I found stray seedlings along the wet ditch behind my big white Crowborough clump in the back corner. They sat in the damp ground past the bed. I never planted a thing there. So I started to cut off the flowers before the berries set seed. The next year no new ones came up, and that small habit stopped the spread cold.
Yes, the arum lily invasive problem is real in mild, wet climates where the plant can spread fast and crowd out other growth. In cold gardens it stays well behaved, since hard winters knock back the rhizomes and frost kills the seed. The risk depends almost entirely on where you live and how wet your soil stays.
The plant spreads two ways, and both are easy to miss. Birds eat the bright orange berries and drop the seed far from your bed, often near water where the soil stays soft. A single plant can make thousands of seeds a year, so even one missed flower head matters.
The second route is the rhizome, the thick underground stem. Break off a small piece while you dig and that fragment can grow a whole new plant. Soil you move between gardens carries these bits. So do cuttings tossed in a damp spot near the fence. This is how the plant slips out of your tidy bed and reaches ditches, creeks, and open pasture. Once it takes hold in a stream bank, it shades out the native plants that hold the soil together.
If your soil stays wet and your winters are mild, treat this plant as a spreader. Deadhead every flower and keep the roots boxed in, or pick a tamer plant instead.
Some places take this so seriously that the law steps in. The arum lily declared weed status is official in a few of them. The rules can put real duties on you as a grower. Here is how three of them handle it.
In Western Australia the plant is a declared pest under the BAM Act 2007. That means you must control it in some zones. New South Wales sets a general duty on you to limit its spread. So the job of keeping it in check falls on the grower. In California, the state plant group rates it at the Limited level. That tag means it does harm in the wild, but on a smaller scale than the worst weeds.
None of this means you have to give up the flower. Responsible arum lily growing keeps the beauty in your bed and out of the wild, and it takes only a few steps. Cut the spent flowers before the green berries turn orange, since seed is the fastest way it escapes a garden.
In wet regions, grow it in pots or a contained bed with a hard edge so the rhizomes stay put. A solid border stops the underground stems from creeping into open ground. Never dump old rhizomes in a waterway or your green waste bin. One scrap can start a whole new patch out there. Bag them for the trash, or let them dry in the sun until they are dead. And check your local rules before you plant. A flower that is fine in a cold garden can be banned a short drive away. A quick call to your council or extension office saves you real trouble later. Treat the arum lily invasive risk with a few careful habits and you get all the bloom with none of the harm.
Read the full article: Arum Lily: Complete Care and Safety Guide
