Selective vs Non-Selective Weed Killer: Which Do You Need?

The Key Difference in 30 Seconds

That’s the core of it. If you’re treating weeds in a lawn, you need a selective product. If you’re clearing weeds on paths, drives or bare ground, you want non-selective. Mixing them up is the single most common reason weed killer doesn’t work as expected — or worse, damages plants you wanted to keep.

How Selective Weed Killers Work

Selective herbicides exploit a fundamental difference between broadleaf plants and grasses. Active ingredients like MCPA, 2,4-D and mecoprop-P are synthetic versions of plant growth hormones called auxins. When absorbed by broadleaf weeds, they cause uncontrolled, chaotic growth — stems twist, leaves curl, and the plant exhausts itself.

Grasses process these chemicals differently. Their narrow, upright leaves absorb less spray, and their internal biology handles the auxin-type compounds without the same runaway growth response. The result: weeds die, grass survives.

What selective weed killers control well:

• Dandelions, daisies, plantain
• Clover (mecoprop-P or clopyralid works best)
• Buttercup, creeping cinquefoil, mouse-ear chickweed
• Thistles and docks

What selective weed killers can’t control:

• Grassy weeds (couch grass, annual meadow grass, Yorkshire fog) — because the product is designed to spare grasses
• Moss — requires a separate moss killer (usually ferrous sulphate)
• Weeds outside the lawn — these products shouldn’t be sprayed on borders, beds or paths

How Non-Selective Weed Killers Work

The most common non-selective herbicide is glyphosate. It works by blocking an enzyme called EPSP synthase, which plants need to produce essential amino acids. Without these amino acids, the plant can’t grow, repair itself or produce energy. It dies within 1-3 weeks.

Glyphosate doesn’t distinguish between weeds and wanted plants. Spray it on your lawn and the grass dies along with the weeds. That’s why it’s essential to use it only where you want total clearance.

Best uses for non-selective weed killer:

• Path and driveway weeds — clear everything from cracks and edges
• Lawn renovation — kill everything before reseeding from scratch
• Overgrown garden clearance — clearing neglected areas
• Tough perennial weeds — bindweed, horsetail, ground elder
• Spot treatment in borders — careful, targeted application to individual weeds between plants

There are also non-selective contact products (vinegar-based, pelargonic acid) that burn foliage on contact. These are faster acting but don’t kill roots, so they’re only effective on annual weeds or as a short-term top-kill. For deep-rooted perennials, systemic glyphosate is far more effective.

Which Do You Need? Quick Decision Guide

Can You Use Non-Selective on a Lawn?

Only in two situations:

Spot treatment: You can carefully apply glyphosate to individual weeds in a lawn using a weed wiper, gel applicator or small paintbrush. This avoids contact with the surrounding grass. It’s the only option for grassy weeds like couch grass that selective products can’t touch. You’ll lose a small patch of grass around each treated weed, but it grows back.

Full renovation: If your lawn is mostly weeds, it’s sometimes easier to kill everything with glyphosate and start again. Spray the entire area, wait 7-14 days, clear the dead growth, prepare the soil and reseed. This gives you a clean slate.

Using Both Together

Most gardeners end up needing both types at different times. A typical approach:

1. Spring: Apply selective lawn weed killer across the whole lawn to control dandelions, daisies and clover as they start growing
2. Spring/Summer: Use non-selective glyphosate on paths, drives and hard surfaces
3. Summer: Spot-treat any lawn weeds the selective missed with a second application (check the label for re-treatment intervals)
4. Autumn: Treat persistent border weeds with glyphosate before they go dormant for winter

The critical rule: keep your sprayers separate. Even trace amounts of non-selective weed killer in a sprayer used on your lawn will cause dead patches. Either use dedicated sprayers for each product or rinse thoroughly between uses. For further guidance on when to apply each type, see our timing guide.

Frequently Asked Questions

What happens if I use non-selective weed killer on my lawn?

The grass dies along with the weeds. Glyphosate doesn’t distinguish between grasses and broadleaf plants. You’ll see yellowing within a week and dead patches within 2-3 weeks. The grass won’t recover — you’ll need to reseed or turf the affected area. If you’ve accidentally sprayed, water the area heavily immediately (within minutes) to try and wash the product off before absorption.

Is selective weed killer safe for all grasses?

It’s safe for established lawn grasses at the recommended dose. However, newly seeded or newly turfed lawns (less than 6-8 weeks old) can be damaged. Fine fescue lawns and ornamental grass varieties may also be more sensitive than standard ryegrass mixes. Always test a small area first if you’re unsure.

Can selective weed killer kill garden plants?

Yes. Selective means it selects between grasses and broadleaf plants — not between weeds and flowers. If you spray a selective lawn weed killer onto flower borders, it will damage or kill broadleaf garden plants just as effectively as weeds. Keep spray away from borders, and apply on calm days to avoid drift. For pet and plant safety tips, see our safety guide.

Which is stronger — selective or non-selective?

It’s not about strength. A selective product applied correctly will kill lawn weeds just as effectively as a non-selective product. The difference is specificity, not potency. If your selective weed killer isn’t working, the issue is more likely timing, coverage or weed type than strength.

Do I need a licence to use either type?

No. Consumer-grade versions of both selective and non-selective weed killers are available to home gardeners without any certification. Professional-strength products (higher concentrations) require PA1/PA6 certification, but the active ingredients are the same — just at lower concentrations in consumer products.

Can I mix selective and non-selective together?

No. Don’t mix different herbicide products unless the label specifically says you can. Mixing can reduce effectiveness, create unexpected chemical reactions, or increase the risk of plant damage. Use each product separately according to its label instructions.