Friday, April 22, 2016


We rented an excavator and dug up our yard in mid-May, 2014.
I'll cover what we did in more detail below, but first, why on earth would you do this?

Earthworks provide several benefits for food production, including:

  • Disturbance management
  • Water management
  • Microclimates suited for different plants and beneficial insects

Disturbance can be a good thing.
Grasses grow well in partial and full sun, but they're difficult to eat, and they compete with other plants for water, sunlight, and nutrients.  If you dig a hole in the lawn and plant a fruit sapling but do nothing to fight the grass, the tree will either die or be severely stunted - either way you'll be waiting longer for fruit.

Disturbing the ground and then planting trees or seedlings and mulching gives your food-producing plants a fighting chance at competing with grass.  Disturbance can convert compacted soil into lighter, better aerated soil that plant roots can penetrate, and also makes more nutrients bio-available to help your plants grow (that's the reason plants see a boost in growth after tilling).

Digging and tilling are a lot of work, and there's another downside too: the nutrients that suddenly become bio-available also become easier to wash away, so tilling the same plot year after year reduces the Soil Organic Matter (SOM) percentage, making it harder and harder for your plants to thrive.  Gabe Brown, a farmer in North Dakota, bought farmland that had been mono-cropped and tilled intensively for 17 years, and when he did soil tests, here's the contrast he found between undisturbed forest soil and nearby field soil on the same property (chocolate cake good, chocolate mousse bad):
Brown has an excellent 58-minute presentation (and a shorter 2-1/2 minute version) on how he restored that field soil and tripled his SOM over 20 years with cover crops, grazing animals, and NOT tilling.

So we used disturbance to convert lawn into swales, ponds, and raised beds, but we want to avoid doing it on a recurring basis.  That's why put in earthworks immediately before trying to grow anything: if we put it off until later, then we'd disturb the food-producing plants we put in and miss out on a great deal of potential growth.

Water management is key to drought-resilience.
Even though we live in a mild climate that rarely suffers long periods without rain, we knew how critical water is to sustaining life and erred on the side of caution: we put in 3 swales to increase snow-melt- and rainwater- infiltration and catch soil particles that might have washed off the property.

This has already come in handy, as we had a dry spring in 2015, and when we finally did get heavy rains (3"+ in 24 hours), the swales helped prevent or slow surface run-off.  We've seen our middle-swale fill to about 6-8" deep and be nearly empty an hour later.

Part of our water management plan was to dig a pond uphill from the annual vegetable garden: we'd store water in it during rainy April & May, then use it to gravity-irrigate as needed in dryer August and September.  Unfortunately the clay content of our soil is too low (30%+ is ideal) for the pond to seal on its own, so it's still not holding water 2 years after we dug it.  When money permits, we'll get an EPDM liner.

Microclimates help biodiversity (which makes our food production more resilient).
Raised beds and other contoured features impact the amount of sunlight, wind and airflow each spot of ground sees.  The south side of a berm can host plants and beneficial insects that thrive with more sun and heat, while the north side hosts those that do better with less.

We're hoping dragonflies will move in near the pond (and eat lots of insects that would eat our food) when we finally get it to hold water.  The pond itself will reduce temperature swings near it; we're also hoping we get a nice warm microclimate just south of the house (where it will be protected from wind and get light that reflects off our white siding), which is also just north of the pond.  With luck this will let us grow things that usually only grow in Zone 6 or warmer.

Preparing for Earthworks

We had some idea what we were doing by helping build raised garden beds with a backhoe at a friends' house the year before.  I even wrote up notes immediately after that with ideas for process improvements.  With a couple dozen people and a piece of machinery to work with, we knew that preparing during the week before the rental was key.

We made an A-frame level and marked off the swale contours with flags.  Since we'd noticed our driveway got wet during the first winter, we added a 2° slope to the front half of this first swale to drain water away from the wet spot and toward the dryer backyard.
We used the same flags to mark off the pond and raised annual beds.  Unfortunately we didn't mark the annual beds well enough and ended up with a smaller number of very wide beds that we can't reach the middle of.  We're slowly re-shaping them now, but it's a lot more work with a hand-shovel than an excavator.

One of our friends had already built hugelkultur beds in his garden, so when he found out we were building them, he offered to truck in a bunch of scrap wood cut from a nearby park that he volunteered to maintain.  He delivered this before the earthworks party.

The key to getting the most out of soil disturbance is immediately planting something in it after you're done disturbing it, so Kate spent a good part of late winter and early spring growing many flats of seedlings.
She also stocked up on straw (for mulch) and cover crop seeds to sow in the disturbed soil.  In retrospect we could have used a lot more mulch to save on weeding later on.

Earthworks Preparation Summary:

  • Measure your site.
  • Plan what you want and where you're putting it all.
  • Mark it clearly.
  • Get seeds, seedlings, soil amendments, and mulch all prepped.
  • Make diagrams and written instructions that describe the plan to all of your helpers.
  • Invite friends to help.

Dig In!

We had nice sunny weather (after a couple of days of rain) for our earthworks party, and about 25 people show up (including 3 high school students from our robotics team that I bribed with the promise to let them operate the excavator).

This is the top swale right after excavating (it's essentially the same spot shown above with flags).  In retrospect we made this much bigger (about 15' from edge to edge) than necessary.  A swale needs to be big enough to hold the largest rainfall you expect to see while accounting for the uphill catchment area and water-retention capacity of the ground (deep-rooted trees hold more water than paved surfaces, for example).  This could have been half as wide and still worked fine.  We made the next two narrower.
After excavating we prepped the berm for cover crops by manually flipping the clods of grass (which I now think is about as effective as an umbrella in a hurricane: it might help, but not much).

Then we put down cover crop seeds and mulched.  The left part of the photo below is all seeded and mulched - the right part got planted with asparagus and mulched later.  Unfortunately the chickens and deer pretty much killed it (more on that later in a post about fencing).
Here's what it looked like 35 days after construction:

Constructing 500' of swale, a small (~20x30') pond, and ~250' of annual garden beds in a weekend was easy with the excavator.  We used the 25 people (mostly just on Saturday) to flip the clods of grass, shape the beds, and do seeding and mulching.

Ideas for next time:

  • More mulch after disturbing soil -> less weeding later
  • Plastic mulch (tarps and black strips staked to the ground) is very effective in killing grass
  • Make sure you have more than enough cover-crop seeds - if you run out and leave soil bare for a week, you'll have more erosion and competition from grass.

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