Overseeding a lawn can help thicken up thin or patchy areas by introducing new grass seed. Many lawn owners wonder if they need to cut the existing grass very short before overseeding to help the new grass seeds better reach the soil. There are pros and cons to cutting grass short before overseeding that depend on the type of grass, time of year, and overall lawn conditions.
Quick Answers
Should you cut grass short before overseeding?
There is no definitive “yes” or “no” answer. Cutting grass short before overseeding can help with seed-to-soil contact but risks stressing the existing lawn. Most experts recommend mowing only slightly lower than usual before overseeding.
How short should you cut grass for overseeding?
Cutting grass 1-2 inches shorter than normal just before overseeding is usually sufficient. For tall fescue lawns, mow to 3 inches. For bluegrass and ryegrass, aim for 2 inches. Avoid scalping the lawn below these heights.
When should you cut the grass before overseeding?
Cut the grass 4-7 days before overseeding. This allows time for grass blades to dry out while still being short enough for good seed-to-soil contact. Avoid cutting immediately before overseeding.
Should you dethatch before overseeding?
Light dethatching can help with seed-to-soil contact but risks lawn damage. Consider verticutting instead of aggressive dethatching. Overseeding without dethatching can still be successful if irrigation and soil contact are adequate.
Do you need to aerate before overseeding?
Aeration is strongly recommended before overseeding, especially for compacted lawns. It allows seeds, water and nutrients to penetrate the soil. However, overseeding can still work without aerating first.
Should You Cut Grass Short Right Before Overseeding?
Many experts advise against cutting grass extremely short right before overseeding. Here’s why:
- Scalping the lawn below 1-2 inches causes excessive stress.
- Overly short grass blades lose the ability to photosynthesize and recover.
- Scalped lawns are more prone to weed and disease problems.
- Exposing a lot of bare soil leads to increased water evaporation.
- Short clippings decompose faster, potentially causing nitrogen deficiencies.
However, not cutting short enough defeats the purpose of preparing for overseeding. Leaving grass too tall prevents solid seed-to-soil contact.
Finding the right mowing height is crucial before overseeding – not too short but not too long.
Ideal Grass Height for Overseeding Prep
Most turfgrass experts recommend cutting the grass approximately 1-2 inches shorter than the regular mowing height just prior to overseeding. This adequately reduces shade and competition for the grass seedlings without overly stressing the lawn.
Here are some typical target heights to cut down to before overseeding:
| Grass Type | Overseeding Height |
|---|---|
| Tall fescue | 3 inches |
| Kentucky bluegrass | 2 inches |
| Perennial ryegrass | 2 inches |
| Fine fescue | 2-3 inches |
These heights favor seed-to-soil contact while avoiding scalping and lawn stress. Go any lower and you risk thinning out the existing grass.
Of course, raising mowing heights slightly leading up to overseeding makes this final height cut less dramatic. Just don’t gradually raise heights during hot, dry summer weather. Doing so encourages shallow rooting.
When to Cut Grass Before Overseeding
Timing the last mowing before overseeding is also important:
- Cut 4-7 days before seeding. This allows grass blades time to dry before seed is applied.
- Never cut right before seeding. Freshly cut leaf blades can form a physical barrier.
- Cut once seeding preparations are complete. Avoid foot traffic on freshly cut grass.
Cutting earlier gives grass time to recover while leaving a relatively short canopy at seed down time.
Aim to cut once the weather has cooled but before temperatures drop below 70°F. Lower temperatures slow growth and recovery.
Ideally time the last mowing so seeding happens as grass growth naturally slows in early fall. Spring overseeding requires more precision.
Should You Dethatch or Verticut Before Overseeding?
Dethatching and verticutting are sometimes used to prep for overseeding as they further reduce shade and thatch buildup. However, both are controversial before overseeding.
Dethatching Pros:
- Removes dead material that can block seed-soil contact.
- Opens up the lawn canopy even more.
- Can provide channels for improved seedling root growth.
Dethatching Cons:
- Causes significant damage and thinning of existing grass.
- Increases demands for watering new seedlings.
- Opens up extensive bare areas vulnerable to weeds.
- Can spread lawn diseases present in dead material.
Many experts advise overseeding a lawn without dethatching first, except in cases of major thatch buildup.
Verticutting may offer benefits with less damage. The verticutter blades slice vertically into the lawn thatch without fully removing it. This can improve seed-to-soil contact with less disruption to the existing grass.
Should You Aerate Before an Overseed?
Aerating is one of the most important components to prepare existing grass for overseeding. Solid tine aeration helps in several key ways:
- Alleviates soil compaction that restricts root growth.
- Creates seed channels that improve contact and growth.
- Allows better water, air and nutrient penetration.
The pores and channels made by aerating promote healthier seedling establishment.
Cool season grasses are best aerated in early fall. Warm season grasses can be aerated during spring or summer before overseeding.
Ideally, aerate the lawn 4-7 days before seeding. Core holes partially close up after several weeks, so aerating long before overseeding loses much of the benefit.
However, seeding without aerating is certainly still better than skipping overseeding altogether in cases where aeration isn’t possible.
Lawn Aeration vs. Dethatching for Overseeding Prep
If you can only perform one major task before overseeding, choose aeration over dethatching. Here is how they compare:
| Aeration | Dethatching |
|---|---|
|
|
Targeted verticutting is an acceptable alternative if thatch buildup is excessive. But overall, aeration is the best preparation for most lawns before overseeding.
Skipping Some Overseeding Preparation
What if you have to overseed without thoroughly dethatching, verticutting, aerating and mowing short? Don’t panic, you can still achieve success. Here are some tips:
- Overseed even if you can’t cut grass as low as recommended. Longer grass only moderately reduces germination.
- Hand rake extremely thick or matted areas before seeding to improve contact.
- Consider slit seeding by barely parting the grass canopy with a screwdriver or knife tip before dropping in seed.
- Water newly seeded areas frequently and deeply to keep soil moist despite less-than-ideal contact.
- Reseed again in future seasons for cumulative improvement.
With extra care and attention, overseeding can still work almost as effectively without intensive pre-seeding lawn preparation.
Best Grass Seed for Overseeding
Choosing the right grass seed mixture maximizes overseeding results. Consider blending 2 or 3 high-quality cultivars that offer the best attributes:
Ryegrass
- Fast germination and establishment
- Dark green color
- Medium leaf texture
- Requires more mowing
Fescue
- Deep root system
- Heat and drought tolerance
- Fine leaf texture
- Slower to germinate
Bluegrass
- Low growth habit
- Rich green color
- Dense, attractive turf
- Slow germination and establishment
Always choose grass seed suited to your climate zone and lawn conditions. Use elite improved varieties over older types. Certified seed ensures quality, purity and viability.
Overseeding in Spring vs. Fall
Fall is usually the best time to overseed cool season grasses like fescue and bluegrass. Spring overseeding can work but faces challenges:
Fall Overseeding Advantages
- Mild weather minimizes stress on new seedlings.
- Cooler soil temperatures deter weed seed germination.
- Less competition from established grass.
- Natural grass growth slowdown over winter.
- Full growing season to mature before next summer.
Potential Spring Overseeding Issues
- Hot, dry weather stresses young grass plants.
- Excessive weed pressure.
- Rapid growth from mature grass competes with seedlings.
- Less time to establish before summer.
- Transition between cool and warm temperatures.
However, spring overseeding can still succeed with proper preparation, seed selection and attentive care. The advantages of fall overseeding make it preferable when practical.
When to Expect Germination After Overseeding
The germination window after overseeding depends on grass type and weather:
- Perennial ryegrass: 5 to 10 days
- Tall fescue: 10 to 14 days
- Kentucky bluegrass: 14 to 21 days
- Fine fescue: 14 to 30 days
Cooler fall temperatures extend germination times. Prioritize watering for 2 to 3 weeks after seeding to ensure adequate moisture for germination.
Look for the first seedlings to appear within 1-2 weeks. It can take an additional 2-3 weeks for full germination. Grass will continue maturing over the rest of the growing season.
Caring for New Grass After Overseeding
Proper lawn care after overseeding gives grass plants the best chance at survival:
- Mow existing grass very high so as not to damage young shoots.
- Irrigate lightly and frequently to maintain moist soil without runoff.
- Apply starter fertilizer low in nitrogen to support seedling growth.
- Consider using tenacity herbicide to deter weed pressure.
- Be patient and wait at least a month before reassessing bare spots.
After the new grass matures, gradually resume normal mowing heights, fertilization and weed control.
Fixing Bare Spots After Overseeding
Don’t be discouraged if some areas remain thin or bare after the initial overseeding. There are several options to further improve coverage:
- Overseed bare spots again if significant issues remain after one month.
- Hand scatter additional seed in troubled areas.
- Try slit seeding by cutting shallow furrows in bare soil and drop in seed.
- Consider spot aerating, dethatching or topdressing troublesome areas.
- Improve irrigation coverage or frequency.
- Assess shade factors limiting growth.
With patience and targeted follow-up, even challenging lawns can fill in beautifully after overseeding.
Conclusion
Preparing existing turf properly is key to overseeding success. Cutting grass too short causes excessive harm, while leaving it tall limits seed-to-soil contact. Mowing approximately 1-2 inches lower than usual just before overseeding balances reduced shade with lawn stress. Aerating, verticutting and dethatching can also enhance overseeding outcomes but require caution to avoid damage. Overseeding in early fall maximizes chances for seedling establishment before winter dormancy. Proper seed selection, frequent irrigation and attentive follow-up care leads to optimal lawn thickening. With the right process, overseeding can thicken up thin, patchy lawns effectively.
