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Re: Lead bioremediation in gardens
Well, Rachael, I'm afraid there are no generalities one would want to trust.
Around 1980, Clark Nickelow, then (and maybe still) of the Waltham Field
Station, Cooperative Extension Service, Waltham, Massachusetts, had
opportunity to do analysis of soil and tissue of crops grown on the soil. He
was keeping records, but so far as I know he never published. Maybe y ou can
run down Clark, or see if the field station still has the records. (You can
probably get your local extension service to run down an adress, or maybe
that is enough info for a phone call.) We (Massachusetts Food and
Agriculture Coalition) has pushed through the legislature funding so that
inner city gardeners could get spectrographic analysis of soil and crop
tissue for $5/test. (The rest of us paid $20 or something like that.) So he
had the opportunity to test many samples of both. Moreover, Ted Live, who
worked in one of the State community agencies (forget the name) was
distributing seed to people in standard assortments (also state funded
courtesy of MassFAC) so there were a lot of the same varieties comming up
that helped a lot in getting trends.
Clark determined that lead uptake of vegetables differs markedly not
only by species, and by plant part, but also by VARIETY! So variety X of
tomatoes will always take up less lead than variety Y. I don't remember any
of the details. Also, certain root crops take up lead in the main tissue
while others take it up mainly in the peel. So the food is safe if you peel
it. Beets and carrots were the comparison Clark used (this is all from one
conversation I had with him incidental to the main business of my visit), and
I THINK I remember that it was beets that you peel. But I wouldn't bet my
health, or anyone elses, on the recollection. If all that data has been
thrown away, which is the most likely scenario, then you need to start over.
This time publish results in our journal (The International Permaculture
Solutions Journal), where it will be ever available to people.
Meanwhile, back at what you absolutely can do, there are several
1) Import soil for raised beds. Far fetched? Boston Urban
Gardeners were getting contractors to do this for their gardeners at least as
far back as the 1970s. They also get organic matter and even manure hauled
for free, often as backhauling so the added energy cost is much less. BUG is
a non-profit, so there are tax writeoffs for contributions of goods and
2) Build soil-less gardens. There are two or three basic types.
One is basically gardening in mulch. Barbar Daniels of CA has done
this with rooftop gardens and using containers. Basically, she applies deep
mulch to a surface, usually an impervious surface, and innoculates it with
some topsoil (very little, a sprinkling). She sets out plants in pockets of
soil and fertilizes and irrigates everything with dilute urine. Her method
was written up in a back issue of the Activist and we have an article on
file to publish in an upcoming isue of TIPS journal, too.
A very similar method is what I call dryland chinampas. This is
written up in Vol. I, No. 3 of TIPS (The International Permaculture Solutions
Journal). Again, this would require much less imported soil than regular
raised beds. Basically, you make a bed of any shape you like (can be a
spiral or concentric circles or straight beds, etc) using thick layers of
mulch alternated with thin layers of soil, topping the whole mess with about
2 inches of soil. Plants can be seeded or transplanted into this. In
Wichita, Kansas, we built a whole system of these beds using yard waste we
picked up by beating the city truck on trash day. Grass clippings are
especially useful, and I like green matter for these beds when I can get it.
I take clippings next to lawns with weeds--no herbicides. A certain amout of
brush trimmings with green leaves attached are ok for the bottom layer.
3) Straw-bale gardens. These are described by Robert Kourik in
DESIGNING AND MAINTAINING YOUR EDIBLE LANDSCAPE, NATURALLY. The bad news is
that this book is out of print. The good news is that we bought out Bob's
inventory of damaged copies (very slightly damaged). Inthis method, a high
nitrogen fertilizer is placed on the surface of straw bales and then they are
covered by 4-6 inches of soil and planted in. Regular watering is critical.
I like to soak the bales down before I start. (Did these in Kansas too.)
Don't use hay--it will rot too fast and you will have an awful mess. (I made
that mistake when I couldn't get straw in Georgia.) It also heats up too fast
an cold cook your seedlings. You can skip the N if you plant legumes that
you innoculate. We got phenomenal crops of Christmas limas this way.
(That's a variety, not the harvest season.)
All methods of soilless gardening require rigorous attention to
watering. This is at odds with realities of urban gardens of this type,
which are always in zone 3 or 4 for the residents, when ideally they should
be no further than zone 2. If you have no capacity to irrigate at will,
forget it. And only DEDICATED gardeners should use this system out in zone 3
or further. Just because you want a zone 1 garden in zone 3 doesn't make it
a zone 1 garden. The zone system does not slide to accomodate the
inconveniences of urban living. This is the commonest mistake in what
sometimes passes (alas) for urban permaculture.
For anyone else out there contemplating such a situation, this
project would be way better off if they had NOT removed the tarmac, which
sealed off the toxic soil (you can remove a few small areas for tests of
course), and used soilless techniques.
Finally, the application of all this organic matter will definitely
reduce lead uptake. Also try to keep soil pH between 6.5 and 7, again to
reduce lead uptake. Happily, most garden crops like this pH best anyway.
I hope I've been helpful. I don't have time for a continuing dialog
on this (unless you have consulting funds), but I think I've given you enough
information to dig out any further data that you need. Try to get a local
college to take this on as a research project and generate your own lead
uptake data. (You do have to throw away some crop.)
OK, one more point. Back sometime prior to 1980, when I heard about
it, a graduate student at Columbia University did a study of heavy metal
uptake in NYC urban gardens. As a "control" s/he measured heavy metals in
supermarket produce. S/he found that the supermarket vegetables were
"heavey" in cadmium and the garden produce "heavy" in lead. Given different
forms of toxicity, it was a toss-up as to which vegetables are more toxic.
In that situation, why not grow your own, improving the soil (which makes it
less toxic), gaining a measure of self-reliance, and making the urban
environment more liveable. But steer clear of carrots.
By the way, CA has a huge surpluse of rice straw.
For Mother Earth, Dan Hemenway, Yankee Permaculture Publications (since
1982), Elfin Permaculture workshops, lectures, Permaculture Design Courses,
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Sparr FL 32192 USA Internships. YankeePerm@aol.com
We don't have time to rush.
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In a message dated 4/9/99 7:24:39 PM, email@example.com wrote:
I'm helping to start a garden on a site that was a parking lot. After
depaving, we got the soil tested for lead and it came back with 700 ppm.
Some extension services say this is "safe to garden" as long as you wash
everything with soap and don't grow roots or greens - in other words almost
no cool-season vegetables.
We're going to do more detailed spot testing to see if it's only in certain
areas, and if it's just one spot we'll probably dig that out and fill it
with city compost. In the meantime I am trying to find out what we can do,
particularly what crops are safe to eat, and what we can grow that would
accumulate/concentrate the stuff that we could then harvest and landfill
(or smelt!). I heard of one person who grew a particular variety of corn
on a lead-contaminated site, then smelted the corn to obtain a lead ingot
(it was an art project). The extension services all say corn, like other
fruit/seed crops, is safe, but maybe the lead accumulates in the stalk and
husks. I would love to find out what variety of corn this is.
If you have any advice, contacts, books, etc, to suggest, I would be
Mariposa Grove Community Garden
828 59th St
Oakland, CA 94609