Gadenin日本語Get the appThe signs that it actually needs a bigger pot
An arrowhead plant grows fast in warmth and will usually want a bigger pot every one to two years, but the plant decides that, not the calendar. Repotting a plant that still has room is a setback, because the unused compost around the rootball stays wet and the roots never move into it.
Look for roots coming out of the drainage holes, roots visible circling the surface, water running straight through within a couple of seconds, a pot that dries out again a day after watering, or growth that has simply stopped through a warm spring with nothing else wrong. Two of those together mean it is time.
Pot size and mix
Go up one size only, an inch or two (2.5 to 5 cm) more in diameter. Moving a plant into a pot far larger surrounds a small rootball with a mass of wet compost, and root rot follows within a couple of months. The pot must have a drainage hole; a decorative cachepot is fine as an outer sleeve, but do not plant into it.
| Component | Roughly | Why it is there |
|---|---|---|
| Peat-free houseplant compost | Three parts | Holds water and nutrients |
| Perlite or coarse grit | One part | Keeps air in the mix so roots can breathe |
| Fine orchid bark | One part | Stops the mix collapsing into a solid block |
| A little worm cast or slow release feed | A small handful | Carries the plant through the first two months |
Do not put a layer of gravel in the bottom of the pot. It does not improve drainage; it raises the level of permanently wet compost above it.
Doing the job
Late spring or early summer is best, when the plant is growing and can push new roots out quickly. Water it the day before so the rootball holds together and the roots are not dry when they are handled.
- Ease it out, do not pull it out Squeeze a flexible pot or run a knife around a rigid one, then tip the plant into your hand supporting the base of the stems. Pulling on the stems tears roots away from the crown.
- Look at the roots Healthy roots are pale and firm. Tease the outer ones loose so they are not still circling, and cut away anything brown, hollow or falling apart. Leave the middle of the rootball alone.
- Set the depth first Put enough fresh mix in the bottom that the top of the rootball sits about half an inch (1 cm) below the rim. Burying the crown deeper than it grew invites rot at the base of the stems.
- Put the support in now If the plant is going to climb, push the moss pole or stake down against the back of the rootball at this point. Driving a pole into an established pot later cuts through roots you cannot see.
- Fill and settle with water Work mix down the sides with your fingers, tap the pot to settle it, and water thoroughly until it runs from the holes. Do not press the compost down hard; the water will do it.
The first month afterwards
Keep the plant in bright shade rather than its brightest position for two weeks, and hold off feeding for six to eight weeks if the mix had any slow release feed in it. Fresh compost has enough to be going on with, and feeding damaged roots does harm rather than good.
Water when the top inch (2.5 cm) is dry, exactly as before, but expect the pot to stay damp longer than you are used to because there is more compost and fewer roots to drink it. This is the point at which a well repotted plant is most often overwatered. Some drooping in the first few days is normal; a new leaf within a month or so tells you the roots have taken.
If the plant has grown lopsided or thin at the base, repotting is a good moment to shorten the longest stems. Cuttings from that pruning root in water in a couple of weeks and can go straight back into the same pot to thicken it up.
Refreshing without moving up a size
Sooner or later you will not want a larger pot. When that happens, take the plant out, cut away up to a quarter of the outer rootball with a clean knife, trim the top back by a similar amount to balance it, and put it back into the same pot with fresh mix around the sides. Done in late spring the plant hardly notices, and it can be repeated every couple of years indefinitely.
Write down the date, the pot size you moved to and the mix you used. When the plant next slows down, that record tells you at a glance whether it has been two years or four, and whether the mix you chose last time held together or turned to sludge.