What is the best time of year to reseed bare patches in the lawn? Can it be done in the spring? If so, please provide tips.
In Michigan, late August to mid-September is the ideal time to seed all grass types. The soil is warm yet the air has cooled down from summer temperatures.
However, most homeowners don’t want to go through the summer with a spotty lawn. Mid to late spring can be a suitable time to reseed bare patches in the lawn, after frost warnings are lifted. The soil temperature needs to be at least 50 degrees for grass to germinate at a normal rate. Waiting longer gives the soil more time to warm up to about 60 degrees and improves your success rate. Given sufficient moisture, the seed will germinate quicker with the added warmth, depending on the seed type.
Do not apply any spring lawn weed killers or crabgrass preventers. If you do, grass seed will not sprout or the seedlings will be killed along with the weeds and crabgrass.
Prepare the patches by removing any weeds. Scratch up the soil with a heavy dirt rake or cultivator. Mix up 1/3 sphagnum peat moss with 2/3 good garden soil to get a light, spongy texture. Add 1-1/2 cups of balanced organic fertilizer per bushel of soil making sure the fertilizer has a high phosphorous (P) content to stimulate root growth. Most “starter fertilizers” are high in phosphorous. Spread this mixture over the bare spot until it is slightly higher than the surrounding soil level. Gently work it into the scratched-up soil originally there.
Use a seed type similar to the existing grass unless it was the wrong kind to start with. Buy new seed. The percentage of seed that will germinate from old seed drops drastically with each year. Also avoid bargain seed. They generally contain the largest amount of annual or rough-bladed grasses.
Hand cast your seed and don’t be stingy. About 15 to 20 seeds per square inch is good. Bury the seed 1/8 to 1/4 inch into the soil by dragging a spring rake over the area with the tines inverted. Do not tamp so hard that you compact the soil. You want water to soak in easily. It is also helpful to cast some of the new seed to the outside of the repaired spot. This helps the new grass blend into the neighborhood!
Grass seed needs both moisture and warmth in order to sprout. Cooler temps will make it germinate slowly. But if there is a lack of moisture it won’t do a thing. Once the seed has germinated, avoid walking on the repaired spots to give the new plant roots time to dig in and acclimate. If you seed with a blended mix, the different types will germinate at different rates. So when you see green sprouts, continue to provide water for the later varieties to germinate.