Small seed potatoes can be planted whole, but larger ones should first be cut into pieces with at least one eye or recessed dormant bud. The pieces should be blocky and 1-1/2 to 2 ounces in weight. If you cut each piece to the size of a large ice cube it will be about the right weight.
Seed pieces can have several eyes each, and be larger or smaller than recommended. Larger ones produce plants that yield a high number of medium to small potatoes. Smaller ones will yield fewer, but larger, potatoes.
While it may be tempting to plant smaller pieces in the hope of getting big potatoes, stick to the middle-sized pieces. Small pieces have less starch stored up to nourish the developing plant, so their food supply is quickly exhausted. Larger pieces have more energy to offer, which can help a young plant recover from an early-season injury. For example, if you plant very early in the season, a late frost could injure the plants after they've sprouted. Plants from a good-sized seed piece can continue to draw on the stored energy of the piece to recover more rapidly and resume normal growth.
There's always talk around the neighborhood at planting time about whether to cut seed potatoes and plant them right away or whether to cut them and store them until the cut pieces heal over.
You can do it either way, but you may have more success if you cure the seeds after cutting them, giving them time to develop a protective covering over their exposed surfaces. Researchers suggest you store or cure the cut seeds for two or three days in a humid environment around 70° F. This will promote fast healing of the surface and keep the seed pieces from drying out. When you plant them, the protective covering will retain moisture and energy and serve as a barrier against rot organisms.
Other people feel you should plant the seed immediately after cutting. In a book for home gardeners, the U.S. Dept. of Agriculture urged cutting and planting right away saying, "Otherwise, viability will be lowered by loss of moisture and entrance of rot organisms." This theory is good advice when the soil is relatively warm -- when you're planting late in the spring, for instance. In early spring, however, the soil is cooler and more moist -- conditions favorable for rot organisms in the soil -- so be sure to cure the seed pieces for a couple of days.
There are other ways to protect cut seed potatoes, too. Sulfur powder is a natural, inexpensive seed protectant available at most drugstores. A couple of ounces protects approximately 10 pounds of seed potatoes. Put several seed pieces in a paper bag, add a tablespoon or two of sulfur and shake the bag. The powder sticks to the pieces and protects them from rot organisms in the ground. It will protect against rot in the ground and help give you a better crop. Follow directions carefully when using fungicides or any other chemical.
To avoid the controversy, order seed potatoes from mail-order companies or on-line that supply seeding tubers just the right size for planting.
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