It's easy to ignore houseplants when the weather is balmy and the vegetable patch needs weeding. But as the days become shorter, it's reassuring to glance at your Christmas cactus and discover, despite your neglect, a fresh crop of buds, ready to burst open during the darkest part of the year.
You may also notice, however, roots coming out of the pot's drainage holes, yellowing foliage or new leaves that are smaller and farther apart than normal. Any or all of these clues might be a warning that it's time to repot your houseplant and give it a fresh start.
To do this, you'll need a bag of fresh potting soil; a clean, sterile pot no greater than two sizes (about five centimetres) larger than the current one; and a trowel.
Water the plant thoroughly 24 hours before repotting. Then, to remove the plant, place one hand across the soil surface, hold the bottom of the container with the other hand and turn the pot upside down. Give the pot a sharp, upward jerk; the plant should easily slip away.
Inspect the root ball. If only a few roots are visible at the edges, the plant doesn't need repotting. However, if many white ones are winding around the exterior, tease them out with your fingers to untangle them. Cut back any that are excessively long by as much as two-thirds.
Some plants may be so pot-bound that it's impossible to unravel the mass of roots. Give them a quick root prune by making five evenly spaced, vertical cuts (about two centimetres deep) from the top of the root ball to the bottom. This slices through the overgrown roots, stimulating fresh growth. Alternatively, use a large, sharp knife to divide the plant into two to four pieces, and repot each piece separately.
Add enough soil to the container so the plant sits at the same level it did in the original one. Centre it in the new pot, and fill in the sides with fresh soil. To avoid creating air pockets, tamp down the soil as it's being added, and fill to about three centimetres of the rim. This will allow water to pool rather than overflow the top.
Irrigate the plant well with a one-quarter-strength solution of transplanting fertilizer (10-52-10) and trim away any yellowing or browning leaves or gangly branches.
Rejuvenating large specimens
Mature indoor trees and shrubs require repotting less frequently than plants in smaller containers. Top-dressing plants annually in late winter postpones the need for repotting, and is much less onerous.
Before top-dressing, water the plant well 24 hours in advance. Loosen and remove the top six to eight centimetres of soil, and as much as possible from the sides. Refill the pot—tamping down as you go—with fresh potting mixture until the soil reaches its original level. Water well.