How to apply lawn weed killer
For a few weeds, dig them out while the soil is moist. For a larger problem, a selective post-emergent herbicide can treat growing weeds without removing the whole lawn, provided it is labelled for your grass.
What you need
A suitable ready-to-use product or concentrate, its label, a dedicated herbicide sprayer if needed, measuring jug, tape measure and required protective clothing.
Step by step
- Identify the target. Broadleaf weeds, grassy weeds and sedges need different products. Check the label lists the weed and permits use on your grass. St. Augustine, centipede and some other grasses are sensitive to products used on northern lawns.
- Read the application limits. Note the rate, maximum treated area, number of applications, reseeding wait and when people and pets may return. New turf may need a minimum age or number of mows. Choose a product approved for home use in your location.
- Prepare the lawn and choose the day. Leave enough time since mowing for weed leaves to absorb the spray, as the label requires. Use the stated temperature and wind limits and rain-free window. Avoid drift toward beds, trees, vegetables and neighbouring property. Do not assume a completely still dawn is suitable if the label warns about temperature inversions.
- For concentrates, calibrate with water. Mark a known area, spray it at a steady pace, then measure the water used. This tells you the carrier volume for an area-based dose. For ready-to-use spot treatments, follow their wetting instructions; do not dilute unless directed.
- Measure and mix. If the label gives an area rate, scale it to the area you will actually spray and add it to the calibrated water volume. Follow the mixing order. Add a surfactant only if directed and at the stated rate; some products already contain one.
- Treat the weeds evenly. Spot-treat where the label permits. Keep nozzle height, pressure and pace consistent, using the specified droplet pattern. Wet leaves as directed without runoff. Do not repeatedly spray one patch until the whole tank is empty.
- Clean up. Follow the label’s rinsing and disposal directions. Keep rinsate out of drains and water, and do not exceed the permitted dose on already treated areas. Store the product in its original container and keep the sprayer for herbicides only.
After the job
Hold mowing and irrigation for the product’s stated intervals. Keep people and pets out until its re-entry conditions are met. Record what, where and how much you applied.
Allow the label’s response time before judging the result. Different herbicides cause different symptoms; curling is not a universal sign of success. Repeat only when permitted, without exceeding application limits.
After the reseeding interval, repair bare ground in the correct season. Improve mowing and density to reduce the next crop of weeds.
Choose by weed and grass
| Problem | What to check |
|---|---|
| Dandelion and other broadleaves | A selective broadleaf product that lists both the weed and your turf species. |
| Crabgrass | A product specifically labelled for crabgrass at its current growth stage; ordinary broadleaf spray may not work. |
| Nutsedge | A sedge treatment compatible with your grass, or hand removal and repair for small patches. |
| Weeds in newly seeded turf | The minimum turf age, mowing requirement and any other establishment restriction on the exact label. |
Video example
Common questions
How long should I wait before reseeding?
Use the exact product’s reseeding interval. It can differ by ingredient, rate and grass species; a generic 30-day wait is not suitable for every herbicide.
Do I need a surfactant?
Only if the product directions call for one. Use their specified type and amount. Extra surfactant can change grass tolerance.
Keep your lawn-care plan together
Use Lawn Care AI to organise care for your lawn and keep track of the jobs you have planned.
Sources and further guidance
- Iowa State University Extension and Outreach — Yard and Garden: Timing and Applying Broadleaf Lawn Herbicides
- Kansas State University Turfgrass — Broadleaf Weeds: Chemical Control
- Rutgers NJAES Cooperative Extension FS385 — Broadleaf Weed Control in Cool Season Lawns
- Clemson Cooperative Extension HGIC — Managing Weeds in Warm Season Lawns
- University of Delaware Cooperative Extension — Weed Control in Turf
- Royal Horticultural Society — Weeds in Lawns: Control and Care