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Photo Credit: ©2002 Dolezal Publishing/John M. Rickard

Healthy and well-prepared garden soil helps yield healthy produce.

Each time you till your garden soil you incorporate large amounts of air into it, fueling a population explosion in the microorganisms it contains. It’s always important to add compost or well-rotted manure whenever you till in order to give these microbes an ample food supply.

Remember that your garden soil consists of layers that extend from the surface to deep within the earth. The top foot, which is most important to your plants, is the most biologically active layer. Beneath the topsoil is a layer of subsurface soil that, while rich in mineral nutrients, is mostly devoid of life. When you till, it’s important to loosen each layer independently, but avoid mixing them together.

As you work your soil, it’s a good idea to go beyond adding organic matter, especially if it drains too quickly or slowly. A loosening agent, like the mineral gypsum, may help prevent clay particles from sticking together. You may need to add garden lime or sulfur to raise or lower the pH, making your soil more alkaline or acidic. Soils that are too sandy will benefit from having clay and silt added to them, while those that are too heavy will profit from additions of sand.

Garden tillers typically mix the topsoil layer, seldom reaching more than 8-10 inches deep into the earth. To loosen the subsurface layer, it’s necessary to double dig the bed using a shovel. While the process is simple, it requires substantial effort if a large area is to be prepared.

To double dig your beds, start by digging a trench 1 foot deep across the width of your bed. Place the soil from the trench into a wheelbarrow or garden cart, reserving it for later in the process. Next, loosen the soil at the bottom of the trench and remove any rocks or debris, working an additional 9-12 inches deep.

Starting a second trench parallel to the first, turn the topsoil layer into the first trench, filling it with the soil from the second row. Then loosen the subsurface layer found at the bottom of the second trench. Continue in this fashion across the bed until a final trench remains, its subsurface layer turned and loosened. Fill the trench with the topsoil reserved from the first row.

When you’ve finished double digging your entire bed, you can spread your amendments, compost and fertilizer. They should be spread in uniform layers on top of the soil, then mixed into the previously loosened top layer with a shovel, working down the length of the bed at right angles to the original trenches.