|Harvest of green beans and cherry tomatoes, May 2012|
First of all, let’s ask the right question. A "garden" grows things like tomatoes, peppers, broccoli, lettuce, etc. The typical suburbanite is not growing wheat and raising cattle. There could be a few fruit trees and a chicken coop out back, but I think the question we can feasibly address is “how big of a garden do I need in order to grow all of my family’s vegetables.” Unless you are a strict vegan you will not be eating solely out of your backyard (even vegans need a source of nuts and oils if they aren’t growing these in addition to vegetables). I’m happy to purchase meat and eggs from local farmers. I also buy oils, nuts, and some fruits from the local food co-op or grocery store (I will get into homegrown fruits in a future post). What I really want to know is how much land would it take to eliminate imports from my household’s vegetable intake.
I’ve spent a lot of time rummaging through articles on the internet trying to figure out what size garden I might need if I wanted to (gasp!) grow all of my family’s vegetables. An unofficial survey of authors and internet gurus gave me widely varying estimates from a few hundred square feet to an acre or more for the average person. There is obviously little consensus, but more importantly, no one was really answering my specific question. A lot of people are talking about how much land is required to provide ALL of the food for a person or family. Being such a commonly pondered question I think it deserves some mathematical/scientific analysis, not another wild guess.
Let’s answer it once and for all.
There are a few things to consider to make these equations work for your own situation. First, how many people do you plan to feed (# people in your household)? That should be an easy answer. Second, how much vegetable matter does your household consume in a year? This is a pretty overwhelming question, so we will need to break it down.
The American Cancer Society says we should be consuming about 5 servings of fruits and vegetables per day, but disregard recommendations for this. Think about your average day. Do you have any vegetables at breakfast (spinach in your frittata)? What about for lunch (leafy salad with tomatoes)? How many servings of vegetables do you usually serve for dinner? Don’t be too critical here. Just try to average it for the day. It’s likely that not everyone in your family is consuming the same amount, so figure out the number of servings consumed by each person individually. Maybe you have 5 servings per day, your spouse has 3 servings, and maybe each of your kids have 2 servings. Add these together so that you have the total number of vegetable servings consumed in your household per day.
I tried to keep it simple for my own estimation. There are two of us in the Suburbindigenous household, and I would like to provide us with 5 servings of vegetables per day each, which is 10 servings per day for the household. The next step is to convert “servings” to a unit of weight, which will help us compare to the yields in the garden. The USDA says that an average serving of vegetables is 4 ounces. I’m sure there is some variation, but this is an estimation, not a space shuttle trajectory. So, simply take your household consumption of vegetables in servings per day and multiply by 4. Now you have the total number of ounces of vegetables consumed in your household per day. Multiply by 365 to get the number of ounces of vegetables consumed by your household in one year. To simplify, divide by 16 to convert this to pounds (there are 16 ounces in a pound). Your math should look something like this:
daily household servings x 4 oz x 365 days
= pounds of vegetables per year
My number is 912.5 pounds per year. The next thing to do is to list all of the vegetables that your family would like to eat that will grow well in your region. Here’s my list...
- summer squash
- winter squash
- sweet potato
Notice I left off any herbs or onion family crops. I use them more for flavoring and accents than actual servings of vegetables, but if you eat a lot of onions maybe you should put them on your list.
I have 18 crops on my list, so the first thing I did was take the total number of pounds of vegetables needed for my household and divided by 18:
912.5 pounds per year = 50.7 pounds of each crop
I'll round down to 50 for simplification.
This means I could grow 50 pounds of each of these crops and be able to feed my family with vegetables for a year. But how much space do I need to grow 50 pounds of okra or 50 pounds of peas? I thought you would ask that.
For the next step, we need to determine the approximate yield per plant for each individual crop. I just did a Google search for each one and found most of my answers in gardening forums and Q&A sites. Remember, this is just an initial estimation. I will tell you how to fine tune it at the end. Here are the results of my yield-per-plant research:
- tomatoes: 10 lbs/plant
- peppers: 2 lbs/plant
- summer squash: 5 lbs/plant
- winter squash: 10 lbs/plant
- pumpkin: 10 lbs/plant
- lettuce: 1 lb/plant
- kale: 1 lb/plant
- chard: 1 lb/plant
- broccoli: 1 lb/plant
- kohlrabi: 1 lb/plant
- cauliflower: 1 lb/plant
- carrots: 1/4lb/plant
- beans: 2 lbs/plant
- peas: 2 lbs/plant
- celery: 1 lb/plant
- beets: 1/4lb/plant
- okra: 3 lbs/plant
- sweet potato: 2.5 lbs/plant
You might have already figured out the next step. Figure out how many plants of each crop you will need in order to achieve the desired yield. Simply take the number of pounds desired divided by the pounds-per-plant yield. For example:
50 pounds of tomatoes desired = 5 plants needed
10 pounds of tomatoes per plant
I am aiming for 50 pounds of each crop, but your number is probably different than mine, so make sure you do the calculation for yourself. Here are my numbers:
- tomatoes: 10 lbs/plant...5 plants
- peppers: 2 lbs/plant...25 plants
- summer squash: 5 lbs/plant...10 plants
- winter squash: 10 lbs/plant...5 plants
- pumpkin: 10 lbs/plant...5 plants
- lettuce: 1 lb/plant...50 plants
- kale: 1 lb/plant...50 plants
- chard: 1 lb/plant...50 plants
- broccoli: 1 lb/plant...50 plants
- kohlrabi: 1 lb/plant...50 plants
- cauliflower: 1 lb/plant...50 plants
- carrots: 1/4lb/plant...200 plants
- beans: 2 lbs/plant...25 plants
- peas: 2 lbs/plant...25 plants
- celery: 1 lb/plant...50 plants
- beets: 1/4lb/plant...200 plants
- okra: 3 lbs/plant...17 plants
- sweet potato: 2.5 lbs/plant...20 plants
That is some great data right there. We are getting so close! Now that we know how many plants we need we can use plant spacing data to determine the number of square feet needed to grow this many plants. You can consult any seed packet for row spacing requirements, but I prefer Mel Bartholomew’s square foot method spacing. It will make this step a lot easier, too. If you don’t want to buy his book there are plenty of forums and websites that will tell you the square foot spacing for each crop. If you are using any of the crops on my list I’ve done the work for you:
- tomatoes: 1 plant per square foot
- peppers: 1 plant per square foot
- summer squash: 1 plant per square foot
- winter squash: 1/4 plant per square foot (i.e. one plant needs 4 square feet)
- pumpkin: 1/4 plant per square foot
- lettuce: 1 plant per square foot
- kale: 1 plant per square foot
- chard: 1 plant per square foot
- broccoli: 1 plant per square foot
- kohlrabi: 1 plant per square foot
- cauliflower: 1 plant per square foot
- carrots: 16 plants per square foot
- beans: 9 plants per square foot
- peas: 16 plants per square foot
- celery: 1 plant per square foot
- beets: 9 plants per square foot
- okra: 1 plant per square foot
- sweet potato: 1 plant per square foot
Next, simply divide the number of plants you need by the number of plants per square foot to get the number of square feet of space required for each crop. For example:
5 tomato plants = 5 square feet
1 plant per square foot
5 winter squash plants = 20 square feet
.25 plants per square foot
Here’s my list:
- tomatoes: 5 square feet
- peppers: 25 square feet
- summer squash: 10 square feet
- winter squash: 20 square feet
- pumpkin: 20 square feet
- lettuce: 50 square feet
- kale: 50 square feet
- chard: 50 square feet
- broccoli: 50 square feet
- kohlrabi: 50 square feet
- cauliflower: 50 square feet
- carrots: 12.5 square feet
- beans: 3 square feet
- peas: 3 square feet
- celery: 50 square feet
- beets: 22 square feet
- okra: 17 square feet
- sweet potato: 20 square feet
We can finally add these numbers together to get a total number of square feet required to feed your family vegetables. My number is...drumroll please...507.5 square feet! That's actual growing space (not including pathways).
While you may find this number useful, don’t stop here! Go back and review your calculations and consider adjusting your initial assumption that your family would really want an equal amount of all of the crops on your list. I will be doing this for myself. I know, for example, that my family would want a lot more tomatoes and probably a lot less chard. Just make sure that your total number of servings equals the number your family consumes for the year and re-run the numbers. Maybe space-saving is important to you, and you now realize that you can get a lot more peas for a lot less space than, say, cauliflower. In that case you might adjust your numbers to grow crops that have a higher yield in less space.
Another thing to consider is how many possible growing seasons you have in your region. Remember my number? 507.5 square feet. If I lived in Maine, I would probably need a garden that had at least 507.5 square feet of growing beds. Luckily, I am in the subtropics, so I can really have 3 growing seasons. I can grow a crop from about September to December, another from December to March, and another from March to June. July and August is not a good time to be in the garden around here...that goes for people and for plants. Now watch what I can do...take 507.5 and divide by 3. That means I really only need about 170 square feet of growing space!
Remember I said I’d tell you how to fine tune your math a little more? I think the most variable part of our estimation is the “yield per plant”. Not only did it come from a non-scientific source, but it also can vary greatly based on your region’s climate, your gardening methods, and your skill level. The data we gathered was a quick way to get us close, but to have a better grasp on how much space you need will take time and record-keeping. Keep a garden journal (or, better yet, start a blog!) and track how many plants you grew and how much produce you harvested. After a season or two you will have a much more accurate “yield per plant” figure for each crop and can modify your calculations and your garden plans accordingly.
You do have a few choices now.
You could go out and dig up a space in your yard to accommodate the exact number of plants calculated. If you think gardening is that precise, you will probably be disappointed. Pests, disease, windstorms, and family emergencies happen. If you want to ensure you are able to grow all of your family's vegetables you will need to plant a little extra of everything. I'd say grow at least 10% more than the number you calculated. You should also consider making room to grow some herbs and onions for flavoring your food. These are some of the easiest things to grow.
You could choose to dig up less than your calculated number. Maybe your goal is to grow 50% of your family’s vegetables. Maybe you only have room for 10%. At least now you have an idea what 10% of your family’s veggie needs are.
Maybe you actually want to produce more vegetables than your family can consume in a year so that you can preserve food for the future or give some away to family, friends, and charities. Whatever you decide to do with your number it’s a place to start, and starting is half the battle!
I know this was a long post, but I really thought others would benefit from this analysis. Hopefully, you found it helpful!