Slender speedwell Veronica filiformis is a perennial weed, frequently found in closely mown turf throughout the UK.
It is also called creeping speedwell and threadstalk speedwell. Of all the speedwell weeds, including germander speedwell, slender is more common in fine turf.
It can be a major nuisance, as it is similar to yarrow and field woodrush, in that it is resistant to most weed killers, making control very difficult.
Slender speedwell spreads via stolons (overground runners) and rhizomes (underground runners) rooting at the nodes. It also spreads when mowing, as the cut stems can regenerate, if the lawn is mown without the grass box.
It can tolerate close mowing, it spreads aggressively and can quickly colonise large areas of the lawn.
The leaves of slender speedwell are small and kidney shaped with toothed edges.
Slender speedwell produces many blue/mauve flowers on thin stems, typically flowering between April and June. Under close inspection you will notice that one of the petals is smaller than the remaining three.
This weed will grow in almost any soil type, especially moist soils that are naturally fertile.
Remove any plants by hand, ideally as soon as they appear. Take care to remove the whole plant.
Remove grass clipping when mowing the lawn, as slender speedwell can regenerate from fragments of old stems.
Slender speedwell can be checked with lawn sand during the early spring, however this will not kill the weed, it will merely knock it back a little.
Mow on a regular basis to prevent seed head formation.
Raking the weed into an upright position, prior to mowing, will help remove part of the plant, again always box the clipping off with slender speedwell.
As we have already mentioned, controlling slender speedwell with chemicals will prove difficult, as the weed is resistant to most weed killing ingredients. More than on application will be needed for control.
If you attempt to tackle this weed with a selective weed killer choose a product that contains Fluroxypyr. There are several product available that contain this ingredient including Verdone Extra, which is a popular product with many gardeners. For more advice on getting the best from weed control check out are weed control page.
Slender speedwell images
Recommended herbicides for the control of slender speedwell
Professional products (All operators must be trained and certificated in using and applying any Ministry Approved professional product)
- ICL Praxys (Fluroxypyr, Clopyralid, Florasulam)
- Barclay Holster (Fluroxypyr, 2,4-D, Dicamaba)
- Headland Cabadex (Flurosulam, Fluroxypyr)
- Mascot Greenor (Fluroxpyr, Clopyralid, MCPA)
- Mascot Crossbar (Fluroxpyr, 2,4-D, Dicamaba)
Products available for non-professional use (These products are available from garden centres and DIY stores and do not require any training or certification for use and application.)
- Weedol Concentrate (Fluroxypyr, Clopyralid, MCPA)
Tips for successful weed control using selective herbicides
- Treat weeds when growth is strong, this is usually in May and June.
- Don’t mow the lawn 3 days prior and 3 days after the treatment, to allow for maximum uptake of the chemical.
- Spray when the leaf/foliage is dry, as this reduces runoff and allows the chemical to stick to the weed.