In short
Weeds come back through a patio because seed blows in constantly and roots in the sand and grit between the slabs, and because pulling the top off leaves the root to regrow. Cutting the roots out with a weeding knife, brushing the joints clean and re-sanding or re-pointing them is what keeps a patio clear for longer.
This is a job for my Weeding service.
Published · Last updated
Where the weeds come from
The RHS describes weeds on hard surfaces as the same ones you find in grassland and waste ground, blown in as seed. Around Wisbech we are surrounded by open arable land, so there is no shortage of seed on the wind. It lands in the joints, where there is sand, a bit of moss and enough damp to germinate. The plants stay small because the root run is shallow and they get trodden on, but the RHS notes many still flower and set seed, which is why the problem feeds itself.
Why they come straight back
Two reasons. First, pulling the green top off a dandelion, plantain or willowherb leaves the taproot in the joint and it regrows within weeks. Second, if the sand or mortar between the slabs has washed out, every joint is an open seedbed. I see this most on older block paving and on patios where the pointing has gone, and on gravel paths laid without a membrane.
It is also a safety issue, not just a tidiness one. The RHS points out that weeds in areas of foot traffic make the ground uneven and slippery when wet, which matters for the older customers I look after.
What works
- Cut the root, not the leaf. The RHS recommends running a block paving knife or weeding knife along the joints to sever the roots, and a dandelion weeder or weed puller for the deep-rooted ones. This is how I clear a patio: slower than spraying, but the weeds do not simply reappear.
- Brush the joints out. A paving brush with angled wire bristles scrubs out the moss, seedlings and debris the next weeds would root into.
- Refill the joints. Kiln-dried sand for block paving, or fresh pointing for slabs. A full joint is a poor seedbed.
- Gravel: lift and re-lay on a membrane. For a small gravelled area with persistent perennial weeds, the RHS advice is to remove the stones, lay a heavy-grade biodegradable membrane and put them back. It smothers what is underneath.
- Keep on top of it. A quick pass every few visits stops seedlings ever getting a root down.
What about weedkiller?
The RHS does not support the use of weedkillers and recommends the methods above instead. That is my approach too: I favour root-level removal that is kinder to the plants in the beds either side and to local wildlife. If a customer specifically wants a path treated I will talk it through first, but on a patio the knife and brush do a better job than the spray in my experience, because they deal with the joint as well as the weed.
I clear patios, paths and drives as part of my weeding work across Wisbech, March, Downham Market and King's Lynn, as a one-off or on a regular visit.