Soil Science: To Till or Not to Till
Tilling has become a polarizing issue in gardening – there are those who can’t imagine gardening without tilling, and those who avoid it at all costs. But like most aspects of gardening, there are positives and negatives associated with tilling. Some of the best arguments for tilling a garden are the same as the best arguments against it!
Weeds. When the weeds get out of hand and you don’t want to use chemicals on your garden, tilling may be your best solution. Plowing the unsightly weeds underground also exposes the roots and dries them out, killing the weeds. On the other hand, if the weeds have already formed seeds, you’re also burying the seeds underground to wait patiently for the next chance to sprout. And the shallower you can till, the better. Deep tilling can raise weed seeds close enough to the surface to germinate.
Soil Structure: Gardening in clay soil can be challenging, and sometimes tilling is the only way to break it up enough to let germinating seeds get through the surface. When you’re adding compost to your garden, tilling can also be an effective way to get it mixed into the topsoil and aerate your soil at the same time. However, tilling can destroy the natural soil structure that already exists, which can increase compaction in the future. This effect is exacerbated in wet soil, so don’t till wet soil if there is any way to avoid it.
Erosion: If you’ve planted a cover crop to prevent erosion over the winter, tilling it under in the spring makes a lot of sense. But the worst possible time to till a garden is in the fall, at least in terms of erosion. The disturbed soil is easily picked up and carried away by wind and water, especially in vegetable or annual gardens that no longer contain plants to block the wind.
Soil Microbes: The only benefit tilling provides soil microbes is aeration in severely compacted soil, or mixing nutrients and humus from compost to where microbes can reach them. But the detrimental effects usually outweigh the benefits for our smallest garden friends. Tilling tears up earthworm tunnels that naturally aerate the soil, and may cause the worms to look elsewhere for habitat. The more shallowly you can till, the better. Or better yet, grab a rake or a hoe and whack those weeds or stir up the soil surface without mangling your microbes!