- Fork the shallow, creeping roots out one at a time, as every small piece left behind can grow back into a new plant.
- Cut or pull the reddish flower spikes each summer before they ripen, and the wind has nothing to carry into the rest of the lawn.
- Test the soil before you buy a single bag of lime, as lime only helps a lawn that really is acid.
Why Pulling Those Little Red Spikes Never Seems to End
You pull one out, and a week later three more are standing in the same patch. That is how sheep’s sorrel behaves, and it is not your technique. The plant runs shallow roots sideways through the soil and sends up new shoots along their length. A small section of root is enough to restart it. The roots are fragile, so a hard tug leaves part of the root in the ground, and that part carries on.
Here is the short fix. Use a hand fork, not a hoe, on established plants. Lift each creeping root and follow it along to get as much out as you can. Bin it, do not compost it. Seed the bare gap. Then watch the spot and repeat for as long as new shoots show. Weedkiller is not needed. Non-chemical methods work, though they take patience.
The longer game is the soil and the thin grass. Sorrel moves into lawns where grass growth is patchy and the ground is acid. Fix the gaps and test the soil, and the weed has far less to work with.
How to Tell It Is Sheep’s Sorrel
Look at the leaves first. Each one is a green arrow, with two pointed wings at the base where the stalk meets the blade. The leaves grow from a low rosette, and the plant forms a tuft.
From late spring to late summer, slender upright stems rise with loose clusters of flowers that run from green to reddish. Those turn into rusty brown fruits, which is the colour that catches your eye across a thin patch of lawn. Left alone, the plant reaches 30 cm (1 ft) tall. It looks like common sorrel, but it is the smaller of the two.
Two facts explain why it keeps winning. First, it spreads in two ways: by those creeping roots and by seed. A plant allowed to flower makes large amounts of seed, many of which drop beside the parent while some travel on the wind. Second, it is a plant of acid ground, so a lawn on acid soil with sparse grass is its ideal home.
It is also worth knowing that the weed is not a villain. Over 50 species of insect feed on it, and ground-feeding birds such as chaffinches and thrushes eat the seeds. It suits wildflower meadows on dry, sandy or acidic soil. If you have a corner of the lawn you are happy to let go wild, you can leave it there. In a lawn you want smooth and green, the choice is yours, and the methods below put you in control of how much of it you keep.
Fork It Out Without Leaving Roots Behind
Use a hand fork and work slowly.
Push the fork in beside the rosette, not through the middle of it. Lever gently and find the root. It is shallow and fragile, so follow it along the surface and lift as you go. Each section you pull is a section that cannot restart.
Dispose of everything safely. A home compost heap can stay too cool to kill roots or seedheads, so pieces survive and spread. Put the roots and seedheads in your council green waste bin or take them to the recycling site.
Then fill the hole. The weed-control advice is to re-seed the bare patch, and spring or autumn are the right times to sow or lay turf. If autumn has passed where you live, wait for spring. An empty gap in a thin lawn is an open invitation, as lawn weeds are quick to colonise bare ground where the grass is patchy. Grass seed in the gap gives the lawn a head start. For the full method of closing those gaps, repairing bare patches shows each step.
Watch the spot. Regrowth means a root piece was left, so repeat the fork-out as often as it takes.
For small seedlings in early spring, a hoe does the job. Pick a warm, dry or windy day so the sliced roots dry out fast. Hoeing keeps soil disturbance low, which protects the soil underneath.
Test the Soil Before You Lime
Lime is the part of this story people hear about first, and it is the easiest to get wrong. Sheep’s sorrel favours acid soil, so raising the pH does discourage it and helps limit its spread. But lime only works on ground that is actually acid. Spread it blind and you gain nothing.
So test. A soil pH kit is easy to use and sold at garden centres and online. Our own walk-through, testing soil pH at home, takes you through reading the result. Two warnings apply here. A test done within three months of adding lime, fertiliser or organic matter can give a misleading result, so test before you add anything. And if the result comes back at pH 7.0 or higher, the soil is alkaline and liming is not necessary. The best all-round pH for most garden plants is 6.5, and that is the target.
If the test shows the soil is acid, the dose depends on the soil type. Clay resists changes in pH, which is called buffering capacity, so clay needs far more lime than coarse sandy soil. The figures below are for finely ground garden lime worked into the top 20 cm (8 in) of soil to bring it up to pH 6.5.
On loam, soil at pH 6.0 needs 0.5 kg per sq m (14¾ oz per sq yd), pH 5.5 needs 0.8 kg (23½ oz), pH 5.0 needs 1.2 kg (35¼ oz) and pH 4.5 needs 1.5 kg (44¼ oz). On sandy soil the amounts drop to 0.4 kg (11¾ oz) at pH 6.0, 0.7 kg (20½ oz) at pH 5.5, 1.0 kg (29½ oz) at pH 5.0 and 1.3 kg (38¼ oz) at pH 4.5. On clay they rise to 0.6 kg (17¾ oz) at pH 6.0, 1 kg (29½ oz) at pH 5.5, 1.4 kg (41¼ oz) at pH 5.0 and 1.8 kg (53 oz) at pH 4.5.
Now the honest catch for a lawn. Those figures assume lime mixed into soil. The lime advice from the RHS says lime applied to the surface around established plants can take years to have any effect, which is why it recommends adjusting pH before planting or sowing. A standing lawn is exactly that situation, and the page gives no separate rate for it. So use the table where you can dig lime into bare ground, such as a patch you are renovating or a lawn you are sowing from scratch. On grass that stays in place, follow the rate printed on the bag, expect a slow change and test again after a few seasons. Winter is the usual time to lime.
Choose finely ground limestone, sold as garden lime, which is the recommended material and spreads easily. Avoid any product with lumps, which take years to have any effect. Hydrated lime, sold to builders, works faster and has a higher neutralising value (70, against 50 to 55 for ground limestone), but it can irritate skin and eyes, so wear gloves and goggles if you handle it.
Feed and Mow So It Cannot Come Back
Check the fertiliser first. Acidifying nitrogen feeds such as sulphate of ammonia lower soil pH and create ideal conditions for sheep’s sorrel. If you are feeding anything near the lawn edge or borders, choose poultry manure pellets, which do not lower the pH.
Then look at the mowing. Cut the lawn very short, especially in summer, and the grass weakens, leaving bare patches for weeds to settle in. Raise the blades. Our piece on cutting height before winter explains how to set it.
Keep the flowers from setting seed. Regular mowing deadheads low-growing lawn weeds, and any plant you have not yet pulled can be removed before it flowers, which stops the seed that would otherwise spread through the lawn.
Keep the grass healthy. A programme of spring, summer and autumn lawn care encourages dense growth, which makes it harder for weeds to establish and spread.
When to Stop Fighting It
A few plants in a thin patch of lawn are not a crisis. If one stubborn corner keeps returning after repeated forking, reseeding and a soil test, ask whether the corner is worth the effort. Acid, sandy, dry ground is where this plant belongs, and it supports wildlife there. You can let that part of the lawn go and keep a tidy cut around it, or leave it as a small meadow.
For the rest of the lawn, the routine is short. Fork out roots when you see shoots, bin them, reseed the gap, cut seedheads before they ripen, keep the blades high and test before you lime. Do those and the weed has nowhere to take hold.
