The Flowering Stage
The final stage of the cannabis life cycle, the flowering stage, is simple to sustain yet unforgiving to mistakes.
The Final Stretch
Contrary to the name “flowering stage”, the first 2-3 weeks of a plant’s final life cycle involves a burst of new stem and leaf growth, increasing the size and height of a plant significantly. The amount of growth is generally tied to the strain, with the rule of thumb being that indica-heavy strains will stretch 50−100% of their current height and sativa-heavy strains can double to triple their current height in growth. Due to this, it is important to note that low-stress training is still a viable option in the flowering stage, so if needed, it can be used to keep the height of a flowering plant in check. After this final growth spurt, the plant will stop growing in height and stop producing new leaves for the rest of its life cycle to focus all its energies on flowering.
While the plant is in the middle of the final stretch, the first signs of flowering will start to appear. For female plants, this comes in the form of pistils — white hairs that will group near large fan leaves, as well as at the ends of each stem, and will continue to develop into buds. For male plants, this comes in the form of pollen sacs, and unless you are trying to create seeds, male plants will need to be removed as soon as possible from your grow space before the pollen sacs have a chance to develop.This is also the time to switch from a grow fertilizer to a bloom fertilizer when growing without fertilized soil, as the plant will need less nitrogen and more phosphorus to help with the development of flower buds. If you are growing with fertilized soil, especially if the organic matter appears to be running low in the soil at this point, you can recharge the soil by mixing in a high phosphorus organic matter fertilizer, such as bone meal.
Once the plant has stopped growing in height, all its energy will be focused on flower growth, with each patch of flowers fattening up. As these buds continue to form, trichomes will start to appear, and along with the trichomes comes the strong odor that cannabis is well known for which will last for the rest of the grow.
Bud Development and When to Harvest
Early on in the bud development, the resin glands will first start producing the trichomes to protect the buds, as trichomes are a defense mechanism created by the plant to deter wildlife from eating it, looking like tiny clear dots on the plant. Over time, as the buds ripen, with some of the first white hairs shriveling and turning dark in color, the trichomes will be in full production, leading to them getting longer in size, looking like tiny clear mushrooms. At this point, the trichomes are still developing and are not at the maximum potency yet. Once the plant is near the end of the flowering cycle — with most of the white hairs shriveled and dark in color — the trichomes are at their highest potency. When magnified, the trichomes look milky and cloudy, and although it could still be clear, it does not glisten and shine the same way it did when it was still developing.
If the plant is left to continue growing after this point, the tetrahydrocannabinol (THC), which is the chemical compound in the cannabinoid that produces the psychoactive effect cannabis is mainly known for, in the trichomes will start to oxidize and degrade, gradually breaking down to cannabinol (CBN), and when this happens, visually the trichomes will start to turn amber in color. This is the biggest signal from the plant that it is ready for harvest if your goal is to get the highest THC content.
When checking the trichomes for maturity, you will also need to know that cannabis plants do not mature uniformly, and typically, the top of the plant will mature faster than the rest of the plant because it is getting more light. This is why some growers actually harvest the top half of a plant first when it is ready, which will open up the light to the lower parts of the plant, and then harvest the rest after letting it mature for another week or two. While we do not recommend beginners try this, one thing we do recommend is to check the trichomes from the buds at the top, bottom, and middle of the plant to get a more accurate idea of the overall plant development. While the top of your plant might be ready for harvest, there could be times where you would want to wait another week or so for the rest of the plant to catch up.
Pre-Harvest Flush (Optional)
For growers utilizing fertilizer feeds, flushing is the process of clearing any fertilizer and salt buildup in the soil before harvest. Flushing washes away all the excess nutrients, salts, and contaminants out of the soil, and while it is commonly used for correcting nutrient imbalance issues, it can also be used near the end of harvest to both clean the soil and to starve the plant so the plant starts using its remaining reserves of nutrients stored in the plant leaves. By having the plant use up its storage of sugars, starches, and other elements, it makes for a smoother burn and cleaner smoke.
Now, if you do plan on flushing your plant, you will need to guesstimate when your trichomes are at the peak cloudiness. Ideally, flushing with soil is a 2-week process. So, if you start flushing after the trichomes start turning amber, you might be harvesting the plant too late by the time the flush has finished. The simplest way to flush a plant is with a two-step watering process. This involves first flooding your pot with water until it is completely saturated. Let it sit for a few minutes, which will allow the water in the pot dissolve the salts, nutrients, and contaminants, and then do a second wave of water to wash out the original batch to get rid of all the excess stuff in the soil. This generally is enough for a simple flush, but if the runoff water still looks dirty after the second watering, you can wait a few minutes and water it again until the runoff water is clear.
Post-flush, water your plant with water only until you are ready to harvest, and you will see all the signs of nutrient deficiency on the leaves, which means the plant is using up its reserves. After 2 weeks, most, if not all, of your fan leaves should be yellow or yellowing, and by then, it is time to harvest. It is also possible to do the final flush of the plant and harvest before 2 weeks if needed, as a flush of 7, 5, or even 3 days will still help use up some of the plant's stored nutrients as well as get all the excess stuff out of the soil.
However, because flushing too early or too late will result in a lower-quality harvest, we do not recommend new growers flush their first plant unless you are confident on when the plant is ready to be flushed. If this is your first grow, it might be more important to focus on learning the natural grow process and seeing the trichomes develop over time to understand exactly what a clear, cloudy, and amber trichome looks like, as well as getting a good feel for the flowering timeline, from the first signs of the flowers to a small bud to what a ripe bud looks like.
Benefits of a Late Harvest
There are a couple of reasons for wanting to harvest later — generally 2−3 weeks after the first signs of amber trichomes — although the latest you will want to harvest is when half the trichomes on the plant have turned amber. By harvesting late, you can maximize the yield, as the buds will still get a little riper and bigger after the first signs of amber on the trichomes. The mature buds can also be more flavorful with a few extra weeks of growth, and a higher CBN/lower THC content from a late harvest will produce more of a sedative effect from the buds.
What to Do in the Flowering Stage - Automatic Seed Edition
The flowering stage is the reason automatic seeds are able to match normal seeds in yield with a shorter grow time. While normal seeds are only able to receive 12 hours of light a day to grow, automatic seeds can receive up to 24 hours of light a day, potentially doubling the amount of grow time in this stage. This allows for the buds to mature at a much faster pace with some automatic seeds able to go through the entire flowering stage in a little over a month.
The key for a successful flowering stage when growing an automatic plant is to switch to a bloom fertilizer at the first signs of flower production and to maintain at least an 18-hour light cycle throughout the entire flowering stage.
Did this guide help? This article was taken directly from The Absolute Beginner's Guide to Growing Cannabis book, so if you like the advice above you'll love the rest of the book, which includes a lot of exclusive content not found anywhere else. You can find both the e-book and paperback copy on Amazon, and it's free with a Kindle Unlimited subscription!