The flowering stage is the last, and most exciting part of growing your own cannabis. This is when your plants grow the crop, the whole reason you’re cultivating cannabis in the first place. However, just because you’re nearing the finish line doesn’t mean the race is over just yet. There’s still plenty that can go wrong, and losing your crop in the flowering stage can mean months of lost time. Here’s how to care for your cannabis plants during the flowering stage and get them safely to harvest.
When to Water Your Plants
Your watering habits shouldn’t change much during the flowering stage. Even if you use a hydroponic system, keep an eye on your plants. In soil or coco coir systems, water when the top inch or two of growth medium is dry. Your plants should never start to get wilty, but the soil should not remain damp to the touch.
This may require that you start to water more thoroughly, but on the same schedule. When plants are expanding their buds, they need more water, so where you used one gallon you might need to use a gallon and a half. However, flowering plants can still suffer from overwatering, so use your best judgment.
When and How to Fertilize
Fertilizer should be added when you water your plants. Plants in the flowering stage need different levels of nutrients than plants in the vegetative phase. The vegetative stage requires a nitrogen-phosphorous-potassium ratio of 3-1-1, because nitrogen is key for vegetation growth. However, potassium and phosphorous are much more important for flowers.
Where many beginner growers go wrong is cutting out nitrogen as soon as they switch to the flowering stage. This ignores the flowering stretch, when plants can gain up to another 50% of their height. Instead of doing this, switch to a fertilizer ratio of 1-3-2 NPK, and then after a few weeks transition into 0-3-3. This gives your flowers the boost they need, while not stunting the greenery that supports your buds.
A standard fertilization patter for the flowering stage is adding fertilizer to every second watering. Nutrient burn and lockout are real threats. Giving your plants some pure water between fertilizations flushes unused and unnecessary nutrients that could otherwise cause problems.
Just before harvest, you can break your fertilization pattern by flushing your plants. Flushing cannabis involves watering your plants heavily with plain, unfertilized water. This removes extra nutrients from the growth medium, and many growers claim that this makes your buds taste and smell better. You can start flushing a hydroponic system four days before harvest. Coir needs a week of flushing, and soil needs two weeks.
When to Trim Cannabis
Just because your plant is in the flowering stage doesn’t mean you’re done pruning it. It’s impossible to definitively tell a plant’s sex until the flowering stage. This is the time to keep an eye out for herms, bananas, and unexpected male plants in your garden. These should all be removed immediately, to prevent unwanted fertilization of female flowers. Seeds ruin the taste of the bud.
You should also spend the first three or four weeks of the flowering phase trimming the plant into shape. The plant’s general shape should have been defined during the vegetative phase. Now, you’re just removing any last buds that don’t receive much light, foliage that is in shadow, or parts of the plant that don’t look like they’re thriving. Taper off by the end of week four, so the plant can focus on flower growth instead of recovering from pruning.
Lighting is really the key to a successful flowering phase. After all, changes in light duration and color are what trigger flowering to begin with. Cannabis plants flower during the “autumn,” or when light transitions for 14+ hours a day to 12 hours of light and twelve hours of dark. In fact, it’s the 12 continuous hours of dark that specifically tell the plant it’s time to flower. During the vegetative stage, plants can be kept lit up to 24 hours a day – that absolutely will not work for flowering unless you have an autoflower strain.
The color of the light is also important. Essentially, blue light encourages vegetation growth, while red light feeds flowers. This is related to how the spectrum of light present in sunlight changes from summer into fall. Bluer light, or wavelengths from 430-450 nanometers, encourages strong roots and lots of photosynthesis. Redder light, or wavelengths from 640-680 nanometers, boosts flowering and fruit production.
This means that cannabis plants do best in the vegetative stage with lots of blue light. To really get the most bang for your buck, don’t just switch over entirely to red light during flowering, however. Your cannabis plants still need to photosynthesize as hard as they can in order to feed the flowers you want to harvest. Instead, supplement the blue light you were already using with additional red light. Just keep an eye on your plants to make sure they don’t start to suffer from heat or light burn.
Temperature and Humidity Control
Because cannabis plants begin flowering during the “fall,” they do better with cooler temperatures and lower humidity than they can take during the vegetative stage. Temperature can be a tricky one in particular. If you’re supplementing your plants with additional red light, you might be heating your grow room up just when it’s time to cool it down.
Ideally, your cannabis plants should be kept between 70 and 75 degrees during the flowering stage. If your plants are kept much warmer than that, the terpenes that make different strains of bud so tasty can basically spoil and taste bitter. If your grow room is getting too warm, a good solution is to turn up your ventilation system and blow the extra hot air out.
This solution also takes care of another problem: high humidity. If the humidity is regularly above 50%, you risk losing your entire crop to mold. Cannabis buds are the perfect place for plenty of different mildews and molds to make their home, and most of these will make you sick – or worse – if smoked or ingested. Once you’ve spotted mold on a bud, you need to cut it off and throw it out. Keep your humidity between 40% and 50% for ideal growth and lack of pests.
When to Harvest Cannabis
Finally, you need to choose the time to harvest. It’s always going to be tempting to harvest too early. Just because the trichomes are visible and sparkling doesn’t mean it’s time to go.
There are two chemicals that you’re waiting on: THC and CBD. THC is at its peak when the majority of trichomes are milky, and just a few are clear. Wait another few days or a week, until all trichomes have turned white and some have shifted to amber, and CBD is at its peak, while THC has started to decay into CBN, a mellow chemical.
It’s worth the time and effort to make sure your plants are healthy and mature before you harvest them. It would be a shame to get all the way through the growth cycle only to harvest too early. If you take good care of your cannabis plants during the flowering stage and harvest when they’re ready, they’ll take care of you.