One of the greatest threats to our native ecosystem and domestic gardens is the arrival of pervasive and invasive species. Anyone who has taken a walk along local riverbanks, which are frequently clothed in Himalayan balsam, can see how these can become a real pest. Himalayan balsam, or Impatiens gladulifera, is a relation of the popular summer bedding plant, busy lizzie. This has colonised huge tracts of river banks, suffocating native plants which our native wildlife depends on for food and nesting. The summertime is when it is most difficult to get in amongst garden plants to weed and sneaky species can get a foothold, so autumn, when you are clearing and cutting back is a good time to look for evidence of unwanted species and dig them out before they become a problem. There are a three categories of invasive plants; the first are the common weeds we all know and battle against year in year out like dandelion, daisy and buttercups. The second category are garden plants like Japanese anemones and Echium that have self-seeded to such an extent that they have become a nuisance, but cause no real damage. The third category are species which were introduced by horticulturalists as curiosities but quickly naturalized and spread throughout the countryside. The latter category causes real ecological and structural damage by escaping from our gardens and into the countryside beyond. A classic example of such a pest is Horsetail or Equisetum arvense. This plant has creeping rhizomes which can go down 2m below the surface, making them almost impossible to eradicate by digging. Even when using a pesticide persistent applications are necessary, you may need to call in specialist help. Japanese Knotweed, or Himalayan Balsam, was introduced from Japan in the nineteenth century and since its introduction it has spread nationwide. It can destroy the foundations of houses as it can grow through concrete and tarmac. It also blocks wildlife corridors and clogs up watercourses.
Removal and control of invasive species causes millions of euro a year. Other pests include Bamboos – Philostachys species which form impenetrable thickets, block out native plants and spreads rapidly, again popping up through hard surfaces with ease.
Obviously the best way to fight invasive species is not to plant them in the first place so here are some tips to keep these thugs out:
- Check a plants habit before you buy it and see if there is a non-invasive alternative.
- If you have been walking along river banks or areas where invasive non-native species have colonized always wash the soles of your shoes thoroughly before wearing them in your garden. Seeds are commonly brought in on the soles of boots or on animal’s coats.
- Never add any part of an invasive plant to the compost heap.
- Invasive aquatic plants have caused considerable problems to our waterways and it is important to stop their spread. Avoid swapping cuttings or fragments from friend’s ponds. Otherwise you may end up with an invasive species in your pond.
- Wash the roots of plants you buy too – I have a dreadful duck weed problem in my pond which came in on a plant bought from a very reputable garden centre.
- Learn to recognise seedlings of invasive plants. Dig out seedlings as soon as you see them in spring and before they establish.
- When weeding out mature plants make sure to remove all of the roots. Plants with tap roots like dandelion species will generate from every little bit of root left in the soil.
- Rhizomatous weeds such as couch grass, bindweed and ground elder respond well to glyphosate if treated twice over a two-week period. It is very important to avoid drift so apply on a very still day. To treat bindweed, spray the weed killer onto rubber gloves and run your hands along the plant.
- To eradicate ivy on trees and old walls cut it back to the ground and dig out the woody stump.