A lawn aerator is a garden tool

Garden tool

A garden tool is any one of many tools made for gardens and gardening and overlaps with the range of tools made for agriculture and horticulture...

 or machine designed to aerate the soil

Soil

Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

 in which lawn grasses

Lawn

A lawn is an area of aesthetic and recreational land planted with grasses or other durable plants, which usually are maintained at a low and consistent height. Low ornamental meadows in natural landscaping styles are a contemporary option of a lawn...

 grow. Aeration

Aeration

Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid or substance.-Aeration of liquids:-Methods:Aeration of liquids is achieved by:...

 improves soil drainage and encourages worm

Worm

The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...

s, microfauna

Microfauna

Microfauna refers to microscopic organisms that exhibit animal-like qualities. Microfauna are represented in the animal kingdom and the protist kingdom...

 and microflora which require oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

.

Lawn problems

Lawn aeration constitutes two things: controlling lawn thatch and reducing soil compaction

Soil compaction

In Geotechnical engineering, soil compaction is the process in which a stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water being displaced from between the soil grains then...

. Lawn thatch is a layer of dead organic tissue that deprives the lawn of much-needed oxygen. Soil compaction makes it difficult for grass to root and it disturbs natural rainwater irrigation

Irrigation

Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

. Watering the lawn the night before aerating can make it easier to aerate a very dense lawn.

It is purported that scientific evidence exists that aeration makes a measurable difference in the long-term health or quality of a lawn.

Also is great for the planting of new lawns.

Types of aerators

There are two types of lawn aerators. Spike aerators use wedge shaped solid spikes to punch holes in the soil. Core aerators have hollow tines and pull out plugs (or "cores") from soil.
Core/plug aerator vs. spike aerator

A core/plug aerator removes soil from the ground and leaves the core on the turf. This reduces compaction in the soil, and the holes can stay open for a long time. Then air, fertilizer, and water will be able to reach the roots, thus benefit the grass. Meanwhile, the soil cores left on the turf will help break down the thatches.

A spike aerator creates holes in the ground by pushing the soil sideways using wedge-shaped spikes. This increases soil compaction, which is detrimental to the grass. Since there is no soil removed from the ground, water will make the compacted soil around the holes to expand and close up the holes in a short period. The lawn will return to its pre-aeration condition. Therefore the benefits of aeration will not be fulfilled.

Any serious lawn aerating should be done with a core aerator.

Powered aerator vs. manual aerator
Powered aerators employ the power from a gas engine to drive multiple tines into ground. They usually weigh hundreds of pounds and can aerate a large lawn in relatively short time (similar to mowing speed). This type of aerators are expensive and often owned by contractors or rental services.

Manual aerators usually have two or three tines mounted on a step bar. Operator puts one foot on the step bar and push it downward, forcing the tines to penetrate into the soil. Then he pulls the handle on the step bar upward to remove the soil cores out of the ground. By repeating the same operation, the cores left in the tines will be pushed out by next ones. Manual aerators are much cheaper than powered ones. The trade-off is the speed. For a typical residential lawn (1/4 acre lot), it will take hours to finish. Some products also have clogging issue, which slows down the operation even more. However, a well-made manual aerator offers advantages such as ease of use, selective aeration, and economy.

Brands

The main brands of aerators in the United States are Agri-Fab

Agri-Fab, Inc.

Agri-Fab, Inc. is a manufacturer of lawn and garden attachments located in Sullivan, Illinois. Agri-Fab operates a . manufacturing facility and at peak season employs nearly 400 employees in a town of 4,700 and the surrounding area...

, EZ CORE, Brinly-Hardey, Ohio Steel, Precision, and Swisher among others.