I imagine that these farmers high up in the Andes are growing potatoes much as their ancestors did when the tubers were first domesticated between 5000 and 8000 B.C. It's pretty staggering to think how long humans have been growing potatoes.
An estimated 4,000 varieties exist worldwide, but here in Northern California we have a smaller selection. Still, seed catalogs offer a variety of types, such as fingerlings and russets, and a range of skin and flesh colors, including pink, white, red, purple and yellow. Varieties vary in size and number of days to maturity. Some are best for baking, others better suited to frying or boiling.
After returning from Peru, I began to grow potatoes in my own garden. I have since learned a lot, having planted them in many different conditions. Potatoes need well-drained soil rich in organic matter; they do not do well in heavy clay. They have shallow roots and need constant moisture but will rot if the soil is too wet. Full sun is required. Being sensitive to frost and heat, they do best as a spring or fall crop in Napa County.
Local nurseries have seed potatoes available for sale now. Potatoes are susceptible to a host of diseases (remember the Irish potato famine?), so you should always plant certified seed potatoes rather than starting with supermarket potatoes.
Potatoes are members of the nightshade family (Solanaceae), which also includes peppers, eggplants and tomatoes. To prevent soil-borne diseases, rotate these crops so that you never grow nightshade plants in the same plot two years in a row. A three-year rotation is even safer.
A day or so before planting, cut your seed potatoes into chunks, each containing one to three eyes. The eyes are the buds from which your potato plant will sprout. If your store-bought potatoes have ever sprouted, they sprouted from an eye.
Bury seed potatoes four inches deep. A few weeks after the leaves emerge, you need to “hill” the plants by mounding more soil around the stems. Hilling will increase your yield because new potatoes grow between the original seed and the soil surface.
Each growing season, Napa County Master Gardeners select a fruit or vegetable to “field test” in our home gardens. We compile and analyze our results for the benefit of the public. We now have a blog called “Spill the beans "where you can find the results of our field trials and other timely gardening information. You can subscribe to the RSS feed for our blog on our website (http://ucanr.edu/sites/ucmgnapa).
Last year the field-test committee trialed three different potato varieties: ‘Mountain Rose' (an early-maturing variety with rose-colored skin and flesh);‘Russian Banana' (an heirloom fingerling variety); and ‘Sieglinde' (a yellow, waxy mid-season type). With more than a dozen Master Gardeners participating, representing a variety of growing conditions and irrigation techniques, it was interesting to see the results.
The greatest yield came from raised-bed gardens with drip irrigation. Several participants planted their potatoes in Grow Bags (porous fabric pots), while others planted in the ground. Some watered by hand while others had drip systems. Some gardeners had success burying their seed potatoes in a tower of straw instead of planting in soil. As the plants grew, the gardeners added more straw.
For all of us, the take-home message was that gardens with regular watering and well-drained and well-cultivated soil produce the greatest yield. I confess that I planted mine in a bed without irrigation. They did not do well in the summer heat, and I never harvested anything. But I am happy to note that the potatoes are coming up again in that bed, and I will try to take better care of them this time.
My family's favorite part of potato growing is the harvest. Early-maturing varieties may be ready after only 60 days. My children and I get very excited when the plants start to flower. That's a sign that you can plunge your hand into the soil and find some new potatoes.
At this point, you should stop watering and let the foliage turn yellow and die back. If you leave the new potatoes in the ground for at least two more weeks, the skins will harden and the potatoes can be harvested and stored in a cool, dark place. Alternatively, you can leave them in the ground until you are ready to eat them.
For more information, consult “Growing Potatoes in Napa County” by former county farm advisor Dean Donaldson. You can find this document online on our website(click on Gardening Resources, then on Healthy Garden Tips). Or pick up a copy during our office hours (address below).
Workshop: Napa County Master Gardeners will host a workshop on “Fruit Tree Pruning” on Saturday, February 22, from 9:30 a.m.. to 11:30 a.m. (indoor lecture) and from 12:30 p.m. to 2:30 p.m. (outdoor hands-on workshop). Lecture location is the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Outdoor location to be determined. Now is the best time to prune your fruit trees. Learn techniques to keep them healthy and productive. Please dress for outdoor weather. Online registration (credit card only) Mail in registration (cash or check only)
Napa County Master Gardeners welcome the public to visit their demonstration garden at Connolly Ranch on Thursdays, from 10:00 a.m. until noon, except the last Thursday of the month. Connolly Ranch is at 3141 Browns Valley Road at Thompson Avenue in Napa. Enter on Thompson Avenue.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( http://ucanr.org/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.