New to lawncare, and roughly 50% of our lawn is crab grass. Is it too early for preemergent? Or will next week’s cold spell going to kill off any germination from the next few days? Or should I just lay grass seed down now to take advantage of the upcoming rain?
by Personal-Beach-6880
5 Comments
The common lawn pre-emergents (prodiamine, pendimethalin, and dithiopyr) work to help reduce the germination of certain seeds… Mostly grasses and only a handful of broadleaf weeds. The labels will list which weeds are targeted. To prevent more broadleaf weeds, a specialty broadleaf pre emergent like isoxaben is required.
Pre-emergents work by preventing the germination of seeds of the target species. So in order to be effective, a pre emergent needs to be applied BEFORE those seeds germinate. For winter annual weeds (annual weeds that are present in the fall, winter, and spring, like poa annua), a pre emergent needs to be applied in the fall before soil temps fall below 70F. In order to prevent summer annual weeds (like crabgrass), a pre emergent needs to be applied in the spring before soil temps reach 55F. (In very southern areas, timing can be more closely tied with periods of higher moisture AND climbing soil temps. Consult your state extension service for more specific guidance)
Pre emergents will not kill existing weeds. Pre-emergents alone will rarely control a weed problem. Pre-emergents are tools to **reduce** the need for post-emergents. They rarely eliminate the need for post emergents.
The labels of pre emergents have many important instructions and use restrictions. ALWAYS READ THE ENTIRE LABEL. For example, you are limited to 2 applications of each active ingredient per year.
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If 50% of your lawn is hndesired weeds (crabgrass in your case), you may want to approach this in more than one season. It will look worse before it gets better. Eliminate the crabgrass first (with chemicals or good ol’ hand pulling), soil sample to know your current soil state, rectify soil if sample says so, then likely wait for fall to do your seeding as it will be the most succesfull due to temps and time to establish before winter time torture. Next spring, pre emergent for crabgrass when temps rise above 55F. This will help combat the crabgrass that is going to grow just like you currently have. Keep pulling weeds as soon as you see them come up.
Crabgrass is a summer annual.
If you think you have crabgrass right now, its something else.
I would rather do pre-emergent too early than too late. I’d do it whenever is convenient before one of those rains. I also like to do another application 6-8 weeks later. In your case you will probably want to spot kill weeds through summer. Then in fall do a seeding. Pre-emergent next spring. And by then you should have a much better lawn that you can keep fertilizing, overseed, spot killing weeds, and pre-emergent treating in spring or maybe fall if you decide not to overseed in a given year.
Put your seed down and maybe some starter fertilizer with it, then put pre emergent on everything that was not seeded. You can always take out the crabgrass with a post emergent later.