Broadleaf weeds are the bane of lawn lovers. Dandelions, clover, dollarweed, and others invade quickly and spread relentlessly.
The right time: Treat actively growing weeds; apply granular products on a dewy morning.
Why timing matters: Used properly, broadleaf weed killers are highly effective, but few pest controls fail as readily when conditions aren't optimal. For example, the granules of weed-and-feed products, which are applied with a spreader, must stick to the leaves of the weeds to be effective. That requires moisture. The perfect time to apply, therefore, is an early morning when there's a heavy dew on the lawn -- the heavier the better. If the grass isn't wet, you'll be wasting your time and money.
Whether you use a granular weed-and-feed or spray a liquid broadleaf weed killer, the weeds must be well watered and actively growing for the chemical to work. Thus, treating during a hot, dry spell in summer may yield disappointing results. Spring and fall, when temperatures are moderate and moisture plentiful, are ideal times.Using Weed Preventers
Pre-emergent herbicides, or weed preventers, control crabgrass and other weeds by stopping their seeds from germinating. An application early in the growing season works wonders; it's like vaccinating your lawn against weeds.
The right time: Apply preventer when forsythia blooms drop.
Why timing matters: Weed preventers are not effective against weeds that have already begun to grow, so you must apply them before germination to gain any benefit. Crabgrass, the primary target of lawn weed preventers, normally germinates just after forsythia blooms, so take your cue from Mother Nature. When you notice forsythia bushes dropping their blossoms (March to May, depending on your region), apply weed preventer, and water as soon as possible to activate it.
Need to reseed? For cool-season grasses, fall is the ideal time; plant warm-season grasses in late spring. But remember: Don't apply crabgrass preventer at the same time that you plant seed; it stops seedlings from growing.