What's a Potato Head to Do? Ask the Snarky Farmer!

     Noted Sacramento heirloom tomato grower Bill Bird asks:

Since everyone and their grandma appears to be OUT of seed potatoes for the fall growing season -- what's wrong with using some of the potatoes from our earlier harvest of All Blue and Cranberry Red to plant a new crop? Is there a difference between 'eating potatoes' and 'seed potatoes?' Thank you, oh master of gardening knowledge."
 

Bill:
Hey! I'm supposed to be the snarky one here. In California's Central Valley, there are two excellent times for planting white potatoes (Solanum tuberosum): now (August-early September) and mid-February through April. Most gardeners know not to plant potatoes purchased from the supermarket. These have probably been treated with a sprout inhibitor and probably have potato virus disease, which will reduce yield, according to the UC Davis Vegetable Research and Information Center. 

Common sense would seem to tell a gardener that if the home grown potato looked healthy and was from a healthy potato vine, it should be OK to use it for planting, however...there are some very good reasons why you should only choose certified seed potatoes, which I'll get into shortly.

Potatoes are planted by chopping the potato into "eyes". The UC Davis experts with degrees in Spudology explain it this way:

"Cut seed potatoes into pieces weighing from one and a half to 2 ounces, each having one or more eyes.

Store cut pieces at room temperature and preferably in a humid place for 1 to 2 days before planting to allow the cut surface to form a callus. This decreases rotting. 

Prepare a planting furrow 3 inches deep, drop seed pieces into the furrows, and fill the furrows to ground level. The rows should be 36 to 39 inches apart and the seed pieces planted 6 to 10 inches apart, depending on the size of the potatoes you want to harvest.

Leave the furrow this way for 4 to 6 weeks, and then add 3 more inches of soil so that the seed pieces will be buried 6 inches deep.

Most of the (potato) crop should be harvested when vines die and/or the skin of the tubers is firm, not flaky. Remove vines before digging."

=====

Potatoes like sandy soil, full sun, a 5-10-5 fertilizer at planting time, and light, frequent irrigations (it's a shallow rooted crop).

But everything I read says, "buy certified seed potatoes for planting". 

Well, what makes a certified seed potato?

Each potato-growing state has tests to certify seed potatoes. These tests include field and storage inspections as well as demanding potato criteria. 

And the Feds have their own criteria (of course):

"U.S. No. 1 Seed Potatoes" consist of unwashed potatoes identified as certified seed by the state of origin by blue tags fixed to the containers or official State or Federal State certificates accompanying bulk loads, which identify the variety, size, class, crop year, and grower or shipper of the potatoes, and the State certification agency. These potatoes must meet the following requirements:
(a) Fairly well shaped.
(b) Free from:
(1) Freezing injury;
(2) Blackheart;
(3) Late Blight Tuber Rot;
(4) Nematode or Tuber Moth injury;
(5) Bacterial Ring Rot;
(6) Soft rot or wet breakdown; and,
(7) Fresh cuts or fresh broken-off second growth.
(c) Free from serious damage caused by:
(1) Hollow Heart; and,
(2) Vascular ring discoloration.
(d) Free from damage by soil and any other cause. (See §51.3005 - 06).
(e) Size:
(1) Minimum diameter, unless otherwise specified, shall not be less than 1-1/2 inches (38.1 mm)
in diameter;
(2) Maximum size, unless otherwise specified, shall not exceed 3-1/4 inches (82.6 mm) in
diameter or 12 ounces (340.20 g) in weight.

Whoosh! Only the Bruce Jenners of the potato world make it into those sacks.

HOWEVER....the University of Illinois offers the heirloom grower a potato chip of hope: 

Q. Should I save some of my potatoes for seed?

A. No, unless you are saving seed of an heirloom variety not commercially available. Saving your own seed potatoes can lead to a buildup of viruses and diseases. Whenever possible, plant seed potatoes certified to be free from certain viruses and diseases.

======

     Planting potatoes that may have been exposed to late blight, nematodes or other diseases might carry those problems over to a new planting area. So, the risk may be not so much to the potato, but to whatever else you might grow in that bed. 

     I think as a precaution, I wouldn't plant potatoes and tomatoes in the same soil within three years of each other. 

     The UC publication, "Potato Production Principles and Tips" also identifies potato problems that many home gardeners may be too familiar with on other vegetables:

"Potential diseases include Rhizoctonia (damping off), bacterial soft rot, early blight, verticillium wilt, potato leafroll virus, several mosaic viruses. Prevention through seed and site selection, crop rotation and proper soil and water management is the best control."

     So, basically, Bill...you have to weigh the pros and cons. Take into consideration the size of your yard and the densities of your vegetable plantings; diseases can spread easily, via the wind, plants, soil, tools. 

 To quote a famous guy with a tomato ("Rowdy Red") named after him: