How to Kill Weeds in Driveway Cracks (And Seal Them Forever)

The Permanent Solution for Weeds in Concrete Cracks

Weeds growing in driveway cracks and control joints are more than just unsightly—they're actively destroying your concrete. As roots grow, they widen cracks, allowing more water in, which leads to freeze-thaw damage and further cracking. This guide shows you how to kill weeds permanently and seal the cracks so they never come back.

Why Weeds Keep Coming Back

Most people pull weeds, but that only removes the visible part. The roots remain in the crack, and the plant regrows in days or weeks. To permanently eliminate weeds, you need to:

1. Kill the existing weeds (including roots)
2. Remove dead plant material
3. Seal the crack to prevent new weeds from taking root

Skip any step, and the weeds will return. Do all three, and you'll have a permanent solution.

Method 1: Boiling Water (Quick Kill)

This is the simplest method for immediate results, but it's not permanent without sealing.

Steps:

1. Boil a large pot of water
2. Pour directly into the crack where weeds are growing
3. Repeat daily for 3-5 days until weeds are dead
4. Remove dead plant material
5. Seal the crack (critical step—see below)

Effectiveness: Kills existing weeds quickly, but they'll return if you don't seal the crack.

Cost: Free (just water and energy)

Time: 5 minutes per day for 3-5 days

Method 2: Vinegar + Salt + Soap (Natural Permanent)

This natural solution kills weeds and prevents regrowth, but you still need to seal for a truly permanent solution.

Recipe:

• 1 gallon white vinegar (5% acidity minimum, 10% is better)
• 1 cup table salt
• 1 tablespoon dish soap

Steps:

1. Mix ingredients thoroughly
2. Pour or spray into cracks (avoid surrounding grass)
3. Let sit for 24-48 hours
4. Remove dead weeds
5. Rinse with water
6. Seal the crack (see below)

Effectiveness: 90-95% kill rate, prevents regrowth for months

Cost: Approximately $5-$10 (materials)

Time: 30 minutes active, 24-48 hours wait

Warning: This solution will kill any plant it touches, including grass. Apply carefully and avoid overspray.

Method 3: Commercial Weed Killer (Most Effective)

Glyphosate-based weed killers (like Roundup) are the most effective, but require careful handling.

Steps:

1. Choose a glyphosate-based weed killer
2. Apply directly to weeds in cracks (use a small brush or spray bottle for precision)
3. Wait 7-14 days for complete kill
4. Remove dead plant material
5. Seal the crack (see below)

Effectiveness: 95-100% kill rate, kills roots

Cost: Approximately $10-$20 (product)

Time: 15 minutes active, 7-14 days wait

Safety: Follow all product directions. Wear gloves and eye protection. Keep away from pets and children until dry.

The Critical Step: Sealing the Crack

Killing weeds is only half the solution. If you don't seal the crack, new weeds will take root within weeks. Here's how to seal permanently:

Step 1: Clean the Crack Thoroughly

Remove all dead plant material, dirt, and debris. Use a wire brush, compressed air, or pressure washer (low pressure) to clean the crack completely. It must be clean and dry for the sealant to adhere properly.

Step 2: Choose the Right Sealant

Self-leveling polyurethane sealant (best): Products like Sikaflex or similar create a flexible, waterproof seal that expands and contracts with temperature changes. This is the professional choice.

Backer rod (for wide cracks): If the crack is wider than 1/4 inch, insert backer rod (foam rope) first to reduce the amount of sealant needed and create a proper seal.

Step 3: Apply Sealant

1. Insert backer rod if crack is wide (compress it slightly so it fits snugly)
2. Apply sealant according to product directions
3. Smooth the surface with a putty knife or tool
4. Allow to cure completely (typically 24-48 hours)

Pro tip: Apply sealant when temperatures are between 50-80°F for best results. Extreme temperatures can affect curing.

Prevention: Stop Weeds Before They Start

The best way to deal with weeds is to prevent them:

• Seal new cracks immediately: Don't wait for weeds to appear. Seal cracks as soon as they form.
• Maintain your sealer: A good sealer on your driveway prevents water from entering cracks, which prevents weed growth.
• Keep cracks clean: Regularly sweep or blow out debris from cracks. Dirt and organic matter provide a growing medium for weeds.
• Apply pre-emergent: In spring, apply a pre-emergent herbicide to prevent weed seeds from germinating. This is especially effective in control joints.

What Doesn't Work (Save Your Money)

Just pulling weeds: Removes the plant but not the roots. They'll regrow in days.

Bleach: Kills surface growth but doesn't kill roots effectively. Weeds return quickly.

Filling with sand or gravel: Doesn't prevent weeds, just gives them a better growing medium.

Rigid sealants (like concrete patch): Will crack and fail, allowing weeds to return. Use flexible sealants instead.

When to Call a Professional

Call a professional if:

• Cracks are very wide (more than 1/2 inch)
• There are many cracks throughout the driveway
• You want a comprehensive solution (cleaning, sealing, and maintenance)
• The cracks indicate structural issues (not just surface cracks)

Professional crack sealing typically costs approximately $3-$8 per linear foot depending on crack width and sealant type. For extensive work, it's often worth the investment.

Maintenance Schedule

To keep weeds from returning:

• Monthly: Inspect cracks and remove any new growth immediately
• Spring: Apply pre-emergent herbicide to control joints
• As needed: Reapply sealant if it shows signs of wear or failure
• Annually: Check all sealed cracks and reseal any that have failed

The Bottom Line

To permanently eliminate weeds in concrete cracks, you must both kill the existing weeds AND seal the crack. Killing alone is temporary—weeds will return. Sealing alone won't work if live weeds remain—they'll grow through the sealant.

The most effective approach: Use a commercial weed killer or vinegar solution to kill existing weeds, remove dead material, then seal with a flexible polyurethane sealant. This combination provides a permanent solution.

Prevention is even better: Seal cracks as soon as they form, maintain your driveway sealer, and keep cracks clean. An ounce of prevention is worth a pound of cure.

Need help with weed removal and crack sealing? Contact Local Concrete Contractor. We provide professional crack sealing services that permanently eliminate weeds and protect your driveway.