But I’ve since learned that pre-flowers can reveal the plant’s sex while it’s still in the vegetative stage! Cannabis plants grow pre-flowers as young as 3-4 weeks from germination for male plants, and 4-6 weeks from germination for female plants. Cannabis Pre-Flowers Are Small Versions of Adult Flowers. Knowing the plant’s sex is helpful because most hobbyist cannabis growers would like to identify and remove male plants from the grow room early in the growing process.
This is because only female plants make potent buds/flowers, while male cannabis plants make non-potent pollen sacs where female plants would grow buds. Additionally, female buds need to avoid pollen from male plants in order to make the highest quality cannabis ( sinsemilla or “no seeds”). Cannabis pre-flowers appear at the base of leaves when male plants are about 3-4 weeks old , and female plants are 4-6 weeks old . Even if you’re not 100% sure about every plant from looking at the pre-flowers, it’s nice to know which plants you need to watch closely and which are definitely female. However, if precision is very important… Chemical Leaf Tests Can Determine Sex & Potency for plants as young as 1-3 weeks. Chemical leaf testing is getting less expensive every day and can be used on cannabis seedlings with just a few sets of leaves to test for sex and future potency . These tests only require a tiny amount of plant tissue (for example a small punch-out from a leaf, or a single cotyledon leaf), so it won’t hurt or slow down your seedlings to take a test sample! In general, the tests are available for seedlings as young as 1-3 weeks.
Sex testing uses a real-time polymerase chain reaction (qPCR) test, and potency tests use Gas Chromatography with a Flame Ionization Detector (GC/FID) or High-Pressure Liquid Chromatography with a Diode Array Detector (HPLC) for testing. Although testing can be done as early as week 1 from germination, waiting until week 3 to conduct testing on seedlings can increase accuracy, and some companies won’t conduct testing until week 3. There are many reasons growers would like to know plant sex as early as possible, as well as be able to estimate the overall THC/CBD ratios of future buds! There are Chemical Leaf Tests that Can Definitively Determine Both Plant Sex & Future Cannabinoid Ratios of Very Young Marijuana Seedlings! But for those of us using our eyes… Male Pre-Flower. Female Pre-Flowers (these turn into buds) This female pre-flower hasn’t released a wispy white pistil quite yet. When starting with “feminized” seeds (which you can usually only get from a breeder), all your seeds should end up being female, so determining male from female isn’t very important. Learn more about buying seeds (including feminized seeds) from breeders online. But for growers starting with “regular” (non-feminized) seeds, about half of the plants can turn out to be male. And unfortunately, there’s no way to look at a seed and be able to tell what sex it is. Unfortunately, you can’t tell a cannabis plant’s sex for sure by looking at the seeds 🙁 How to Figure out Sex of a Cannabis Plant by Examining Pre-flowers. Vegetating plants usually reveal their sex when they’re just 3-6 weeks old from seed, but you have to know where to look. What you’re looking for is “pre-flowers.” These are tiny versions of adult sex parts, and when you see them you can tell what sex the plant is going to be. They usually show up in the upper parts of the plant, closer to the lights, but sometimes you’ll search the whole plant and only find a pre-flower on a random branch lower down on the plant. Vegetating cannabis plants reveal their sex with “pre-flowers” that usually appear 3-6 weeks from when the plant first germinated. Although these are the general shapes of male and female pre-flowers, if you continue looking through the pictures below, you’ll see there’s quite a bit of variation on what pre-flowers look like from strain to strain. Most male plants have grown a pre-flower by week 3-4 from seed, while female plants don’t show until week 4-6. Basically, all vegetative plants will have revealed their sex by about the 6th week from seed. So, without further ado, here are pictures showing what you’re looking for when it comes to pre-flowers. Remember, pre-flowers are found at the V where stems meet a main stalk. But pre-flowers don’t usually show up all over the plant. Make sure to look around in different places, especially near the top of the plant and closer to the lights. Note: Pre-flowers show up most often near the top of the plant and closer to the lights but could be anywhere on the plant.
There may be just one on the whole plant so you may have to search all over! Male pre-flowers tend to have a “spade” shape, like the spades from a deck of playing cards. Male cannabis plants often (but not always) reveal their sex sooner than female plants. Male pre-flowers tend to be shaped somewhat like a spade.
This male plant was only 3 weeks when it made its first pre-flower. Notice how tiny it is compared to the giant-sized thumb!