In the Food Police, I wrote the following about local foods when critiquing the argument that a larger local food system would be better for the environment and for food security:
This new paper in the Journal of Agriculture and Applied Economics by some Hawaiian researchers provides some empirical evidence of the price volatility I mention surrounding local foods. Here's a graph from their paper showing production and prices of local tomatoes over 12 months of the year
There is a very clear negative correlation between production and price. When tomatoes are "in season" and local producers have a lot to sell, prices are low, and vice versa.
Of course, that inverse relationship is true for most of agricultural production. But, here's the difference for a lot of local food production: A) with grains you can store the commodity to help smooth out prices over time (something much harder with perishable fruits and vegetables) and B) with trade you can ship to locations with different seasons (where there is less supply and therefore higher prices).
In short, by limiting sales to local consumers, producers are opening themselves up to a lot of potential price volatility, and to lower prices at the exact time they have produce ready to sell. How can the producers partially mitigate such effects? Find people in other locations with different seasons with whom to trade.
The authors write: