I'm gonna wait, partly because I put out some more seed, but it's gonna get cold again, so I think those weed seeds should hold. Now if I misjudge and it down't get cold again (I wish), then it'll be mild like it's been the last several years and those weed seeds will get going earlier. Just keep an eye on the soil temps map and if it stays above 50 for a number of days then you better put it out. Can't remember how many days, though. Maybe someone can chime in with that tidbit.

I wonder where these ideas generate from. You have a mix of things going on. The time to apply any preemergent is prior to your yard reacting to the spring time weather. The forsythia is usually the first indication of the events of spring. Thus the earliest blooming of the earliest forsythia is the trigger. You are already late for this year. The "good news" is that crabgrass will germinate under proper watering and sun conditions all summer. Chemical fertilizer should not go down until you mow real grass twice. By waiting you will ensure that you are fertilizing your grass and not your weeds. When you apply has nothing to do with root or leaf growth. I'll tell you what has everything to do with leaf AND root growth, AND it controls your weeds to boot, is setting your mower to the highest setting. By growing longer leaves you will grow deeper roots. Deeper roots can get water deeper in the soil, so you can water more deeply and less frequently. Tall grass shades the soil keeping it cooler and less prone to evapotranspiration of the moisture, so you water less. You don't have to use a weed-n-feed. You don't have to do anything until you mow (tall) twice. Then use regular fertilizer. By then some of the winter annual weeds will be dead anyway. By letting your grass grow up tall, weeds like dandelions will die out. Why? Because the surrounding grass will force the broad dandelion leaves to point up and they don't get enough sunshine. The plant will die. Any seeds that blow off the dandelion will not be able to get down to the surface through the tall grass so no new ones will crop up. And if they did hit the surface, and you did water them daily so they would sprout, the tall grass will provide enough shade that the seedling dandelion will not get enough sunlight to take root. If you fertilize in a few weeks, many of the weeds will be gone by then. Then in two more weeks, a few more weeds will be gone but the remaining weeds will be healthy enough to absorb a spot spray like weed-b-gone. This is a less expensive idea than the weed-n-feed and seems to work better. But if you water infrequently and deeply, and mulch mow at your mower's highest setting, you should not have crabgrass this year regardless of your use of preemergents. Mother Nature can throw you a curve and apply enough water to germinate the crabgrass, but that is not the end of the world. The tall grass will severely curtail any spread and may choke it out. It needs plenty of sun to thrive.

The spreading of a good quality compost is always recommended to inject organic matter into the soil which, when carried out as a spring program, will encourage moisture retention, worm production, and good overall soil which grass seed will grow much better. Pre-emergent is, what it means....a means to prevent the germination of seeds which come from weeds, et al, It is usually applied at a specified time when the weeds are going to seed. Pre-emergent then is a weed seed killer. It is therefore, also a killer of any kind of seed---including grass. I believe a minimum time of interval between application of the pre-emergent and seeding a lawn, is about 6 weeks. This is the reason why the pre-emergent is applied when the weeds are sprouting their seeds which will deny germination of the vast majority ---but not all--of them. The company that did the application of the pre-emergent should have known when you can safely carry out a seeding program. Give them a call.

A pre emergent is a product meant to stop a plant from continuing growth after it germinates so it needs to be applied early enough to prevent that from happening but not so early that the weather will dilute that material and render it ineffective. Just when you apply depends on what you are trying to suppress, but generally at least 7 days before your target "weed" will germinate.