First Signs of Flowering Stage in Cannabis Plants
Home gardeners who’ve raised bountiful crops of tomatoes, green beans, and lettuce may be in for a rude awakening when they decide to take advantage of marijuana legalization in their state and plant a new crop.
That’s because growing weed isn’t like growing vegetables — especially if you’re growing indoors.
Sure, you still have to water and fertilize your weed plants and watch for signs of pest infestation. But cannabis plants have distinct growth stages, which each require different environmental conditions if you want to produce large amounts of high-quality flower.
You can’t do much to control the sun and rain when you plant marijuana outdoors. Indoors, it’s an entirely different story. An optimal harvest depends on managing light, water, nutrients, heat, and humidity to match the stage of the plants’ growth.
To do that, you need to understand the growth stages of cannabis. And one of them, the flowering stage, can be particularly tricky.
Let’s go in-depth.
The Growth Stages of Cannabis
It can take anywhere from a few months to 32 weeks for a weed plant to grow from seed. Starting with a clone will shave a little time off that schedule.
No matter how long it takes until you can harvest your bud, though, a cannabis plant goes through four stages of growth.
- Germination: This is only a concern if you’re growing from seed, of course. This stage can last a week or a little longer, during which time the sprout will emerge and can be transplanted into soil.
- Seedling: During the next 2-3 weeks, the plant will develop fan leaves in greater and greater numbers. A cannabis plant is considered a seedling until the leaves that emerge have the distinctive 5-7 blades of weed leaves.
- Vegetative: This stage lasts anywhere from a few weeks to four months, depending on the strain. The plant grows rapidly and requires a larger pot, and it’s when the plant has to be topped (particularly if it’s a sativa plant). Male and female plants are separated either during this stage or early in the flowering stage.
- Flowering: Welcome, buds! They begin to develop in this stage which lasts 2-3 months, and as flowering progresses, they become fat and sticky. At the end of this stage, they’re ready for harvest.
The flowering stage is when it’s crucial to pay close attention to your cannabis plants. That’s when the quality of your grow can really be determined.
The Cannabis Flowering Stage
While the length of the flowering stage averages 2-3 months, indica and hybrid plants will usually be at the lower end of that spectrum, and sativas will be at the higher end.
The flowering stage is triggered by changes in light.
Outdoor weed plants will switch from vegetative to flowering when daylight hours grow shorter, normally around August or early September. Growers must give indoor plants the cue to enter the flowering stage by providing them with less light. The vegetative stage requires at least 16 hours of light each day; switching to 12 hours of light per day will trigger vegetation.
(In reality, the plants don’t use light as their cue. They actually recognize how much darkness they experience each day. It’s just easier for gardeners and weed experts to talk about hours of light.)
So if the final stage of growth is flowering, why don’t you see flowers on a cannabis plant?
You do; they just don’t look like flowers. Marijuana plants’ flowers are the buds that are so familiar to weed smokers — and that’s why the terms “bud” and “flower” are synonymous.
At the end of the flowering stage, it’s time to harvest the crop, although it still has to be cured and dried before it’s ready for use.
The Ideal Environment for the Cannabis Flowering Stage
As we’ve said, you can’t alter the outdoor environment if that’s where you’re growing your plants. The rest of this article will deal with indoor grows.
Light
The most important element of the environment to regulate is light. That can be difficult if your grow room has windows that let in ambient light.
You should set your timers to a 12/12 schedule: 12 hours of light, 12 hours of darkness. But if other light can get into the room, be sure to cover all windows with opaque material.
Temperature
You’ll need to turn down the temperature. The ideal temps for the vegetative stage are 70-85°, but plants will produce the most trichomes when it’s about ten degrees cooler. (They’ll look and smell better, too.)
Lower temperatures are most important during the second half of flowering, and you’ll get the most vibrantly-colored buds if it’s 10° cooler at night than during the day.
Humidity
It’s a good idea, if possible, to slowly reduce humidity in the grow room during the flowering stage. Plants don’t need any extra moisture in the air at that point, but high humidity encourages mold growth. By the middle of this stage, 30% relative humidity is ideal.
Water and Nutrients
Plants should be watered once every 2-3 days; obviously, water them more often if the soil gets dry. Nutrients are still crucial in this stage; flowering plants need lots of potassium, phosphorus, and calcium.
The Cannabis Flowering Stage: Week by Week
Here’s a closer look at what to expect (and do) during each part of the flowering stage.
Weeks 1-3
In the first two weeks, flowering plants will grow much taller, stretching out to receive as much light as possible. That also creates more room for their buds. Some plants may double their height during this period.
If the plants are growing too high, you can still gently bend the stems down and away from the main stem at the start of this period (a technique called “low-stress training”). It will probably be too late to train the plants by week four because it will harm the buds.
During these three weeks, you’ll see lots of white pistils growing where fan leaves join with the plant’s main stem. If plants grow pollen sacs instead of pistils, remove them from the room immediately; they’re males, which will fertilize the female plants, and your harvest will suck.
Weeks 4-6
Rejoice! Small buds will be forming on your plants, and they’ll grow fatter every day. The plants will start to smell wonderful, too.
Your plants will still be stretching, but the growth will have slowed. If the leaves are out of control, you can remove some of them, so the buds get enough light. But don’t overdo it. Those leaves are still important for the plant’s development and the buds’ protection.
Weeks 7-10 (or so)
No more leaves or stems should be growing by now; the plants’ energy will be spent on those luscious buds and the trichomes on them. Pistils will be changing color to white, tan, or brown, and they’ll curl inward. Remember that temperature and humidity are crucial at this point.
When the leaves begin to turn yellow and trichomes begin changing color from clear to milky white, it’s time to “flush” the plants by giving them clear water until harvest.
Finally, when most of the trichomes have turned white, all of your work has come to fruition — and it’s time to harvest.
The Cannabis Flowering Stage: FAQ
Q: Does all of this apply to autoflowering strains as well?
A: Most of it does. Autoflowers do what their name say; these strains automatically switch from the vegetative to the flowering stage after about 3-5 weeks, with no need for special light conditions. The overall time frame will be shorter, though; for most autoflowering strains, flowering will last about 5-6 weeks.
Q: What happens if you harvest “too early” or “too late?”
A: That’s always possible since only experience will teach you exactly when your plants are ready. Bud that’s harvested on the early side of the timeline will often provide a more energetic head high, while flower that’s on the late side may be more relaxing and liable to lock you to the couch.
Eichhorn Bilodeau, S., Wu, B. S., Rufyikiri, A. S., MacPherson, S., & Lefsrud, M. (2019). An update on plant photobiology and implications for cannabis production. Frontiers in Plant Science, 10, 296 [1].
