When is the best time of year to spray weeds?

By The Weed Guy·Last updated 2 September 2026

While they are actively growing, which in the UK runs from roughly late spring through to early autumn, and always on a dry day with no rain due for a few hours. A spray works by being drawn in through the leaves and carried down into the root, and that only happens when the plant is growing, so hitting a dormant winter weed mostly wastes the treatment.

The weeds that take hold in a drive, path or patio are tough perennials and grasses rooted down in the joints and sub-base, and the root is the part that has to die. A systemic weedkiller only reaches it when sap is moving, so the weed needs to be up, green and growing. That is why the window is the growing season, warm soil and active leaf growth, rather than a bare winter surface. Spring catches the weeds while they are young and taking up the treatment readily; early autumn is strong on established perennials, because as the plant pulls energy down to its roots for winter it carries the spray down with it. Spray outside that window and you are treating a plant that is barely drinking, so the root survives and the weeds are back.

The other half of the answer is the weather on the day. It needs to be dry, with no rain forecast for a few hours after, because rain landing too soon washes the spray off the leaves before the plant has taken it in, and that treatment is gone. Beating heat in a dry spell is no good either, as a stressed weed in a drought shuts down and takes up very little. A still, dry day in the growing season is the sweet spot, and if the forecast turns on you, wait. A day's delay costs nothing; spraying into rain costs the whole treatment.

Time of day matters more than most people think. Spray mid-morning, once the dew has dried off. Put it onto wet leaves and you are diluting the mix and watching half of it run off before it can get in, and a mid-morning pass also gives the leaf the longest dry stretch of the day to absorb it. Pick a still morning too: even a light breeze will drift a fine mist onto plants you want to keep.

Timing is also why one treatment a year rarely keeps a hard surface clear. Weeds do not all come up at once. Fresh seed blows into the joints and germinates in flushes right through the season, and a glyphosate-type weedkiller kills what is growing but leaves nothing in the ground to stop the next lot, so a surface cleared in spring will often show new green by mid-summer. If you want a drive that stays clear, think in rounds rather than one big hit: a pass in spring while the weeds are young, one in mid-summer for the fresh flush, and one in early autumn to catch the perennials as they draw down to the root. Each round is smaller than the last. One more thing worth knowing: most of the timing advice online is really about lawns, when to feed and when to use a selective weedkiller between the grass. For a driveway, path, patio or gravel the rule is simpler. A dry, still day between late spring and early autumn, on weeds that are green and growing. Hit that window and the root dies; miss it and you have watered the weeds with expensive weedkiller.