Deryn Davidson, Colorado State University Extension – Boulder County

After our last round of heavy wet snow, spring has sprung along the Front Range. Birds are chirping, flowers are blooming and spring chores abound! On a recent neighborhood chat group, the topic of core aeration came up. This is one of the best things you can do for your lawn and now is a great time. It helps reduce soil compaction, increases water infiltration to the turf roots and helps keep thatch build-up to a minimum. This relatively simple task improves the overall growing conditions of your turf and will result in a healthier lawn.
It is recommended that you aerate your lawn at least once a year, twice if you can swing it. Spring and/or early fall are ideal times because the grass will have time to quickly recover and it’s not too hot when the grass might be stressed.

You can aerate your lawn yourself by renting a machine, or hire a professional. In most instances I’m a DIYer, but this is a service I would look to the pros for help with. The machines are big and heavy, and the job is done fairly quickly, so why not let them handle it. Landscape and lawn care companies are on the list of essential services, so they are out there and ready for work.

Whether you hire someone or tackle it yourself, make sure the machine being used is a core aerator. It will have metal tubes or tines that remove plugs of soil and that is the key. The goal of aeration is to make your lawn “Swiss cheese” with as many holes as is reasonably possible. Different, seemingly similar machines have spikes that push holes into the ground which compacts the soil more.

There are few steps you’ll want to do before aerating. Check the moisture level of your soil. You don’t want it too dry because the machine won’t be able to pull good, deep plugs and you don’t want it too wet because the weight of the machine may tear up your lawn and the plugs can get stuck if the soil is too muddy. If you need to water your lawn a few days prior, go for it, or if you can time it after a period of natural precipitation that’s even better. You also need to mark your sprinkler heads, cable lines and any shallow irrigation lines with flags, paint or really anything that shows whoever is running the machine where those are. The metal tines should ideally go 2-3” deep and will easily punch through most things in its path.

Now, back to the Swiss cheese. For a typical lawn you want the holes to be on roughly 2” centers which means several passes going in different directions; up, down, diagonally, etc. If you’re doing the work yourself you can make that happen, if you’re hiring someone, you can ask them to make several passes to ensure adequate aeration.

Once the work is done, your lawn will be covered in the plugs and look pretty roughed up. That’s ok! It’s best to leave the cores on the lawn as they will break down over time, especially once you start mowing regularly, and add great organic matter to your lawn. If you don’t want to leave them, you can rake them up and add them to your compost pile.

Post-core aeration is a great time to seed or fertilize. The holes make perfect germination chambers for seeds, and fertilizer will drop down to the root system after a good watering. If you plan on putting down crabgrass preventer then you’ll want to wait until August to seed because the crabgrass preventer will kill all seeds including the grass seeds.

By Deryn Davidson. Deryn is an Extension Agent – Horticulture at Colorado State University Extension Boulder County. For more information contact CSU Extension at the Boulder County Fairgrounds, 9595 Nelson Road, Box B, Longmont, 303.678.6386, e-mail [email protected] or visit