April 10, 2012
With the warm weather that we have had, people have been asking about whether they should seed now or wait a few weeks.
Spring seeding is hard, no matter when you do it. Spring seedings often turn to crabgrass and other annuals and may take a year to mature into a real lawn. You can use a selective preemergence herbicide called Siduron which will selectively kill the annuals and let the perennials like Kentucky bluegrass and perennial ryegrass emerge, but that is expensive and difficult.
The best time to seed remains late summer to early fall. I would set August 15 as the best time to plan your seeding in central Iowa.
If you must spring seed, give it a little time yet. I am currently telling those who contact me to wait until after May 1. As we saw this morning, we are not past the frost-free days yet. Seedlings, particularly perennial ryegrass, can be susceptible to cold temperatures in the spring.
If you have to spring seed, I would recommend the application of Siduron with the starter fertilizer to control the annuals. If you end up with a lawn of crabgrass, don't give up. The perennial grasses will be in there. The annual will die in the fall and next spring you can put on a standard preemergence herbicide to control them.
Other standard preemergence herbicides will not work at the time of seeding. They will kill the crabgrass, but they will also kill the grasses that you are trying to seed.
The new herbicide Tenacity (mesotrione) can be used for spring seeding of Kentucky bluegrass, but leave that to the experts. Your local lawn care professional can tell you more about the product.