Killing weeds in autumn

Tim Rumball explains which weedkillers are the best and how use them safely

- Tim Rumball

I CAN’T see the point of using a weedkiller to tackle annual weeds, unless you have a huge infestation. It’s almost as easy to pull them out or to hoe them as it is to spray, and they make great compost or will feed the soil like a green manure once well hoed or dug in (do it before they set seed).

Perennial weeds are different. Deeprooted invasive species like convolvulus, dandelions and couch grass, and lawn weeds like clover, can be nightmarish once they gain a foothold. Digging them out is often not an option when they’re in an established flowerbed or lawn, but there are products that will kill them without damage to surrounding plants when used correctly – and autumn is a great time to treat them.

Autumn is a good time because most perennial plants, including weeds, are drawing goodness from their foliage back down into the roots to overwinter safely. If you can get weedkiller into their systems at this point it will be much more effective in killing them.

Preparation and care

If you are killing weeds in an area that does not contain plants you want to keep – for instance, when you’re making a new flowerbed or clearing space for a veg plot – then spray all green leaves with a weedkiller containing glyphosate. This chemical only works when in contact with green (living) parts of a plant, so spray before the weeds die back for winter.

Choose a dry period (it shouldn’t rain for at least eight hours after spraying) with no wind, and follow instructions for mixing on the label, though ready-to-use spray packs are available. Wear a protective facemask and gloves. Use a fine spray and wet weed leaves – don’t let spray drift! You should see signs of the weeds dying back within a week. After two weeks rake-off plant debris and bin or burn it. The ground should then be safe to cultivate and plant.

Suitable choices