Double digging helps condition poor soil> Less than perfect medium can reach potential

Is your perennial garden filling in with mature plants that require division and transplanting? Interested in turning over a small area for an intensive vegetable garden? Want to form some raised beds for a cut flower garden? Perhaps early summer will afford you an opportunity to turn some of your lawn area into more productive ground. If your soil isn’t in the best condition to support flowers or vegetables, you might consider a technique that for years has given gardeners the opportunity to really work poor soil into a lush garden media: double digging.

Double digging is a tried and true method for converting less-than-ideal soils into a fabulous horticultural mixture. While classically used to form raised garden beds, the method can be employed when preparing any new bed area.

Double digging loosens the soil to a greater depth than ordinary bed preparation techniques such as tilling, and improves soil aeration and penetration of roots through the soil profile. The double-dig practice also allows the gardener to apply to and work into the soil to a greater depth soil amendments such as compost and other natural soil conditioners.

While the benefits of double digging are well documented and well worth the effort, it is also hard work. If you choose to double dig a garden plot, be prepared to move lots of heavy soil. You’ll likely need to do the work over time, taking frequent breaks, and completing the project over several days. Be sure not to bite off more than you can chew: A garden bed 3 feet wide and 30 feet long is probably a very sizeable project for most.

To help reduce the risk of hurting your back, keep the spade close to your body as you work and use your legs rather than your upper body to heft the load.

To begin, mark off your garden plot using stakes and string. If you desire a circular or curvilinear bed, use a can of white, orange or red spray paint to outline the shape of the bed on the turf or ground. You might consider using the stake and string to measure and square off your area. Then use paint to mark a line on the ground directly beneath the string. This will free you to remove the stakes and string and will eliminate the hazard of tripping over them as you work.

For this project you’ll need a spade, a wheelbarrow, a tarp, soil amendments and a spading fork.

First you’ll prepare to remove the sod from the area. Starting on one side of the garden plot and using the full depth of your spade, make a slice through the soil profile about one foot out from the edge of the bed. Continue slicing through the soil the length or width of the bed. To remove the sod, use your spade to make a horizontal cut through the roots of the sod, to include about 4 inches of soil. Roll the sod and move it away from the garden area.

Once the sod is removed from the entire area, let the double digging or trenching begin! Dig a foot wide, foot deep trench the full length or width of the garden. Remove the top foot of soil by spading it onto a tarp beside the bed. Using a spading fork, loosen the now-exposed subsoil to the depth of another foot. Don’t turn the soil over, simply fork it around so that it loosens and becomes a more agreeable media for roots to penetrate.

Now make a second 1-foot-wide by 1-foot-deep trench adjacent to the first. Spade this next foot of topsoil over onto the first trench of freshly worked subsoil. Once this second trench is dug, loosen the subsoil below and move down the bed, filling in with the adjacent topsoil.

When you reach the end of the bed, drag around the tarp with the first section of topsoil and use it to fill the top of the last trench.

Now that the bed has been double dug, break up the largest soil clods with a spade or the spading fork. Work in compost, lime, manure, peat or other soil amendments to a depth of 6 to 8 inches.

If double digging the entire area seems a bit intimidating to tackle all at once, do a fraction of the bed in the first year and complete the job over successive seasons.

Double digging, even with the great effort it requires, is a one-time effort. The results of your efforts will be visible in the quality of your plants and the ease with which they grow and flourish in their newly prepared soil.

Diana George Chapin is the NEWS garden columnist. Send horticulture questions to Gardening Questions, RR1, Box 2120, Montville 04941, or e-mail them to dianagc@ctel.net. Selected questions will be answered in future columns. Include name, address and telephone number.