Double digging is the process of removing the top layer of soil to the depth of your spade shovel (8” to 12”). Set the top layer aside then loosen the layer underneath with your garden fork. When putting the topsoil layer back incorporate compost.
Having a double dug bed is better for water retention in your bed. The bed is insulated by the ground around it. This reduces temperature and prevents as much leakage and water loss due to evaporation.
To double dig your bed:
- Remove all grass or weeds in your selected area.
- Take your spade fork and remove the top layer of soil to the depth of the shovel. This should be somewhere between 8 and 12 inches. Set the soil to the side of your bed. Sometimes I put it on a tarp so I don’t damage the existing sod too much.
- With your garden fork loosen and aerate the soil you’ve just exposed. You’ll want to stick the fork down to the whole depth. This could be hard at first so work at it. Wiggle it around in there and really work it.
- Once you’ve loosened all that soil you’re ready to put a layer of compost. Spread out about an inch of compost with your steel rake.
- Put a couple of inches of topsoil in. Get your fork out and mix them together turning and twisting the fork.
- Repeat this process incorporating 3 inches of compost. I recommend the revitalizer compost mix from theNaturalGardener. They have a calculator that will help you determine how much you’ll need. If you need to you can bag your own and haul it in your car. For an 8’ x 4’ bed you’ll need 6 bags.
- If you use all of the topsoil then the bed will be taller than the original soil level. You will need some barrier to keep everything in. If you don’t want to face this problem find some other place to dispose of the excess soil.
- Another amendment that will help with water retention is expandedshale. These are porous rocks that hold water and release it when the soil dries. They recommend a 3 inch layer. That can be costly. The shale does not break down in your soil and will be there forever. I usually add a half inch every year with an inch of compost and some additional green sand to prep my bed for a new season. Fall planting is a perfect time for this.
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