PlantRepot in spring when roots have filled the pot, and go up only 2–5 cm (1–2 in) in diameter; an oversized pot surrounds the roots with wet mix they cannot use.
Signs a plant really needs a new pot
Most actively growing foliage plants need repotting every 1–3 years, but the plant, not the calendar, should tell you. Slide it out of its pot when the mix is slightly dry and look at the root ball. Roots wound in dense circles around the outside, with little mix visible, mean it is ready. So does water that runs straight through without wetting the mix, a pot that needs watering every 2–3 days in spring, or a plant so top-heavy it keeps tipping over.
The mix itself also wears out. Bark and peat break down over 2–3 years into fine, soggy material that holds less air, and a white crust of fertilizer salts builds up on the surface. Refreshing the mix is a valid reason to repot even when the pot size stays the same.
Reasons not to repot yet
A single root poking out of a drainage hole is not enough on its own; roots explore any opening. Avoid repotting a plant you have just bought, since it is already adjusting to your light and humidity, and avoid late autumn and winter, when low light means roots regrow slowly and fresh, wet mix stays wet. Spring to early summer, when the plant is putting out new leaves, is when root damage heals fastest.
Some plants prefer snug pots. Snake plant (Dracaena trifasciata), ZZ (Zamioculcas zamiifolia) and spider plant store water in rhizomes or tuberous roots and are prone to rot in oversized pots; peace lilies also tend to flower better when slightly root-bound. For these, wait until the roots start to deform the pot.
Choosing the next pot
Go up 2–5 cm (1–2 in) in diameter for small and medium plants and up to 5–8 cm for large floor specimens. The reason is water, not space: mix the roots do not reach stays wet far longer than mix full of roots, and that unused wet zone is where rot starts. Always use a pot with drainage holes.
Terracotta loses water through its walls and dries noticeably faster than plastic, which suits succulents, snake plant and heavy-handed waterers. Plastic and glazed ceramic hold moisture longer, which suits peace lily, ferns and anyone who tends to forget watering.
Step by step
Water the plant a day ahead so the root ball holds together and the roots are hydrated, then work through these steps:
- Ease the plant out by tipping the pot and pressing on its sides; cut a stuck plastic pot rather than pulling the stem.
- Tease out circling roots with your fingers. A badly matted root ball can be scored with three or four shallow vertical cuts to encourage new outward roots.
- Trim dead roots (brown, hollow or mushy) with clean scissors; keep firm, healthy ones.
- Set the plant at the same depth it grew before; burying the stem invites rot, especially on snake plant and ZZ.
- Fill around the sides with fresh, slightly damp mix, firming lightly with your fingers; do not pack it hard.
- Water thoroughly until it drains to settle the mix, then top up any low spots.
The first four weeks
Keep the plant in bright indirect light but out of direct sun for 1–2 weeks while roots recover. Check moisture by feel, because the new pot and fresh mix will dry on a different schedule from the old one; many repotted plants need less water than expected for the first few weeks. A little leaf drop or droop is normal.
Hold off fertilizer for about 4–6 weeks. Most fresh mixes contain starter fertilizer, and newly cut roots are vulnerable to salt damage. If you are repotting a monstera or climbing philodendron, add a moss or coir pole now, while the root ball is out; inserting one later tears roots.
