How to Overseed a Lawn

19341219 – hand planting grass seed for overseeding green lawn care

Cool Season Grasses have a growth cycle that is most active in the Spring and Fall. Therefore overseeding will have the highest likelyhood of success if done while temperatures are generally more moderate and natural moisture is more prevalent.

Kentucky Bluegrass is a cool season grass which takes about 14-21 days to germinate therefore you need to make sure you can plant and maintain the overseeding for at least 21 days. Here are some tips to ensure that you successfully increase the health of your lawn.

Before you start: Plan and Prepare

Several factors need to be considered before overseeding your lawn. If the daily high temperature is over 85 degrees F you should wait until more temparate weather.

  • Stop fertlizing at least 1 month prior to overseeding.
  • Calculate the square footage of your lawn. Multiply length by width in feet to get the square feet. If the lawn is not perfectly rectangular break it into smaller sections, calculate the square footage of each section and then add the totals together to get a final size.
  • Ensure that you have an adequate irrigation system to water your lawn. Fix sprinkler heads, check for coverage from head to head, and make sure you know how to program the master controller. If you plan on using a hose end sprinkler ensure you have a plan on how to keep the soil from completely drying out for at least 21 days.

Mow, Dethatch & Aerate

Thatch is the layer of dead grass that lies between the base of the grass blades and roots. Thatch helps to choke out weeds and foriegn grasses, but if it is too thick can also prevent Air, Water and Nutrients to arrive at the roots of your lawn. A healthy thatch layer should be 1/2″ or less. Mulching clippings when you mow will help the clippings to break down faster and will generally prevent the thatch from getting too thick. It is a good idea to rake thatch out of your lawn early in the growing season, and especially before you overseed.

  • Start by mowing your lawn to 1-1.5″ For this mowing it is best to remove the clippings.
  • Using a metal hand rake or a power rake go over your lawn twice, in opposite directions and remove the thatch that is raked from the lawn. Be careful not to be too agressive so as not to damage the blades of the existing health lawn.
  • Aerate your lawn to loosen up the soil bed. If you plug aerate, leave the plugs on the lawn as these will break down and return soil and other nutrients back to the growing bed.

These steps allow the seed easier access to the soil bed and give seed a better chance to start growing it’s roots.

Treat Bare Spots

Overseeding can also help with any bare spots in your lawn. To remedy bare spots, rake the spots down to the soil, add fresh topsoil before you overseed. This will improve the quality of the soil and help the grass grow. 

If bald spots are caused by water drainage problems first make sure that you aerate the area. This can be done with a shovel overturning the soil to loosen it up. If you have clay based soil this is necessary to break up compaction which may prevent seed from putting roots down into the soil bed.

Overseed & Fertilize

  • Spread your grass seeds evenly around the lawn. Use a broadcast spreader, drop spreader or handheld spreader. 
  • Apply the lawn fertilizer that works best for your type of grass. Slow-release fertilizer provides nutrients gradually, for as long as three months in some cases. 
  • Lightly water the lawn immediately after overseeding. 
  • Ensure that the soil doesn’t dry out for 14-21 days. Do not overwater, just make sure the soil isn’t completely dry. This will help the seeds germinate. 
  • If you are overseeding bare spots consider putting straw or mulch down over the seeds to prevent birds from eating the seed and to help slow evaporation.
  • Once the grass is an inch tall, cut back to watering once a day. After about 6 weeks you should be back to your normal watering schedule of about 1″ every 7-10 days.

Ongoing Maintenance

  • Maintain your lawn at 2-3″ throughout the warm season. Always wait until the grass is dry before you mow. Never cut more than 1/3 of the blade at a time to prevent excess thatch. If you cut more that 1/3 of the blade it can put the lawn into shock which will require increased water and fertilizer.
  • Fertilize the lawn about six weeks after you sow the seed. We recommend 3-4 fertilizer applications each season (Memorial Day, Independence Day, Labor Day, and Halloween). Apply a pound of quick-release nitrogen fertilizer for every thousand square feet of lawn space. For example, if your lawn is 5,000 square feet, you would need five pounds of quick-release nitrogen fertilizer for your specific grass type.  Download our Watering and Fertilizer Guide Here.

Once you know how to overseed a lawn, you’re well on your way to a better lawn. Overseed your lawn to keep it healthy, repair damage or fill in bare spots. Remember to identify your grass type before you begin. Then mow, dethatch and aerate your lawn. Ensure the soil bed remains damp for the first several weeks. After you can see the seed has germinated you can start cutting back on water. Wait at least six weeks before fertilizing. 

For a more in depth explanation on lawn care maintenance download our Residentail Lawn Care Guide.