How can I get rid of this invader?
Q
We have a large garden of 795 square yards, and over the past 15 or so years we have slowly been overtaken by horsetail weeds. They now cover threequarters of the garden, including the vegetable plot, grass, greenhouse and plant borders. How can we get rid of it – we are too old to dog them all out! Valerie Flude (via email)
A
Bad luck! An infestation of horsetail (Equisetum arvense) can be difficult to eradicate. The easiest way to control it is to trample over it in late spring, when it’s at its peak, to crush its impermeable silica-rich stems.
You can then treat it with a systemic glyphosate-based weedkiller, such as Fast Action Roundup, which travels in the plant’s vascular system to kill cells en route. Pleasingly, the herbicide breaks down into a harmless substance in the soil.
The problem is that horsetail has a deeply questing root system which, when broken, regenerates to produce more shoots. It’s vital, therefore, to treat the regrowth the moment it appears.
With luck, you will eradicate the weed if you tackle it several times a year, from April to September.
Alternatively, you can cover strips of soil with a weed-proof membrane, generously overlapping it, and keeping it in place for at least a year. No light means no growth.