We are using Round-up ® to kill weeds and grass in the back third of our lawn. How many days should we wait before laying new dirt and planting new seed? Should the seed be protected by straw?
Follow the label directions. The herbicide you used is one that works primarily by absorption into the leaf with little or no residual activity in the soil, so you can sow seed as soon as the spray dries. However, you should wait for the weeds to die before sowing. Until then, the weed foliage would keep some seeds from making good contact with the soil and shade others. Either condition would prevent seed germination.
Anyone who spreads grass seed hopes for quick sprouting. For you it's especially important because it's late to sow a lawn. Mid-August to mid-September is the ideal time to sow lawn seed in southern Michigan, into a bed already prepared for this. The resulting seedlings sprout by late September and grow wonderfully in the cool fall, establishing roots that put them in great shape by next summer. Seed sown later when it's too cool doesn't have such a great edge since it may not sprout until spring. Late sown seed may even be blown away or wash away over winter.
If you applied a herbicide just now you can't spread seed until mid-October, after waiting 10- to 14 days for the weeds to die. Then you should work the soil for sowing. This is more involved than simply spreading new soil. Plant roots need oxygen as well as water, but both will be in short supply in soil that consists of loose material on top of denser stuff. I realize you may have seen sod and seed put down on top of just such soil in countless new-home situations but don't follow that example which is a mistake born of ignorance and economic pressure. Those new lawns fail or go downhill after just a few years.
Adding soil may not even be necessary. If the ground is poor, adding compost may be a better move. That way you bring in fewer new weed seeds and do more toward improving the soil structure and subsequent root growth. However, you should loosen the existing soil before adding anything, or till lightly after spreading to combine the old and new.
You might save yourself time and have a better lawn in the long run if you spread an annual rye seed this fall, let it sprout among the dead weeds, then till the area in April before spreading new perennial bluegrass seed. The rye is a "cover crop." Its roots can improve the soil and its presence even after death can inhibit the growth of weed seeds. By the time you till it's additional organic matter, like compost.
It's a good idea to spread a thin layer of straw over new-sown grass seed, provided the area is not so windy that it will simply blow away. The straw can help shade new grass seedlings and keep the soil cooler and more moist.
to those who keep their wits about them and seek a second opinion in the face of outrageous advice such as "cut your maple down if it has tar spot." I can't fathom why a competent landscape care firm would recommend this. Unless compounded by other problems, a disease that affects only the leaf is not life-threatening, especially when it's something like tar spot that comes late in the growing season. If your maple has tar spot, relax. As bad as it looks it may need nothing but time and a change in weather patterns to put it back into the "rarely seen leaf disease" category.
to leaf blowers in your garden and groundcover areas. Bad enough that you should remove the leaves that by all the principles of soil renewal and fertility should be recycled where they fall. It's worse to blow-dry plants already parched by weeks of drought just when they most need every bit of water if they are going to survive until spring. That's not all! Your perennial flowers and groundcovers have spent the last half of the season setting buds at and just below ground level, all for naught when those vital parts are crushed by the blower-wielder's feet. If you can't do the best thing and leave the leaves, use a long handled rake to remove them.
Originally published 10/9/04