Plant Doctor Archive

Pesky weeds

WHAT will eradicate sheep's sorrel from among bearded irises?

SHEEP'S sorrel (Rumex acetosella) is closely related to the common broadleaved dock (Rumex obtusifolius) but it has quite a different growth habit. Where broad-leaved dock has a deep tap root and large leaves, sheep's sorrel is shallow-rooted with small leaves, but it's almost as pernicious with creeping stems that enable it to spread through mulch and among desirable plants.

Hand weeding is one approach to take, removing as much of the plant and creeping stems as you can, but among plants like bearded irises it would be almost impossible to remove it completely and regrowth would soon appear.

There are several weedkillers available that may be suitable, but my recommendation is to use a glyphosate-based one, such as Roundup, Glyphosate and Zero, as the chance of any soil residue which could affect your irises is extremely low. You'd need to make sure not to get any spray on the irises, so my advice is to dilute the product according to the label recommendations then wipe it on to as much of the weed foliage as you can with a piece of sponge - make sure you wear rubber gloves. Or use a Zero Weeding Brush which you can buy in garden centres. It takes a few weeks to work and you may have to treat some regrowth, but if you keep it up you should eventually be able to eradicate the problem.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.