Overseeding a lawn twice in the spring is possible, but it’s generally not recommended. There are a few key factors to consider when determining if a second spring overseeding is a good idea for your lawn.
When to Overseed in the Spring
The optimal time for spring overseeding is early to mid spring, which gives the new grass seeds time to germinate and establish before the heat of summer sets in. This window generally falls between late March and late April, but can vary slightly depending on your region and climate conditions.
Cool season grasses like fescue and bluegrass do best when overseeded in the spring, as the moderate temperatures and increasing daylight provide ideal growing conditions. Warm season grasses like bermudagrass are best overseeded in the late summer/early fall when temperatures start to cool.
Challenges of Overseeding Twice
There are a few potential challenges and drawbacks to overseeded twice in one spring:
- Overseeding too early when soil temps are still cool can lead to poor germination. Air and soil temperatures should be consistently above 50-55°F.
- Overseeding too late can mean new grass doesn’t have enough time to establish before summer stress sets in.
- Two rounds of overseeding can thin out existing grass and cause competition between new and old seedlings.
- Double overseeding leads to higher costs from extra seed, materials, water, etc.
- You run a higher risk of disease or fungus outbreaks in the dense, newly seeded areas.
Because of these potential issues, overseeding twice is generally not recommended. The new seed from the second round would be going into conditions that are not as ideal and would have less time to get established.
When a Second Overseed May Make Sense
In some cases, a second spring overseeding may be justified:
- If the initial seeding was done too early and resulted in poor germination, reseeding once the soil warms up can improve results.
- If your lawn has extensive thin or bare areas, a second overseeding may help fill them in.
- If a significant disease or pest issue damaged the initial overseeding, reseeding may be needed.
- When renovating or establishing a completely new lawn, a second overseed round can help thicken things up.
Even in these cases, however, the second round of overseeding will face challenges. Get the timing right based on soil temps, don’t overseed too heavily, and be prepared to water appropriately.
Keys to Spring Overseeding Success
If you do plan to overseed twice in one spring, here are some tips to help improve your chances of success:
- Wait at least 4 weeks between seedings – This gives the first round time to establish without excessive competition.
- Use half the seeding rate – The reduced seeding density helps prevent overcrowding.
- Mow existing grass low – This helps the new seed make good contact with the soil.
- Aerate if needed – Core aeration reduces compaction and improves conditions.
- Time it right – Overseed when soil temps are optimal, not too early or late.
- Water lightly and frequently – Encourage germination without oversaturating.
Overseeding an already thick, healthy lawn twice in one spring is unlikely to provide good results. But in the right circumstances and with proper timing, technique, and care, a second spring overseed can help fill in bare spots and thicken up a thinning lawn.
Best Practices for Overseeding
To maximize your chances of overseeding success, whether you seed once or twice, follow these best practices:
| Practice | Details |
|---|---|
| Choose quality seed | Select a seed variety well-suited to your climate. Look for high germination and purity rates. |
| Aerate first | Aeration reduces compaction and helps seed make soil contact. |
| Mow low | Mow existing grass down to 2-3 inches before seeding. |
| Apply starter fertilizer | Starter fertilizer provides nutrients to help new grass establish. |
| Scatter seed | Use a spreader for even coverage and proper seeding rate. |
| Rake lightly | Raking helps work seed into soil contact. |
| Roll or press | Rolling firms up seed-soil contact. |
| Water frequently | Keep top 1/4 inch moist for 10-14 days until germination. |
| Mow young grass | Mow as soon as the new grass reaches 3-4 inches tall. |
Following proper overseeding practices will support healthier grass growth and establishment. Adjust your technique based on whether you’re doing a single spring overseeding or an unusual second round.
How Long Does Overseeded Grass Take to Grow?
When you overseed in the spring, the grass seed will take 10-28 days to germinate and begin growing depending on species and weather conditions. Here’s a typical timeline:
- Days 1-10: The seeds absorb moisture and germinate. Little growth is visible above ground.
- Days 10-14: The first new shoots and blades begin to emerge and grow.
- Days 14-28: The new grass continues growing and thickening up. Mowing can begin at around 3-4 inches.
- 4-8 Weeks: The young grass becomes well established and blends into the existing lawn.
So expect to start seeing results in 2-4 weeks after spring overseeding, but wait 4-8 weeks for the new grass to fully mature and achieve an even thickness.
Factors like seed variety, weather, moisture, and sunlight can affect how quickly or evenly your grass fills in. Be patient, and continue proper lawn care through the first couple months of new growth.
Tips for Caring for Newly Seeded Grass
Once you’ve seeded, proper care is crucial for your new grass to thrive. Follow these tips:
- Water lightly and frequently to keep the top 1/4 inch of soil moist.
- Apply a starter fertilizer 2-4 weeks after seeding when grass reaches 3-4 inches.
- Let the new grass grow to 3-4 inches before the first mowing.
- Set mower high (3-4″) on that first cut and gradually lower it over the next few mowings.
- Avoid heavy traffic on newly seeded areas for 4-6 weeks.
- Reseed any bare or thin spots you notice while the new grass is still young.
- Overseed again in fall for winter hardiness in cold climates.
Proper watering and fertilization are especially crucial while new seedlings are establishing their root systems and building strength. Give your lawn what it needs in terms of moisture, nutrients, and care for your seeding investment to pay off.
Should I Use a Lawn Starter Fertilizer When Overseeding?
Using a starter fertilizer when overseeding is highly recommended. Starter fertilizer provides a boost of phosphorus, which helps stimulate root growth and establishment in young grass plants.
Look for a starter fertilizer with a higher phosphorus content, around 25-35% or more. Many also include an even balance of nitrogen and potassium. Slow-release nitrogen is ideal, providing longer-lasting nourishment.
Apply starter fertilizer after seeding at the recommended rate when the grass reaches 3-4 inches tall. This “kick-start” helps the tender new blades develop a strong root system and makes them more resilient.
Applying starter fertilizer gives your new grass the nutrients it craves when growing from seed. An early feeding sets your lawn up for success.
When to Apply
Seed down in spring or fall, starter fertilizer gets put down 2-4 weeks later when the grass reaches mowable height but before it gets too long. This timed application targets the crucial establishment window.
Looking at the Label
When comparing starter fertilizer products, check the phosphorus (P) content. Opt for at least 25-35% phosphorus as P2O5. Avoid “weed and feed” products.
How to Apply
Apply starter fertilizer with a broadcast spreader for even coverage without risk of burn. Follow the product rate for new seedings, usually 1/2 to 1 lb of nitrogen per 1,000 sq ft. Water in lightly after application.
Second Feeding
Give your new lawn another feeding of starter fertilizer in 4-6 weeks for continued root growth and establishment. Then you can switch to a regular balanced turf fertilizer.
Conclusion
Overseeding twice in the spring is possible in certain situations, but it’s generally not ideal or recommended compared to a single spring seeding or seeding again in fall. The best practice is to overseed once when soil temperatures hit the optimal range, usually late March through April.
If you do a second spring overseeding, wait at least 4 weeks between rounds, reduce the seeding rate, and time it based on soil temperature. Follow proper seeding, watering, mowing, and fertilizing practices to support the delicate new grass growth.
Be patient after spring overseeding. It can take 10-28 days for new seed to germinate and 4-8 weeks for the new grass to fully establish and blend into your existing lawn. Proper seeding technique paired with vigilant follow-up care results in the strongest, healthiest spring overseeding results.
