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  • Professor Sprout

Cannabis Grow Guide: How To Know When To Harvest Your Buds

Hey Professor Sprout,

I’ve read that for sleep aids, flowering should be longer to give the plants time to convert THC to CBN. Should I aim to be on the higher end of suggested flowering times, like 8 weeks for A’98 (Angel ’98) instead of 7, or should I just go by how coloured/curved the pistils are and how amber the trichomes are?

I’m asking this question months in advance, I’m already nervous about harvesting at the wrong time, lol.


Thanks for the question, G:

This is something I am also personally concerned about, since under-ripe or early harvested cannabis is not a pleasant experience for me. I often find it anxiety producing and too heady for my needs. I find a much more reliable medicinal effect when I take my plants down a week or two after they reach peak ripeness. As a side note, this is an excellent benefit of growing your own medicine; as commercially produced cannabis is always harvested as early as possible (I would argue much too early) in order to make room for the next crop and more profit. Thus many people consuming commercial cannabis products are going to find the effect not as ideal as it could be.

Lucky 13 Seed Company’s White Diesel Strain Reaching Peak Maturity

Many people think that ripening times are set in stone, and as cannabis breeders we are certainly partially to blame for that. We have to list flowering times in order to help our customers effectively plan their grow, so in our marketing materials we will may list a particular Indica variety as taking 8 weeks to ripen once flowering has initiated, when in actuality some phenotypes may be ripe at 7, and others at 9. Further confusing the topic is the sneaky trick that some breeders use where they list flowering times based on visible flower formation. This is misleading to many growers since once you have initiated the flowering cycle by switching your lighting to 12 hours of uninterrupted darkness, it can take up to two weeks before you begin to see actual flower formation. In this case, a strain that is listed as 8 weeks, could actually take 10 weeks or more to complete the flowering cycle.

To be clear, all of Lucky 13 Seeds listed flowering times are averages based on known phenotype differences and are calculated from the moment the lights are switched to the flowering cycle; and not when flowers begin to form.

Further complicating matters is that in actual practise there are many environmental factors and stressors that can delay the ripening of your plants. Even genetically identical clones grown in different conditions can vary as much as three weeks in their ripening time.

As an example, I once did a stress-test on a flowering clone to see if it was susceptible to hermaphroditism. 6 weeks into flowering, I put it outside in my garden during 8 degree celsius daytime highs with nighttime temperatures hovering just above freezing. Growth and ripening of the buds came to a complete standstill for the two weeks that these conditions persisted. The plant was basically frozen in time. However, after bringing it back into the grow room with ideal environmental conditions, it picked right back up and kept on flowering like it hadn’t missed a beat.

This particular plant ripened just as well as it would have had it remained indoors, however it took an additional three weeks over and above it’s usual flowering time of 8 weeks to reach peak maturity.

This goes to show you that even genetically identical plants can vary in flowering time if they aren’t growing in a happy environment. All the more reason to get those environmental controls dialled in folks.

So how can you tell when a plant is truly ready to harvest?

With time, experience, and growing a particular variety many times, eventually you can get to the point where you can accurately tell when to harvest just by looking at the plant. There are many visual cues to let you know when it’s time to chop. As you already mentioned, the pistils or stigmas will turn brown and shrivel up, new stigma growth will have ceased, calyxes will have swollen, and under magnification you can see the trichomes will have turned from clear, to opaque, and ultimatley amber in colour. And 10 points to you, G, for correct spelling! If I had a nickel for every time I’ve read triCHROME…I would have a shitload of nickels.

After many years of growing experience, I know my plants well, so I can eyeball a plant and know how ripe it is just by looking at it. But before I could reliably do this, the only way I could tell for sure was to view the buds under magnification. I picked up a lighted USB microscope on eBay for less than $100 and started taking small samples from the top buds (the top ripens faster) starting at week 6 of flowering. I would photograph the bud under 100x magnification, set aside to dry, and repeat each week thereafter. Once nearly all the trichomes had turned golden, I chopped the whole plant down, then got to sampling the buds to determine which level of ripeness was the most effective for me (which, as it turns out, is about 50% amber, 50% opaque).

Purple Prozac Trichomes Under Magnification

Differences in Ripeness Create Differences in Effect

As you correctly mentioned, G, the cannabinoid profile will change as the plant ripens. Levels of THC, CBD, and the myriad of other phytochemicals reach their peak and then begin to degrade into other substances. A slightly early harvested plant may have very high levels of THC, but the CBD will not have fully developed yet. And since CBD is known to mitigate the effects of THC, for some people (myself included) this can result in a very heart-pounding, anxiety producing high that is neither pleasant nor effective for treating my symptoms. Other individuals may find this stimulating effect quite pleasant. Thus the importance of growing your own, and doing your own testing.

Here is What I Suggest You Do

As I mentioned, if you are growing Lucky 13 Seeds, we list our flowering times as an average of all known phenotypes, and beginning from day one of the light cycle change. Using our listed flowering time as a guide, begin taking small samples from your topmost buds one to two weeks prior to this. Examine the bud under 100x magnification to examine the colour of the mushroom shaped trichomes. Translucent glands are immature and will not have fully developed their cannabinoid cocktail. Opaque or milky glands will be peaking in their THC production, while amber glands will contain higher levels of CBD and CBN.

Continue taking samples until better than half of the glands are amber in colour, at which point you can harvest the entire plant.  However if you really want to test things out thoroughly, leave a few buds on the plant to continue ripening until all the resin glands have turned amber and test those as well.

Make sure to carefully label each sample taken, dry and cure appropriately, then take them for a spin with your preferred method of delivery.  

Chances are you will find the early harvested bud weak and not very medicinal, the in-between bud very powerful and heady, and the late harvest sedative and stony, Once you’ve determined your preferred week to harvest, the next time you grow this plant (you remembered to take clones, right!?) you’ll know exactly when to take her down for your preferred effect.

Happy Gardening, Professor Sprout

Note:  Outdoor grown cannabis is a completely different story since the number of daylight hours decreases ever so slightly each day after the summer solstice (the longest day of the year).  In this case, counting the number of weeks of flowering will be next to impossible since you will have no way of knowing exactly when the plant initiated it’s flowering cycle.  Some cannabis will begin flowering under 15 hours of light, others will bloom once the daylight hours decrease to 14 or less, and all remaining varieties of cannabis will flower under 12 hours of light and 12 hours of darkness (this is why indoor growers set their light timers to 12 on 12 off).  To add a further element of difficulty, the closer you live to the equator, the less variation in daylight hours there will be.  So for outdoor grown cannabis under natural lighting conditions you’ll have to rely heavily on your microscope and visual indicators of ripeness to know when it’s time to reap your reefer. 

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