LONG green grass blades pierce the surface of the grey bits of grit across the lawn as dew shimmers everywhere.
That's what a good lawn top-dressing should look like. Unfortunately, properly done lawn top-dressing is a lost practice, some might say art form. Unlike old-school lawn maintenance, modern lawn maintenance relies on continual input of disconnected techniques and low yield but expensive products.
Each spring the annual clatter of the lawn aerator begins in earnest in lawns everywhere but top-dressing noise is nowhere to be heard. There are now even companies that drop off enthusiastic but naive young people into subdivisions who go door to door selling lawn aeration or dethatching. Such distasteful practices combined with a lack of understanding lead many people to think that lawn aeration done as a stand-alone practice is healthy for grass; nothing could be farther from the truth.
Each time an aerator pulls a core of grass out of the lawn, it leaves behind a hole in the surface of the lawn. Aeration holes are cored into the lawn to improve oxygen flow into the lawn's root zone. Those holes are also intended to be filled with some type of medium that either provides food or changes the lawn's soil structure. If the aeration holes are not filled with medium the grass roots are exposed to air pruning and stress while the sides of the aeration holes slowly collapse causing surface undulations.
Lawn aeration and topdressing are interrelated and generally inseparable practices. Both practices were originally developed to provide a means to restructure the lawn's root zone and soil type to achieve improved user performance.
The aeration cores that are spit out onto the lawn's surface are supposed to be drag-matted to break them up or raked off the lawn to allow top-dressing application. But somewhere along the way lawn aeration became a stand-alone spring ritual sold to consumers as the most valuable spring lawn maintenance option.
Lawn aeration is done to relieve soil compaction and soil aeration or to change the soil's texture and structure but those changes can only occur if a soil medium is added to the aeration holes to implement the change.
There are various types of mediums used in lawn top-dressing including sand, manure, topsoil and compost. Sand is used to improve drainage and provide firmness to weak turf surfaces. Only coarse, angular sand should be used for lawn top-dressing. Angular sand does not hold water very well, unlike round sand that holds a micro-fine film of water around its surface, ultimately increasing water retention in the lawn.
Manure has antibiotic and nutritional benefits when used as a lawn top-dress medium. Topsoil, as long as it is a sand-based top soil, is used to fill in low spots or add bulk volume. Compost is also a good top-dressing medium and it provides the same benefits of manure and topsoil.
Top-dressing can be applied on its own or as a followup practice to aeration and dethatching operations. Old-schoolers will tell you that top-dressing the lawn used to be an important annual lawn maintenance practice that was done to feed, weed and improve the lawn's usability. But with the advent of larger residential lawns and the massive lawns found in parks and golf courses, top-dressing has become too labour intensive and expensive. Hence, the modern shift to lawn maintenance involving aeration only and an increased reliance on chemical fertilizers.
In general, top-dressing should be applied 1 to 2.5 centimetres (half to one inch) thick all over the lawn as needed. Spread, scatter and rake the top-dressing across the lawn's surface to fill in undulations and aeration holes. Some areas of the lawn may need more soil, some areas may need less.
The lawn will quickly grow up and through the topdressing, developing new roots and increased vigour. If there is a need to apply more than the recommended thickness, then apply some grass seed to allow new grass to grow in to cover the thickest layers of topdressing.
Top-dressing can be applied to the lawn anytime of year between early March and late October. Top-dressing helps decompose thatch while providing a layer of soil for improved root growth. Topdressing will not kill perennial weeds.
A well done top-dressing installation using a properly prescribed soil medium is a thing of beauty and done regularly, it can drastically improve the lawn's presentation and durability. But in the end, if all of the lawn aeration, topdressing, dethatching, liming and fertilizing that is done year after year does not improve your lawn's performance and presentation does not work, you can always install artificial turf to solve the problem.
Todd Major is a journeyman horticulturist and chief horticulture instructor at the UBC Botanical Garden. For advice contact him at stmajor@ shaw. ca.
