Two of the most important things you can do for your lawn are core aeration and power dethatching. The best time for aeration is either early Spring or late Summer early Fall. Just make sure if you do aerate in the spring that you put down your crabgrass preventer and fertilizer after you aerate, and if you are going to be doing overseeding in the Spring, you will have to use a crabgrass preventer called tuppersan, which will allow the new grass seed to germinate but will not let the crabgrass seed germinate.In my opinion August and September are the best times for aeration. Once you have aerated your lawn it's a good time to fertilize and overseed, make sure to water the new seed 2-3 times a day and your lawn will really start to thicken and green up.
