World Wide Opportunities on Organic Farms (sometimes Willing Workers on Organic Farms) is a grassroots organization that brings together organic farmers and farmhands. They have a small yearly membership fee in many countries, which covers the cost and continued production of the WWOOF handbook & listing for the area. Stays can last from several days to months (or even years) on end. WWOOFing and hitchhiking can compliment each other nicely.
From their website:
"WWOOF is a world wide network - It started in the UK in 1971 and has since become an international movement that is helping people share more sustainable ways of living.
WWOOF is an exchange - In return for volunteer help, WWOOF hosts offer food, accommodation and opportunities to learn about organic lifestyles.
WWOOF organisations link people who want to volunteer on organic farms or smallholdings with people who are looking for volunteer help."
Prepare to meet some very unusual and demanding people and prepare to be exploited. It's an unfortunate fact of the WWOOFing experience. There's a reason most WWOOFers tend to be young, naive and overseas backpackers: this is the variety of person preferred if you are an isolated middle-class evacuee from the suburbs looking for unquestioning slave labour.
Experiences vary widely, but be on your guard. Ring first - if the host sounds barking mad, they are. Don't risk it, no matter how desperate you are. Otherwise you'll find yourself being the object of affection and sexual harassment and possibly worse. Some WWOOFing hosts are religious and cult groups, and fail to mention this on their advertising.
Your first meal will be delicious and expensive, your second meal will be salad and you worked six hours for it. You might be sleeping with several species of cockroaches and a resident python and a few bats.
Hosts are often suburban types fleeing from some sort of personal crisis and often have few real friends and little money, perhaps like you, so it could work out, or it could be a nightmare.
On the other hand, there are also very nice WWOOFing places with very nice people out there...