It also depends alot on the sort of the weed you are growing and what quality are the seeds you are putting into ground.

Now weed that is being grown outside usually takes longer to grow. I don’t know why but it just does. Also the very hard part it is to tell when it is “ready”. Since there is no formula on how long does weed take to grow, you will have to search for some pictures online and compare it to your plant.

But in general, weed takes around 3-5 months to grow. Usually it is ready to use within 4 months but as I said, you should make sure it is ready otherwise it will be a waste.