I see your using soil, you will want to wait until you see 10% amber thrichomes before starting flush. Flush meaning water only for the last 2 weeks. Your plant will fade and change colors this is OK.
If you want a really sedative high with couch lock. Wait till you see 30-40% thrichomes then start flush.
If you want cerebral head high that's uplifting then start flush when you see all thrichomes are cloudy.
If dont know and want good smoke that offers some of hoth then go 10-15% amber thrichomes.
Those balls are called calyxces. They are what hold each bud to the plant. When those swell almost completely around the hair then it's almost time to harvest or start looking to harvest.
Those have more THC, cannabinoids, and terpenes then the rest of the entire plant. I save those and if you have enough try rolling a joint with just them, it's amazing.
Those calyxces are where I check my trichomes. I do look at the buds high and low buds. Then the thrichomes as their the most mature part of the buds. Then average every thing out.
Get a 60x magnification jewlers loop. Ac infinity sells one for ten bucks, use this to look at the thrichomes.
Use the % I gave you earlier to determine when you want to harvest depending on your desired effect.
You did great, enjoy your harvest my friend.
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