Three summers after I dropped one white Crowborough rhizome into the damp back corner, that single tuber was a broad clump of white spathes. It spread to the size of a dustbin lid. Yes, an arum lily perennial comes back every year. In a mild climate it returns on its own and gets bigger as it goes.
That first season fooled me. I planted the lone rhizome in spring and it pushed up a few arrow-shaped leaves and then sat there. No flowers, no spread, just green. I half wrote it off as a dud. But the roots were busy underground the whole time. The next spring it sent up twice as much growth, and the year after that it flowered for the first time. You may see the same slow start, so give your plant a chance.
The reason an arum lily perennial comes back sits below the soil. Your plant grows from a fat rhizome. That is a swollen underground stem that stores energy and survives winter while dormant. The leaves die back in autumn and the rhizome rests through the cold. Fresh spears push up when the soil warms again in spring. You can count on that cycle to repeat for years, which is why people say an arum lily return each year is so reliable.
So do arum lilies multiply as well? They do, and the rhizome is the reason. Each year it grows offsets, which are small new rhizomes that branch off the main one. Every offset can throw up its own leaves and its own flowers in time. So your single plant fans out into a wider clump season after season. That is exactly what turned my one tuber into a thick stand of spathes.
Hardiness decides whether yours returns without help. The white species is the tough one to grow. It rates RHS H4, which means it survives roughly -10 to -5°C (14 to 23°F). It also sits in USDA zones 8 to 10, so it shrugs off frost and overwinters outdoors in mild areas. The coloured calla hybrids are far softer and rarely make it through a hard winter in the ground.
Give a new plant time to bulk up before you judge it. An arum lily takes 5 to 10 years to reach its full size of around 1 metre tall. Each year the clump widens and the flower count climbs. A thin first planting slowly turns into a real stand. So the slow start you see is normal. Don't dig it up in a panic, because the best years are still ahead.
In mild zones leave hardy clumps in moist ground and they return on their own. Divide congested rhizomes every 3 to 4 years to keep flowering strong. Wear gloves every time, since the sap stings skin and eyes.
Cold gardeners have one extra job to do. In zone 7 and below, you should lift the rhizomes after the foliage dies back. Dry them off and store them somewhere frost-free and dark over winter. Replant them in spring once the worst frosts pass. They pick up right where they left off. Done this way, your arum lily comes back every year no matter how cold your garden gets.
One last tip if you want fewer plants, not more. Cut off the spent flowers before they set seed. Your rhizomes will still spread underground, but you stop new seedlings popping up where you never planted them. That keeps a happy clump from turning into a takeover in a warm, damp spot. I do this every autumn in my own border so the patch stays where I want it, and you can do the same in yours to keep things tidy.
Read the full article: Arum Lily: Complete Care and Safety Guide
