If your lawn is looking thin or you have lots of bare spots, overseeing in spring can help fill it in. Overseeding cool-season and warm-season grasses in spring is a fairly easy task, and it can net you a healthy lawn, help with weed control (including crabgrass) and promote strong root growth in your lawn.
Although warm-season grasses are generally overseeded in the spring, there’s a lot of confusion and debate around overseeding in spring for cool-season lawns. Some people overseed in late summer or early fall, while others spread new seeds as soon as we “spring ahead” into March and April.
This is my personal guide to spring overseeding for your cool-season lawn in spring rather than in fall. Overseeding can be successful with the right seed and a range of early spring lawn care steps.
Table of Contents
- When Should You Overseed Cool Season Grass?
- Preparing Your Lawn for Overseeding in Spring
- How to Overseed Your Lawn
- Fungicides for Overseeing the Lawn
- Add Fertilizer & Pre Emergent
- Watering the Lawn After Overseeding
- Lawn Care After Overseeding
When Should You Overseed Cool Season Grass?
The best time to aerate and overseed bare spots on the lawn is when the temperatures are consistently in the 50s and there is no snow or ice left on the ground. Warmer weather ensures successful seed germination. Overseed your lawn too early, and you’ll risk killing newly germinated grass and stifle growth due to the cold.
Preparing Your Lawn for Overseeding in Spring
The first step to overseeding lawns (in spring or fall) is to clean up all the debris. Thoroughly rake the lawn to remove leaves, sticks, mulch, dead grass, and rocks. Then, follow these steps to finish preparing your lawn for seeding.
Aerate your lawn
Core aerate your lawn — do a double pass to ensure optimal aeration. Lawn aeration prepares the soil by loosening it up so the grass seed is more likely to germinate. Preparing the soil properly for seeding ensures your grass will grow strong, healthy roots for a lush, green lawn come summer. If you aerated in the fall as part of your winter preparation strategy, you may not need to do it again before reseeding in spring.
Enhance the soil
Healthy lawns need healthy soil. Test your soil’s pH, and add soil amendments as necessary. Add compost to the soil of your lawn if it’s needed.
Enhance the soil with Kelp4Less ExtremeBlend or Green Lawn & Turf. These contain essential nutrients for your soil, including humic, amino, and fulvic acids, along with sea kelp. Green Lawn & Turf also contains molasses powder and iron sulfate — use coupon code NELCA for 25% off. These products can be applied to lawns before or during overseeding.
Level, scarify, scalp, and dethatch
Level and scarify the existing lawn to get good seed-to-soil contact. If there is any turf on the lawn, scalp it by mowing with the blade set as low as possible. Rake or bag and compost the grass clippings to keep them off the soil so they don’t prevent the seeds from germinating.
Dethatch your existing lawn with a rake to ensure there’s nothing standing between the soil and the grass seed.
How to Overseed Your Lawn
Overseeding your lawn each spring is part of a holistic lawn care routine that ensures your turf will enjoy optimal root growth and natural weed control once summer temps arrive. Here’s how to overseed existing lawns.
Choose the right grass seed
Find a good quality grass seed like Jonathan Green Black Beauty Ultra or GCI TTTF, and aim for 5-9 lbs. per 1,000 sq. ft. of lawn, depending on how many bare spots you have. For a lawn with a lot of bare spots, you’ll want to do a heavy overseed (5-7 lbs. per 1,000), but if your lawn is brand new, you’ll get by with less seed. Whatever type of grass seed you choose to use, make sure it’s a high-quality seed for the best results.
Choose the grass seed species and blend that is best suited for your exact zone and your lawn. Websites such as Seed Super Store and Natures Seed can answer questions about what type of seed is best for overseeding lawns in spring (or fall.) Choose the season grass seed species and blend that is best suited for your exact zone.
Spread the seed on the turf
To spread your grass seed on the lawn, use a rotary spreader, drop spreader, or slice seeder. Follow the directions on the grass seed bag, and make sure the seeds are evenly distributed throughout the lawn. Remember: more grass seed isn’t better! Over-overseeding your lawn means the seeds have to compete with each other for soil space, and you’ll end up with a bunch of die-offs.
Fungicides for Overseeing the Lawn
Springtime temperatures are ideal for lawn fungus to start brewing in lawns, so as soon as it starts getting warm, it’s a good idea to add a fungicide to your spring lawn care routine. Increases in the daytime and nighttime temps, high humidity levels, and rain provide the perfect conditions for lawn diseases.
As the new grass seed germinates at the start of the warm season (between 7, 10, and 21 days for ryegrass, fescue, and KBG respectively) the new grass is particularly vulnerable to fungus growth. To ensure your new grass grows healthy with strong roots, add a preventative after overseeding, such as Propiconazole and/or Azoxystrobin.
Liquid or granular fungicides will not interfere with your overseeding and will ensure a healthy lawn later on.
Add Fertilizer & Pre Emergent
Adding fertilizer and a pre-emergent herbicide to your lawn is very important for controlling weeds like crabgrass. But for preventing weeds in new grass, you’ll need Tenacity. Add these to your lawn immediately after you spread the new grass seed. We can go a couple of different routes here:
- Use an organic (slow release nitrogen) or synthetic starter fertilizer (fast release nitrogen) with crabgrass control. I prefer Jonathan Green 10-15-10 starter with crabgrass control. This contains Siduron (tuperspan) which has an efficacy of ~6 weeks in the soil as a pre-emergent for weeds.
- Same as above, but you may substitute Scott’s Starter with Mesotrione (Tenacity) for Jonathan Green. However, the pre-emergent qualities won’t last quite as long in your soil as Siduron, so you’ll need to watch out for crabgrass and other weeds and treat them as soon as possible.
- Use a combination of an organic (slow release nitrogen) and synthetic starter fertilizer (fast release nitrogen) at full bag rates. Milorganite is popular, but some milorganite alternatives that I’m partial to include Jonathan Green 8-0-1 (for 0.6 lbs of N per 1,000) and Lesco Starter 18-24-12 (for 0.72 lbs. Of N per 1,000). Mix ½ tsp of Tenacity to 1 gallon of water to cover 1,000 sq ft. of lawn. Do not use a non ionic surfactant (NIS).
Watering the Lawn After Overseeding
After you overseed your lawn, water the new grass seed thoroughly. To help prevent runoff and keep the birds from eating your new seed, lightly cover your seeds with peat moss, straw, or Pennington’s Slopemaster. This will also help keep your grass seed damp and promote seed germination.
The most important thing of all is to make sure your soil stays moist after you overseed. If the soil dries out, the overseeding won’t be successful, because the seeds won’t germinate. A quick 10-minute shower anywhere between 2 to 3 times per day should do the trick.
Lawn Care After Overseeding
The most important lawn care tip for overseeding is to keep off the grass! If you trample on the new grass, you’ll prohibit its growth and damage the delicate new grasses. Put signs up on your lawn to keep people off until the seeding is successful and the new growth is fully established. Here are some other important considerations for lawn care after overseeding.
Before you start to mow your new lawn, take your lawnmower in to have it cleaned and get the blade sharpened. Sharp blades prevent the new grass from bruising and tearing, which can increase the risk of common lawn diseases. A dirty lawnmower can cross contaminate your new grass if any fungus or diseases are present. Mow your new grass once it’s grown to at least 3 inches in height.
Add a post-emergent to the lawn
Roughly 6 weeks post-germination, and after the lawn has been mowed 2 to 3 times, add Lesco 19-0-7 Dimension. This product has post-emergent weed control qualities that can kill crabgrass and dandelions up to the 3rd leaf stage. It also acts as a fine pre-emergent that can help you control crabgrass and ward off any additional weeds throughout the summer.
Add nitrogen regularly
Continue to spoon feed Nitrogen at 0.25 lbs. per 1,000 every other week. Use a Nitrogen Calculator to help with application rates. I also highly recommend soil amendments – specifically Kelp4Less – bi-weekly throughout the growing season to provide your lawn with the nutrients it needs to grow tall and strong. This is a fantastic product and is safe to use for all-season grasses, all season long.
I hope this helps demystify and take the stress out of spring seeding. Would love to hear feedback in the comments!