The aliens have landed

Summers by the river brings many fabulous things, but also some unwanted floral visitors. There are several alien invasive species that we have to battle. They were brought to this country for their decorative properties and have been causing havoc almost ever since.

Floating Pennywort is a water plant that you could buy from British garden centres until depressingly recently to cheer up your garden ponds. It has now made the move to wild watercourses and made itself very much at home, and is taking over. The problem is it likes it too much. Just one small sprig or even leaf can soon proliferate into a huge dense mat that shades and smothers everything else.

Pennywort Newark

Another of our alien invaders is Himalayan Balsam. It was brought over from the Americas in the 1830s and was much prized for its beautiful pink flowers. The problem is that the explosive seed pods, when ripe, can catapult 1500 seeds over 7 metres. As you can imagine, the odd plant soon becomes a dense, rapidly expanding patch and it can colonise areas downstream of the original plant very quickly. A single plant can grow over 2 metres high and once they have taken hold, all native vegetation is shaded out and over-run.


While that might all seem like doom and gloom, and the presence of both can be a serious problem, the solutions are happily low-tech and chemical-free.

If you get to it early enough, Floating Pennywort can be removed with wellies and a 3 pronged cultivator. The trick (as I’ve found through a great deal of trial and error) is to get a good hold on the raft of weed and pull gently. If you are too vigorous or  impatient you will invariably find you separate a small portion from the main raft and spread the problem. If you loosen things enough, some will float away and start a new colony somewhere else. If you take it slowly however, you are usually able to coax the whole raft to the bank. Rather than transport it, and potentially cause a whole new problem somewhere else, it is best to let it sit out on the bank in the sun where it soon dries out and dies quietly in a corner.

With Himalayan Balsam the best tool is person-power … as much of it as you can muster, cajole or bribe into service. I was lucky enough this week to have a dozen or so volunteers to help me clear a couple of sizeable patches for the price of an ice lolly and a beer. In my book that is fantastic value for money, if I was on my own I’d still be there now! It is a very fleshy plant that spends all its energy creating height (and the best chance to distribute its seeds), not roots. That means that individual or small groups of plants are fairly easy to pull up, roots and all, there are just soooo many of them. Again a day or two in the sun sees them wither into a mass of innocuous dry leaves. The seeds only remain viable for a couple of years usually, so a couple of brave seasons of Balsam bashing can see pretty good results.

Even if you think you have ‘won’, I’m afraid that vigilance is the key with both of these and complacency is not an option. The fight goes on.