Although they're cheap and plentiful year-round at the supermarket, many gardeners still set aside garden space for potatoes (Solanum tuberosum). That's partly because the humble spud simply tastes better when it's homegrown and freshly dug and partly because they're one of the few long-storage staple foods home gardeners can grow effectively. In fact, if your growing season is long enough, you can have both an early crop to eat all summer long and a fall crop for winter storage.
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Plant fall-crop potatoes 90 to 110 days before your expected frost date — needed for the specific cultivar to reach maturity. Depending on your climate, that might be as early as June or as late as mid-August.
Staggering Your Potato Crops
You'll need to allocate two "potato patches" in your garden — one for the early crop and one for the late crop. Most places don't have a long enough season for you to dig the potatoes from your early crop and then plant a late one in the same spot; and even where that's possible, it's a bad idea. To minimize the risk of pests or disease accumulating in the soil, you should avoid planting potatoes repeatedly in the same spot.
Instead, plan to plant your first crop at the earliest practical date for your zone. That can be as early as February in Florida, but later in most other parts of the country. Early to midspring is a good rule of thumb. This early crop should be short-season varieties, so you can begin enjoying your bounty as soon as the new potatoes reach harvestable size. It's also an ideal use-case for fingerling potatoes or any exotic varieties you want to try.
For your fall crop, choose long-season varieties so the beginning of their season will coincide with the end of the harvest of your earlier crop. These typically take 90 to 110 days (and sometimes longer), so look up the expected frost date for your area and then count backward by the days-to-maturity for your specific cultivars. That may place the planting date for your autumn potatoes anywhere up to mid-August, depending on your climate.
Special Considerations for Fall Potatoes
Most sites (and seed catalogs) assume you're planting in spring, which is the more traditional option. Growing a fall crop requires a few adjustments, starting with your supply of seed potatoes. Those are often unavailable by midsummer, unless you store your own or arrange them in advance with your supplier of choice. Alternatively, you can buy your seed potatoes for both early and late plantings in spring and keep the seed for your fall potatoes in the refrigerator until planting time.
To help ensure healthy, vigorous plants from your second crop, cut the seed pieces bigger than usual — skewing to 2 or 2 1/2 ounces rather than 1 1/2 — and then let them cure for a few days so the cut surfaces are scabbed over.
The soil may be too warm for potatoes to perform at their best by the time you plant your late crop. They prefer a cool soil, so minimizing heat at planting time is helpful. Plant in the cool of the evening, water them in well and ideally apply a couple of inches of loose hay, straw or similar mulch to help shield them from the sun's heat. Water regularly until the days begin to cool, and provide some shade if you're in an especially hot growing area.
Harvesting Your Fall Potato Crop
Outside the zones with very short growing seasons where spring-planted crops are the fall potatoes, gardeners may be unfamiliar with the autumn harvesting routine. At this time of year the plants will typically not begin to die back on their own as they do in the heat of summer, but will, instead, be killed by frost. That's fine — a few light frosts won't kill the tubers themselves. You can leave them in the ground, harvesting a few at a time as needed until there's a risk of the soil itself freezing.
Dig the potatoes carefully, discarding the original seed pieces (which should still be visible at the plants' roots) and any diseased potatoes you find. Potatoes with rot should be discarded; those with insect damage or physical damage from your garden spade or digging fork can be set aside to eat first. The remaining potatoes will need to "cure" for three to five days in a warm, dry, well-ventilated place so their skins can mature. Then, any excess soil can be brushed off, and they can be moved to an unheated basement or root cellar for long-term storage.
Your autumn crop probably won't be as productive as the spring-planted crop, but the slower-growing fall potatoes are typically denser and of higher quality, which makes them well-suited to long storage.