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.

I probably wouldn't use preemergents before laying new sod, as many of them prevent cell division, thus preventing or slowing your grass' roots from growing. Weed killers on the other hand should be fine (check the labels first) as the grass is considered mature and the selective herbicides shouldn't affect them a few weeks after it is installed (I say a few weeks because weeds will probably take a while to pop up through the sod).

Here's my strategy, see what you think. Clear the ground of trash and sticks, etc. Trim up any small shrubs or perennials so you can see what you're doing. Take old newspapers and make a pad with 7 layers of newsprint. Starting at the outward edge, begin layering sections of pads, like you're shingling a roof. Overlap the pads so that it's not easy for soil to wash under the edges. Do not put the newspaper right up next to shrub trunks or perennial crowns. Next, mulch at the proper depth with material of choice. Next, sprinkle the Preen over the mulch, keeping it from staying on the leaves of shrubs or other plants. This helps keep perennial weeds from coming up and starving them of light. The Preen helps prevent blown in seeds from germinating. You have to reapply the Preen after 3 months, by the way. The newspaper will degrade over a single season, but by then it's prevented many weed seeds from germinating. The earthworms like it too! If you do this regularly, weeds become less and less.

Crabgrass seeds will begin to germinate when the soil temperatures mean is about 60 degrees for several days, but wi8ll increase in rate when that mean temperature is around 73. The simplest method of determining when these seeds will germinate is when Forsythia blossoms. Any pre emergent control should be put down about 6 weeks before the seeds germinate. kimmq is kimmsr