Grass mulching mowers on amenity turf

The benefits of mowing grass areas with mulching mowers

By Lance Bassett

A chore which every landscaper hates because it is heavy, time consuming and wasteful, is emptying the grass collector on the mower and carrying the clippings to a compost heap or other disposal point.

Because of this most grass clippings from landscape sites are left on the surface of the turf, where they gather on peoples shoes and clothes, or are removed and dumped, though a small but increasing amount are composted by local authorities, along with other forms of green waste.

It is a surprise to many but a well-documented fact backed up by research that return of grass clippings to the turf by a mower does not contribute significantly to thatch build-up. The reason for this is that grass leaves originate in the crown of the turfgrass plant and are much softer near their tips than at their bases, where they tend to be more fibrous. It is the tips of the leaves that are removed by the mower. Thatch is derived more from what is left behind at the base of the turfgrass plant in the form of fibrous leaf bases than from the small pieces of sappy grass clippings cut from their leaf tips.

Grass clippings are composed largely of water, soluble compounds such as carbohydrates, and others, such as cellulose and hemicelluloses, which break down over a period of a few weeks, depending on temperature. They also contain the mineral nutrients taken from the soil by the turfgrass plant during its growth. The less easily decomposed components of thatch do still break down eventually and, in a healthy area of turf, worms are also involved in dragging any fallen leaves or grass clippings deposited on the surface of the lawn down into the soil beneath the thatch.

The smaller the pieces of leaf the greater their surface area and so the naturally occurring microbes, fungi and bacteria, are more effective at breaking them down. This speeds up the decomposition process and thus the release of nutrients. This has been known for many years but in the past would have meant mowing daily to get the pieces small enough. The mulching mower produces small grass clippings while mowing less frequently.

Because the grass clippings contain the nutrients that grass needs for healthy growth, returning them to the turf means that less fertiliser need be applied to the turf area. There is therefore a lower risk of run-off of excess fertiliser, which can pollute waterways, and lawn maintenance is cheaper because less fertiliser has to be bought.

A further advantage of the mulching mower is that in the autumn a conventional mower picks up fallen leaves as well as collecting the grass clippings, making the emptying operation more frequent. In contrast, a mulching mower shreds the leaves as it goes, saving the need to sweep them up or use a blower to remove them from the lawn. Mixing fallen leaves from deciduous trees with grass clippings is helpful in getting rid of them and they soon break down and disappear.

In the traditional private garden, grass clippings are more likely to be composted by the resident gardener. The garden compost heap is often less used than it should be because the largest component is grass clippings, which become slimy and smelly if not adequately mixed with other garden or household waste. If grass clippings are eliminated, healthy compost can be made using other types of garden waste such as weeds, cut back perennials and possibly shredded prunings.

EU legislation means that over the next few years the UK has to divert almost 5 million tonnes of biodegradable material, mainly garden and kitchen waste, from landfill sites. By 2020 this amount will double. Anything that reduces the production of this type of waste is beneficial. Compost heaps are one way to do this but mulching mowers also have a part to play in reducing landfill and thus reducing council tax bills.