Chances are good that the lawn hasn’t been aerated in the past few years . . . if ever.
Compaction is a physical process that slowly reduces the amount of oxygen contained in the soil and nutrient movement to the roots . . . the critical part of a healthy grass plant. Roots of the plant need oxygen, and as a product of their growth process, give off carbon dioxide. As compaction increases, less and less oxygen can enter the soil and less carbon dioxide can escape. The net result is a gradually thinning lawn until, ultimately, the soil can no longer support any turf growth.
Aerification will prevent or help a number of problems, including compaction and thatch build-up. It opens passageways in the soil, allowing better air, water, and nutrient movement. During drought conditions, aeration helps water reach thirsty roots. When rain is heavy, it allows air to penetrate and help dry up excess moisture. Each is a stress condition for your grass.
Fall and spring are the best times to aerate . . . and also for overseeding and renovating with improved varieties of cool-season lawngrasses. Mid-spring to early summer are best for warm-season grasses like bermuda or zoysia. When the existing lawn is in fairly good condition and overseeding is being used to thicken the lawn, one or two passes with a core aerator may be the only soil preparation required. Weak existing grass, with a greater need for seed, may require additional passes with the aerator to open the soil properly.
For the best overseeding results with core aeration, rake the cores to the point where the holes are filled one-half to three-quarters with soil before applying the seed blend or mixture. Next spread a starter-type fertilizer that is higher in phosphorous (P) and potassium (K) than nitrogen (N). Then rake the remaining cores back into the soil. With this procedure, the seed should be covered enough to allow germination.
If you decide to pickup the cores, spread a light topdressing to partially pre-fill the aeration holes before seeding. Then lightly cover the seed and fertilizer with additional topdressing.
Proper watering is the major key to success. Like establishment of a new lawn, renovated or overseeded lawns need to be kept moist, but not soaked, until the new seeds begin to develop and grow a new root system. In 4 to 6 weeks, a normal watering program can be resumed.
With more than 50% of the lawns in North America more than 10 years old, most could benefit from aerification and the planting of new lawn seed varieties to produce a healthier, denser lawn.
-The Lawn Institute