When to Repot Plants

We “pot up” or “pot on” (repot to a larger container) (a) when the roots have completely filled the pot; (b) when the plant seems to be needing more and more watering as if the water you supply is not being taken up; (c) when the roots are coming out the drainage holes (the plant has become root bound); or (d) when the plant gets too tall for the container and is subject to tip over and become top heavy.

Orchids and bromeliads, which don’t have soil roots, should be potted up every couple years as their aerial roots need more room. A rootbound plant that is ready to be re-potted.
To confirm that a plant should be potted on: Wait until the medium in the pot is good and dry, then slide the rootball out and examine it. Use your hand to cover the top of the medium while holding the plant’s stem between your index and middle fingers. Invert the pot and tap it on a hard surface to dislodge it. You may need to run a knife around the inside edge of the pot. If the root system is all jammed up at the bottom or around the sides, it’s time to pot on. 

Best Time to Repot Plants

Springtime is the best time of year for repotting plants. We usually pot up every couple years or so for healthy, well tended houseplants. Slow growers (like some cacti, ficus, or palms) can go for several years between repottings.

When it’s necessary to pot on, move up to the next larger pot size, or at most, two sizes larger. (Pot sizes go by diameter in inches across the top: One size up from a pot five inches in diameter at the top would be six inches across the top.) Most container plants do best when slightly crowded, with their roots close to sides, so don’t pot up to a bigger pot that is a lot larger thinking that will save you from repotting soon again. A lot of soil in the pot holds a lot of water, and this could be too much for a small rootball, leading to root rot.

For a standard shaped clay pot, the diameter of the top should be about a third to a half of the height of the small plant. If the container is wider on its base, taller plants can be accommodated.

How to Repot a Plant

Terra cotta pots with plants and shovel on a table in garden. If you’re using a clay pot, soak it overnight so it’s saturated and won’t pull moisture out of the new potting medium or desiccate delicate root hairs. Thoroughly water the plant an hour before repotting. Dampen the new potting mix before starting. Put some shards or broken pieces of clay pots on the bottom of the pot over the drain hole to keep the potting mix from washing out the hole, while still allowing excess water to drain freely. Prune the circling roots of the plant to encourage new, fresh roots to grow in its new container. Prune any roots that are circling around the pot. Use a sharp knife to make 3 or 4 one-half inch deep cuts from top to bottom through the root ball. This will stimulate new root growth from the cut ends. Don’t reduce the size of the rootball by more than 25%. Loosen the roots that are not old enough to be pruned back.

Put enough potting mix in the pot so that the repotted plant will be at the same level it was before repotting. If the plant has a tap root, use your finger to make a depression in the center of the mix to accommodate the tap root without bending it. If the roots are more fibrous and lack a taproot, mound up the soil surface in the center, then spread out the roots over the mound.

Fill the pot around the roots to about a half inch or so below the top of the pot, so that when you water you can fill it up to the top and that should be enough to wet the soil thoroughly while some runs out the bottom drain hole. Tamp down the fresh potting soil mix as you refill the container so that all the roots are in contact with the new medium.

Water very thoroughly this first time. In fact, it’s best to soak the whole pot in a bucket of tepid water for 15 minutes or so, while pouring more water on top. This thorough soaking will ensure that the old soil within the rootball will mesh with the new medium and that the delicate root hairs will be completely surrounded and within the new potting medium. The root hairs must never be allowed to dry out. Repot quickly!

Wait about a month before fertilizing a newly repotted plant to be sure you don’t “burn” the roots.