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What is it?
Bed preparation is the number one important thing you can do for you plants. Double-digging is a method of bed preparation that aerates soil to a depth of 24 in (2ft). This creates an environment in which plant roots thrive due to a more even distribution of nutrients, water, and air and loose soil so roots can spread out and reach a farther depth.
When is it necessary?
Traditionally, double-digging was done when first starting a new bed and then repeated as necessary. In soils that are dense, hard packed, or have a high clay content it may be essential to repeat the process every year until the soil has improved. For pre-existing beds every 3-5 years is sufficient. The worst thing you can do to your soil is double-dig when it is too wet.
- 5 or 6 five gallon buckets
- D- handled spading fork
- D- handled spade
- Digging board (which is a old piece of plywood)
- Deep aeration on soil
- Minimal disturbance of soil microbes
- Improves soil structure
- Plants can be closer together
- It is a lot of work in the beginning
- May upset mycelial networks (see No-till farming)
This is the technique that works best for me. It is mostly based on John Jeavons methods from Bountiful Gardens.
- Mark out the location you are going to turn into a bed.
- Water this area well and let it sit for a couple days. I recommend putting a sprinkler on it for a couple of hours to insure a deep infiltration of moisture. This step will make the rest of the process much easier.
- Remove weeds. If you are working with a hard soil or lots of clay after you de-weed the area you may want to water it again and allow it to sit for a couple more days before double-digging.
- Spread 1 inch of compost over the entire beds surface.
- Place your digging board down on the bed to stand on when digging. You will move this along with you as you progress down the bed. This is important to reduce the amount of compaction caused by your feet.
- Remove the first square foot of soil from the beginning of the bed. Put this soil in buckets to be used later. The spade of a shovel is usually close to 1 ft so this can be used as your measuring tool.
- With a spading fork loosen the ground under the soil you just removed. The depth of a spading fork is also about one foot.
- Move the digging board back a foot so that you can access the next section of the bed. Dig out the top layer of the next one foot by one foot and transfer it into the first section. Try to mix the soil layers as little as possible when moving the soil from one trench to the next. This is because most of the microbial life in soil lives in the top six inches of soil and you want to disturb it as little as you can.
- Repeat steps 7 and 8 until you reach the end of the bed.
- Shape and level the bed. I have found that the bed becomes so aerated that there is no need to add the soil from the first trench back but if you feel there is a really low point at the end of the bed after it has been leveled then by all means put it in. I usually use the soil from the first trench for my starts in the spring. I mix this soil with compost and it makes a great start mix that gets plants ready for their specific environment.
- Spread any amendments over the bed that you want to add and sift them in with a spading fork.
There are a number of ways to double-dig. Everyone has their own preference on how wide of a trench to dig out, how big the bed will be, what to do with the soil at the end, etc. If you try this way and don’t like it play around with the technique and find a way that works for you. That is what gardening is all about and have fun.