How to Kill Weeds on Patios

Weeds growing between patio slabs are one of the most common garden weed problems. Those cracks and joints that looked pristine when your patio was first laid gradually fill with greenery, making the whole area look neglected and unkempt.

The problem goes beyond appearances. Left unchecked, weed roots can work their way under paving slabs, lifting them and creating uneven surfaces that become trip hazards. Removing established weeds becomes harder as their root systems spread, and the longer you leave them, the more damage they cause.

Why Weeds Grow in Patio Cracks

Weeds don’t actually grow up through your patio from below. The seeds are carried by wind and land in the gaps between slabs, where they find ideal conditions for germination. These cracks are damp, sheltered, and accumulate organic debris that provides nutrients for seedlings.

Over time, the original sand or mortar between your slabs breaks down, creating deeper pockets of soil where weed roots can establish. Once a weed gets its roots into these gaps, it becomes remarkably difficult to remove completely.

Common patio weeds include annual meadow grass, dandelions, bittercress, and chickweed. You may also find creeping weeds like speedwell and mind-your-own-business spreading from adjacent lawns or borders into patio joints. The same weeds cause problems on block paving and gravel driveways.

Manual Removal Methods

For small infestations, removing weeds by hand is effective and satisfying. The key is extracting the entire root, not just snapping off the visible growth.

A patio knife or weeding knife is the ideal tool. These have thin, hooked blades designed to slide into narrow gaps and lever out roots. Push the blade down alongside the weed, hook it under the root, and pull upwards. A billhook works well for larger weeds with tougher roots.

If you don’t have specialist tools, an old kitchen knife does the job. Dampen the patio first to soften the soil in the joints, making extraction easier. Work the knife blade around the weed from multiple angles before attempting to pull it out.

After removing weeds manually, sweep the gaps clean of loose soil and debris. This removes any weed seeds waiting to germinate and prepares the joints for filling with sand or jointing compound.

Using Weedkiller on Patios

For larger areas or persistent weeds, a systemic weedkiller provides the most effective solution. Unlike contact weedkillers that only burn the leaves, systemic products are absorbed by the foliage and transported throughout the plant, killing the roots as well. For stubborn perennial weeds, the strongest weed killer available gives the best results.

Apply weedkiller when weeds are actively growing, typically between April and October. The leaves need to be dry and no rain should be forecast for at least six hours after application. Spray directly onto the weed foliage, avoiding any plants you want to keep.

Results appear within one to two weeks. The weeds yellow, wilt, and die back completely. Once dead, remove the brown remains with a stiff brush or scrape them out with a patio knife. Leaving dead weeds in place creates organic matter that helps the next generation establish.

For patios surrounded by planted borders, take care to avoid spray drift onto ornamental plants. A concentrated weedkiller applied with a targeted spray nozzle gives better control than ready-to-use trigger sprays in these situations.

Boiling Water and Natural Alternatives

Pouring boiling water directly onto patio weeds kills the foliage and can damage shallow roots. It’s free, chemical-free, and works instantly on small annual weeds.

The limitation is that boiling water doesn’t penetrate deep enough to kill established perennial weeds with extensive root systems. These will regrow within a few weeks. For boiling water to be effective as an ongoing control method, you need to repeat the treatment every fortnight throughout the growing season.

Vinegar and salt solutions are sometimes recommended as natural weedkillers. While these can kill weed foliage, they work as contact herbicides only and don’t affect roots. Salt can also damage paving materials and harm soil structure if it washes into adjacent beds.

Preventing Weeds From Returning

Once you’ve cleared your patio of weeds, preventing their return saves significant effort. The most effective long-term solution is filling the joints with a weed-resistant material.

Polymeric jointing sand is a specially formulated product that hardens when wet, creating a solid barrier between slabs. Sweep it into the cleaned joints, compact it with a vibrating plate or by walking over it, then spray with water to activate the binding agents. Once set, it prevents weed seeds from germinating while still allowing water to drain.

Resin-based jointing compounds offer even stronger weed resistance. Products like Joint-It create a flexible, weather-resistant seal that stops weeds for years rather than months. They’re more expensive than sand but require less frequent reapplication.

Regular sweeping removes organic debris and weed seeds before they can establish. A quick brush over your patio every couple of weeks during the growing season takes minutes but prevents hours of weeding later.

Pressure Washing

A pressure washer can blast weeds out of patio joints, but use it with caution. Too much pressure or lingering too long in one spot can dislodge slabs, erode jointing material, and damage the paving surface itself.

Use a medium pressure setting and keep the nozzle moving. Work systematically across the patio rather than focusing on individual weeds. Pressure washing is best used as part of an annual deep clean rather than regular weed control.

After pressure washing, always re-fill the joints with sand or jointing compound. The high-pressure water will have removed much of the existing material, leaving gaps ready for weed seeds to colonise.

Frequently Asked Questions

What is the best weedkiller for patios?

A systemic glyphosate-based weedkiller kills weeds to the root and prevents regrowth for several months. Apply to actively growing weeds in dry conditions for best results.

Will bleach kill patio weeds?

Bleach can kill weed foliage but doesn’t affect roots, so weeds regrow quickly. It can also discolour paving and harm nearby plants, making it a poor choice compared to proper weedkillers.

How do I stop weeds growing between slabs permanently?

Fill joints with polymeric sand or resin-based jointing compound after removing existing weeds. These create barriers that prevent seed germination for years.

Does salt kill patio weeds?

Salt kills foliage but not roots, and repeated use damages paving materials and soil structure. It’s not recommended for patio weed control.

How often should I treat my patio for weeds?

With proper jointing compound, annual treatment should suffice. Without it, you may need to weed or apply weedkiller every few months during the growing season.

Fed up with weeds spoiling your patio every summer? A professional-strength systemic weedkiller clears the problem in days and keeps your paving weed-free for months. For more tips on hard surface weed control, see our guide to killing weeds on driveways.