We've all been cautioned not to walk on our garden soil. Plants need oxygen and water, and compacted soil reduces the amount of these essential ingredients available to plants. So fluffing up the soil with a tiller in preparation for planting should be a good thing, right?
But look at this comparison of compaction weights:
Person walking ~ 6 pounds per sq. inch
Crawler-type tractor ~ 12 pounds per sq. inch
walking ~ 23 pounds per sq. inch
Horse walking ~
40 pounds per sq. inch
Tractor with disk harrow ~
150 pounds per sq. inch
Garden-type tiller ~ 107 to
750 pounds per sq. inch
Tilling leaves a compressed layer of subsoil below the tilled layer. Depending on how deep you have tilled, roots may have difficulty entering the compacted layer, and water may gather there, causing roots to rot.
If you are starting a garden in an area covered by turf, you may think tilling is the only way to prepare the soil. There are two other methods which are better for your garden.
Double Digging involves a lot of work, and there are conflicting opinions about whether it is necessary in an existing garden. However, if you are preparing a new bed and have a relatively small area to dig, this method will work well.
Sheet Mulching (or Lasgana mulching) Even better is preparing your bed with no tilling. Mow or cut any tall grass or weedy growth. Cover with a layer of cardboard or newspaper, compost, and mulch. Wet it down good. The layers will decompose and the worms will move in, tilling your soil for you.
After sheet mulching, future crops can be grown by just parting the mulch and planting. No digging or tilling necessary, and all the good microbes and worms you have encouraged will be undisturbed. More later about the no-till method of growing, and how to harvest your crops to improve your soil.