I classify weeds in our yard into two categories, "weeds" and "terrible weeds".
"Weeds" include those ordinary plants that occur everywhere here, many of which are on the local environmental or noxious weeds lists, such as crofton weed, Ageratum, camphor laurel, farmer's friends, and Lantana. They grow readily in my garden and come back very quickly if you pull them out and are a big nuisance, but they have one essential characteristic that distinguishes them from "terrible weeds" - when you pull them out, or poison them, they die.
"Terrible weeds" are almost impossible to kill.
If you pull them out, every little bit of stem has the potential to regrow if it is left in contact with the ground. And/or every bit of root left in the ground can grow into a new plant. If you poison them, only the above-ground bits will die, leaving living roots, or stolons or bulbs beneath the surface that will regrow. In fact, often, killing the original plant will make the problem worse, and one plant will be replaced by many new plants shooting out from different roots, underground.
And, I am very sad to say that it has frequently been my fault that I have so many "terrible weeds" because many of them are garden escapes.
I didn't always have a rainforest garden. When we first moved here my thought was to have a garden of pretty flowers and trees near the house, plant fruit trees on parts of the slope, and have rainforest on the flat area on the other side of the creek.
But our garden was hot and dry and there were some spots where it was difficult to "get anything to grow", so in those places I put things that grew easily. I planted Monstera on the steep slope at the back of the house, and honeysuckle (Lonicera japonica) on the far corner of the front fence, sword fern (Nephrolepis) on the bank that fronted the road, Philodendron and Syngonium on the slope near the mango trees, Pilea and polka dot plant (Hypoestes) down near the creek, firespike (Odontonema) on the slope at the back of the house. In addition, when I dug up weeds from one area I was often careless about where I put the remains. After all there were remote parts of our yard where hardly anyone went. It didn't matter if things went wild there, did it? Yes it did! In this way, Oxalis was transferred to new spots in the garden, and sweet potatoes, and we now have several escapees from what was formerly our compost heap.
So my New Years resolution this year was to finally pull out, poison, get rid of and generally kill off all of the remaining garden escapes.
My current target is the sword fern (Nephrolepis cordifolia). This rampant weed had spread to completely cover an area about 15 by 20 metres, in soil that we had moved to a sunny slope facing the road. It has little round, water-storing tubers strung along its roots that are able to grow new plants. These can remain viable for many years and resuscitate the plant long after the original shoots are dead.
At first I tried digging it up and smashing the tubers. This worked, but it was very slow. So then I poisoned it with glyphosate (not recommended, but all that I had to hand) and managed to kill all of the parent plants.
But new little plants keep growing from the tubers, many of which have remained alive after poisoning, and I have realized that I may have to re-poison many times to get rid of them all. So now I have reverted to my original technique of digging them up, removing as much of the root and as many tubers as possible, and dumping the lot into a tub of water to be left to rot.
Will this work? Time will tell. At least I feel more hopeful than I did years ago when surveying the original patch of prolific growth.
And there are a hundreds of baby rainforest tree seedlings growing amongst the remaining fern shoots. That must be cause for hope! I will let them develop under the light canopy of rainforest trees and eucalypts that now gives overhead protection to the area.
And when the sword ferns are finally gone I will plant native ferns to form an understorey. One thing about growing plants that are native to your local area - you never have to worry that they might naturalise and become a weed. That is precisely what is intended!