Postharvest Recommendations for Small Horticultural Farms
The general steps in postharvest handling are
1) harvesting, 2) taking out field heat (generally done when washing produce or circulating air around the produce in a cooler), 3) cleaning, 4) culling damaged or infected items, 5) curing if needed (garlic & onions, pumpkins & winter squash, potatoes & sweet potatoes), and 6) storing.
If you want to search for handling recommendations for vegetables and fruits commonly grown in Minnesota, here's a spreadsheet that lists the crops in alphabetical order.
Detailed postharvest recommendations for a more extensive list of fruits, vegetables, and ornamental crops (geared primarily for wholesale operations) can be found in USDA Handbook 66.
Storage recommendations for vegetables for small gardens can be found at https://extension.umn.edu/planting-and-growing-guides/harvesting-and-sto.... If you have more than one cooler, you can learn what commodities can be stored together here.
More postharvest information, including sources of equipment and supplies, recommendations for handling individual fruits and vegetables, information specific for small operations, information in languages other than English, can be found at the University of California - Davis Postharvest Technology website.
Postharvest recommendation for organic operations can be found here.
General information on building root cellars are available from the University of Alaska. Note that root cellar temperatures often do not get below 40F, and can fluctuate over time. Click on the Root Cellar Construction tab in the main menu above to read about Food Farm's controlled temperature root cellar.
Information on building walk-in coolers were provided by Jim Thompson of the University of California - Davis. Build a walk-in cooler if you can afford it and are planning to sell wholesale, such that you need better temperature control than what a root cellar can provide. You can build one in a garage (courtesy of Bob Cramer):
You can use a CoolBot to control the temperature, although you might want to read Sam Knapp's article in the February 2021 Growing for Market newsletter to learn more about technical aspects of cold room temperature and humidity management.