Hey there , the best way you can determine when your plants are ready to harvest is to watch the trichomes . You cant really see it with the naked eye unless you have had tons and tons of practice . The best way you to see them would be through a portable microscope or a magnifying glass that is atleast 10X or stronger . You can get both items from your local grow shop or you can search amazon for them . They are pretty cost friendly here are some links to a couple items , portable microscope = https://www.amazon.ca/Carson-60X-120X-Lighted-Pocket-Microscope/dp/B00LAX52IQ/ref=sr_1_5?keywords=portable+microscope&qid=1551435970&s=gateway&sr=8-5 and the magnifying glass = https://www.amazon.ca/Fancii-Lighted-Slide-Pocket-Magnifying/dp/B019UYLIYI/ref=sr_1_1_sspa?crid=3VD6RFOJ21I9G&keywords=magnifying+glass&qid=1551436039&s=gateway&sprefix=magnifyin%2Caps%2C168&sr=8-1-spons&psc=. Both of these items or items simular to them will help you see the trichomes . Once the trichomes are 15 % amber 75 % milky and 10 % clear thats when I would take them down . You dont wanna wait too much longer then that as the longer you wait the more chance you have on running the plant until the potency starts to decline . I hope this information helps you understand "when" you should harvest as well as the factors needed to have a good harvest . -Happy Growing !