When to Apply Pre-Emergent

How pre-emergent works

Pre-emergent does not kill weeds you can see. It creates a thin chemical barrier in the top layer of soil that stops weed seeds from sprouting as they try to germinate. That is why timing is everything: the barrier has to be in place before the seeds wake up, not after.

The manual way

1. Know what you are stopping. A spring application targets crabgrass and other summer annual weeds. A fall application targets poa annua (annual bluegrass) and winter weeds. Most lawns benefit from both.
2. Watch soil temperature, not the calendar. Crabgrass germinates when soil reaches about 55°F at a 4-inch depth, so you want the barrier down while soil is consistently 50 to 55°F. A cheap soil thermometer or a local soil-temperature map takes the guesswork out.
3. Use nature's signal. The old gardener's rule: in spring, apply when the forsythia bushes finish blooming. That tends to line up with crabgrass germination in most areas.
4. Apply at label rate and water it in. Spread the product evenly, then water with about half an inch so it settles into the soil and forms the barrier. Need the amount? The calculator works it out from your lawn size.
5. Do not disturb the barrier. Skip aerating or dethatching after you apply. Breaking up that top layer of soil opens gaps that weeds slip through.

The easy way with SimpleLawn

The hard part is not applying pre-emergent, it is remembering to do it in the narrow window before weeds germinate. SimpleLawn watches the calendar for you. Pick your grass type and it shows your pre-emergent window, then reminds you when it is time.

See your full schedule on the free lawn care calendar, no download needed.