Just the other day i found a mass amount of ditchweed but i'm not sure its mature yet. i took a little just to be on the safe side (of course). its really seedy and looks like it would be premature but i can't be too sure. can't add a picture since i have no camera, but any help would be greatly appreciated!
I'm a little confused by what you're asking, if you stumbled across someone else's grow then leave it be, it would be impolite if someone messed with your outdoor grow, but then again if it could be found than it's not in the best spot. Assuming you mean you found a still growing plant it's a bit early in the season since fall is just starting, harvest time depending on the sativa/indica content is around Oct- early Dec. You can tell how mature it is by looking at the flowers and THC glands magnified. White hairs are premature unless its a characteristic of the phenotype. THC glands (crystals) will appear amber, clear or cloudy depending on THC, CBN, CBD content. When you're harvesting you can actually decide if you want a head or body high depending on the harvest time and how mature the plant is, as the plant gets older the CBN and CBD cannabanoids convert to THC which gives you more of a head high while the former gives a the feeling of a couch lock or body high.