De-mystifying the art of Dethatching, Core Aerating, and Overseeding
by our Turf Tech Vance
Lawns can be beautiful, but great turf takes a bit of effort to maintain.
What is Thatch?
Thatch is the layer of light brown matter that builds up between the soil and the green grass of your lawn. Thatch is necessary to promote a healthy lawn. It contains living, Decaying, and dead organic matter that naturally feeds your lawn. However, too much thatch can make it difficult for moisture to penetrate to grass roots, and can become a breeding ground for pests and pathogens. It’s generally recommended that homeowners seeing 1/2 inch or more of thatch invest in dethatching. Please note: you should only dethatch your lawn if it is needed!
What is Core Aeration?
Core aeration is the process of pulling out a plug of grass and soil approximately 1/2 inch wide and 3 inches long. This is usually done with an aerator – a small machine or attachment that quickly pulls up multiple plugs simultaneously with consistent spacing.
By removing plugs of soil from the lawn, homeowners relieve soil compaction, increase gas exchange and water availability to the roots. This promotes healthy grass growth in the coming year. Two or three passes in different directions with an aerator annually should do the job.
Grass isn’t Immortal
After several years, mature plants begin to slow down their reproduction rate. Since a blade of grass lives for a limited time – only an average of 45-60 days – your lawn must continually produce new blades of grass faster than old blades die off. Young grass produces blades faster than older grass. As a result, one of the best ways to maintain a healthy, thick lawn is to make sure your grass is young. The practice of overseeding is the easiest way to accomplish this.
When should I Dethatch, Core Aerate, and Overseed?
Ultimately, it depends on the type of turf you have. Dethatching can be stressful for your lawn, so timing is important. Warm season grasses should be dethatched (if needed), aerated, and overseeded in the late spring or early summer. This gives the turf its entire growing season to recover from the dethatching and to get the most benefit from the aeration.
If you have a cool season turf you should dethatch (if necessary) in late August or early September. Follow up with core aeration and overseeding. There are many reasons for this. Cool season grasses that germinate in the fall will have 2-3 months to become better established before temperatures drop too low and growth stops. The following spring they will have another couple of months to develop a stronger root system before the summer heat sets in.
How should I Dethatch, Core Aerate, and Overseed?
Simple – one step at a time! But the order it’s done in is important.
Step 1. Mow your lawn a little shorter than normal. This might sound strange, but it’s an important first step. Grass seed can’t germinate unless it lands on the soil and has enough sunlight. By cutting the lawn a little shorter, you’re increasing the odds your seed will begin to grow.
Tip: Don’t mow again until the seed germinates and reaches at least 2 inches in height (approximately 2-3 weeks, depending on the seed type). If you mow before the seed germinates, you run the risk of picking up loose seed. Remember, contact with soil and moisture is important!
Step 2. Dethatch – but only if needed.
Step 3. Core Aerate.
Step 4. Overseed. After overseeding your lawn, the seeds will need moisture to germinate. Keep the soil moist (but not overly wet) by lightly sprinkling 2-3 times a day throughout the required germination period. Once your grass begins sprouting, you can move to watering less frequently and more deeply.
The greatest danger to seedlings is overwatering and soaking the soil, which could lead to disease (root rot) problems or under watering and drying out the tiny roots. The second greatest problem is if you have high heat periods that cook the tender roots when the ground gets too dry.
Generally when overseeding lawns, the existing grass provides cover and shade. In poor lawns with lots of exposed dirt, the soil will need to be raked to cover the seed with a thin layer of dirt or straw.