When it’s time to repot, should you increase the size of the pot? Photo: Hall’s Flower Shop and Garden Center
Repotting. Potting up. They’re the same thing, right?
Repotting is a more generalized term. It means moving a plant to a new pot. There is no implication of pot size.
Potting up specifically implies moving the plant into a larger pot. And that’s not always what you want to do.
Pot Size Is Linked to Growth
Potting up (moving a plant to a larger pot) tends to encourage it to grow faster and become larger. It’s the sort of thing you do to a younger plant, sometimes more than once a year. For example, you’d want to start a stem or leaf cutting in a small pot, but as the cutting grows into a plant, it will need more space, so you’d move it into a larger one, perhaps only a few months later. And likely a larger one again the following year. But as it attains the size you want, you reach a pot where giving it a larger pot is no longer worthwhile.
Perhaps it has already reached its full size and will grow no further. That would be the case for an African violet or a cyclamen, for example, also many orchids. So, no need to pot up. But you’d still need to change the soil. So, you’d repot into a container of about the same size.
Another possibility is one you run into most often with larger houseplants, especially indoor trees. There is practically no limit to how large these will become, but there may be limits on how large you want them to grow. If your dieffenbachia or ficus is already as big as you’d ever want it to be, or nearly so, you wouldn’t want to repot it into a larger pot: that would just encourage it to become even bigger. Instead, you could repot into a pot of the same size and slow it down.
I have plants that have been in the same size pot for more than twenty years. Two examples are a huge, bulky croton that I certainly don’t want to see grow any larger and a money tree (Pachira aquatica) that is nearly up to the ceiling. Yes, I could replant these giants into bigger pots, then prune them back when they go into a growth spurt, but why bother? Essentially, I’m underpotting them: repotting them into pots smaller than they would like, and that nearly stops their growth cold. Neither of these two plants has grown to any noticeable degree in twenty years.
Essentially, underpotting is the equivalent of bonsaiing your plants: using pot size to keep their growth to a minimum, as bonsai masters do.
Repotting to Change the Soil
The main reason for repotting a young plant is to give its roots room to grow. But the main reason for repotting a more mature plant is to change the soil.
Over the years, mineral salts tend to build up in potting soil: minerals from tap or spring water, from fertilizer, etc. And as they do, they become toxic. When minerals in the soil around the roots are more concentrated than in the plant itself, water begins flowing out of the plant rather than in, leaving it in a constant state of drought stress. By unpotting the plant, then removing most of the old contaminated soil before repotting into fresh soil, you give the roots a new lease on life.
I find that I can get away with repotting small to medium-size plants (ones I don’t want to see grow, that is) every 2 to 3 years. Big ones in big pots can hold out for 4 to 5 years. Or you can try top-dressing and delay repotting even further. Read the article, If You Can’t Repot, Top-Dress for further information on that technique.
Clean Pot Needed
Do either thoroughly clean the pot before reusing it (minerals build up on the pot surface as well as in the soil) or, more logically, repot into a new or clean pot. (That way you can take your time and clean the old pot later.) And it can be a pot of exactly the same dimensions.
So, you decide. If you want your plant to grow, pot it up. If you want to limit its growth, yes, do remove the old soil, but repot into the same size pot, thus keeping it underpotted. Simple, isn’t it?
Repotting is best done in early spring, just as the plant begins a new growth cycle. And it can be carried on throughout the spring and summer if that’s more convenient. It’s best not to repot houseplants when their growth is at a standstill, usually from late fall through winter.