What it takes to create an urban garden bed in hard clay
How to make an urban garden a fellow MasterGardener, 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 habitat for human 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. , For 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
Displacement Area
- 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 then is sometimes very hard and sometimes not. As a result, I found that I needed
to both transfer my body weight in 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 needs 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 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.
Posture
- 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 fewer 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 afoot
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 the 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 is 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 as 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 the 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 the 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 considerable 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 applied compost be in the top 3 to 6 inches.
Last thoughts
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.
0 Comments