For the first few weeks, autos (auto-flowering plants) only make vegetative growth - stems and leaves. After their short “vegetative stage” ends, the plant will start making buds and continue to grow taller even while their buds are forming.
It’s only until a few weeks before harvest that most auto-flowering plants stop growing “up and out.” At this point, auto-flowering plants put all their energy into fattening buds, and buds can gain substantial weight during the last few weeks.
When purchasing auto seeds, good breeders will be able to tell you how long the strain will take until harvest. It’s important to note that most strain breeders will tend to provide the shortest time frame they can, and many autos will produce better yields and higher potency if left for a week or two (sometimes even three) longer than recommended.
How do I know when to harvest my plants? - Basically in addition to the visual appearance of buds, you can look at your buds under a magnifier to know exactly when to harvest for top THC potency.
Photoperiod strains usually take longer to harvest than autos. In general, photoperiod strains are ready to harvest 3-4+ months after being sprouted from seed, though the final time depends heavily on your grow style and which strain you choose. Even photoperiod plants flowered from seed tend to take longer than an auto-flowering plant to be ready to harvest, and the yields are much lower. Photoperiod plants do best when given some time in the vegetative stage before they start flowering, and aren’t as well suited to quick harvests.I