How do I stop weeds growing between paving slabs?

This is a maintenance problem disguised as a weed problem. Windblown soil, moss and organic debris accumulate in an open joint and make a perfect seedbed, and no amount of killing what has grown addresses the seedbed itself.

Safety

What you'll need

• Paving knife or joint scraper
• Stiff brush
• Bucket
• Jointing compound (optional)
• Weed burner (optional)

Step by step

1. Understand where they are rooting.In the debris in the joint, not in the sub-base. That is why they return so quickly and why refilling the joint is the answer.
2. Scrape the joints out mechanically.A paving knife, an old screwdriver or a proper joint scraper. Rake out weeds, moss and accumulated debris to a decent depth.
3. Use boiling water for a chemical-free kill.Poured slowly along the joint it kills annual weeds and moss outright. Repeat on regrowth. Keep it away from adjacent planting and away from anyone nearby.
4. Consider a weed burner for large areas.A gas weed burner wilts the foliage rather than burning it to ash, which is enough for annual weeds. Perennials need repeat treatment.
5. Dig out perennial roots.Dandelion, plantain and bindweed regrow from root fragments. Get the whole root out or they simply return.
6. Brush the whole area clean.Sweep the debris off rather than into the next joint. A blower or a stiff broom and a shovel.
7. Refill the joints properly.This is the step that makes it last. A resin jointing compound suitable for the joint width fills the gap completely, leaves no seedbed and resists weeds for years.
8. Use path weedkiller only as a stopgap.It clears what is there. It does nothing about the debris in the joint, so it becomes an annual job. Follow the label and keep it away from drains and borders.
9. Sweep the patio regularly.The single best preventative. Sweeping leaves, moss and soil off before it works into the joints keeps the seedbed from forming at all.
10. Fix the drainage if it is always damp.A patio that stays wet grows moss, and moss holds the debris that weeds germinate in. Improving the fall or clearing a blocked gully addresses the root cause.

Tips

• They root in the joint debris, not in the ground. Refill the joint and the problem largely disappears.
• Boiling water is free, immediate and works on annual weeds and moss.
• Sweeping the patio monthly does more than any spray.

Common mistakes

• Spraying the weeds and leaving the joints open — The debris that they germinated in is still there, so a fresh crop appears within weeks. Clearing has to be followed by refilling.
• Using a pressure washer to blast the joints out and leaving them — It removes what was holding the slabs' joints together, lets water into the bed, and leaves a perfect open seedbed. If you pressure wash, re-point afterwards.

If it doesn't work

Questions people ask