A fellow Master Gardener, Emily, who has space in a different community garden recently asked me for help setting up a new garden bed. She’s gotten interested in the system that I’m using to grow grains in order to make high-quality compost and so she wants to give it a try. I’m very excited to help, and I’m learning a lot from the experience.
Here’s the funny thing: I had an idea in my head about what it would take to grow in that space and prepare the bed. However it has of course turned out to be a lot more complicated than I first thought.
Fortunately before I showed up there with seedlings ready to plant, I stopped by to have a look at the soil. I brought my usual digging tools and thought that we would dig a test hole in order to see what we were up against. Well I discovered very quickly that we were up against a very solid clay. In the course of about half an hour I was able to dig a modest 9 inch hole that held water for as long as we looked at it. Obviously we weren’t going to do the whole hundred square feet this way.
Options for setting up a new garden bed
Another raised bed?
The normal advice in this case would be to get wood and do a raised garden bed. However I didn’t want to advise this road for a few different reasons. For one, it’s been my experience that having at least 2 feet of loose soil for plant roots is a big win. It would take a lot of ways and construction in order to make a 2 foot deep, 5 x 20 raised garden bed. Also we had no reason to believe that the heavy clay soil was polluted and so I figured that we might as well try and make use of it. Emily had a soil test done, and it didn’t indicate any problems.
So we basically had two options: a slow one and a quick one.
The slow way: water, forking, and patience
The slow route is one that takes a reasonable amount of effort over a long period of time. The general idea is to wet and then loosen the soil with a garden fork on a regular basis, and work further and further into the soil. This can work especially well if it’s done during the rainy season, when there’s lots of water falling from the sky and when the ambient temperatures are not going to dry out the bed. However given that it is late May in San Francisco, and also given that Emily and I have energy around this project right now, I encouraged her to look at the fast option.
The fast way: water, jackhammering, and guts
Normally I wouldn’t use the words “jackhammer” and “organic gardening” in the same sentence but it just made too much sense here to ignore. When I was doing under slab plumbing last year for a habitat for humanity development, I got lots of first-hand experience on the magic of a 30 pound jackhammer outfitted with a clay spade attachment. If you were to naively watch this tool in action, you might think that the soil was a little on the hard side, but not too bad. However if you were to then try taking your strongest garden digging fork to that same soil, you would find it bounced right off. The jackhammer is a thing of beauty in this situation. However I have discovered that it is not quite as simple as I thought.
So I admit that going in I had a model in my head that I would simply be using the jackhammer as I use my digging fork. And that as such I could do a standard double date using this jackhammer, and get it done in a reasonable amount of time. Well I discovered that it isn’t so simple.
Before you dig
Emily did a fantastic job of covering the many checkboxes that one needs to cover before doing a dig like this:
- Check with the utility companies to make sure that there aren’t any gas, electrical, or communications lines where you’re digging. They’ll either tell you that there aren’t any lines nearby, where they will send somebody out to mark the spaces where the lines are. Fortunately we didn’t have anything nearby.
- Do some “exploratory poking” to see if there’s any existing hardscape where you plan to dig. We discovered a concrete curb about 3″ underneath half of the area we’d planned to dig.
- Get a soil test done to check for heavy metals such as lead. The University of Massachusetts offers inexpensive soil testing that many people like to use.
- As appropriate, check in with the neighbors and see if there are any special events to know about. As an example, her garden is next to a church and so we timed our dig so that it didn’t intersect with any of their activities.
- Get familiar with your city’s noise ordinance. I looked into this and discovered that we were allowed to make this kind of noise between 7 AM and 8 PM, seven days a week, including holidays.
- Research the safety equipment you need to properly use a tool such as a jackhammer. Some typical pieces include hearing protection, eye protection, gloves, a hard hat, steel toed boots…you get the idea–look into it. We had no injuries, btw.
And I’m sure there are other things to check as well.
Key learnings from double digging with a jackhammer
- The displacement area on the clay spade is much less than that on a digging fork. As a result, every dig down into the soil (if you can call solid clay soil) displaces far less ground than a digging fork would, if one were using it in a normal situation. But in terms of the sheer number of digging motions, I’d say it’s about four times as many. This is particularly an issue when you go to loosen the soil for the second foot of the dig, in part because it’s hard to tell how much you’ve actually loosened.
Inserting in the Ground
- Furthermore the amount of energy to do each dig is much greater. With a digging fork I merely need to position it in the right place and then step on the side of the fork with my right foot and transfer my weight. Then I can lean my weight on the handle in order to move the fork up. But with the jackhammer it’s a different game altogether. In order to get the camera to do the hammering action, it needs to feel resistance underneath it. If you are hammering solid rock band this isn’t an issue at all but if you are hammering clay than is sometimes very hard and sometimes not. As a result I found that I needed to both transfer my body weight on September and also continually reposition the hammer so as to find a hard enough surface to pound into. Granted, it’s much much easier than it would be with hand tools, but it’s not effortless either.
Lifting Out of the Ground
- And then with the jackhammer there is an extra step of needing to lift it out of the hole each time. It’s easy to forget about this when you have a 5 pound garden fork, but with a 30 pound plus jackhammer, the extra lifting adds up.
Moving the Soil
- The start of a double dig is the digging of a 1′ x 1′ trench. So for a 5 foot wide bed, 5 ft.³ of soil need to be removed from the bed. And as you might imagine, heavy clay soil is indeed heavier than typical garden soil. So it takes more effort to get out it out of the trench and move it around. I also noticed that when we dug the second trench and moved that soil into the first trench, that soil was more “unruly” than I’m used to. As a result it was hard to clear space in the second trench in order to cleanly do the second foot of digging on the second trench.
- Given the amount of dirt to move around, and the weight and power of the jackhammer, your posture will make you or break you. Get savvy about how to do this well. The same thing goes for shoveling–if you know how to do it properly, it’s much easier and you won’t hurt yourself.
- I’ve taken the foundation courses at The Balance Center and Gokhale and both were excellent. Accordingly, the day after this intensive dig, I have no pain, no soreness. It’s not because I’m a tough guy, it’s because I used biomechanical principles that work.
How the dig turned out
In the end, through a lot of effort by the five of us, we were able to take the entire bed to varying levels of depth, from 2 feet to 6 inches, depending on the spot. We simply ran out of time to do it all. And as I describe further below, I have some specific ideas on how to structure the dig differently next time to make the best use of time and energy.
Watering before the dig
For several days before the date, Emily had been watering the space thoroughly. Granted it was so compacted that were not sure how much of the water actually made its way down, but during the dig I was able to clearly tell which areas got more water than others. Needless to say they were much easier to work with.
Setup and first (slow) hour
Emily rented the jackhammer locally for four hours and so including transit time that gave us about three hours of digging. The initial hour went relatively slowly as we got set up and figured out what we wanted to do. One of the participants sagely pointed out that we’d be better off digging from both ends of the bed at once, so that two crews of people could be working parallel to clear away loose dirt. He was absolutely right, as this sped things up, although it meant less breaks for me and for the jackhammer.
Steady (but slow) progress on the second hour
The next hour was more steady however we ran into the realities that I described earlier concerning how a jackhammer is different from a digging fork. Nonetheless we were able to dig some trenches 2 feet deep, and work in straw and a fertilizer strong in humic acid, to help break down the clay. We had originally planned to put this humic acid mix on some of the bed, but not the rest of it, to see if we would notice a difference. But between heat, fatigue, and a nagging worry that the clay would reharden if not properly tamed, I decided to just put it everywhere.
Third hour: we’re almost out of time!
The final hour was an increasingly frantic scramble to loosen as much of the remaining area as possible, even to a shallow level.
I would say that we dug about a quarter of the bed 2 feet deep, another quarter of it about a foot deep, and the rest somewhere between 6 inches and 9 inches deep. It isn’t what I was initially hoping for but it’s a start, and I think it’s something we can build on.
As a sage teacher once said to me, “With the ideal comes the actual.” To me this means “do what you can and keep moving forward.”
How I’d do this next time
If I had to do it all over again here’s how I’d do it. One of the key points is that in “version 1.0” I tried to do a traditional double dig, and parts of it took forever, for limited marginal benefit. So for “version 2.o” I’d focus my time and energy on the methods of digging, given the tools, that give the best return.
Dig the bed at least 6″ wider than needed on each side
When we came back to set up the corners and the borders of the bed, I discovered that the length was a bit on the short side. In practical terms it just means that one side of the bed will be “hardly dug,” and so the alfalfa that grows there will have to work that much harder. But if I’d just loosened another 6″ beyond, then we wouldn’t have that problem.
Do an initial pass on the entire bed down to about 6 to 9 inches.
I observed that the deeper I got the jackhammer into the ground, the harder it was to maneuver it and pull it out again. Thus I optimize for only going down as deeply as I could do quickly.
Have people with shovels following the jackhammer and moving that top 6 to 9 inches off to the side of the bed.
A complication of the jackhammer is that it can be hard to tell at a glance what soil is loosened and what isn’t. Thus it would have been very helpful to get the loose soil moved away so we could more easily get to the next part in layer.
After the loosened soil is moved to the side, have somebody hose down the hardened layer that’s now exposed.
I noticed that if an area had been watered just a few minutes before, it made a big difference in terms of how easily I could maneuver the jackhammer.
Do a second pass on the whole area of the above process, in order to get 12 inches or more of soil moved off to the side.
My thinking is that this would make the next loosening step a lot easier, and is a reasonable trade-off in terms of how deep to go.
Now that the top 12 inches have been cleared away, use the jackhammer to loosen the next 6 to 9 inches of soil.
Although ideally we’d like to get 24 inches down, my experience with the jackhammer is that it was a tremendous amount of work to try and loosen any further than 9 inches down at a time. So this is about going after the somewhat low hanging fruit, although nothing is particularly easy about this process.
After each trench is loosened, add in materials intended to help break down the clay and generally improve soil texture.
One of the big concerns with a project like this is preventing the soil from returning to its previous compacted state. Thus we added materials that we thought would help with texture. Ultimately, I think it’s the roots of the grains that we’ll grow that will do the most, but for now, we wanted something to at least make us feel better.
Water each trench thoroughly.
Or as the bag of clay loosener said “Water it good,” which I got lots of amusement out of while sweating behind the jackhammer. Anyhow, this is a unique opportunity to get a lot of water into the soil while it’s loose, which will support plant growth.
Move the original layer of soil back into place, and water thoroughly.
Not surprisingly, we found that the bed was now a fair bit higher than it had been when we started. We had injected a lot of air into the soil by loosening it.
A few other things to keep in mind
Keep people off the garden bed
It is really critical to keep your soil at and fluffy as possible. This way the soil can hold a lot more moisture, support more biological activity, and be the best possible home for the roots of your plants.
Thus I strongly advise having some kind of barrier to remind people not to step on your garden bed. Put up signs if you need to.
If you need to get into the bed to work on it, have a plywood digging board. I have a main one that is 2′ x 4′, and several smaller ones that are 2′ x 2′. They spread your body weight and really help to minimize soil compaction.
Keep the bed moist
Now that you’ve put all of this energy and effort into preparing the bed, it’s really important to water it every day in order to establish a good level of moisture and have the bed ready for growing. Once you get your garden going, then it’s the plants, the roots, and the canopy that’s going to hold in the water.
I also think it’s a smart idea to put landscaping cloth on top of the soil in order to hold in more of the moisture. I am consistently delighted when I peeked under the hardware cloth that I put down on a recently prepared and watered area of my garden and find a day or two later that it still looks moist and is considerably moisture to the touch than surrounding uncovered areas.
Add your compost to the top 3 to 6 inches
The core of the root systems will be in the top 3 to 6 inches of soil and so this is where you want the compost to be present. Although the next 18 inches of soil are very helpful for the root system, and for things like drainage, you’re going to get the best bang for your buck by having your apply compost be in the top 3 to 6 inches.
After a pretty intense three hours on jackhammer duty, you might’ve thought that I would’ve wanted to do nothing but lie down under a tree. However I was so excited to see the workable garden bed that we’d just created that I couldn’t help but take my trusty garden fork and do some additional loosening. We went from an impenetrable clay to a heavy but workable garden bed that I am confident we can plant into. It was a wonderful team effort of hard working people. I look forward to discovering how well our grains grow on this elevated, windy spot in San Francisco.