One of the most asked questions in our grow shop is probably the one for a complete guide to growing cannabis indoors. For this reason, we have decided to summarize all the important requirements for hemp cultivation.
Here, of course, a distinction must first be made between indoor and outdoor cultivation. In this “Growguide” we want to focus exclusively on cannabis cultivation within closed rooms. In the indoor section, there are also significantly more factors to consider, as for natural factors such as; Sun time, the right climate, etc. must be provided artificially. The big advantage is that we are not dependent on Mother Nature. No matter when and where we can produce a crop of the same quality throughout the year!
In this guide to cannabis cultivation, we will go into all the requirements for indoor cultivation! In the same way, we will point out all the utensils needed for hemp cultivation indoors. The aim should be to pave the way for beginners in cannabis cultivation to a successful harvest. Again and again, we meet in our Growshop disappointed faces, who put a lot of time and work in the cultivation, and yet it did not come to a successful harvest. Often, the lack of basic knowledge is responsible.
All tips from our experience can also help experienced growers to improve the conditions here and there!
Let’s start with our guide to cannabis cultivation in the indoors!
1. The suitable place:
Of course, it is possible to prepare a complete room for hemp cultivation. However, building a grow room is quite expensive. In addition, not everyone has the appropriate space available. For this reason, we recommend simply to buy a cultivation tent and to use this instead! This is the easiest way to create a self-sufficient system. Factors like; Lighting, ventilation, and irrigation are adapted in this system to ideal cultivation conditions. Also, the odor produced during cannabis cultivation must be isolated to the outside.
Now it is about the choice of a suitable space. The place where the cultivation tent, also called a grow tent, should be installed, should meet some requirements. We would like to comment briefly on these requirements:
The room in which the tent is to be set up should definitely have an external ventilation option. Ideally, a duct or window hatch. This is the prerequisite for the installation of a ventilation system that will be needed later. Furthermore, a reliable power source should be available. In other words, a working outlet, all good! In addition, it is important that the room in which the Growbox should stand is dry and germ-free. Damp cellar rooms with mold on the walls are therefore rather unsuitable or would have to be processed accordingly.
As soon as a suitable place for the grow tent has been found, it must be equipped with the necessary technology. In the following part, we would like to go into more detail on all technical components and necessary utensils. The growing project can only start as soon as the grow tent is set up and equipped. We start with the first technical component, the lighting.
Growing cannabis indoors
2. The right lighting:
In order to produce optimal lighting for hemp plants, it is important to understand the difference between the red and the blue spectral range. The blue spectral range is generated in nature by the spring sun. Due to the position of the sun and the break of the light in the atmosphere, the light of the spring sun differs from the light of the sun in midsummer. The blue spectral range promotes primarily the growth of a plant. The red spectral range in turn particularly supports the flowering period.
This is a very important aspect of hemp cultivation under optimal conditions. There are two ways to perfectly simulate mother nature; There are lamps that cover the entire color spectrum. This task is fulfilled by LED panels. Alternatively, two different bulbs can be used for the respective color temperature, red or blue. The color temperature, ie the color spectra are measured in Kelvin (K). For the growth phase, metal halide lamps (MHL) are used. They emit white, colder light at about 5000K – 7000K. Sodium vapor lamps (NDL) take over the lighting during the flowering phase. Its light radiates warm summerly at about 2500K – 3500K. Both bulbs are also available as an energy-saving lamp.
Another key figure that is relevant to the right lighting in hemp cultivation is the light intensity. It is measured in lumens and in this case, indicates how bright a lamp is.
During the growth phase, the value of 30,000 lumens / m² should be maintained. For flowering, the value for optimal yield is about 50,000 lumens / m². Both values should not be undercut, as it would have a negative impact on returns!
The brightness differences cannot be detected by the human eye. For this reason, when buying a lamp, it is important to make sure that it is a trusted manufacturer. A good Growshop also offers its customers the opportunity to test the lamps. Above all, however, a luxmeter should check whether lamps already in use still provide enough light intensities for a growing process. A little tip: The bulbs should never be touched with bare hands on the glass, as the body fat on the skin could negatively affect the performance.Last but not least, there is the question of how much power is needed for which acreage. There are several rules of thumb for this. However, it is not only a question of the lamp itself but also which reflector is used.
Growing cannabis indoors
3. The right ventilation and venting
We had mentioned beforehand that we must try to reproduce the qualities of free nature as well as possible. Of course, this also includes the winds to which the hemp plant would be exposed in the outdoor area. A good supply of fresh air is no less important for the plants than for us humans. The heat generated by the lamps is also compensated by the ventilation. In the Grow tent, this task is taken over by a simple axial fan that supplies the room with fresh air from outside. In order to prevent pests from reaching the grow tent in this way, we recommend corresponding protection. This can be, for example, a nylon pantyhose from mom, which is simply pulled over the air inlet.
However, for sufficient air circulation in the tent of the supply air fan is not enough. Depending on the size of the tent, at least one fan with a swivel head should be additionally installed. The already mentioned winds, avoid asparagus growth of the plant and provide for more stability. The risk of mold growth is reduced on this.
Somewhat more complex than the subject of supply air and circulating air is the exhaust air area. After fresh air has been supplied, of course, the used air must be transported out again. At the same time, the vent ensures the regulation of the climate within the grow tent. The additional use of an activated carbon filter prevents the spread of pleasant cannabis odors outside the grow tent.
The output of the exhaust fan must match the size of the grow tent to prevent overheating or under pressure. Since additional parts such as activated carbon filter or ventilation hose inhibit the performance of the fan, it is important to take this into account in the calculation. To reduce the power of the carbon filter, one adds 35% of the room volume. The same applies to the air hose. Here 1m3 are added per running meter.
Use this formula to determine the extraction fan size of your grow box or grow tent:
Using the example of a 1m x 2m x 2m grow tent and the use of a 2m ventilation hose:
(Room volume + surcharge for activated carbon filter + surcharge for air hose) x 55
Important: If the room volume is larger than 8m³ the multiplier 30 must be replaced by 22 !!
So let’s first calculate the volume of our grow box:
- Length x width x height: 1m x 2m x 2m = 4m³
Then we determine the surcharge for the activated carbon filter:
- 4m³ x 0.35 = 1.4m³
Taking into account the 2 meter long air hose, the following formula results:
- (4m³ + 1.4m³ + 2m³) x 55 = 407m³/h
This means that the fan should have an output of approximately 450m³ per hour. The choice of a suitable activated carbon filter should also be based on this measure. This should have a little more power than the fan. In our example, an activated carbon filter – 480 m3/h would be the right one.
Attention, the calculation is based on a grow room with a 600 watt lamp. If several lamps are used, the output of the exhaust fan must be adjusted upwards.
If a sodium vapor lamp (which has the strongest heat development) is used for illumination, the use of a Cooltube is recommended. At the same time, the discharged air ensures the cooling of the lamp.
Growing cannabis indoors
4. Air, temperature, and climate
We would like to subdivide the optimum temperature and humidity for indoor cultivation of cannabis plants into four maturity cycles, as the climatic conditions should vary slightly depending on the growth phase.
1) The germination stage:
During the germination phase or even with freshly cut cuttings, the root system is not very strong. From this, the patches absorb most of their water needs through the foliage. Depending on the plant species, the germination phase is complete after approx. 10 to 14 days. For this period we recommend a humidity of 65% – 70%. The air temperature should be between 20 and 25 degrees during the lighting time.
2) The vegetative stage:
During the growth phase, the humidity should be reduced by 5% per week. Until it settles at 40% – 70%. During this time, the air temperature may be raised to 28 degrees, as the leaves give off an evaporative cold due to the better root system. The duration of the growth phase is determined by the breeder. On average, it is about two to six weeks. This is also dependent on the plant species, so Sativas should e.g. be sent to the flower a little earlier.
3) The flowering stage:
The flowering phase, as already mentioned, initiated by the breeder. This is done by shortening the light cycle 18 to 12 hours. Since a very dense foliage has formed in the meantime, and the plant begins to form flower buds, it is important to avoid the formation of mold and pest infestation. This is achieved by lowering the humidity to 40% – 50% and controlling the temperature to 20 – 26. The duration of the ideal flowering period should be found in the product information of the purchased seeds.
4) The late flowering:
As late flowering, we refer to the last 1 – 2 weeks before the harvest. In this phase, the risk of mold growth (botrytis) in the flower heads, or even buds, is particularly high. For this reason, the humidity must be reduced to a minimum. Ideally between 30% and 40%. The temperature should be 18 – 24 degrees when the lights are on.
The suitable soil for hemp cultivation indoor:
Of course, other substrates are also suitable for hemp cultivation, such as coco, rock wool, or expanded clay. However, first we want to focus on the most common of all substrates, the good old Earth.
We want to make it our goal to provide our plants with the optimal breeding ground. We will be very specific about the individual factors to be considered here.
What demands do we have on good soil for hemp cultivation?
- The earth should have good drainage
- The density of the earth must provide the root system with sufficient space for development
- A good CO2 exchange of the earth is very important
- A balanced nutrient ratio must be present
What does that mean in plain language?
Let’s start with the drainage: Without delving too deeply into the geosciences, we must briefly deal with the not-too-common word perlite. Perlite is a rock that expands immensely when heated. The result is a firm, foam-like texture that does not store moisture. Perlite prevents excessive compaction of the soil and thus ensures ideal drainage. As a result, the nutrients are easier to get to the roots of our plant.
Since we have already gone into the second point, namely the density, all that remains to be mentioned here is that, when filling the pots, attention must be paid to an appropriate density. But how exactly is that? Well, let’s just say that the earth should not be over-pressed in any case. However, if you simply pour it into the pot, you will notice after a few irrigations that the pot is only half full. We would like to avoid both scenarios.
A good substrate is characterized by the proportion of microorganisms. Microorganisms are microorganisms that use their farts to produce CO2.
Regarding the nutrient ratio, it should be noted that only a weak nutrient content is required in the germination phase. We have already described this in our article germinating cannabis seeds. That’s why a light mix is the right choice at the beginning. Once the plant enters the vegetative phase, a substrate with a higher nutrient ratio should be used.
The water to be used for cannabis cultivation:
Without water, there’s no life! The good quality of the water is crucial for the healthy growth of our plants.
In order to provide our little ones with good water on an ongoing basis, we need to look at the PH value and EC value.
The pH determines the acid/base balance of e.g. Liquids. On a scale of 0 to 14, it indicates how acidic or alkaline a liquid is. Values from 0 to 6.5 are considered acidic. The golden middle, so 7 is considered neutral. Pure water has this value. All values above 7 are defined as basic or alkaline.
The optimal EC value varies during the growing process. In addition, some different optimal values for individual fertilizer manufacturers apply. Especially the grower’s experience is in demand. the pH, on the other hand, must be adapted to the particular substrate used. For the complete cultivation cycle, we differentiate between the four phases already described above.
Recommended EC values for the entire growing process
|Germination/Seedling Stage||~ 0,8|
|Vegetative Growth||~ 1,0||~ 1,1||~ 1,3-1,5|
|Flowering||~ 1,8||~ 1,8||~ 1,8||~ 2,0||~ 2,2|
|Late Flowering||~ 2,1||~ 2,0||Flushing*|
Flushing* = Flushing is the cleaning of the root system of the plant without the addition of nutrients.
Week 7* = For a longer flowering stage, e.g. 63 days or 70 days, repeats each week 7.
7. Necessary fertilizers for indoor growing:
When using fertilizers, we differentiate between organic and mineral fertilizers. The subject of plant fertilization is extremely extensive. Therefore, we would like to begin with only on the necessary basis. The following nutrients and vitamins belong in the fertilizer rack:
- Root stimulator
- NPK fertilizer (growth)
- NPK fertilizer (bloom)
- PK booster
These four basic fertilizers alone enable a high-yield harvest!
Step 1 – Indoor cannabis cultivation | The germination and growth phase
The time has come, the grow tent is in place and is adequately equipped. All necessary utensils are now in stock. All you need to start are good cannabis seeds !! Right from the start, all climatic conditions listed under point 4 should be created and continuously monitored.
- Germination: The cannabis seeds need to be germinated. We have described exactly how this works best in this article.
- Distance between lamp and plant: When using a 400 or 600 watt HPS, the distance should be between 50 and 60cm. If the distance is too short, symptoms of burns can occur. If the distance is too large, however, the plants tend to sparrow.
- Lighting times: The following rule applies to the germination and growth phase: 18/6, which means 18 hours of light and 6 hours of darkness. In order to prevent uncontrolled growth, this lighting time already applies during the germination phase, before the first shoot is visible. LED, LEC and halogen lamps give off less heat than HPS lamps. This allows a smaller distance between the lamp and the plant, which enables vigorous and healthy growth.
- Week 1 – 2: first plant shoots penetrate the surface. You should be exposed to light ventilation right from the start. This strengthens the cell structure of the plant and also prevents mold growth.
- Regarding watering: The plants should be watered for the first time at the beginning of each light phase. The requirements for the quality of the water specified under point 6 must be observed. The soil should always be kept moist without submerging it.
Start of plant fertilization: In the first three weeks you can still be cautious about adding fertilizers. Much of the nutrients, such as nitrogen, phosphorus and potassium, provide good earth mixes. Nevertheless, there are fertilizer components, such as root stimulator and growth stimulator, that can be fed to the plant as a liquid fertilizer or spray at an early stage. For less experienced growers, we recommend a starter box offered by common fertilizer manufacturers. Concerning. the information of the respective manufacturer should be used as a guide for the quantities. In any case, it is advisable to record everything in a fertilization plan!
Repotting: Approx. a week after the first shoot appeared, the plant should have developed the second pair of leaves. A strong root system has also built up in the meantime. At this point, the plant should be repotted in a larger flower pot. Beware, if the substrate around the seedling is too moist, there is a risk that parts of the roots will tear off. Therefore, the soil in the small pot should be a little drier when repotting.
Step 2 – Indoor cannabis cultivation | Initiation of the flowering phase
Every grower decides for himself when exactly he wants to send his cannabis plants into bloom. The time depends e.g. Plant type, nature of the grow room or simply the individual intentions of the grower.
We recommend inexperienced growers to adjust the right time to the space conditions of their grow room and the type of plant. With a common grow tent of 1.80m or 2m high, sativa-heavy plants can be sent into bloom as early as the 3rd week. At this point the plant is about 15cm – 20cm tall. During the flowering phase, the plant then grows up to 3 times as high. Indica dominant plants can tend to flower a week later.
- Indoor grow – Initiate blooming phase: By changing the light cycle from 18/6 to 12/12, i.e. 12 hours. Light and 12h. Darkness, we signal to the plant that the days are getting shorter. This artificial late summer causes them to start blooming.
- Adjust fertilization: Change the fertilization scheme to flower fertilization. Again, the information provided by the fertilizer manufacturer should be used as a guide.
- The flowering phase lasts between 50 and 90 days, depending on genetics. In addition to adhering to the fertilization plan, fungus and mold prevention can also be applied. Plant growth and foliage should be checked regularly to ensure that they look healthy. The reaction to the fertilizers should also be closely monitored.