Once you’ve chosen the strain of cannabis you’re going to grow, decided on the grow medium, and collected all the equipment you’ll need to get started, there’s only one thing left to do: actually grow your cannabis.

In part 3 of the series How to Maximise Yield for Cannabis Plants we will show you all about the grow. This post is a follow on from:


This is where it starts to get really exciting, as you’ll begin to see your plant flourish and grow. And although there are some things you should know before you get started, the good news is that cannabis has gotten the nickname ‘weed’ for a reason. It’s actually pretty easy to grow and, under the right conditions, will do most of the work itself.

What nutrients should I use?

If there’s one area in which novice growers are going to get tripped up, it’s with the nutrients. But, just like people need food in order to survive, so too do plants. And giving marijuana nutrients is really just about feeding the plant.

Marijuana plants, like many vegetable plants, need three main nutrients in order to thrive: nitrogen (N), Phosphorous (P), and Potassium (K). Because so many types of plants rely on these nutrients, there are mixes or solutions that can be found at home improvement stores, and Marijuana Nutrientseven in many grocery stores. These solutions will also contain other micro-nutrients, but it’s these three that growers need to concern themselves with the most.

These solutions come in “general purpose” formulas, which have higher nitrogen contents; or
“bloom” formulas, also known as low nitrogen formulas. Growers will need to use both of these during the life of the plant, but at different times.

During the vegetative stage, marijuana plants need nutrients that are high in nitrogen and potassium, but have a medium level of phosphorous. A typical nutrient ratio for the vegetative stage is 3-1-2 for N-P-K, respectively. This will give the plant all the nutrients it needs in order to grow healthy and strong, and be able to start producing beautiful buds.

When plants are being grown in soil, and that soil is very rich and high quality, the plants may not even need nutrients for their first three or four weeks. In these cases, some expert growers recommend waiting until the plant has absorbed all the nutrients from the soil to add any more, which would be about the time the first leaves start to open.

Once the plant moves through the vegetative stage and into the flowering stage, the plant begins to require fewer nutrients, although it will still require some. The biggest nutrients cannabis plants need during this time are phosphorous and potassium, as these are the two nutrients responsible for creating the buds growers are looking for.

While it’s important that these two nutrients are given during the flowering stage, it’s even more important that nitrogen is lowered during most of this stage. Nitrogen can hinder the development of the buds the potassium and phosphorous and working so hard to create; but it can also negatively affect the taste and aroma of the buds once they’re cured and smoked. Some growers even choose to withhold nitrogen altogether during the last month or so of flowering.

While most of the nutrient solutions available today are perfectly suited for growing cannabis, those that are time-released should be avoided. These can provide the plant with too much nitrogen during the flowering stage, once again hindering bud development.

Organic and chemical nutrients

Plant nutrients are really just plant food, and like much of the food available for people, these nutrients are available chemically or organically. And just like some people will always argue for organic food, some growers are convinced it’s the only way to go when growing cannabis. But that’s just not true. Both have advantages and disadvantages, and are suited to different types of grow setups.

compost-tea_resultOrganic nutrients are created using compost and other organic nutrients that have been balanced with natural sources. These nutrients actually create a living ecological environment that delivers the best nutrients to plants in the most natural way possible. Because this creates an environment for the plant that most closely resembles the plant’s natural environment, it makes a great home for roots that are in soil. And, it can also increase the taste and smell of the buds that are grown.

However, organic nutrients are never suitable as hydroponic nutrients.

Plants that are grown hydroponically should never be given organic nutrients, as this will introduce organic matter into the reservoir. This can cause bacteria and diseases to begin to grow in the water that’s feeding the plants, which can damage the plants.

Chemical nutrients are just that – nutrients that don’t rely on living organisms or organic matter, but rather use chemicals to replicate what those living organisms do. While some may think this means that organic automatically means ‘better’, it doesn’t, as chemical nutrients bring with them many benefits that you just can’t get with organic.

Not only are chemical formulas the only ones that should be used as hydroponic nutrients, they can also greatly increase the potency of the buds. So while using organic nutrients might increase taste and smell, those wanting a more intense high might opt for chemical nutrients over organic.

One last word about nutrients – it’s essential to be able to tell nutrient formulas from the supplement formulas that are on the market. Supplement formulas can be thought of as very low-concentrate formulas for cannabis plants, and will have very low ratios (typically 0.2-0.1-0.1). These are used on other plants that sometimes need a bit of a ‘boost’ during their growth. Most growers don’t ever look at supplements, focusing only on the actual nutrient-rich formulas.

How often should I water my cannabis plant?

Those who are growing cannabis soil or in a dry hydroponic solution such as coco coir will have to water the plants at some point. Even those growing outdoors may have to water during long naturally dry periods of time. And just as giving too many or too few nutrients can hurt the plant, the same is true with water. So, how do you know exactly how much water to give your plants?

The rule of thumb when it comes to watering cannabis plants should actually be called the rule of ‘knuckle’. In order to determine how much moisture is in the soil, you just have to place your finger into the soil – about an inch deep or, up to the first knuckle – and feel for moisture. If the soil feels dry and it doesn’t cling to the skin, the plant should definitely be watered. If it feels moist, and clings to the skin afterward, the plant likely still has enough water for the time-being.

Once you understand how often plants should be watered, the next question is then “how much?” This will depend on how large your plants have gotten, how efficient your grow mediums are at draining, and how much soil you’re using. When adding water to dry plants, it’s best to provide water in a constant stream until there’s about 10% - 20% of extra runoff water drain from the bottom of the plants. This shouldn’t take very long and if it does, there may be a drainage problem with the grow medium.

These numbers are just guidelines, and it’s important to remember that there should not be more than 20% of extra runoff water. Not only can this overwater the plants, which could kill them, there are also nutrients in the water and if they’re carried out of the pot, the plant will never have the chance to absorb them.

Many growers, especially novice growers, consider how much and when to water, but they don’t think about the type of water they’re putting into their plants. And this is important. While many growers simply use tap water and their plants don’t suffer any ill effects, those growers may be lucky enough to live in an area that has clean, pH balanced drinking water. Those who rely on well water however, or in rural areas may not be as lucky and in the case of hard water, the high acidity can be very difficult for plants.

If the tap water in your area is undesirable for growing cannabis, pouring a lot of it and leaving it to sit out to evaporate the chemicals and hard minerals is not enough. Not only is this somewhat ineffective, but it also evaporates the air out of the water, which the plants desperately need.

Experienced growers typically use a reverse osmosis (RO) machine, which purifies water or ozonated water, which puts oxygen into the water while freeing it of bacteria, viruses and spores.

Trimming, training and protecting cannabis plants

When plants are watered and fed properly, they will begin to thrive and flourish – sometimes a little bigger than growers expected. When this happens, training may be needed in order to get the plant to grow in the space provided. Training can also produce bigger yields, as the grower has more control over the plant and can actually decide where they want buds want to form.

There are two different ways to train cannabis plants: using high stress training techniques, or low stress training. High stress training is any type of activity that’s invasive to the plant, such as breaking or cutting branches. While these are very effective methods of training, low stress training can also be just as effective.

The different ways to trim and train marijuana plants are:

  • Topping cannabis plants. Topping plants involves cutting the top shoot so that the lower branches have a chance to grow larger and provide more spots for buds to grow. Topping cannabis plants also allows plants to grow out rather than up, as the plant will no longer grow tall once it has been topped.
  • Super cropping. This technique involves pinching the branch of a plant, slightly damaging it while keeping it intact and not breaking it entirely. Using this method, the plant works extra hard to repair itself and when it does, a large node appears, turning that small narrow passageway for water and nutrients into a super highway. This method is usually used to increase the yield of the plant.
  • Tying the branches down is a low stress training technique that does the same as topping cannabis, but doesn’t actually hurt or break the plant. When branches are tied down to the pot, the plant assumes that they’ve broken off and will continue to put additional efforts into the lower branches and stems.
  • SOG or SCROG. Creating a Sea of Green (SOG) or Screen of Green (SCROG) is another low stress training technique that does the same thing as tying the branches down, but it utilizes a screen to tie them, and doesn’t require bending the branches quite so much.

Remember that as buds begin to develop and grow denser to keep an eye on the water levels, no matter what type of training method you’re using. Overwatering is one of the biggest causes of mould forming on buds, as is a lack of air circulation. If you think the buds are too damp or you start seeing signs of mould, make sure to lessen the amount of watering and to increase the fans or ventilation in the room.

Best light schedule for cannabis plants

Light is one of the biggest components marijuana plants need in order to survive. And for growers not growing outdoors, it will need to be supplied artificially, and it will need to be supplied in the appropriate amounts.

When it comes to cannabis, that means mimicking the effects of the sun as much as possible – and taking into consideration that the sun shines longer during the day at some points in the season than at others. This means for those using lamps, they need to know when to turn them on – and when to leave them off.

Growers that are new to the whole experience often become intimidated thinking about light schedules. But while different strains may have slightly different schedules, the light schedule for cannabis plants is fairly straightforward.

Under outdoor conditions when a cannabis plant first begins to grow, it will likely be springtime, which means long days and lots of sunshine. Because of this during the vegetative stage, plants need 18 – 24 hours of light per day.

As the season starts to come to an end in the fall, those days (in an outdoor environment) start to get shorter, with the sun rising later and setting earlier. During this period cannabis plants do best when they receive 12 hours of light each day, followed by 12 hours of darkness. When the light changes to this schedule, it’s a signal to the plant that it’s time to start flowering and producing buds, which is why some growers force the 12-12 schedule early.

Some growers don’t want to worry about light schedules and for those growers, there are auto-flowering strains. Auto-flowering strains don’t depend on light schedule and cycles in order to flower, but rather maturity, so they’ll flower when they reach a certain age. While the plant will still need light to survive, auto-flowering strains typically go through their entire life cycle in about three months.

Using CO2 to maximise cannabis yield

While humans use oxygen to breathe, plants use carbon dioxide found in the air. And just like getting extra oxygen can help people heal faster or perform better, so too can extra carbon dioxide for plants. In fact, introducing additional CO2 into a grow room can result in stronger, healthier plants and can even significantly increase yields.

The two best ways to increase the CO2 of a grow room are to use a CO2 generator or to buy CO2 bottles or tanks and use it as a mist. Either way it’s best that the CO2 comes from above and rains or drifts down over the plants, so that as much of the plant will get as much CO2 as possible.

There are many ways to incorporate CO2 into the grow room and while the initial setup may take some time and effort, it can be set to run automatically for the rest of the plant’s grow period.


The elements that have been covered in this section of our how-to guide on marijuana include some of the most intimidating components of growing cannabis, especially for new growers. Once the nutrients, watering and CO2 setups are taken care of without stressing the plants, it’s just a matter of finishing the plants’ growth cycle and figuring out the best way to dry weed. We’ll cover that and so much more in our next, and final, section.