When To Harvest Cannabis Plants

Max Sargent

Cannabis Journalist & Psychedelics Expert

Max Sargent

Last updated: September 16, 2022

But how do you know when to harvest cannabis? There are several methods available, all of which vary in their accuracy, and here we review each of them.

The importance of a well-timed harvest

Harvesting cannabis at the right time ensures a couple of things. First, that you get the maximum amount of bud that your plant can produce, and second, that the cannabinoid ratio of your buds is optimised (regarding THC content).

In fact, by honing in on when to harvest, we can maximise the cannabinoid content of the final product, giving us some control over the type of high we experience when we go on to consume these buds.

For most people, having as much THC as possible is what they’re after. So for the rest of this guide, we’ll be assuming that’s what you’re after too.

What happens if you harvest too early?

If you harvest your cannabis flowers too early, there are two problems that might occur. First, if you harvest much too early, then you’re going to be losing out on bud, as there will be some that haven't had a chance to grow yet. If you manage to do this, though, you’re way off in terms of estimating the best time to harvest.

Second, and more likely, the cannabinoids in the trichomes (the resin-producing glands on the outside of the flowers) won’t be fully developed. This means that there won’t be as much THC in them as there could be, ultimately meaning that your weed won’t be as strong as it could be.

It might be tempting to start harvesting a week or so early, as you’ll probably have waited a long time already and you’ll be keen to sample some of your homegrown weed. But for the best results, exercise a last bit of patience, and you’ll be well-rewarded.

What happens if you harvest too late?

If you harvest cannabis flowers too late, then the THC in the trichomes will degrade into CBN, which doesn’t get you high in the same way that THC does. The effects of CBN are not fully understood, but it is thought to contribute to a more lethargic high. For those who use weed for this reason, it’s worth understanding that you may be able to increase this effect by harvesting a little late. For most people, though, it’ll mean missing out on a potent, euphoric high.

You can spot that you’ve left it too late if more than around 15% of the trichomes have turned amber, or if more than 90% of the pistils have turned orange/red. This second option is less reliable, though. More on this shortly.

How to know when to harvest weed

There are a few methods available to determine when to harvest cannabis. However, note that some are much more reliable than others. While some methods serve as general signals of harvest approaching, others can tell you exactly when to make the chop.

Using trichomes to judge when to harvest weed

Checking the trichomes with a handheld microscope is by far the best method to figure out when you should harvest. As these are where the cannabinoids are produced, it is the state of the trichomes that ultimately tells you at what stage of development the plant is (regarding THC production).

The picture below demonstrates the four different stages that trichomes go through, and what you can expect if you harvest at each point.

If you find that holding a microscope up to a plant is tricky, then cut a little bit of bud off the plant, and view it somewhere more stable, under good light. This sample should indicate how the whole plant is doing.

In terms of THC production, the following proportions are thought to be a good indication that the plant is at the optimal stage for harvest:

• 60–70% milky trichomes
• 15% clear trichomes
• 15% amber trichomes

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Using pistils to judge when to harvest weed

If you don’t have a pocket microscope, then you can use the naked eye to ascertain whether it’s harvest time or not. However, be aware that this method is much less effective than checking the trichomes. That being said, for those who aren’t after perfect results, it should suffice in most cases.

The pistils are the hairs that grow on cannabis flowers, beginning life as white and ending life as red/orange/brown. The purpose they serve is to catch pollen from males, allowing the females to be pollinated.

The following estimates can act as a guide to figuring out if your plant is ready for harvest:

• 0–50% orange/red is too soon
• 50–70% orange/red is good but not optimal
• 70–90% red/orange is the perfect time to harvest
• 90–100% red/orange, and THC will convert to CBN

The following picture demonstrates the different stages.

Note: cannabis plants experiencing heat and light stress will continue to produce new pistils. This means that even as the plant matures, it will have a disproportionate amount of white pistils, which can make it difficult to use this method to determine harvest date.

Other methods to know when to harvest cannabis

Although taking cues from the plant’s trichomes and pistils is your best bet, there are some other signs that a crop has reached harvest time. Though, be aware—these methods are far from perfect.

• Soil: The soil of a fully mature cannabis plant should be very dense and absorb water less easily. Highly developed root systems will, by now, have taken up much of the space in the pot.
• Leaves: As cannabis plants mature, they naturally shed leaves to direct energy toward flower production. If many of the leaves are turning yellow and crispy, it may signal the end of a plant’s life. Although, yellowing and dying leaves could also be a sign of many other problems that do not mean the plant is ready for harvest, such as a nutrient deficiency.
• Indicas: On the whole, indicas and indica-dominant plants have shorter flowering periods, meaning that they should be ready to harvest around 8–10 weeks after flowering begins in earnest, or the end of September/beginning of October when growing outdoors.
• Sativas: These have longer flowering times, taking anywhere from 10–16 weeks indoors or until the end of October or early November outdoors. Note that judging when to harvest solely by a plant’s genetic makeup is not a good idea.
• Autoflowering plants: Autoflowers have shorter life cycles. In fact, they tend to be ready to harvest in around 8 to 11 weeks from germination. Again, though, this alone is not a sufficient method of judgement.
• Strain: If you buy a strain from a reputable breeder, they should give an indication of the flowering/harvest time. Though this is a good guide, they cannot be relied on as absolute numbers, as a variety of factors can change the actual harvest time.

Knowing when to harvest weed — a crucial skill

So now you know a little more about when to harvest your cannabis plants. Though there are several methods available, investing in a pocket microscope and checking the trichomes is by far the most reliable. So if you can use this option, we’d highly recommend it.

One more tip: when you can tell a plant is almost ready for harvest, consider flushing it to force it to use up residual nutrients that it has stored, potentially improving the flavour of the final product.

Also, check out our article on how to harvest cannabis plants to know what to do when the time comes. Good luck!