How to stop weeds growing between pavers

Weeds between pavers start with the joints. Seeds land in the gaps, and if the sand there has washed down or filled with dirt, they root. Stopping them means three things: clear the joints out deep, refill them with polymeric sand that sets firm, and keep the surface swept.

Pulling or spraying only buys you a few weeks. In Ontario you can’t use glyphosate on a patio or driveway, so the joint itself has to do the work.

If you’d rather hand it off, clearing weedy joints and re-sanding them is what our polymeric sand and weed removal service covers.

Why do weeds grow between pavers?

Weeds grow between pavers because the joints give seeds somewhere to sit and stay damp. Unilock says weeds come up when the jointing sand washes away and leaves room for seedlings, and the moist, dark gap suits germination.

The usual causes are:

• Plain sand that has washed down over the years, leaving joints half empty.
• Polymeric sand that was never cleared deep enough, so it cracked and flaked out.
• Dirt, leaves and grass clippings that settle into the top of the joints and turn into a thin layer of soil.
• Shady, damp edges and spots under trees, where moss gets going first and weeds follow.
• Sunken or rocking pavers, where joints open up and water sits.

Techniseal lists shade, moisture and soil or grass clippings left on the joints as causes of moss and early joint breakdown.

Is weed killer legal on interlock in Ontario?

Some weed killers are, but the common ones aren’t. Under Ontario’s Pesticides Act and Ontario Regulation 63/09, you can’t use certain pesticides to kill weeds on patios and driveways, or on lawns and gardens.

The province names glyphosate, 2,4-D and diazinon among the banned ingredients for cosmetic use.

You can use products made only from active ingredients on Ontario’s Allowable List (version 5, effective November 28, 2022). That list includes:

• acetic acid
• soaps of fatty acids
• iron in the form of FeHEDTA
• sodium chloride
• corn gluten meal

Acetic acid (vinegar) products only kill the parts of the plant they touch, so deep-rooted weeds can grow back. Read the label and follow it.

Which ways of killing weeds between pavers work?

Pulling, scrubbing and spraying all deal with the weed you can see. Only the last row in the table fixes the joint, which is why weeds keep coming back after the quick fixes.

So kill or pull what’s there first, then fix the joint. Do only the first half and you’ll be pulling the same weeds again next summer.

Does polymeric sand stop weeds for good?

Polymeric sand stops most weeds, but not every one. Techniseal says its RG+ sand hardens after it dries, stays put where plain sand washes out, and prevents weed growth. A full, hard joint gives roots nowhere to go.

It can’t stop a seed landing in dirt that has built up on top of the joint. Alliance Gator says to clean the surface from time to time and not let dirt pile up on the joints, and Techniseal says the same about soil and grass clippings. Regular sweeping takes care of most of it.

The sand only works if it goes in properly:

1. Clear the old sand out. Alliance Gator says to remove it at least 1.5 inches deep before refilling, and Techniseal lists a minimum joint depth of 4 cm (1.5 inches).
2. Fill and compact until the sand sits at the bottom of the paver chamfer, or at least 3 mm (1/8 inch) below the paver tops. Techniseal warns that joints left full to the top can break down early.
3. Blow the surface clean before any water goes on.

Our polymeric sand guide explains how the product works and how much you need, and how to apply polymeric sand goes through the mistakes that make it fail.

When should you re-sand pavers in Ontario?

Re-sand between late spring and early fall, on a stretch of dry days. Techniseal’s conditions are:

• the temperature stays above 0°C for 48 hours after installation
• the pavers and joints are dry
• no rain is forecast for the next 24 hours

Alliance Gator also says its sand should go down above 0°C.

In Markham and the rest of the GTA, late fall is a gamble with cold nights, and winter is out.

Pulling and brushing has no season. Do it whenever weeds show up, ideally while they’re small and before they set seed.

If you’re cleaning the surface anyway, our guide on how to clean interlock without damaging it covers pressure settings and cleaners.

Why do weeds come back after re-sanding?

Weeds come back after re-sanding when the job took shortcuts. These are the common ones:

• Sweeping new sand over old, weedy joints. The roots are still there and the new layer has nothing solid to bond to.
• Clearing joints only an inch or less. Alliance Gator and Techniseal both want at least 1.5 inches (4 cm), and a shallow layer is more likely to crack and come loose.
• Blasting the joints with the pressure washer on high, held close to the surface. Unilock warns against both.
• Sanding pavers that are still damp. The sand sticks to the surface instead of running down into the joints, and can leave a haze.
• Leaving sand dust on the paver faces before wetting.
• Re-sanding over sunken or rocking pavers without fixing them first.
• Putting seeding weeds in the home compost. The RHS notes home compost may not get hot enough to kill the seeds.

Keeping the joints clean afterwards

After the sand has set, upkeep is mostly sweeping. Unilock recommends sweeping paving stones regularly so seedlings can’t settle in.

A leaf blower is faster, and it’s worth a pass after the leaves drop in the fall. Pull any weed that does show up while it’s small.

When it’s worth calling someone

A small patio with mostly sound joints is a reasonable weekend job if you have a dry forecast and patience for the drying step.

Get help when weeds cover most of a driveway, the old sand is packed hard, or some pavers have sunk. Those jobs take longer than people expect.

A rushed re-sand with shallow joints or no compaction is the kind that cracks and lets weeds back in.

If that sounds like your interlock, call or text us a photo at (437) 684-2535, or have a look at our polymeric sand and weed removal page.

If parts of the surface have dropped, we handle that as interlock repair before any new sand goes in. Quotes are free.