When starting a new garden, or to start the new gardening season, home gardeners have been known to rev up the rototiller and hack away mercilessly at the ground break up compacted soil, eliminate weeds and sod and improve aeration. New research suggests this may not be the best choice to prepare a new bed; in fact, it may be the worst thing we can do to our soils!
Tilling, it has been argued, aerates and loosens the soil allowing the roots of plants to spread and grow. Tilling is also thought to mix in any compost that has been added, giving roots immediate access to nutrients and oxygen. The reality is tilling destroys the natural soil structure in many ways. For example, the use of heavy foot and machine traffic from the tiller causes soil compaction. Compost mixed in by the tiller or shovel can end up below the root level of plants rendering it useless. More importantly, tilling breaks apart the soil into smaller pieces increasing the overall surface area of the soil particles, which in turn leads to decreased water retention in the soil. The dry, tilled soil is far more likely to suffer from erosion due to wind or rain than non-tilled soil.
There are many harmful drawbacks to tilling.
Although tilling allows for the immediate planting of seeds, the physical process of turning over the soil can cause dormant weeds to be exposed to the sun and germinate.
Most of the damage caused by tillage is the destruction of the soil’s macro and microfauna. Soil bacteria and other microbes, most of which live within the first few centimeters of the soil surface, have adapted to very specific niches and are very sensitive to the effects of tilling. Entire microbial populations can be wiped out by being moved a few centimeters up or down in the soil horizon. Tilling can throw predator – prey population numbers out of whack, allowing crop pests to gain a foothold in an otherwise controlled environment. Above all, the loss of earthworms can have a devastating effect on healthy soils. Worm tunnels aerate the soil, allow water filtration, drainage and root penetration. They ingest decaying matter and returning it to the soil as nutrient rich castings high in nitrogen, phosphorus and potassium. Without worms, soil has decreased aeration, poor water retention, and decreased infiltration, all of which leads to surface sealing and run off during rainstorms. Run off also means mineral leaching, which is compounded by the fact there is less available minerals to begin with due to reduced worm populations.
So, what can be done for a yard with clay or compacted soil?
The best practice includes laying down newspaper, to kill the grass and weeds, then adding several centimeters of compost, topping with good quality weed free soil and a layer of mulch.
For an established garden bed, add ten to fifteen centimeters of compost in the fall or early spring. The natural freeze – thaw pattern of winter and the rains of spring will naturally mix the compost with the existing soil. Whatever the weather doesn’t do, earthworms will finish the job.
Save your back and let the worms and other microbes do the tilling for you, the natural way.
– Contributed by Helen Stephenson, Community Garden Coordinator
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