Till vs. No-Till

A 3-D view of tilling in Russia c1915

My post on lasagna gardening, which linked to a brief article by horticulture professor Linda Chalker-Scott seems to have opened a can of worms, so to speak.  Two issues came up in the comments on my post: the wisdom of using cardboard in a lasagna mulch and the pros and cons of double digging/tilling. Let’s address them in separate blog posts, beginning here with double digging/tilling.

There are some very persuasive arguments in favor of a no-till, leave the soil alone approach. Chalker-Scott in the comments section of her post on lasagna gardening says,

. . . double digging (the equivalent of tilling in agriculture) disrupts natural soil building. No-till agriculture is increasingly preferred as being more protective of the soil ecosystem. I think the same philosophy could be applied to home gardens as well. You’re right, you can boost production with a more aggressive approach to soil amendment – a similar argument is often made in conventional agriculture (compared to organic agriculture) to till, use excessive fertilizers, pesticides, etc. I guess it depends on how you regard the soil – as a medium for growing vegetables or as an ecosystem (and I’m not being judgmental). It’s a philosophical choice.

No-till agriculture advocates argue that tilling oxidizes organic matter leading to a loss in soil fertility and the creation of carbon dioxide which, in turn, leads to global warming. A case can also be made that tilling creates a soil “crust” that interferes with water penetration. And tilling disrupts mycelial networks and other soil organisms that, research has shown, form important symbiotic relationships with plant roots. 

But what about heavily compacted soils? How do you turn a lawn or driveway into a garden? It’s in these cases that I, in the past, have used double digging.

Double digging proponents would argue that the practice should be distinguished from tilling in that, unlike tilling, you don’t invert the soil structure as much when you double dig. Double digging keeps the same soil profile while loosening heavy compaction. Double-digging advocates distance themselves from the use of roto-tilling machines which invert deeper layers of soil with surface layers that contain more organic matter.

But there are alternatives to double digging and tilling that will break up compacted soils. Scott Kleinrock at the Huntington Ranch turned a former construction parking lot into a productive edible landscape without double digging or tilling. Kleinrock used what I’d call a kind of toolkit of de-compaction strategies:

  • The application of a thick mulch (Chalker-Scott suggests a minimum of 12 inches). It’s surprising how many earthworms start doing the tilling for you with a thick mulch layer.
  • Planting soil busting cover crops with thick tap roots like Daikon radish
  • The use of a broadfork or deep spader
Peaceful Valley’s “Deep Spader”
A broadfork in action

Broadforks and deep spaders get air and water into compacted soils without the damage tilling can do. Unfortunately broadforks and deep spaders are very expensive (around $200) and heavy. The deep spader Kleinrock used came from Peaceful Valley Farm and Garden Supply. I’ve tried it and it works nicely, though it’s still hard labor. If you knew how to weld you could probably make a home brew deep spader or broadfork. I’ve also successfully used a regular, inexpensive garden spading fork in moderately compacted soils.

This is clearly a topic on which reasonable people can disagree, but the no-till folks seem to have the upper hand in terms of the science. As with all gardening problems, though, context is king. Environmental factors and economic issues (those expensive broadforks) intersect in our urban gardens in complex ways. You have to make up your own mind. I’d say if you’re going to double-dig do it only as a last resort and after considering all the alternatives. While, under some circumstances, I might double-dig I would never till with a roto-tiller or invert soil structure with a shovel. But after seeing the dramatic improvement in soil at the Huntington Ranch in less than a year, I’m more inclined to try de-compaction alternatives. You could also just build raised beds and import better soil (though that strategy gets expensive).

I’ve created a poll on the right side of this blog on which you can cast a vote on tilling vs. not-tilling vs. double digging. And consider leaving a comment–I’m interested in what readers think about this complex issue.

Lasagna Gardening Simplified

First popularized back in the 1970s, “lasagna gardening” involves piling up thick layers of cardboard and uncomposted kitchen scraps on top of (sometimes) double-dug soil. The practice is touted as a way of removing lawns and improving soil with little work.

Linda Chalker-Scott, Extension Urban Horticulturist at Washington State University, proposes a vastly simpler version of lasagna gardening.  Chalker-Scott suggests skipping the double digging, cardboard and kitchen scraps. The double digging disrupts soil texture, the cardboard interferes with water penetration (I know this from experience) and the kitchen scraps create a plant nutrient overload. Instead Chalker-Scott suggests simply a very thick layer of mulch–12 inches.

Mulch is often free, as many cities give it away, and it does wonders for the soil. Mulch, in fact, breaks down into soil, retains moisture and creates habitat for earthworms.

Read more in Chalker-Scott’s post, “Is lasagna gardening really worth the effort.

Geoff Lawton Soils Video

Help, I’m turning into a soil geek. I just spent an evening viewing a video entitled Soils featuring permaculturalist Geoff Lawton.

What I like about this video is that it’s not just about soil, but Lawton actually shows you what you can do to improve your soil. In the DVD he demonstrates how to build a compost pile (lots of carbon material), contoured vegetable beds, a compost pile heated shower and a simple vermiculture system using an old bathtub to name just a few projects. You get practical tips in a professionally produced DVD. Here’s a trailer:

Soils is available for around $40 US on the Permaculture Research Institute of Australia website, which also has an interesting blog. In an email the Institute said that they allow educational screenings of Soils as long as you don’t charge admission. So get some friends together, watch this video and then go shovel some manure! It would also make a nice addition to a school library.

Thanks to Scott Kleinrock of the Huntington Ranch for the tip on this one. Scott said the Geoff Lawton Food Forest DVD is also worth viewing.

UMass Soil Testing

I finally got around to trying out the University of Massachusetts’ soil testing service and can report that it’s fast and cheap. I tested two areas of my yard for both nutrients and heavy metals and found out, more or less, what I expected, that I need to add a small amount of nitrogen. Surprisingly, for having such an old house, I don’t have a lead problem. It costs just $9 for the basic test and $13 for the basic test + heavy metals. The order form and instructions can be found at http://www.umass.edu/plsoils/soiltest/. Why test? UMass sums it up nicely:

  • to optimize crop production.
  • to protect the environment from contamination by runoff and leaching of excess fertilizers.
  • to aid in the diagnosis of plant culture problems.
  • to improve the soil’s nutritional balance.
  • to save money and conserve energy by applying only the amount of fertilizer needed.
  • to identify soils contaminated with lead or other heavy metals.

The brochure they send with the results is geared towards New England soils, but beggars can’t be choosers. This test is a bargain, but I’d check first with your local extension office to see if they offer free or low cost soil testing first. Should you want the Cadillac of soil tests, vegetable gardening expert John Jeavons recommends Timberleaf Soil Testing. I’ve seen some Timberleaf reports and they are quite detailed and informative.

The cutting edge of soil testing is about the living inhabitants of the soil, all those microorganisms, fungi and other critters rather than just old “NPK.” Dr. Elaine Ingham is a pioneer in this field. She offers “Soil Foodweb” testing via her website. I’ve read some grumbling from academics about some of her ideas and her commercial endeavors, particularly related to aerated compost tea. However, soil foodweb testing makes intuitive sense to me, though I have not tried it. You can read her interesting Soil Biology Primer here, and make up your own mind. There’s also an excellent book based partially on her research, Teaming with Microbes: The Organic Gardener’s Guide to the Soil Food Web.

Thanks to Cool Tools for the tip on UMass.

A Cheap Soil Testing Service

I’ve started a new method in the garden: test the soil, amend according to the recommendations and grow. Lather, rinse, repeat. In many parts of the U.S., you can get free or low cost soil tests from your county extension service, but not here in Los Angeles. Some time ago I answered a reader’s question about where to get soil testing done, only to have to correct my response several times. Last week, Homegrown Evolution pal and the editor of Cool Tools, Elon Schoenholz, gave me a definitive answer on where to send soil for testing: the University of Massachusetts Amherst, Department of Plant and Soil Sciences Soil and Plant Tissue Testing Laboratory. A standard soil test is $9, $4 more for the standard test plus organic matter. The standard tests includes heavy metals. That’s a bargain, and you don’t have to be a resident of Massachusetts. They also offer compost, fertilizer and plant tissue tests at reasonable prices.

Read a review of UMASS soil testing by master gardener Amy Thompson at Cool Tools.