Calculating the Impact of Local vs. Non-Local

Salon had a very intersting article recently that took a second look at the assumption that eating local necessary reduces your carbon footprint. The author, based in San Francisco, compared the fuel used per pound of produce for bringing local and non-local items to his nearby markets. Because the Bay Area growers drove smaller trucks, the fuel used per pound was usually higher than the corresponding ratio for non-local produce, which came in high-capacity trucks from places like Arizona and Mexico. For example:

Apple distributors got almost all their apples from Washington’s Yakima Valley, about 700 miles away. (Safeway’s California stores get Granny Smith apples from Stockton during fall and winter, and from Washington the rest of the year.) While the two local apple farmers traveled one-tenth the distance, their loads averaged less than 700 pounds — and generated six times more carbon dioxide per pound of apples than the semi-trailer trucks.

The article did acknowledge (though perhaps not thoroughly enough) that this discrepancy may be unique to California, where the line between local and non-local is blurrier:

Local oranges didn’t fare much better. Part of the reason is that “conventional” oranges are local, too. Distributors shipped most of their oranges from California’s Central Valley, a mere 200 miles from San Francisco and the home of several farmers market vendors.

Conventional oranges in my supermarket here in DC are still going to be from California. Indeed, in those grocery stores that list the place of origin of each item (such as Whole Foods), it often feels like almost everything in the produce section comes from California. So instead of dealing with distances of a few hundred miles for “conventional” produce, we’re looking at 3,000.

Or perhaps even more. The author noted that his calculations for non-local produce included only the mega-truck’s distance driven between the distributor and the far-away grocery store. But presumably the produce has to travel at least some distance from the mega-farm to the distributor to get to the mega-truck, and perhaps that distance is traversed in smaller vehicles than the eventual mega-truck. The article touches on this idea, but then provides no follow-up:

For one, I’d asked the wholesalers how far their produce traveled to the terminal market — but what about the extra leg from the terminal market to the retail store? For that matter, how much carbon dioxide was emitted while consolidating 45,000 pounds of produce from various farms into one semi-trailer truck? And how about the distance traveled by the consumers themselves, whether to the grocery store or to the Farmers Market? What kind of cars did they drive?

Food researchers felt my pain. “There are so many complexities,” says Holly Hill, author of a 2008 food miles review for the National Sustainable Agriculture Information Service. “Trying to make those real exact calculations is nearly impossible.”

Which is too bad.  It would be good to know those calculations.  Of course, any time you’re able to grow food yourself, your mileage will be definitively low.

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One Year Ago Today: Evil Walnut Edition

From time to time I’ll be recycling some of the garden-related posts from my old blogs – but I’ll try to insert them at the same point in the season they were originally posted. It will be interesting to see if my tomatoes and peppers and so forth start fruiting at the same time. So far, I think I’m behind schedule.

Today’s year-old post concerns the shocking discovery I made one year ago of a black walnut tree, which releases a chemical called juglone that is toxic to tomatoes. I am living in the same house this year as I did that summer, so I’m still facing down this enemy.

There has been some attrition in the potted garden. For some reason, the little bell pepper that started a few weeks ago stopped growing and is now shriveling up and looks like it will fall off. But the tomatoes are doing well. The beefsteaks continue to swell:

The cherry tomato plants are getting a little too rangy for their own good, as they got knocked over in a recent windstorm. However, I am extremely grateful for their good health in light of a terrible discovery I made this morning. As I walked out the back gate, I noticed a small half-sphere on the ground. It was a black walnut shell. Having read the Inadvertent Gardener’s tragic tale of poisoned tomatoes, I knew that black walnut trees exude a substance toxic to tomato plants (and pepper plants, although I think the pepper attrition is unrelated). The toxicity can even collect in rainwater beading up on a walnut tree’s leaves, which spells doom for any tomatoes in the tree’s “dripline.”

Looking at the trees above me, there was only one that was not identifiably a maple or a birch. I picked up a small branch from that tree and took it back to my room for analysis.

A quick internet search of black walnut photos confirmed the origin of the leaves and shell. Yes, indeed, we have a totally freaking enormous black walnut tree towering a scant 30 feet from the deck on which all the potted plants sit. Fortunately, I think the tomatoes are just outside of its dripline. But an errant leaf falling into the tomato pots could spell doom. Who knew gardening could be so fraught with lurking enemies?

I never did experience walnut wilt that summer, so I feel confident that I can keep this year’s tomatoes out of the dripline. Of course, my biggest problem that summer turned out to be Blossom End Rot. Now I know that I need to help my tomatoes have higher calcium uptake. And as for storms, looks like they came at the same this year as last. We’ve gotten doused in the last few days, but everything seems to be pulling through. In this heat, there’s no such thing as over-watering.

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