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How to Grow Potatoes
All tubers the size of a hen's egg (1-3 oz.) should be planted whole. Seeds this size are highly desirable. Using big tubers for seed is a dilemma. As a general rule the larger the seed the larger the harvest. On the other hand, the larger the seed, the more seed it takes to plant an area. Each seed in any case should weigh 1-4 oz. and must contain two or more strong eyes.
Most people cut of larger potatoes immediately before planting using a sharp, clean knife. Seed may be held for a day before planting to heal the cut surface, but do not let it dry out. Spread cut pieces on a table in the shade or in shallow boxes one layer deep. Avoid placing them in direct sunlight; it will shrivel and weaken the seed. Organic gardeners may wish to dust newly cut pieces with powdered sulfur by placing the potatoes and the sulfur in a paper bag and shaking. This will reduce the threat of infection and scab.
Chit Your Seed
The practice of pre-sprouting seed potatoes before planting encourages early growth. It is widely used abroad, but less known to Americans. Chitting is simple. Spread the seed tubers in boxes or flats one layer deep with the seed end up. Look closely at a seed potato and you will notice one end was attached to the plant. The other end has more eyes from which sprouts emerge. The end with the eye cluster is called the seed end. Place your flats in a warm area (70°) where light is bright but indirect. The warm air stimulates the development of strong sprouts from the bud eye clusters, which, in the presence of light, remain stubby and are not so easily broken off.
Usually chitting is done a week or two before planting. Do not cut large seeds before pre-sprouting or they will dry out. Chit, then cut just before planting.
Chitting will get your seed up and to maturity faster. It is also believed pre-sprouting results in a heavier yield. If you store potatoes and they sprout before eating don't throw them away! Use them for planting.
Ideal potato soil is deep, light and loose, well-drained but moisture retentive. Oh well! Fortunately, the potato adapts well and will produce well even in less than perfect conditions.
All soils, be they ideal, too heavy, or too light, should be deeply tilled and amended before planting. Compost is important because it contains humus. Humus lightens and aerates heavy soil, and increases the moisture holding capacity of sandy soil. Compost can also meet the potatoes' overall nutritional needs for moderate amounts of nitrogen, phosphorous, and potassium. Don't overfeed with nitrogen. You'll get big vines but fewer tubers. Potatoes do best in a slightly acid soil with a pH ranging from 5.5 to 6.5. Alkaline soil will tend to make them get scabby. Potatoes respond well to calcium, but fresh lime can induce scab so it is better to add the fall before for spring-planted potatoes.
Seeds can rot in cold, waterlogged soil. For gardeners in southern climes, this means fall and winter crops must go in well drained locations. For routine spring planting you can safely plant your earliest seed tubers 6-8 weeks before the last frost date. Wait to plant main crop tubers until about two weeks before the last frost date. The width between seed tubers in the row, and the distance between rows is determined by the type of garden. In field settings you need about three feet between rows to permit adequate room for cultivation and hilling. In backyard raised bed gardens you can get by with two feet between rows. If water is at a premium, you can dry farm potatoes but you need to allow about five feet between rows so the root system can expand throughout the soil without competing with neighboring plants. Plant the seeds about 18" apart in the row when you are using this method. Otherwise, about 12" between seeds is appropriate. Always plant in trenches dug 6-8" deep. After seeding the trench cover with about 3-4" of soil - do not fill the trench completely.
Hills create a space for potatoes to get large in abundance. When your plants are about 8" tall pull soil from the sides of the row using a draw hoe, mounding it up within 4" of the top of the plant. Do this again in about 2-3 more weeks, and yet again 2-3 weeks later. This keeps the soil down below cooler (which potatoes like), reduces weeds, and hides the forming potatoes from light which can make them turn green and distasteful.
Most potatoes have a very aggressive root system and can cope with surprisingly dry soil. What happens when a potato plant struggles for moisture is that the size and number of tubers decline while the dry matter content of the tubers actually increases. This makes them less watery and more flavorful. If water is not a problem in your area then moist, but not damp, soil is your goal. If the leaves and stems remain vigorous and healthy looking, your plants are receiving adequate water.
After emergence and until blooming, periodic feeding with fish emulsion, either to the roots or as a foliar spray, keeps the vines growing vigorously. Foliar spraying may be done every two weeks. Root feeding every four weeks. When the plants begin to flower they are forming tubers down below. Vegetative growth stops at this stage and no further fertilization is needed.
The Colorado Potato Beetle is the most widespread and destructive potato pest. The adult and larval forms both bed on leaves and stems and can defoliate entire plants. If you start early in the season handpicking can be effective if it is done regularly. As you pick, check the undersides of the leaves for yellow egg clusters. Crush them by brushing with your thumb or finger. Bacillis thriftiness (Bt.) var. san diego is an organic spray that is effective against Colorado Potato Beetle larvae. If you spray every ten days to two weeks as soon as anything edible begins to appear in the garden the larvae never get a chance to develop to adults. You can make a significant and lasting impact on the beetle population in your garden using this method. If adult beetles are out of control try dusting plants with rotenone or pyrethrum.
Seven or eight weeks after planting the early varieties (Yukon Gold, Bison) are blossoming. Early potatoes may be ready. Poke your hand into a hill at the edge of your patch to see what can be found. If potatoes are ready, you may wish to take them one plant at a time. They keep quite well in the ground. You may let the soil dry out as much as a month before harvesting. This intensifies the flavor of your potatoes, allows the skins to toughen, and they come out easier and cleaner.
Harvest in the morning when the air is cool and move them into cool storage as soon as possible. If they are wet, let them air dry on the surface before gathering. If it is raining spread the wet potatoes out under cover and let them dry. Separate out damaged tubers as they will rot early and encourage potatoes in storage next to them to rot as well. Potatoes with firm skins store longer. Consider this when deciding which tubers to eat first.
Potatoes keep best in the dark at 36° - 40° F with enough humidity so they don't dry out, and given enough air circulation so they can respire (they're alive). Light and warmth promote sprouting and will turn the potatoes green. Cold potatoes bruise easily, so handle with care in storage. Burlap sacks, slotted crates or baskets, produce lugs or wooden bins are good storage units over the winter. If you heap the potatoes in piles several small ones are better than one large pile because those on the bottom can be bruised by the weight of the pile. Large piles also inhibit ventilation to the center of the pile which shortens storage life. Partially heated garages, sheds, closets, porches, or unheated back rooms can all be cool, dark sites suitable for potatoes. If the temperature is below 36° F their starch turns to sugar and ruins their flavor. If this happens you can reverse the process by keeping them at room temperature for a few days. Below 32 degrees they are ruined. Don't store potatoes near apples. Apples give off ethylene gas which will make the potatoes turn green and sprout.