Spring is ideal for targeting weeds in their pre-growth stage before they fully sprout, and fall is effective in eliminating weeds before the winter season. · discover the key to a lush, weed-free lawn this spring in our comprehensive guide on when to apply weed killer. The best time of year to use weed killer is spring , followed by fall. Treat your lawn once soil temperatures reach 50 degrees fahrenheit when many weed seeds sprout. · learn when to put weed killer on lawn in spring. Learn the ideal timing for pre-emergent and post-emergent herbicides, along with effective application techniques tailored for your lawn type. · the best time to put weed killer on your lawn is in the spring or fall. Fall is similarly effective because, ahead of the winter, this is when weeds are most vulnerable. Find out the best time of spring to apply weed killer to a lawn, along with temperature ranges. The herbicide label provides definitive information concerning the turf growth stage, time of day, and weather conditions when the product may be applied, but this simple chart can help in making a plan for the timing of lawn weed control. Early spring , typically before the soil temperature consistently reaches 50°f, is the time to target overwintering weeds. Spring is an effective time for catching weeds in their pre-growth season, in order to prevent them from sprouting. Timing is critical here, as pre-emergent herbicides wont work on weeds that have already sprouted. · to understand when to apply weed killer in spring , it’s essential to grasp the weed lifecycle and its relationship to seasonal changes. · these weed killers are usually applied in early spring in the south.