How do you tell when a potted plant needs repotting? There are several clues. Perhaps your soil moisture tester is no longer able to penetrate the soil. Maybe your plant has to be watered every day. You may find that the water you add to the pot takes forever to soak in.
The sure way to find out is to pop the plant out of its pot. When the pot is small this chore is easy—simply turn it upside down and rap the edge of the pot on a hard surface like your potting bench. Don’t forget to have your hand beneath the plant to catch it when it falls out! Now check the roots. If they are crowding around the edges, it’s time to repot. Now if you have a larger pot, simply get a strangle hold on the basal neck of the plant and tap the top of the pot. We find a rubber mallet works well with this, but a short piece of wood like a 2 x 4 would work.
If you have a plant in a pot that has a constricted top like in the photo below, you have a problem. When you plant in such a pot, repotting will be a real chore. Your two main options are to cut down through the roots all around the periphery with a narrow blade, or you could simply break the pot. A third option is simply to let the plant die a slow, agonizing death. Of course, you could shorten the demise with a quick severing with a pruner. Then you are merely left with the struggle to remove the impacted remains.
Now once you perfect plant popping technique, you may consider using it while checking out the condition of a plant at a nursery before purchase. It would not be wise to invest a great deal in a plant that has been kept in the same pot too long and is now root bound.
LaVille is a professional propagating plant popper and uses this technique constantly to tell when a plant needs repotting. With a little practice you could be a proper popper too.
Stan, The Popper Man