It is good to aerate the lawn every year. The best time is usually after the plant has emerged from dormancy and established itself in the spring usually in April or May depending on the area of the country.
Lawns can also be aerated mechanically late in the growing season, usually August or September. Mechanical aeration which can be performed by commercial lawn services will serve to open up the soil, especially if your soil is compacted and if you have excess thatch. It will also tend to smooth the unevenness in lawns.
The natural and organic liquid fertilizers mentioned in this post can be easily ordered online, as are the amendments and other natural lawn care products.
A very good alternative to hiring a service to mechanically aerate the lawn is the use of natural and organic liquid soil amendments such as ECO Lawn & Garden Super Soil Plus or ECO Lawn & Garden Soil Amend Plus. These liquid lawn aerators serve to aerate the soil without using mechanical aeration. They are easily applied with a hose-attached sprayer.
The liquid lawn aearation products penetrate the soil — a process called Flocullation — using a plus-minus attraction principle to loosen the soils to allow more air and water to penetrate the soil.