First, consider whether this can be done using non-chemical means such as digging out or suppressing with lime. Where these methods are not feasible, chemical controls may need to be used.

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Cultural control

Sheep’s sorrel is difficult to eradicate by cultural methods alone as it can regrow from sections of root left in the soil. It is more vulnerable to hoeing in spring.

• Liming: Lime borders to pH 6.5-7 unless ericaceous plants are grown. Mulch with spent mushroom compost which is alkaline and would act in a similar way to liming
• Top-dressing lawns with lime to raise soil pH to 6.0-6.5 will reduce the vigour of the weed as it prefers acid soils. Apply lime as suggested by a test kit or soil analysis
• Top-dressing lawns with calcium nitrate at 35-70g per sq m (1-2 oz per sq yd) will raise the pH quicker than lime and feed the lawn
• Avoid using ammonia and urea fertilisers if sorrel is present as these acidify the soil

Weedkiller control

In borders

• Apply glyphosate as a spot treatment to individual plants or spray areas that have been cleared of cultivated plants
• Glyphosate is a non-selective weedkiller applied to the foliage, where it is translocated throughout the weed. Tougher formulations are worth trying (e.g. Roundup Ultra or Rootblast Super Strength Weedkiller)
• Being non-selective, it is essential to avoid spray drift onto neighbouring plants. It is important to have good leaf coverage so that as much chemical is absorbed as possible
• Sprays are most effective if applied from early June to mid-August
• As this weed is so persistent several applications may be necessary

In lawns

• Sorrel can usually be eradicated in lawns by one or two applications of lawn weedkiller containing 2,4-D plus mecoprop-P ( Vitax All in One Lawn Feed, Weed & Mosskiller or Westland Aftercut All-in-One Feed, Weed & Moss killer (also contains fertiliser and moss killer)). See more on selecting lawn weedkillers
• Apply when both turf and weeds are growing strongly with a second application four or five weeks later

In rough grassland

• Apply a selective weedkiller which contains triclopyr (SBK Brushwood Killer) as this would leave the grass unharmed
• This herbicide is systemic, travelling from the weed foliage down into the root system
• However as it is non-selective any broad-leaved plants will be damaged (e.g. wildflowers) and so should only be used in grass where such action is acceptable

Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.

Download

Weedkillers for gardeners  (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see sections 1a, b, d and 4)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale
Weeds: non-chemical control