Question: Can you advise on the best way to get rid of ground elder? It has grown into my herbaceous border from next door and my garden is open for charity on June 23.
Answer: Ground elder is not deep rooted, but is incredibly good at creating mats of roots that infiltrate those of favourite plants. The best way to control it is to apply a glyphosate-based weed killer such as Roundup, with the sprayer set on delivering large droplets to limit drift onto foliage of plants you need to keep alive.
There is a roll on gel made by Roundup which makes it easy to target the leaves of the offending weed. The chemical is taken down to the roots of the weed to help prevent its return.
Since the weeds are coming from next door, consider installing a root barrier which is a strong, flexible fabric that you bury vertically into the soil. The following company supplies these: www.green-tech.co.uk/. There will be enough time for the chemical to work before the garden opens.
Send your questions for the RHS to: firstname.lastname@example.org.
Only a few questions per month can be answered. For further advice on handling problems in your garden, visit www.rhs.org.uk/advice/index.asp.