In Colorado, there are two times of the year that you should have your yard aerated:
SPRING AND FALL
As soon as the ground has thawed from that winter chill, you should be looking to get your yard aerated. The conditions are perfect to get great plugs. Any recent snow has melted and the Spring heat has thawed the ground. You won’t have to do much prep.
Mid-March is the perfect time to start and you can get your lawn aerated until the end of May. After May you run the risk of burning your lawn by exposing the roots to early summer heat.
A good rule of thumb is to always fertilize the same day as your aeration. During your Spring applications, you should apply a higher Nitrogen(20%) fertilizer with a good blend of Phosphate(5%) and Potassium(10%). The 20-5-10 mixture is a good basic blend for a Spring application.
As the season starts to wind down but before your yard goes dormant, you should have your Lawn Care Professional complete the second aeration for the season. The soil is still ideal for pulling great plugs and if it’s done before mowing stops, you’ll be able to mulch the plugs back into the lawn to retain its nutrients.
The timing for your Fall aeration should start by the beginning of September. You can obviously aerate your lawn until the soil freezes but the earlier in the Fall the better.
Once again you’ll want to apply fertilizer after the aeration. An ideal Fall blend will have Nitrogen(24%) Phosphorus(4%) and Potassium(12%) with Isobutylidene diurea.
A good aerate in the Spring creates space in the soil and roots that promotes growth in the Summer. The holes that the plugs create allow water to keep the soil moist. A good aerate in the Fall also creates holes for snow and early Fall rain to keep the soil moist also.