Killing weeds is easy with contact herbicides. They are designed to kill whatever plant the spray lands on. Unfortunately, these weed-killers can’t distinguish between valuable landscape plants, favorite flowers and the weeds you want to get rid of. And being sprays, often very fine sprays, they can drift onto desirable plants, even in the slightest breeze, and you might not even know it. To ensure you don’t have an herbicide mishap and damage plants you love, try some of these tips. And always read and follow label instructions.
Weed Killer Missteps
Many spray-on weed killers are post-emergent or contact herbicides. They contain active ingredients that don’t discriminate between weeds and desirable plants. This type of herbicide damages or kills any plants it contacts.
When a contact herbicide inadvertently drifts onto desirable plants, its referred to as overspray or spray drift – and it can mean the difference between killing weeds and killing a cherished plant. Sometimes, spray drift will only damage plants instead of killing them. Depending on the amount of drift and how much foliage is sprayed, you may only see leaf spotting or burning, stunted growth, stems that die back or leaf drop.
To prevent problems with herbicide spray drift or overspray, follow some of these techniques.
Protect Desirable Plants
- Read the herbicide label. One popular weed killer label warns against using a high-pressure sprayer because the smaller particles are more likely to drift.
- Spray when the air is calm. Early mornings are often good times.
- Be careful when spraying weeds in beds with bulbs that have died back. Many bulbs, even when dormant, can be damaged by weed killers that seep into the neck of the bulb.
- Rinse sprayers or applicators used to apply herbicides after each use. Many product labels will include rinsing directions. Dump the rinse water on a non-planted area, well away from desirable plants. Don't dump rinse water on hard surfaces or anywhere it might drain into nearby planting areas or street gutters.
- Dedicate one sprayer for contact herbicide use to avoid accidentally dosing desirable plants with residual weed killer.
- To protect nearby plants from spray drift, cover them with plastic sheeting or cardboard. Remove the plastic only after the herbicide dries.
- Avoid walking on areas you've just treated. You risk carrying herbicide on your shoes into other areas, like your lawn.
- Make a spray collar or barrier to isolate weeds. Remove the top and bottom of a plastic 2-liter bottle, plastic milk jug or metal food can. Place the collar over the weed, and apply herbicide directly into the top opening. To spray a large patch of weeds, use an open-ended cardboard box to form a targeted spray zone. You can also use large pieces of cardboard to create a spray barrier between desirable plants and weeds.
- Kill a weed growing in the middle of desirable plants by cutting a small opening in a piece of plastic. Lay the plastic over the desirable plants, and pull the weed through the opening. Spray the weed, then remove the plastic after the herbicide has dried.
- Isolate weeds in planting beds by anchoring the weed or the desirable plants to the ground and out of the way with a u-shaped anchor pin. Spray the weed after you have clumped and pinned the leaves.
- Treat only the targeted weed by painting herbicide onto leaves with a sponge applicator, often sold in nurseries and garden centers. You can use a paint brush, just take care not to flick herbicide onto nearby plants. Always wear plastic gloves.
More on Weeds
Learn more tips for killing weeds.