In a previous post, Living off the land: How much land?, I estimated the amount of land it would take to grow a complete vegetarian diet: 4700 sq m of land per person, which is 50590 sq ft., or 1.16 acres. That estimate supposes one growing season per year of about 4 months. If weather and time permits two growing seasons per year, you can halve that estimate. On the other hand, if you want to be very conservative about how much land is needed, taking into account possible crop failures and reduced yields due to bad weather or other circumstances, you might want to set the estimated amount of land as high as 1.5 acres per person.
In this post, I’d like to continue the discussion and address some additional possibilities. Suppose that you are still buying some food, and your land is used only to supplement food from the grocery store. Now how much land is needed?
I think of growing food in terms of macronutrients: protein, fat, and carbohydrates. Those three macronutrients are absolutely essential for your dietary survival. They are called macronutrients because you need large quantities of each. As for micronutrients (vitamins, minerals), you only need a large garden, not a small -farm, in order to grow all the vitamins, minerals, antioxidants, and a variety of fruits and vegetables needed to make your meals healthier and more enjoyable. I suggest a garden size of about 50 sq m (just over 500 sq ft.) per person for that purpose.
Now the most difficult macronutrient to grow is dietary fat. Relatively few crops, suitable for a backyard mini-farm, can provide sufficient quantities of fat from whole food (e.g. peanuts, pumpkin seed, soybeans). Most vegetable fat sources require pressing an oilseed (e.g. camelina, canola, flax seed, safflower seed) to obtain the oil. But pressing your own oil is difficult and time-consuming. So let’s suppose that you buy all the vegetable oil that you need. Cooking oil is inexpensive and stores fairly well. If you plan ahead and buy while this food is plentiful and inexpensive, you won’t be too concerned if prices rise and availability falls.
How much oil do you need to buy? Maybe you are on a low-fat diet (as I am) and have a sedentary lifestyle, and so you need fewer calories from fat. But if some disaster strikes, you might need to be more physically active to deal with that circumstance. So I’m going keep the estimate of the amount of dietary fat and total calories that you need on the high end: 2740 kcal total per day, with 30% of those calories from fat. That value works out to about 300,000 calories from fat per year, or about 34 kg of fat (37 liters or 39 quarts) per year. Most types of vegetable oil will keep for about 1.5 to 2 years in storage (if kept cool and away from light). This works out to about 104 liquid ounces per month, and about 3.5 ounces per day (7 tablespoons of oil per day). If you feel you need to limit your fat intake, you can drop that to 20% of total kcal and about 4 to 5 tablespoons of oil per day (24.5 liters or 26 quarts per year). I suggest buying only a 3- to 6-month supply of vegetable oil, so that it does not become rancid in storage.
Currently, 48 ounces of vegetable oil costs 3 to 4 dollars (according to CompareGroceryPrices.org). So, on the high end, $4/quart and 39 quarts per year (26 of the 48 oz bottles), the cost is about $104.00. (Note any and all prices stated at Prep-Blog are as of the time of writing, to the best of our knowledge, subject to change.) Growing your own vegetable oil is costly, both in terms of money and your time/labor. So if you are going to grow some food and buy some food, the first item to buy is vegetable oil.
How much land does this save you? Based on my previous analysis (Living off the land: How much land?), 1750 sq m of land per person is sufficient to grow all the dietary fat you need in a year. Buying and storing vegetable oil reduces the 4700 sq m (1.16 acres) of land per person per year to 2950 sq m (0.73 acres) of land. So this reduces the amount of land needed by 37%, and it also reduces the time and labor that you would put into growing food. With two growing seasons per year, you could halve that acreage to about 0.35 acres (1500 sq m).
If you buy and store some carbohydrates, let’s say in the form of rice, you reduce the land needed even further.
The amount of carbs needed per year, at 2740 kcal/person-day and 55% of kcal from carbs, is 550,000 kcal/year or 142 kg of carbs (at 3.87 kcal/gram of carbohydrate). Rice is 80% carbohydrate (USDA data), so if all those kg were met by rice, you would need 177.5 kg (390 pounds) of rice per year (about 486 g or 17 oz. per day). A large serving of rice (as the main course, rather than a side dish) is about 6 ounces (dry uncooked white rice) or 170 grams. Two 6 ounce servings of rice per week would provide 1/10 the carbs needed per week. For 104 servings of rice per year (2 x 52 weeks), you would need 39 pounds of rice/year (6 oz x 2 servings x 52 weeks, divided by 16 oz/lb). Let’s round that up to 40 pounds of rice per year.
You could substitute 40 lbs of white pasta, for about the same result. Or you could use 20 lbs of each, rice and pasta, per year.
One 10-pound bag of rice, store-brand, is typically well under $10; individual one pound bags of rice might be just over one dollar. So let’s conservatively price the rice at $40 for 40 lbs. We can then reduce the amount of land needed to grow carbs (2500 sq m) by one tenth (250 sq m). Starting at 4700 sq m of land for a complete diet, we subtract 1750 sq m if you buy vegetable oil, and 250 sq m for the rice, leaving us with 2700 sq m of land or 0.67 acres. And if you make use of 2 growing seasons per year (3 to 4 months each), then you can reduce that amount of land by half to one third of an acre or 1350 sq m (14,500 sq ft).
Just by purchasing rice and vegetable oil, at a cost of about $144.00/year, we can reduce the amount of land needed to grow a complete diet by 42%, from 4700 sq m to 2700 sq m per person per year. And if you buy and store some additional types of food, especially staple foods that provide protein or carbs, you can reduce the amount of land needed further.
Some other estimates (off-site) of how much land is needed per person:
Homesteading Quantified: How Much Land You Need To Go Off The Grid
Self Sufficiency: How Much Land to Feed Your Family?
How Much Land Can Ten Billion People Spare for Nature?