Gardening, land area, etc.

Abby wrote to say hello from Madison, and wondered how much land is necessary to grow your own food.  Her first concern was about the cold weather in Wisconsin, but I don’t think this is a big deal.  Good yields of wheat and potatoes are grown further north and west of that area, and whenever I’ve been there in the summer it has been a riot of green.  On the subject of space requirements, my last post was aiming in the direction of saying that it’s not possible in practice for most people to grow most of their own food, but let’s run the numbers, just for the heck of it.

The technique I’ll use is basically the same as before – I’ll figure out how many people per acre can be fed by different types of food, then I’ll estimate what fraction of a person’s calories would come from that type of food, and add up the required space. Here it is in tabular form:

Category Area to feed 1 person Fraction of diet Area required
Spuds 0.1 0.25 0.025
Grain 0.2 0.25 0.05
Oil 0.33 0.1 0.033
Vegetables 0.5 0.2 0.1
Fruit 1 0.1 0.1
Sweetener (1.2) (0.1) (0.12)
TOTAL 1 0.43

This is obviously very rough.  The fractions are by calorie, and represent what seems to me a reasonable tradeoff between what is space-efficient and what I personally would want to eat.  The oil is canola (can’t grow olives where I live); perhaps a more palatable option would be to have a cow and make butter etc, but this takes a lot of land – probably an acre or two of nice pasture plus some hay ground to keep a cow – not something you can pull off even in Madison.  The sweetener is figured based on maple trees, which aren’t really a garden crop but they take up a lot of space.  Of course to sugar off the maple sap you need a bunch more land that you can harvest wood sustainably from, but that’s a whole other story.  Also need a good bit more fruit land for cider if (as is quite possible) you decided you really wanted some alcohol to help wash down all those spuds.

So, counting for rabbits, aphids, bad weather, and the like, you’d want a bare minimum of about a half an acre per person.  That’s a lot more arable land than most people have access to.  Doing just the vegetables is more reasonable – that’s about 0.1 acres or 4400 square feet per person.  So if a couple with no kids had a quarter acre lot with a small house at the north end and turned the entire balance of the land into garden, they could cover a fifth of their calorie needs and eat a lot of terrific organic vegetables.

There’s more to the story than this though.  Gardening is very nutrient intensive, and while composting the non-edible portions helps a lot, something must be done to replenish the nutrients that are removed (in the form of food) to the soil.  Nitrogen can be replenished by fixation of atmospheric N2 vi leguminous cover crops, but phosphorous and potassium are harder to gin up.  I’m reading a book that discusses this from a historical perspective for the eastern Massachusetts area, but generally speaking it is very difficult to maintain yields without inputs of some kind.  And some places just literally don’t have enough land at all.  Massachusetts only has about 0.8 acres per person for the whole state.  If you cultivated fully half of the state (leaving the rest in forest and houses/roads etc), you could only just barely pull it off, and you would need massive inputs to keep the fertility up since there would be no space for green manure, cover crops, etc.

There’s also the question of how much time it would take.  Eliot Coleman (who is something of an expert in this field) says one person can tend about 2.5 acres in intensive production.  This means that one person doing high intensity small scale organic agriculture could feed only about 5 people – that means we would need 60 million people working at agriculture in the US – as it stands we only have maybe 3 million (just a rough guess based on what I’ve heard).  This would be a remarkable cultural shift; not a passing fad but a social earthquake.  I believe my usual rule of thumb holds here – anyone who predicts (or advocates) massive change needs to identify the sufficiently powerful forces and demonstrate how they will bring about that change.

So while I will continue to grow my garden and tend my orchard, I’m not holding my breath for the entire nation to join in the fun.


One Response to “Gardening, land area, etc.”

  1. Urban Homesteading – meh « Five Islands Orchard Says:

    […] in their food requirements. I’ve done the math in several previous posts, on industrial meat, crop area requirements, and energy requirements to grow food. Living in the city can potentially have very low […]

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