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. Moreover, this requires an understanding of the cannabis birds and bees.
Factors in 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 which can germinate the following spring and keep the life cycle going. In the natural plant cycle, seeds germinate in spring, grow all summer, then flower in fall in one-year periods.
In cultivation, we aim to change this up dramatically. 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 to be grown into clones, the cycle is shortened to 12 weeks (cuttings, clones two weeks, veg growth two weeks, bloom eight weeks). Well-cultivated cannabis in large production shops can bring the cycle down to 8 weeks. Moreover, 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 the plant is dioecious, meaning there are separate female flowers and male flowers on different plants. Differing from most annuals, like tomato plants, where the male and female flower parts are on the same plants.
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 energies into building 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.
And it’s important to know, 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 critical variables you can control to help ensure you get excellent, consistent yields. We’ll start from the premise that you have healthy plants; plants which started 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 a schedule of 18 hours ON, with short nights at 6 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. The best way for a cultivator to determine the harvest date is by controlling the day they begin flowering.
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 its indeterminate growth as its cells keep dividing.
Interrupting the darkness—even for a couple of minutes—will cause hormonal changes in the plant which can result in the growth of male flowers, leading to unwanted pollination, which translates to seeds. If a cultivator needs to do maintenance, best to do it during the light hours.
Light intensity is vital as well. As the rate of growth increases, you want to boost light to feed the rapid pace 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 they begin to damage your plants.
You have options when selecting lights—HPS or LED. HPS lights or a less expensive investment upfront but may end up costing more in the long run. You can run your numbers through AEssenseGrows’ online cost calculator to determine the best choice for your operations.
We like to standardize on General Hydroponics’ nutrients for plants. As you’ll see, nutrient dosing gets a bit complex, so this is where a consistent supplier and fertigation automation can help out.
As flowering starts, the rate of growth increases rapidly. To fuel this, you’ll want to improve 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, now is the time to taper off the nitrogen and increase potassium, which helps plants absorb more water to elongate cells, like a water balloon, enabling the buds to swell. We like to automate this scheduled nutrient transition through our Guardian Grow Manager recipes.
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 as you convert cuttings to clones (~80%) and transition down to 60-65 percent at the end of the vegetative growth phase. In flowering, we transition down to 50 percent by the fourth week of flowering and down to 40% or so by the end of the flowering cycle. The reduction in humidity helps prevent fungal infection along the way.
Delivering plenty of carbon dioxide to your plants is essential 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 proliferate and develop dense buds.
Supplementing CO2 also helps carbon fixation become more efficient, reducing the unwanted photorespiration which grows dominant with the higher temperatures you will want to fuel photosynthesis. So the increased carbon dioxide needs to go hand in hand with increased light intensity because, without the corresponding increase in light energy, the plants will not be able to use the additional carbon dioxide. A good general rule of thumb is to increase your CO2 level always to be higher than the PPF output of your light intensity. For example, a thousand watt light requires 1000-1400 PPM CO2 density for effective photosynthesis utilization.
Increasing air temperature will increase the rate of photosynthesis to a point. However, above 85 degrees, plants go into photorespiration. Moreover, if you don’t match the higher air temperatures with higher levels of carbon dioxide and light intensity, your plants will be doing more photorespiration than photosynthesis, which will take an enormous 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 healthy 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 the terpene profiles.
Cultivators should plan 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 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 a plant helps ensure the entire plant gets maximum airflow 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. The AEssenseGrows’ Guardian Grow Manager central management system, for instance, enables growers to program their growing environment so the changes in nutrients fed 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 a unique 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 growing environment. AEssenseGrows is happy to help and answer questions on best practices as you go.