Pocket BotanistRepotting is the job most people put off, and the one plants forgive most readily. A plant that has outgrown its pot is not in danger; it is just stuck. Its roots have filled every gap, water runs through the compressed root ball before it can soak in, and there is nothing left in the soil to feed on. Give it a slightly bigger pot and fresh mix and it gets on with growing. Here is how to know when, and how to do it without setting the plant back.
When a plant needs repotting
Four signs, and any one of them is enough. Roots are growing out of the drainage holes, or circling visibly at the surface. Water runs straight through the pot and out of the bottom in seconds, because there is more root than soil left to hold it. The plant dries out much faster than it used to, needing water every couple of days where it managed a week. Or it has simply stopped growing during the season when it should be growing.
Most houseplants want a bigger pot every one to two years while young, and every two to three years once mature. Fast growers like pothos, spider plants and monstera hit the limit sooner; slow growers like snake plants and ZZ plants can sit happily for years, and actually flower more readily when a little cramped.
The right time of year
Spring and early summer, as the plant comes into growth, is the best window. Roots damaged in the move heal fastest when the plant is actively growing, and there is a whole season ahead to fill the new space. Autumn and winter repotting is not fatal, but a plant that is resting cannot repair itself quickly, and wet, unused soil around a dormant root ball is how root rot starts.
The exception is an emergency: a pot that has cracked, soil that has gone sour and smelly, or a plant that is clearly rotting. Then repot whenever it happens, and keep the new soil on the dry side afterwards.
Choosing the pot
One size up, which means 2 to 5 cm (1 to 2 inches) wider than the current pot. It is tempting to jump two sizes to save doing it again, and it is the most common repotting mistake. A root ball surrounded by a thick band of empty soil stays wet for a long time after each watering, because there are no roots there to drink it, and that wet band is where rot begins.
Drainage holes are not optional. A pot without them can only be used as a cover for a plastic nursery pot inside. Terracotta breathes and dries faster, which suits succulents, cacti and anyone who tends to overwater. Plastic and glazed ceramic hold moisture longer, which suits ferns, calatheas and anyone who tends to forget.
Choosing the mix
Fresh potting mix, never garden soil, which compacts in a pot and brings pests with it. A general houseplant mix suits most things. Add a third of perlite or orchid bark for aroids like monstera and philodendron, which want air around their roots. Use a dedicated cactus mix for succulents. Orchids need bark, not soil at all.
Old soil is spent: its structure has collapsed and its nutrients are gone. Replace as much of it as comes away easily, but do not scrub the roots bare. Loosening the outer inch of the root ball and teasing apart any circling roots is enough.
The method, step by step
Water the plant the day before, so the root ball slides out whole and the roots are turgid rather than brittle. Put a layer of fresh mix in the new pot, deep enough that the top of the root ball will sit about 2 cm below the rim. Tip the old pot on its side, support the stem between your fingers, and ease the plant out. If it is stuck, run a knife around the inside of the pot, or squeeze a plastic pot to break the grip.
Loosen the outer roots with your fingers. Cut away anything black, mushy or smelly with clean scissors. Set the plant in the new pot at the same depth it was growing before, then fill around it with mix, pressing gently to remove large air pockets without compacting it. Water until it runs from the drainage holes, and let it drain fully.
The two weeks after
A freshly repotted plant often sulks: a slight droop, a yellow leaf or two, a pause in growth. It is normal. Keep it out of direct sun for a week, do not feed it for a month (fresh mix has all it needs, and fertilizer on damaged roots burns them), and water only when the top of the mix has dried. The pot is bigger now, so the interval between waterings is longer than you are used to.
If the plant wilts badly and the soil is wet, it lost more root than it could afford in the move, and the fix is less water, not more. Wait it out. New growth within three or four weeks means the roots have taken.
Let the app do the remembering
Pocket Botanist keeps a care log for each plant, so the date you last repotted is there when you wonder, and the watering reminder adapts when a plant moves into a bigger pot. Save a plant with a photo and the app suggests a watering rhythm for its pot size and material. Free on iPhone and Android.
Sources
- Royal Horticultural Society, "Houseplants: growing and care." rhs.org.uk