Your focus should be on local growers, rather than those overseas.
Grist's advice columnist Eve Andrews was asked an interesting question by a reader: "When I buy local, does it hurt farmers in other countries?" Andrews made an equally interesting point in response – that farmers in other countries don't see much of our money when we do 'support' them, so your dollars are much better spent within your own local community.
The reason for this is that international food trade is a convoluted network with "a lot of middlemen, including agricultural conglomerates, distributors, and grocery chains." (You can learn more about the issues with grocery chains here.) Buying a lemon from South Africa doesn't boost the income of a South African lemon farmer because so much of the profit is lost along the way.Another factor is that there aren't a whole lot of small-scale farmers supplying the foreign-grown ingredients at your grocery store. The farmers you might like to think you're supporting are in fact occupied with supplying their own local grocers, food stands, and buyers – not necessarily growing crops for export markets. Andrews writes,
"The food that’s coming to the United States from other countries is grown by huge agricultural conglomerates in those countries. Douglas Gollin, a development economist at Oxford University, points out that the most vulnerable farmers in the world aren’t connected to global markets at all. They’re much more affected by things like drought and floods and other natural disasters than by the purchasing decisions of Westerners."
If you are determined to support small-scale farmers overseas, the best thing to do is to buy certified fair-trade goods, such as coffee, tea, spices, sugar, coconut products, and other tropical products that cannot be produced in North America. Fair-trade certification ensures that farmers are receiving their fair share of the profit and have access to funds to improve their own communities and agricultural practices.
Taking care of one's own local farmers has significant benefits. You get fresher and better-tasting produce that hasn't been transported long distances to reach your table and local growers get more money for their food because it has passed through fewer hands. The same rule applies to processing, as Andrews explains: "The less processing a food item goes through, the greater the proportion of what you pay for it goes to the farmer."
I'm a big fan of the CSA (community supported agriculture) model that provides farmers with a reliable income source, regardless of crop failures, and helps people to eat more seasonal vegetables that they might not purchase otherwise; it's a win-win situation all around. There are, of course, many contributing factors to building a more sustainable, ethical food network. Farmer payment is a single aspect of that, but an important one, because happy, well-paid farmers are a sign of a healthy food system.