Modern lawns require a great deal of care and attention in order to nurture a thick green carpet of grass. Such care includes consistent mowing, watering, and thatching, as well as periodic overseeding and fertilization. In addition, it is imperative that a healthy lawn be aerated at least twice a year and, preferably, even more often. Aeration usually entails creating a multitude of closely spaced small holes in the surface of the ground to assist in the absorption of oxygen and nutrients into the soil. The holes also tend to increase moisture penetration into the soil and serve as receptacles for grass seed to prevent the seed from being washed away and to promote germination and growth.
Numerous lawn aeration devices have been available. One such device comprises a large cylindrical drum studded about its periphery with a plurality of short radially extending spikes. The drum is rolled or pulled over the ground and, as it rolls, the spikes are driven into the soil to create shallow holes. While this device is widely used and has proven somewhat successful, it is nevertheless plagued with numerous problems and shortcomings inherent in its design. For example, since the spikes necessarily engage the ground at an angle and are rotated laterally through the soil, significant force is required to penetrate the ground and move the spikes through the dirt. As a result, the drums of these devices generally are relatively large and usually are filled with water or sand to provide sufficient weight to drive the spikes into and through the soil. In some instances, auxiliary racks are provided to load even more weight onto such aerators. To frustrate matters more, the density of spikes on the drum and thus the density of holes the aerator can make in the soil is severely limited since the weight of the device is inherently inadequate to drive more than a few of the spikes at a time into and through the soil. Finally, as each of the spikes of this device is forcibly driven into the soil, it pushes aside and down the dirt to make room for the spike. This is the action that actually creates the hole; however, it also necessarily compacts and hardens the soil around the sides and bottom of the hole. As a result, penetration of air from within the hole into surrounding soil is reduced as is the penetration of moisture. Consequently, the efficiency and advantages of the aeration are reduced.
Another lawn aeration device seeks to address the soil compaction problems of drum and spike aerators by providing hollow spikes that actually pierce the ground and remove a plug of soil to create a hole. During each penetration of the ground, another soil plug is forced upwardly through the hollow spike and the plugs are simply ejected from the spike at its upper extent. While these types of devices, commonly known as pluggers or core type aerators, tend to reduce the compaction of soil around the sides of the holes, they nevertheless do not eliminate it. This is because the soil must still be parted to accommodate the thickness on the walls of the hollow spikes as they pierce the soil. In addition, such hollow spike aerators still require significant force to drive them into and through the soil and thus still require large, heavy, and cumbersome structures for proper operation. This is due to the relatively high sliding friction of the soil plug through the hole in the spike requiring extra force to drive the plug through the soil. As a result of this extra force, the extracted plugs are usually highly compacted dowel-like plugs, which do not break up and disperse quickly.
Because of their weight, many lawn aerators, and almost all commercial lawn aerators, are motorized. This not only makes them expensive but also renders them difficult to use. When the heavy spike drums are driven over the ground by their motors, they naturally bump, bounce, and shake about as the spikes are driven into and through the soil. This can create significant fatigue for users of these aerators. Further, the unitary drum construction of these devices renders them very difficult to turn at the end of an aerating run and the drum often must be manually scraped about in an arc to achieve the turn. This is not only cumbersome, it also tends to destroy healthy grass already growing in the lawn and can create an unsightly mess, particularly in moist or wet soil.
Slicer aerators having harrow-like discs or thin curved knife blades that create or cut a narrow furrow, slice, or series of narrow slices in the soil, are also available. These devices embody a problem in that they tend to create narrow soil openings that close up very quickly, especially when stepped upon. In addition, the force required for penetration of the soil can be significant in these types of aerators so that substantial weight must be provided for their operation. As a result, these type of aerators, which are common for commercial use, tend to be mounted on frames that can be pulled behind a tractor. Obviously, this limits the use of these aerators significantly and generally makes them useful only for large scale operations such as the aeration of golf courses and sports fields. Even if a slicer aerator concept was adapted to a small lawn, the thin easily closed slices produced by these aerators still would be unacceptable.
Many of the problems associated with prior art lawn aerators have been addressed for small scale consumer aeration through the inventions described and claimed in applicant's pending U.S. patent applications, of which the present application is a continuation-in-part. The inventions disclosed in these pending applications are hereby incorporated by reference. In general, these unique inventions include a novel aerator wheel having a hub and four curved tines projecting therefrom. The placement, curvature, size, and configuration of the tines has been found to provide surprisingly exceptional soil penetration as the aeration wheel rolls across the ground. This is because the configuration of the tines takes advantage of knife-like soil piercing and the assistive force of a previous tine pulling itself out of the soil to provide much of the force necessary to drive the next successive tine into the soil. As a result, these aerator wheels require relatively little additional downward force for their proper operation. This phenomenon makes it possible to mount two or three of the aerator wheels on the back of a consumer lawnmower where the small force required to drive the wheels across the ground for aeration is provided by the weight of the mower itself.
While the inventions of the parent applications hereto have proven especially useful for attachment and use with consumer lawnmowers, they have not proven completely acceptable for use with large commercial walk-behind lawnmowers. This is due at least in part to the fact that, with commercial lawnmowers, it is desirable to provide six or more spiked aerator wheels across the mower breadth for providing aeration holes in the ground of sufficient density. This requirement in conjunction with the weight distribution on a typical commercial lawnmower makes it undesirable to use the weight of the mower itself to drive the aerator wheel spikes into and through the soil because the resulting lift on the mower can cause it to loose traction.
Accordingly, there exists a continuing need for an aerator assembly that can be conveniently mounted to the back deck of a commercial lawnmower for aerating the soil as the lawn is mowed. Such an aerator assembly should provide at least six spiked aerator wheels for acceptable aeration density and should not make use of the weight of the mower itself to drive the aerator wheels into and through the soil. In addition, such a commercial aerator assembly should track the movement of the lawnmower, even when the mower is engaged in tight turns and even when it is reversed and moved backwards. The aerator assembly should not interfere with the normal operation of the lawnmower to which it is attached and should provide superior aeration by producing holes in the soil with loose dirt sides and by depositing dirt from the hole onto the top of the ground for disbursement. Finally, such a commercial aerator should be economical to produce, market and use and should be simple to install on the back of a commercial lawnmower deck. It is to the provision of such a commercial aerator assembly that the present invention is primarily directed.