Overseeding a lawn can help thicken up thin spots and revive tired grass. However, proper preparation is key to ensure the grass seed you sow takes root and flourishes. Before overseeding, there are a few other things you should put down first to prep the lawn and give your grass seed the best chance of success.
Remove Debris
The first thing you’ll want to do before overseeding is give your lawn a good cleaning. Use a leaf rake or power rake attachment to remove any leaves, sticks, or other debris that has accumulated. Removing this material will allow for better seed to soil contact when you sow the grass seed later. Any large sticks or rocks should be picked up as well.
Mow Low
Next, give your lawn a very low haircut. For cool season grasses like bluegrass, ryegrass, and fescue, mow the lawn down to 1-2 inches in height. For warm season grasses like Bermuda and zoysia, scalp the lawn down to 1/2 inch tall. Mowing low removes excess leaf tissue and thatch so your grass seed can reach the soil easily. It also reduces competition from existing grass blades for sunlight, water, and nutrients as the new seedlings establish.
Dethatch If Needed
If your lawn has a thick layer of thatch – more than 1/2 inch – you’ll want to dethatch before overseeding. Thatch is a spongy buildup of dead grass stems and roots between the green grass blades and soil. Too much thatch can block grass seed from reaching the soil and prevent proper rooting. Use a dethatching rake or power dethatcher to remove excess thatch and expose the soil. Go over any bare spots a second time to further open them up for seeding.
Aerate Compacted Soil
Soil compaction is another obstacle for grass seedlings trying to establish. Compacted soils have too much density and not enough air space for roots to grow well. Before seeding, use a core aeration machine to punch holes and provide aeration without excess soil disruption. Aim to aerate when the soil is slightly moist but not soggy wet. Let the soil dry for a day or two before applying grass seed. The holes serve as perfect seed beds for the grass to start growing.
Apply Starter Fertilizer
Fertilizing is important both before and after overseeding. Apply a starter fertilizer high in phosphorus before seeding to fuel root establishment. The quick start of nutrients helps young grass plants grow stronger faster. Look for fertilizers with a higher middle number, such as 10-20-10 or 12-24-12 analysis. Follow packaging rates for how much to apply based on square footage. Water in after application to avoid burning tender new grass shoots.
Top Dress with Compost
Adding a thin layer of compost or quality topsoil over your lawn before overseeding can provide an optimal seed bed. Aim for around 1/4 inch depth. The organic matter and nutrients in compost give grass seeds what they need to thrive. Rake gently over topdressed areas to lightly work in the compost before seeding. Irrigate afterward to moisten the seed bed.
Mulch with Straw
Mulching over newly seeded areas is highly recommended. Straw is an ideal mulch material that allows sunlight and air to permeate while keeping seeds from drying out. Spread clean wheat or oat straw to a depth of around 1/2 inch. The straw protects tender new grass shoots and helps maintain consistent soil moisture. Take care not to make the mulch layer too thick or it can restrict growth.
Consider Erosion Control Blankets
For overseeding steep slopes or drainage areas, consider erosion control blankets in addition to straw mulch. These blankets provide an extra layer of protection from rain washing away exposed soil and grass seed before it can root. Biodegradable options are available that stabilize the area just long enough for new grass to establish.
Use a Seed Starter
Using a seed starter fertilizer or soil inoculant when overseeding can boost the rate of germination. These products contain nutrients tailored for seedling growth, helpful microbes, and compounds that retain moisture. Mix an appropriate amount into the soil before laying down grass seed. Follow label instructions based on the product and size of area being seeded.
Consider Peat Moss
As a soil amendment before overseeding, peat moss offers useful benefits. It lightens heavy clay soils for better drainage and seed contact. It retains moisture well to keep seeds hydrated longer. And it adds organic matter for beneficial microbes and nutrients. Incorporate a thin layer no more than 1/4 inch deep before sowing your grass seed. Then water thoroughly.
Time Overseeding Carefully
When you do your overseeding is almost as important as what you put down before seeding. For cool season grasses, aim to overseed in early fall when temperatures start to cool but before the first frost. The soil is still warm enough for germination, rainfall picks up, and the lower sun angle puts less stress on tender new growth. Wait 6-8 weeks after spring greenup to overseed warm season grasses.
Allow Time Before and After
Be sure to prep your lawn at least a few days to a week ahead of the planned seeding date. That allows time for any dethatching, aeration, fertilizing, composting, and other steps to settle in. After sowing grass seed, continue light irrigation and leave straw or blankets in place for at least 4-6 weeks until the young grass plants are well established and have been mowed a couple times.
Follow Seeding Directions
Always carefully follow the application rates and instructions on your particular grass seed variety. Use a drop spreader for the most even coverage over your lawn. Divide the amount of seed recommended for your square footage into two batches and apply in perpendicular passes over the lawn. Aim to seed just before an expected period of rainfall if possible.
Conclusion
Proper lawn preparation is crucial prior to overseeding for the best results. By removing debris, mowing low, dethatching, aerating, fertilizing, topdressing, and mulching beforehand, you set up optimal conditions for grass seed to flourish. Pay close attention to timing and seeding directions as well. With the right steps before and after overseeding, you can achieve a lush, thick lawn.