Each fall I am asked by homeowners, “I missed the August to September window to plant a lawn; when can I take care of this?”
My response depends on just how late in the fall it is, however by December I advise him or her to choose either to wait until spring or to consider dormant seeding, sometimes called frost seeding. Dormant seeding involves the placement of seed outside of the normal growing window. The seed remains dormant until it warms up, hopefully in the spring, when it germinates. The freezing and thawing action of the ground over the winter creates small cracks in the soil surface which creates a nice seedbed.
While late summer is the best time to seed turf, dormant seeding often yields better results than spring planting. Soils tend to be so wet in March and April that establishing a good seedbed is difficult or even impossible.
The most important factor in the success of any turf planting is establishing good seed-to-soil contact. Remove any material which may interfere with this. It may be impossible to work the ground the way you would in the fall however it should be smooth enough to be suitable for a lawn.
Use slow-germinating species such as tall fescue or Kentucky bluegrass. Fast-germinating species can sprout more easily during a warm period in the middle of the winter. These are prone to winter kill when the weather cools back down. Perennial ryegrass is often mentioned as a species to avoid.
Plant at about a 25 percent higher rate than is recommended for late summer seeding. Avoid planting during warm stretches, or when heavy wind or rain is expected. Mulching is not required but may help reduce erosion. Be sure to use a light-colored mulch such as straw. Dark mulches absorb heat from sunlight and can warm soil temperatures.
Dormant seeding has several issues. Weed control can be a significant problem. Early-season weed suppression is important to keep weeds from shading out newly emerged seedlings. This will likely cause some damage to young plants but less overall harm than allowing weeds to grow unchecked.
The usual method of crabgrass control is to apply a pre-emergent herbicide which prevents it from forming a root system. These products also prevent desirable species from developing roots so they should not be applied until new turf is well established. If you have not had serious crabgrass problems in the past, consider avoiding this treatment the first year after dormant seeding. If absolutely necessary, wait until late in the application window; in mid-April for Central Indiana.
An extended warm period during the middle of the winter may allow seeds to germinate, resulting in winter kill when the weather turns colder. This is unusual for Central Indiana, but not unheard of. While soils generally remain moist over the winter, if the area dries out you may need to lightly irrigate it.
Once spring arrives, make sure the area is properly irrigated. If necessary, apply frequent, light waterings to keep the top quarter inch of soil moist. As seedlings become established, transition to less frequent, deeper irrigation. By summer turf should receive 1-1.5 inches of water per week, either naturally or through irrigation. Initially you should mow the area shorter than for established turf. Set your mower height to about 2.5 inches for the first three to five mowings, then increase it to 3-3.5 inches.
You should also apply a starter fertilizer — one high in phosphorous — once germination begins. This should be applied over the entire area at a rate of 1.5 pounds of phosphorous per thousand square feet. If possible, avoid adding nitrogen until late May or early June. You will likely have some thin patches in your turf at first but do not to try to “fix” these too quickly. Slower-germinating turf species often take several weeks to fill in as they emerge and trying to do too much too quickly can do more harm than good.
Dormant seeding can be done once the soil temperature falls below 40 degrees and is expected to stay there. This is usually between Thanksgiving and early March in Central Indiana. While late summer is the ideal window for establishing turf, dormant seeding generally results in better germination and fewer weed problems than planting in the spring.