Repotting a root-bound fern, step by step
How I repot a fern that has outgrown its pot, what size to choose, and how to avoid the sulky weeks afterwards.
Last spring I finally repotted the bird's nest fern that had been pushing roots out of its drainage holes for most of the winter. It went well, and I have since repotted three other ferns the same way, so here is the process as I now do it.
How to tell it is time
A fern does not need a new pot every year. I only repot when I see at least two of these signs:
- Roots growing out of the drainage holes or circling on the surface.
- Water running straight through the pot without soaking in.
- The soil drying out in a day or two, even in cool weather.
- The plant looking top-heavy and tipping over.
Spring is the best time, when the days are getting longer and the plant is about to start growing again. It recovers much faster than in autumn or winter.
Choosing the new pot
The most common mistake is going too big. A huge pot holds a lot of wet soil that the roots cannot reach, and that soil stays soggy for days. I go up only one size, usually two to four centimetres wider than the old pot. It must have drainage holes. I prefer plastic or glazed pots for ferns because they dry more slowly than bare terracotta.
What I prepare
Before I start, I lay out everything on an old towel on the kitchen table:
- The new pot, rinsed.
- Fresh potting mix, slightly damp, never bone-dry.
- A blunt knife or a chopstick for loosening roots.
- Clean scissors.
- A jug of room-temperature water.
I water the fern lightly the day before. Moist roots slide out more easily and suffer less damage than dry ones.
The actual repotting
First, I tip the pot on its side and support the base of the plant between my fingers. If it does not slide out, I squeeze the sides of a plastic pot, or run the knife gently around the inside edge.
Next, I look at the roots. Healthy fern roots are firm and dark brown to black, often fuzzy. Mushy, grey or bad-smelling roots are rotting, and I cut those away. If the root ball is a solid tangle, I tease the outer roots loose with my fingers so they will grow outward into the new soil rather than keep circling.
Then I add a layer of mix to the bottom of the new pot so that the top of the root ball will sit about two centimetres below the rim. Ferns should end up at the same depth as before. Burying the crown, where the fronds emerge, invites rot.
Finally, I fill around the sides with mix, pressing lightly with my fingers to remove big air pockets but not packing it hard. I water slowly until it drains through, let it settle, and top up any spots that sank.
Afterwards
For two weeks I keep the plant out of any direct sun and I do not feed it. Fresh mix has enough nutrients for a while, and new roots are easily burned by fertiliser. A frond or two may yellow; this is just transplant stress.
The bird's nest fern sulked for about ten days, then produced a new tightly curled frond from the centre. That first new frond is always the moment I relax.
Dividing instead of upsizing
Some ferns, like Boston ferns, can be divided instead of moved to a bigger pot. I cut the root ball into two or three pieces with a clean knife, each with its own crown and fronds, and pot them separately. It is a good way to keep a plant at a manageable size and end up with spares to give to friends.