If the future of the planet depends on us all learning to grow our own vegetables, we're doomed. Today I picked the best of the half dozen cabbages I've been trying to cultivate. I planted them back in April - autumn here - so they've been growing for eight months. The one I picked had the biggest heart, big enough to fill the palm of my hand, and it was solid feeling, so I decided it really wasn't going to grow much bigger. It was just about enough for three of us.
Meanwhile, at the greengrocer I could have bought a cabbage for around $1.50, and it would have been the green vegetable portion of four meals.
So - considering that I paid $3.25 for a punnet of six seedlings, and that of the other five, two have no heart at all, and three have hearts so tiny that I'd be lucky to get even one more meal out of them, I'd say my efforts have not been very successful. It's a good thing that we're not charged for water. And that I didn't spend any money on compost, fertiliser etc - or tools for that matter, since we have garden tools anyway.
Then there are the lettuces. I thought it would make more sense to buy seeds than seedlings, since it's much cheaper. Or would be if I hadn't bought seed raising mix to start them off in. Of course I ended up with far more than I needed. Eventually I planted out about a dozen, and at first I checked on them every night, and made sure they had enough water. But P has the automatic sprinkler system going, and we've had rain in the last week, so I hadn't checked for a few days. Then when I did go to see how they were getting on, they had vanished. Completely. Not even a single withered stalk to be seen.
On this occasion, I suspect slugs. In the past, I've had flower beds destroyed by blackbirds digging for grubs, and I've lost a whole crop of pansies to a marauding human. That was in a previous house, which had a grass strip and a narrow flower bed between the front stone fence and the pavement. The pansies were disappearing one by one, and I couldn't figure it out, until the neighbour told me she had seen a woman stop by, dig out a plant and pop it into her handbag!
So - back to the vegetables. To be honest, I suspect it is actually more sustainable (i.e. lower carbon footprint) not to grow your own. If a market gardener can get cabbages to the market at $1.50 each and still make a profit, he has to be doing it pretty efficiently. A large crop all in one place will probably need less water than a few in a garden bed, where the sprinkler system waters some of the path and lawn as well. Then, there are no plastic punnets to dispose of (or little foil packets if you're buying seeds). Sure, the cabbages travel to market by truck, using fuel, but there are a lot of cabbages in that truck per gallon of petrol. It really doesn't make too much difference whether I drive to the garden centre or the supermarket - except that the supermarket is closer. In fact I often walk to the supermarket.
As for farmer's markets, each grower there grows in smaller quantities, and many of the shoppers at a farmer's market seem to have travelled further to get there, so I suspect the fuel per cabbage is considerably higher than it is for those at the local supermarket.
If you want pesticide free organic vegetables, it may make sense to grow your own or buy at the Farmer's Market. If your carbon footprint is all you're concerned about, then it wouldn't surprise me at all to learn that the local supermarket is the best choice.
(I may just try again with the lettuces though. I don't want the slugs to beat me!)