It’s not easy to be patient with your garden when it’s filled with huge buds, but knowing how to tell when buds are ready to harvest is of utmost importance. If you harvest before the buds reach full maturity, the potency and yield of your crop will not reach its potential. On the other hand, If you wait too long, potency can actually decrease. As the bud becomes overripe the THCA begins to degrade into CBL and CBN.
As the buds grow close to full maturity a visible layer trichomes will begin to cover the flowers and leaves. These trichomes are very small resin glands on the surface of the plant that will sparkle in the sun like little diamonds. You have probably heard these referred to as crystals or "Trikes". Some cannabis strains will have pronounced trichome development four or five weeks before maturity, others will develop as late as two weeks before they reach full maturity.
As the buds mature, the crystals, or to use capitate stalked trichomes, begin to swell and resemble tiny mushrooms as they fill with cannabinoids and terpenes. Under magnification from a jewelers loop, the bulbous tips of these trichomes will appear clear while still developing, but will begin to turn amber or milky as they reach and pass full maturity. This milky or amber is color is what shows you the cannabinoids have reached full maturity and have begun to degrade. When about 20% of the trichomes on a bud begin to turn amber or milky, this is the time to harvest.
To be clear, trichomes are not the hairs on the buds that turn from white, pink, or purple to a rust or brown color. These hairs are called pistil and despite what people might tell you, their color is not a good indicator of a buds maturity or ripeness.
Some cannabis plants may reach full maturity all at once while other plants may begin to ripen from the top colas down. Ideally you will be able to harvest the plant all at once, but it’s not uncommon for the top colas or outer buds to mature faster. You can harvest the mature buds and leave those not quite ready for a week or two longer. Often the extra light provided by removing the ripe buds will speed the others along pretty quickly.
The trained eye may be able to identify when a bud is ripe without magnification. Considering how important it is to get this right, we suggest a jeweler’s loupe (see below for some options) until you have the experience under your belt.
When it comes to magnifying tools for growing, there are a few options:
Jeweler's Loupe - This is the cheapest and most low tech way to get the job done. Unfortunately, it is still difficult to get the best insight into how your buds are doing unless you have really great eyes, though the one we linked to is the best that I've tried. Will definitely get the job done in a pinch!
Handheld Magnifier - Some people prefer these to jeweler's loupes. They can create a good picture and typically can magnify more than a jeweler's loupe. However, this power makes them a bit harder to focus.
Digital Microscope - A digital microscope is the final word in determining harvest time. It costs a bit more and many models need a connecting laptop, but it'll get you face-to-face with your trichomes. You'll be almost uncomfortably close to your trichomes!
Sources: http://marijuanagrowershq.com/ / http://www.growweedeasy.com/harvest