Non-chemical controls
Deep-rooted weeds such as dandelion and dock require the removal of their tap root. This can be tricky in crevices or cracks. Specially designed narrow-bladed weeding tools – sometimes called ‘dandelion weeders’ – for tackling such weeds are the most effective. More generally, a ‘block paving knife’ can be run along between pavers to sever most weeds. A wire-bristled ‘block paving brush’ is good at removing moss and the smaller weeds.
On loose gravel drives, hoeing on a dry day may be successful on shallow-rooted weeds.
Flame guns or flame weeders can work on hard surfaces, especially in warm dry weather. The localised heat ruptures the plant cells, causing it to die back. Two applications work best; the first applied to cause discoloration of foliage and, a week later, the second to burn the dead leaves. Control is best on annual weeds and young perennials. Gas canisters to power the gun can be bought at hardware stores.
Hot water weed control equipment for hard surface use is available to professionals. In a garden it is possible to use hot water from the kettle or left over from cooking vegetables, to achieve similar results. On lush growth, cut back the tops of the weeds first to expose the crown. Keep the spout very low to avoid splash. Wear heat-proof gloves to protect from steam and closed-toe shoes. As with the flame gun, persistent perennial weeds may regenerate, but should succumb to repeated treatments.
Chemical controls
Annual and young perennials weeds can be scorched off with a contact weedkiller such as diquat (Scotts Weedol 2), fatty acids (Bayer 3 Hour Weedkiller) or acetic acid (Scotts Weedol Fast Acting) or pelargonic acid (Doff 24/7 Superfast Weedkiller).
For more troublesome weeds a glyphosate-based weedkiller (e.g. William Sinclair Deep Root Ultra Path & Patio Weedkiller or Doff Path & Patio Weedkiller) is better suited. Treatment is most effective when the weeds are actively growing, usually between April and September. Some (Westland Resolva Path & Patio range and Scotts Weedol Rootkill range) are combined with a contact weedkiller to knock back the top growth quicker.
Weedkiller treatment should be directed as a narrow spray to treat only the weed infested cracks and not the whole paved area. Weeds growing around manhole covers and drains should be treated by other methods.
As drives, paths and patios are usually unplanted areas, a more long-lasting solution is to use a residual weedkiller combining glyphosate/flufenacet/metosulam (Bayer Ground Clear Weedkiller), or glyphosate/diflufenican (Scotts Pathclear range).
The use of bleach or salt to kill weed on paths and drives is strongly discouraged, as this can cause pollution and damage plants.
Download
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see section 3, 4 and 5)
Links
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale weedkillers
Weeds: non-chemical control