Many of these plants naturally grow in the gloomy floor of a rainforest, and although they have adapted to cope with much root competition, the pot limits will eventually become too restrictive. Certain houseplants like to be a bit attached to pots – clivias, scheffleras, fragrant lilies, and ficus – but they will even need replanting on time. Now, at the beginning of their annual growth cycle, it’s time for that.
In addition to dealing with root congestion, plants that are too long in the pot sit in soil that has thickened and depleted and may have a harmful buildup of fertilizer salts.
How do you tell whether a plant needs repotting? Turn the pot over: The most obvious sign of a pot-bound plant is roots are growing out of the drainage holes. Hold the lower stem of the plant firmly and pull off the pot. If you see a thicket of pale roots in the shape of the pot, it’s time for action. If the pot won’t slip off, it’s probably gripped by congested roots. If the pot is plastic, you can cut the container away – I use pruners, but mind your fingers. If it’s clay, you may have to break it with a hammer.
Another sign of a problem is if the plant is acting constantly thirsty – or rather, veins – despite diligent watering. This is because the root-to-soil ratio has become too large. The same problem can also lead to an obvious decline in plant energy.
Water the plant thoroughly the day before watering again to reduce stress and force roots.
Once you remove the plant from the pot, you need to feed the roots to a more natural state. The degree of effort depends on their level of overpopulation. I asked Nate Roehrich of Brookside Gardens in Vheaton, Mariland, USA, how to handle this task. We went in search of a plant begging to be moved, and we found wire suffering in one gallon pot.
As we were doing business, I noticed that he was gentler with roots than I usually am. This may be because, a week earlier, I had to take a large knife to the most congested root system I had seen – in the closed palm I had purchased just a month earlier. This leads to another point: just because your houseplant is new to you does not mean it is happily harvested. Plants purchased late in the growing season or winter have had months to grow thick roots. Buy them – especially if they are on sale – but be prepared to prepare them for the coming season.
The nicer the roots, the gentler you should be. One way to remove them with minimal damage is to wash the old soil with a light jet of water, preferably not ice.
On roots that are fine but tough cut them with scissors. If they are thick and tight, you can use a knife to cut the sides. On really congested roots, such as my palm, you could use a sharp knife or even pruning saws to remove the bottom inch or something and then take a three-way cultivator to release the roots from each other and the old soil.
Roehrich used no tools on the wire except his hands. As a rule, it does not remove more than one-fourth of the root mass when replanting.
A root pruning plant may return to the same pot, but it is better to give it a slightly larger house – a pot that is one or two inches higher in diameter. Any higher and you risk rotting the roots due to increased soil moisture. Some pots are set in a decorative outer or casserole pot, while others have an integral pan at the base, but in any case, the new pot must be drained.
There is a bewildering array of soil and compost products for sale, but what you want for most houseplants is soil for sprinkling soil (or a potting mix). This is a typical peat-lit peat-based agent. Some gardeners find the cookware soil still too prone to freezing and prefer to add extra perlite. Orchids and succulents need their own special blends.