Q How do weeds get into my lawn?

A Weed seeds can be blown in, brought in with unsterilised lawn dressings or dropped by birds. Alternatively, small pieces of creeping stem that root on contact with the soil can be introduced on tools, turf or by birds. Seeds from weeds such as clovers and speedwells are spread by mowing.

Caption: Spot weedkillers can be used to target individual weeds

Q Do I have to control lawn weeds?

A In any lawn, weeds will compete with the grass for moisture and nutrients. Fine lawns are spoiled by the presence of weeds, which create a patchy effect. But in a utility lawn, a scattering of weeds is usually acceptable.

Q Do weeds benefit lawns in any way?

A A few weeds, such as clovers, can fix nitrogen from the air in nodules on their roots and stimulate grass growth. However, many weeds are more vigorous and drought-resistant than the grass and gradually take over.

Q Can regular mowing help to reduce weed growth?

A In a fine lawn, close mowing thickens up the sward, leaving no room for weeds to develop. In a utility lawn, regular mowing will weaken coarser weeds.

Mow three times every fortnight while the grass is growing vigorously. Avoid mowing too short, as this weakens the grass and encourages very low-growing weeds, such as parsley piert (Aphanes arvensis), pearlwort (Sagina procumbens) and mosses, to take hold. Daisies also thrive in closely mown grass.

Q How else can I discourage weeds in my lawn?

A Lawns that are vigorous and well-maintained leave fewer spaces for weeds to germinate or take root. Feeding, aerating and scarifying all encourage grass growth by providing nutrients, improving drainage and allowing more oxygen to the roots.

Q Is the pH of the soil important?

A A neutral soil (pH7) is ideal, as this favours the growth of lawn grasses. Most weeds prefer an alkaline soil. To deter weeds, use acidifying fertilisers, such as sulphate of ammonia, or moss killers with sulphate of iron.

Acid soils tend to encourage weeds such as mosses, sorrel (Rumex spp) and field woodrush (Luzula campestris). If these are a problem, test your soil pH and add lime in winter if necessary.

Q How can I tackle lawn weeds without using chemicals?

A Individual weeds, particularly rosette-forming types, can be removed one-by-one.

Use a daisy grubber or hand fork to take out fibrous-rooted weeds, such as daisies or plantains. For plants with a long tap-root, such as dandelions, use Fiskars Weed Puller, or an old knife, to cut out a plug of soil with as much root as possible. Rake over creeping weeds before mowing. This lifts the stems so that the mower cuts through them, gradually weakening the plants.

Where weeds occur in patches, whole sections of turf can be cut out, together with as many weed roots as possible. Then, after restoring the soil level, the area can be reseeded or returfed.

Q If I need to use chemicals, what types are available?

A There are many different types of treatment available that combine weedkillers, fertilisers and moss killers in various ways. There are ready-to-use trigger sprays, spot weeders, lawn weedkillers, lawn weed and feeds, and lawn weed, feed and moss killers. These come in soluble powders, liquid and granular formulations.

Q What should I use on my lawn and how is it applied?

A The type of chemical treatment you use and the way you apply it safely varies with the size of your lawn.

• A ready-to-use trigger spray is an easy way to treat lawns not badly infested with weeds.
• For medium-sized patches of weeds, or the whole of a small lawn (up to 150 sq m), go for a soluble powder or liquid concentrate. To apply, use a watering can with a coarse rose or dribble bar. Watering cans are unlikely to cause spray drift that could damage nearby plants. Do not use a sprayer. Once a watering can has been used for weedkillers, it shouldn’t be used for any other purpose, as weedkiller residues can be disastrous to other plants, even in tiny amounts.
• For large lawns (more than 150 sq m), a granular product is much quicker to apply, either by hand (wearing gloves) or using a fertiliser spreader. Water well if it hasn’t rained within 48 hours after application.

Q How do I get even coverage?

A This can be tricky. Underdose, and you waste the expensive chemical; add too much and the grass can be scorched. The easiest way is to divide the lawn into metre-wide strips using canes and string. Measure out the dose for each strip and spread as evenly as you can. Ideally spread half the dose in one direction, then mark out the strips again at right angles and apply the second half.

Q Do different weeds need different treatment?

A Lawn weeds vary in their susceptibility to different weedkillers. Some weeds may be controlled by a single application and others may need two or three doses. Many lawn weedkillers consist of a combination of two or more ingredients to allow for this varying susceptibility.

Caption: Weed and feed treatments give the turf a boost as well as killing the weeds

Q What about resistant weeds?

A Some weeds, such as helxine or mind-your-own-business (Soleirolia soleirolii), seem virtually immune to weedkillers. If these become a problem, you may have to use a total weedkiller containing glyphosate. This also kills the grass, so you will need to reseed or returf.

Q When is the best time to apply weedkillers to my lawn?

A Weedkillers work best when the weeds are in active growth. This means that good results should be achieved from April to September. Avoid periods of drought as the results will be poor and the grass may be scorched.

Q What if I decide to use separate weedkiller and fertiliser products on my lawn?

A Feed the lawn two to three weeks before using a weedkiller, so that both the lawn grasses and the weeds will be growing strongly. Lawn weedkillers work best on strongly growing weeds, and lawn grasses can colonise bare patches left by dead weeds more quickly if they are growing vigorously.

Q Can I use lawn weedkillers on a new lawn?

A Lawns grown from seed should not be treated with weedkiller for at least six months. New turf can be treated once it is growing strongly, which will depend on the time of year and local conditions.

Weeds occurring in new lawns are likely to be annual weeds, provided the site was cleared thoroughly of perennial weeds before seeding or turfing. Annual weeds usually die out once regular mowing is underway.

Q Will treated mowings harm other plants?

A Potentially, yes; although lawn weedkillers break down fairly quickly. Avoid putting clippings from the first two cuts on the compost heap and don’t use them as mulch. Leave them where they fall or bin them.

Q How do I deal with coarse grasses?

A Regular mowing, and removing the clippings, will limit their spread. Yorkshire fog, the coarse pale grass frequently found in lawns, can be discouraged by slashing the turf with an old knife. Make cuts about 2.5cm apart. Repeat this on a regular basis. Where it's widespread, reduce it by raking before mowing. This helps it to blend into other, more acceptable grasses. If all else fails, spray the worst patches with a glyphosate weedkiller and reseed.