What is speedwell?
Slender speedwell (Veronica filiformis) was introduced to Britain from Turkey and the Caucasus during the early 19th century. It was much grown as a rock plant until gardeners realised how invasive it could be. It is now widely naturalised in many parts of the country and is a common and troublesome lawn weed.
Slender speedwell (Veronica filiformis) is a low-growing plant with bright blue, long-stemmed flowers early in the year, usually March to May. It is low-growing and can form dense patches in a lawn.
Germander speedwell (Veronica chamaedrys) is a stronger growing, coarser species than V. filiformis, flowering March to August. It is native in grassland, open woodland and hedgerows throughout the British Isles. It is usually troublesome in less frequently mown grass but can adapt to, and survive under, close mowing.
Why is speedwell a problem?
Speedwells are perennial plants, producing numerous, slender-branched stems, creeping and rooting at the nodes as they spread to form a dense weed carpet.
The flowers are rarely followed by seeds as the plants are self-sterile and most appear to be from the same clone.
The commonest methods of spread include:
- Stem sections scattered by the mower
- Lawn clippings put on the compost heap, which spread the weed around the garden if the compost is spread before it is completely decomposed
- Nesting birds can spread speedwell while gathering moss from the lawn to line their nests
- Weak grass growth allows the weed to spread
Even when lawn clippings are raked up and disposed of, or the lawn is raked thoroughly to remove moss and weeds, numerous small rooted sections of the weed usually remain.
Speedwell is less likely to be a problem in healthy lawns. Boost grass growth to discourage the spread of the weed by feeding with spring and summer lawn feeds. In autumn, scarify, aerate and top-dress as necessary.
Though the lawn should be mown regularly, do not cut it too close, as slightly longer grass will help smother the weed.
Ensure that compost containing lawn clippings contaminated with speedwell is thoroughly broken down before use.
Speedwells are resistant to the majority of lawn weedkillers available to amateur gardeners. However, products containing the active ingredient fluroxypyr as one of their ingredients will provide some control in lawns. It is best to seek the advice of a professional to help to deal with speedwell. More than one application of weedkiller is likely needed.
Speedwell in new lawns
Weedkillers often cause severe damage if applied to lawns within six months of sowing or turf-laying. Materials containing fluroxypyr as one of their ingredients, however, are claimed to be safe to use after only two months.