Getting Your Cannabis Grow Off to a Great Start

By Karl Kulik
Published: February 10, 2020 | Last updated: December 7, 2021 11:15:04
Key Takeaways

There’s nothing a cannabis cultivator enjoys more than harvesting the dense, fragrant buds at the end of a successful grow. But getting there takes a touch of finesse, as well as an understanding of basic plant biology.

Today’s automated grow systems can help dramatically simplify indoor growing and reduce labor costs, but cultivators still need to keep a close eye on their plants and make adjustments and decisions throughout the early stages. This requires an understanding of the cannabis birds and bees.


Let’s start with flowering.

Flowering is the cannabis plant’s way to produce offspring, which is its primary goal.


Cannabis wants to produce flowers so when winter comes it will leave seeds behind that can germinate the following spring and keep the lifecycle going. In the natural plant cycle seeds germinate in spring, grow all summer, then flower during the fall in one-year cycles.

In cultivation, we aim to dramatically change this. We don’t want seeds to form during flowering, and we certainly don’t want cycles to take a year.

In the simple linear case, the cannabis cycle can take 12-14 weeks (seed germination, veg growth, blooming). By using mother plants, taking cuttings that are grown into clones, the cycle is shortened to 12 weeks (clones two weeks, veg growth two weeks, bloom eight weeks). Well-cultivated cannabis in large production shops can bring the cycle down to eight weeks, and seeds are not even part of the process. Mother plants, cuttings, cloning, and veg growth all happen in parallel to blooming in separate rooms and on separate light cycles.


To have this fast turnaround of seedless cannabis, we need to understand that the plant is dioecious, meaning there are separate female flowers and male flowers on separate plants. This differs from most annuals, like tomato plants, where the male and female flower parts are on the same plants.

Read also: From Seed to Bud: The Cannabis Life Cycle


Because they are dioecious, it’s easy to control pollination in cannabis plants and keep seeds at bay. As long as the female plant doesn’t become pollinated, it won’t form seeds. Instead, it puts its energy into forming more flowers in hopes of becoming pollinated.

On the flip side, if a female plant does become pollinated, it focuses on growing seeds rather than flowers. Of course, if you’re growing from seed, you don’t initially know if your plants are male or female, so once flowering starts you have to kill the males to prevent pollination.

If you’re not careful, or just plain unlucky, your female plant can form male flowers, leading to unwanted pollination. Stressing a plant can cause this, as can bad plant genetics.

Now that we’ve covered the ins and outs of cannabis reproduction, let’s look at some of the key variables you can control to help ensure you get great, consistent yields. We’ll start from the premise that you have healthy plants; plants that started out sick and weak will never be able to match the potential of plants with a healthier start.


Cannabis is a photoperiodic plant, which means it’s easy to control its flowering. Indoors, we simulate long summer days for mother, clone, and veg plants with lights that are 18 hours on, with short nights at six hours off. When the summer ends and we move into the short days of fall, we change the light cycle to 12 hours on and 12 hours off. This tricks the plants into the hurry-up-and- bloom cycle. Controlling the day they begin flowering is the best way for a cultivator to determine their harvest date.

Equally, if not more important, than lighting is darkness. Uninterrupted darkness is the key to flowering in cannabis. If you don’t allow a long dark period, your plants will continue their indeterminate growth as their cells keep dividing.

Interrupting the darkness — even for a couple of minutes — will cause hormonal changes in the plant that can result in the growth of male flowers, leading to unwanted pollination, which translates to seeds. If a cultivator needs to do maintenance, it’s best to do it during the light hours.

Read also: Lighting Elements to Consider for Indoor Cannabis Gardens

Light intensity is key as well. As the rate of growth increases, you want to boost light to feed the rapid rate of growth. High light intensity is crucial for promoting bud density. Of course, you want to make sure you don’t turn up the lights so high that they begin to damage your plants.

You have options when selecting lights — high pressure sodium (HPS) or LED. HPS lights are a less expensive investment upfront but may end up costing more in the long run.

Nutrient Concentration

Nutrient dosing gets a bit complex, so this is where a consistent supplier and fertigation automation can really help.

As flowering starts, the rate of growth increases rapidly. To fuel this, you’ll want to increase your nutrient concentration and feed high levels of nitrogen — which forms amino acids and proteins — during the first few weeks of flowering. Around the middle of the flowering period, cell elongation becomes dominant over division and that’s the time to taper off the nitrogen and increase potassium, which helps plants absorb more water to elongate cells, like a water balloon. This will enable the buds to swell.


As plants begin to increase their rate of growth, you’ll want to lower humidity slowly to encourage transpiration, which allows more water to flow through the plant. As the plant consumes more water, the elongated cells fill and bring nutrients up to the growing parts of the plant. Humidity should start high (about 80 per cent) as you convert cuttings to clones. This will transition down to 60-65 per cent at the end of the vegetative growth phase. In flowering, we transition down to 50 per cent humidity by the fourth week of flowering and down to 40 per cent or so by the end of the flowering cycle. The reduction in humidity helps prevent fungal infection along the way.

Read also: As Temperatures Rise...Don’t Forget About Humidity

Carbon Dioxide

Delivering plenty of carbon dioxide (CO2) to your plants is important for healthy plant growth. Plants take carbon from the air and use it to build cells and body structure. As more cells are created, supplementary CO2 will allow your plants to grow rapidly and develop dense buds.

Supplementing CO2 also helps carbon fixation become more efficient, reducing the unwanted photorespiration that becomes dominant with the higher temperatures you will want to fuel photosynthesis. The increased CO2 needs to go hand-in-hand with increased light intensity because without the corresponding increase in light intensity, the plants will not be able to use the additional CO2. A good general rule of thumb is to increase your CO2 level to always be higher than the photosynthetic photon flux (PPF) output of your light intensity.

Air Temperature

Increasing air temperature will increase the rate of photosynthesis to a point. But above 85°F, plants go into photorespiration. And if you don’t match the higher air temperatures with higher levels of CO2 and light intensity, your plants will be doing more photorespiration than photosynthesis, which will take a large toll on your plants’ health. At a certain point, enzymes won’t perform their functions and will fall apart, and your plants won’t establish a normal metabolism.

There’s a balance you’ll need to find for your particular strain. In some cases, cultivator preference plays a role, with grow temperatures impacting such things as the taste of your cannabis or its terpene profiles.

Read also: Promoting Terpenes in Cannabis

Plant Height

Cultivators should plan ahead to determine plant size, realizing the plants will double to triple in size during flowering, mostly during the first four weeks. Once flowering starts, you can trim or bend the branches and use a trellis to control your grow. By trellising the heavy buds that come in the latter stages of flowering, you can prevent energy from being diverted to growing new stems to support the plant rather than its target, building stronger flowers.

Pruning is another important step. Pruning and sculpting helps ensure the entire plant gets maximum air flow and consistent, equal light distribution. The weaker undergrowth should be removed as it draws energy from the healthier parts of the plant and is more susceptible to pests and pathogens.

Pruning and trellising practices vary by strain, and you’ll learn best over time through trial and error.


Automation can play a huge role in making precision indoor growing manageable. Automation enables growers to program their grow environment so the changes in nutrients feeding the plants will occur automatically; growers can monitor and override the settings from their smartphones or laptops.

While automation helps, there is no replacement for a cultivator’s basic understanding of cannabis plant science and that special sense of your plant’s health and well-being. Every cultivator will build this experience as they go through a few lifecycles to determine what adjustments to make for their specific strain and grow environment.


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Written by Karl Kulik | Plant Scientist at AessenseGrows

Profile Picture of Karl Kulik

From planting bulbs in grade school to gardening science experiments in middle school, Karl has always loved plants and figuring out what makes them grow best. Still driven by this same curiosity, you can now find him developing cannabis cultivation tools and technologies on the team at AEssenseGrows.

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