Sometimes a large house plant cannot be repotted, because it is growing in a permanent room divider or planter too big to turn on its side. Or you may have a house plant that looks tired and needs new potting mixture, but you don’t want it to grow too large. And certain house plants, particularly bulbs and flowering shrubs, thrive and flower best when their roots are left undisturbed (the list below contains the most popular ones). In all these cases, it is best simply to top-dress the plant with fresh compost.
Each spring, carefully scrape away the top 2.5-5cm (1-2 inches) of old potting mixture, using your fingers, a kitchen fork or spoon, or even a blunt pencil. This is easier to do with a dryish potting mixture than a wet one. Try not to break or damage the roots, or scrape below the main roots. Replace the worn-out potting mixture with fresh, of the same type as used before. Let the mixture trickle through your fingers, until it is at the same level as the old compost. Tamp it down gently and water lightly to settle.
How to top dress
Using a fork or your fingers, gently I tease out the top 2.5-5cm (1-2 inches) layer of old compost. Take care not to break or damage the roots.
Trickle new compost, of the same type as the old, through your fingers, and gently work it into the roots. Water lightly to settle.
