Double Digging’s Finer Points

For most of us, double digging provides all the benefits we need and pays true dividends. There are, however, a few finer points, options, and differences of opinion within double digging that are helpful to know, especially when starting out. Plus, it might be beneficial to know how someone else deals with these, often contradictory, issues as a starting point. 

Soil Mixing: How Big of a Deal Is It?

Some people are sticklers for not mixing soil as they move one trench to fill another, wanting to avoid killing their aerobic and anaerobic microbes by inverting them. Others turn their soil right over, either not aware of this issue or figuring the microbes will figure it out. It is true that inverting your aerobic microbes from the top six to eight inches with the deeper anaerobic microbes causes their death and disruption of your soil’s microbial life. But, try as one might, honestly, it’s difficult to keep the different soil layers from mixing. As the soil you’re moving over cleaves off into the previous trench in haphazard chunks when you initially insert your spade and the soil you’re piling in a previous trench continually falls back into your current trench while you’re trying to dig it to the full depth, you’ll likely come to some compromises about soil inversion. As just one person’s example of a compromise, I try hard not to mix them but still take a middle ground,  favoring well-loosened soil over unmixed soil, but trying not to completely invert the soil at any point. For your own sake, I’d say try as much as is realistic. 

How Loose Is Loose Enough?

Some people, likewise, are sort of casual about loosening their soil as they move it, especially when mixing compost into the deeper layer, only moderately turning it in. They’re probably thinking, “Aw, that’s good enough. I’ll get back in here next year anyway.” Other double-diggers are kind of intense about it, breaking up any clumps in the top layer as they move it and fluffing the soil and mixing in the compost into that bottom, foot-deep layer as much as possible. Again, as just one example for what it’s worth, I’m in the latter category, even to the point where a digging fork dropped from any height completely buries the tines and several inches of the shaft. The entire time I’m thinking, “I’ve already expended significant effort to remove the top foot of soil; why not take the extra effort to make it as good as possible now and maybe not have to get back in here for a few years.”  Either way, the more effort you put in over time, the better your soil and the better your plants.

Should I Add the First Trench’s Soil Back or Not?

Similarly, some put the first trench of soil they removed back in on the far end. Others keep it out for use in their compost, thinking the bed, having been loosened so much as to be a high mound, is tall enough as it is. Either way works fine and depends more on your local conditions and how high you want your bed.

First Trench: One or Two Feet Wide?

Likewise, the width of your first trench can also be a finer point and benefit from some variation. Following the exact directions and starting out with a one-foot-wide trench, as is typically specified, makes piling soil from the next trench difficult. There’s just not enough room; it spills out the sides of the bed and constantly falls back into the second trench as you’re attempting to dig it. It also tends to leave you doing quite a bit of soil moving from that end to even out the height of the bed at the end of the project. Making the first trench one-and-a-half-to-two feet wide helps. Less soil falls back in your second trench. And once you have that initial width, the amount taken out to add back on the far end and the bit that spills over the sides of the bed when you dig the second trench are both about what you end up needing to make the bed uniform with the least soil moving. 

How Often Should I Double Dig?

Finally, some will wonder how often a bed needs to be double dug. Some say every year. For others, that’s unnecessary or unrealistic. For my own sake, it’s easy enough to see when it’s time to redo the double dig: The tomatoes tell me when they need a boost. The first year, they’re two feet above their five-foot cages, and, even though it’s only four plants and one’s a cherry variety, I’m wondering if we really can use all the tomatoes we’re getting. Each year, however, they grow to a slightly lesser height. Three to five years after digging, they’re just barely reaching the tops of their cages at their peak, and, although they’re still beautiful, I start wondering if I’m limiting their potential. That’s when I know it’s time to redo the bed. For your sake, whatever fruits or vegetables you grow in your double-dug beds will tell you the same thing over time.

Is It Worth the Effort?

This can all be a lot of effort, and it’s great for those who want to undertake it. They’ll be richly rewarded for it. However, keep in mind that less effort can still get amazing, if a bit lessened, results. You have multiple options based on your desired level of intensity. Double digging might be an ideal method, but there are plenty of other good methods and plenty of people who might not want to, or be able to, put in that level of intense effort for their whole garden. The underlying point is that people grow fruits and vegetables and enjoy it, not that they follow any one method.

I should also be honest: I’ve made my compromises. I know what “ideal” is, but I also have people who desire time spent with me, other activities I enjoy, work, and a body that can only do so much anymore. The mix of methods I use is my attempt to make the ideal out of all of those parts of my life, not just my garden.

Plus, over the years, I’ve double dug quite a few beds, most of which I, and the people for whom I dug them, can no longer use. They were at a couple of different community gardens (which rotated spots each year) and at my and my sisters’ and friends’ now-previous homes. It was a lot of work to not be able to keep the fruits of it—a lot of time spent improving the soil two feet deep on areas the new owners have returned to relatively shallowly rooted, short-cropped lawns. 

Also, over that time, I’ve noticed that only a few plants I regularly grow really benefit greatly from double-dug beds: tomatoes, peppers, broccoli, and cauliflower. Therefore, I only double dig the areas for those plants that really benefit from it. The rest do well enough in other formats. Being in such loose soil can actually mean requiring extra support for some plants. Typical for tomatoes anyway and easy enough for peppers, it’s not hard to add extra, but it’s awkward for plants like corn.

If I were as full of vigor as I was when I was digging all those multiple beds for friends and family, I’d probably still do it for all my garden plants every year. However, I’d be ignoring the wisdom of it not being needed for some, and possibly even a bit detrimental for a few. Plus, it’s quite a commitment (The last single bed, 20’x5′, took me 17 hours of intense work.), so I limit it. 

Double digging can be a lot of work, so let’s turn to a few easier methods.