The arum lily vs calla lily split is really a naming habit. It is not a clash between two separate plants. Both names sit in the same genus, Zantedeschia, so you are looking at close cousins. In everyday garden talk the two names tend to line up with colour and hardiness. Arum lily means the tough white plant. Calla lily means the tender coloured types you see in florist bunches.
The white arum lily you spot in damp borders is almost always Zantedeschia aethiopica. It carries that classic pure white funnel, called a spathe, wrapped around a yellow finger of tiny true flowers. This is the plant most people picture when they hear the word arum. It grows tall, and it spreads at the roots. It copes with wet, cool spots that would finish off its cousins. You will often see it thriving right at a pond edge.
Calla lily is the name shops reach for when they sell the coloured Zantedeschia hybrids. These come in pink, yellow, orange and a near-black plum shade that looks almost gothic. Breeders crossed several smaller species to get those rich tones. The plants stay more compact than the white species. Their leaves often carry pretty silver speckles too. So you can sometimes pick out a calla before the flower even opens. Look down at the foliage and the spots give it away.
Hardiness is where the split really matters for you. The white species is the toughest of the whole genus, rated around RHS H4 and happy in USDA zones 8 to 10. It thrives in boggy ground and loves wet soil, so a soggy corner suits it well. The coloured hybrids tell a different story. They are frost tender, and they want richer, free-draining ground. Standing water will rot their tubers. So you should never plant your callas where the soil stays wet, and you should hold off until the frosts have passed.
A pure white flower in damp soil is almost always the hardy arum lily. A pink, yellow, orange or deep plum flower in a pot is a tender calla hybrid that needs lifting before winter.
Both plants share the same basic shape, and that is why the names get muddled. They both grow from a fleshy tuber. They both throw up that curled spathe around a central spike. And both have arrow-shaped leaves on long stalks. So you cannot trust the flower outline alone. You have to look at the colour and the growing spot to know which camp your own plant sits in. Once you know that, you can give it the care it wants.
Here is the practical advice I always give. Do not trust the common name on its own, because shops swap arum and calla around without much care. Check the botanical name and the hardiness rating on the label before you buy. If the tag says Zantedeschia aethiopica with an H4 rating, your plant can stay outdoors through most winters and shrug off frost. That tells you it is the hardy white type, not a tender hybrid. So you can plant it out and leave it in place for years.
If the label lists a coloured hybrid or gives no hardiness at all, treat the plant as tender. In my own garden I lift those tubers each autumn and store them somewhere dry and frost-free until spring. Get the name right and you will know straight away where your plant belongs. The white one wants a wet border. The coloured ones want a cosy pot or a sheltered bed. That one quick check on the label saves you a lot of dead plants.
Read the full article: Arum Lily: Complete Care and Safety Guide
