Lots: If your goal is to grow as much food as you need, year round, it's almost impossible for an urban gardener to have too big a garden. One figure out there is that a family of four probably needs a bit less than half an acre of land (0.2 hectare) to grow sufficient vegetables and fruit for a year. The average lot size here in Vancouver is about 4,000 square feet - less than a tenth of an acre, including space for the house and garage - so even a single person would need more land than they likely have.
So if you have the time, space, and a few other resources discussed below, you just can't grow more food than you can eat. In which case, let's make a huge garden!!
Not Much: But even in a very small garden, you can grow quite a bit of food. And there are always a few other questions to consider, too:
Time and Energy: Balancing harvest against labour, growing vegetables is pretty easy-going in terms of the time and work you need to put into it. To be sure, at certain times of the year, bigger chunks of work need doing, and designing and building a garden from scratch constitutes a pretty big chore up front.
But in the gardens we work for our clients, we spend 3-5 hours a week in a small garden (three or four 5x10' beds, for example), once it's up and running. And even if you skip the odd week, the garden will be fine, so long as the watering is covered.
Your Food Preferences: Some crops are pretty land-intensive and take up space for a whole season before you can harvest them at the end of summer. These include cauliflower, cabbage and broccoli, tree fruits, and root crops like beets, parsnips and potatoes (left). And, unfortunately, tomatoes - at least the larger ones - though they're so good, there's no question they're worth it!
So if your eating habits draw you to potatoes and cabbage, you may need to consider a larger garden. But if you mostly want to eat fresh, organic salads and green smoothies all summer, you can grow a lot of food, with successive plantings and ongoing harvesting, from a pretty small garden.
Storage and Preserving: If you do want a larger garden, consider incorporating some storage and preserving practises into your gardening plans. In the long run, you and your family or friends can definitely eat the whole harvest, but it does need to be preserved - and fast.
A big garden is a great excuse to build that root cellar you always wanted, or to dip into Aunt Ethel's canning recipes and stack your larder to the rafters with apple butter, homegrown tomato sauce, canned plums, and lots and lots and lots of zucchini chutney. It's an extraordinarily satisfying experience.
Otherwise, you might want to plan a slightly more modest garden, or else expect to make regular drop-offs at the food bank - also a rewarding outcome for your garden produce.
A Sample Bed: To give you an idea of just what you can grow in a single garden bed, a fairly intensive planting plan for a 5x10' bed, in full sun, might include: 4 or 5 tomato plants, one squash or cucumber (if trained up a trellis), a row of beans (trellis again), a few parsley or basil plants, and a couple rows of greens (lettuces, mescluns, arugula, smallish kale, etc.). Maybe a few strawberries or well-trimmed perennial herbs squeezed in.
Or if you devote the entire bed solely to potatoes, you'd have a good stock of potatoes for 2 or 3 months in the fall, depending on your cooking habits and family size. And if you wanted to grow only fresh greens, you could have three rows of lettuces and mescluns planted on a three week schedule, as well as a row of kale and/or swiss chard. This should allow you to have a 2-person salad and a few other greens just about every day all summer.
Our Most Common Advice - Start Small: There's a fair learning curve, if you're a beginner gardener, in getting your garden going and keeping it running - though it should be an enjoyable curve. It takes awhile to get a sense of the habits and rhythms of your garden, and it can even be a shift to get used to eating from your garden - remembering that you don't have to get lettuce from the store, or that it's no problem that you forgot to buy broccoli, because the bean vines are heavy with food in the garden!
A Final Word: You will never, ever - not ever - need more than a couple of zucchini plants. Never.