative growth. By Vic High.

Figure 5.25 - A Picture of seedlings finishing their seedling stage and going into vegetative growth. By Vic High.

Growing Marijuana Indoors Soil

Figure 5.26 - Top shot of an Indica plant in veg by Ralpheme.

Figure 5.26 - Top shot of an Indica plant in veg by Ralpheme.


During your plants vegetative cycle it will begin to grow quickly and produce more leaves and new branches. The stem will also grow thicker. This is when your plant begins to look like a marijuana plant.


Water your plant ever second or third day or better still when they dry out. Never let the soil dry out completely for long periods of time. I find that the following method works best with good size pots.

Day A - watering, Day B - let dry, Day C - let dry, Day D - check soil and water if needed.

This really does depend on the size of your pots though. If you pick up your pot when it is dry and pick up the same pot when it is has been watered, you can tell the difference in weight. This is a good way to judge if your pots need water or not.

It is easy to see signs of over-watering. Watch your plants after you have watered them for the next 2 - 3 days. Do the fan leaves point outwards to receive more light? Or do they wilt downwards and look like claws. If they wilt then you may be under-watering or over-watering. Check the soil. Is it dry? If it is then add more water. If it's wet, then leave the soil dry out for more time until your leaves pick up again. You will eventually understand more about your plants needs as it grows along. What you need to do is form a pattern or relationship with your plants watering needs.

Over-watering does kill plants if the watering continues. If this happens let it dry out and hope for the best. Use a fan near the surface of the soil if you can. You may find that you need to water everyday because your light may be discharging a lot of heat.

Your plant needs all the light it can get in vegetative growth. Leave your light on 24 hours a day and enjoy watching your plant as it grows.


If you have a good stand or light support you will be able to lower or heighten your light. This is great because the closer your light is to the plant the more light it will receive. However make sure it is not too hot or it will burn your leaves. If you can keep your hand at a certain area under the light and not feel discomfort then your plants should do okay too. If you feel discomfort, so will your plants. Use common sense and adjust your lights accordingly.

Some Cannabis plants can grow as fast as an inch a day! So you need to watch out that your plant does not push up against the light. Be safe and know your plants grow rate before attempting to place your light very close to the plant.

If you do suffer a burn use a pair of clippers to remove the burnt areas. This is only advised for light burns and not for soil or nutrients burns.

Continue reading here: The Basics Of Indoor Environment Control

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  • gina
    How many lumens to grow weed?
    4 years ago