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Potato Growing and Harvest Information

by chuck.mcmullan
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Where to Grow Potatoes

Potatoes grow best in regions where there is a temperate climate with cool growing weather, ample rainfall, and deep fertile soil. Potatoes are a warm-season crop in the North, tender to frost and light freezes, and a cool-season crop in the South and West.

Recommended Varieties of Potatoes

“Seed” potatoes that have been certified disease-free are essential. Potatoes sold for eating are usually treated to prevent sprouting, and will not grow well if planted.

Early – Irish Cobbler; Chippewa; Norland (scab resistant); Pontaic (red-skinned)
Main – Green Mountain; Katahdin; Kennebec (blight resistant)
Baking – Russet, Burbank

Soil for Growing Potatoes

A deeply fertile sandy loam with a high acid content, pH 5-5.5 is best since overly limed soils activate the scab fungus. The soil should be well-drained and, at the same time, able to retain moisture. Other soils can be improved by incorporating organic matter which tends to lighten heavy soil and enrich sandy soil. Use high phosphorous fertilizers, such as 5-10-5, or 4-8-4, or ground-rock phosphate to prepare the soil.

If your soil is compacted, you’ll want to loosen it up with a shovel, broad fork, or rototiller. If turning in compost, ensure the compost is mixed into a depth of about 6 to 8 inches. If digging with a shovel, don’t completely turn the soil over, simply dig one spot with the shovel buried 8-12 inches and toss it back in. The idea is not to destroy too many of the beneficial soil microbes. If your soil is highly compacted, it will benefit from a good turning to a depth of approximately 12 inches, incorporating compost. The long term goal for potato soil is to have a loose living soil full of beneficial microbes.

Planting Potatoes

When –

As soon as the frost is out of the ground and the soil can be worked thoroughly. The rule of thumb to follow for the earliest planting time is to plant 2 weeks before your last spring frost. You can plant any time after that, as long as there are 3 months of frost-free growing season left.

Temperature
Germination65 - 70 F
For growth50 - 65 F
Soil and Water
FertilizerLight feeder, apply compost when planting.
Side-dressingApply 2-3 weeks after first hilling
pH5.0 - 6.0
WaterHeavy when potatoes are forming
Measurements
Seed Planting Depth3 - 4"
Root Depth18 - 24"
Height24 - 30"
Width24"
Space between plants
In Beds9 - 12"
In Rows10 - 12"
Space Between Rows20 - 26"
Average plants per person10 - 30
Harvest
For small "new" potatoes, harvest during blossoming; for varieties that don't blossom, harvest about 10 weeks after planting. Harvest regular potatoes when the vines have died back halfway, about 17 weeks after planting. Gently pull or dig out tubers with a garden fork. If not large enough, pack the soil back and try again at 2-3 week intervals. If you have many plants, remove the entire plant when harvesting to make room for another crop. For storage potatoes, dig near the first frost when plant tops have died back. To minimize tuber injury, always dig when the soil is dry.
First Seed Starting Date: 14 - 28 days before last frost date
Last Seed Starting Date: 90 - 120 Days before first frost date
Companions
CompanionsAll brassicas, corn, marigold, pigweed
IncompatiblesCucumber, pea, pumpkin, raspberry, spinach, squash, sunflower, tomato
Starter Potatoes

How –

Start potatoes with seed potatoes, each containing one to three “eyes” or small indentations that sprout foliage. To prepare seed potatoes for planting: Spread the tubers out in boxes or crates one layer deep. Bring the boxes into a warm living space and to a location with medium intensity light. The warmth tends to stimulate the development of strong sprouts from the buds, which in the presence of light remain short and stubby and are not easily broken off. This process is called greening/pre sprouting and is usually done for a week or two just prior to planting outside to encourage growth and hasten the development of good tubers.

Tubers the size of a medium egg may be planted whole, cut larger tubers with a clean sharp knife so that each piece will contain 1 or more eyes. Pieces should be cut with plenty of flesh around the eyes, as the plant will utilize this stored food during the first few weeks of growth. Seed potatoes may be planted immediately after cutting if soil moisture is properly controlled; if there is a chance the soil will be too wet, allow the cut pieces to dry out a couple of days prior to planting, shriveling is to be avoided at all costs.

Place in shallow trenches 6″ wide, spaced 10-12″ apart, and cover with 3-4″ of soil. Space rows out approximately 20-26″ apart. The spacing can be adjusted to suit your conditions, wider spacing can help alleviate stress due to drought or poor soil. Tighter spacing tends to provide a uniform canopy of foliage to cool the soil in summer. One to two weeks after the shoots emerge, mound the soil around the base, leaving a few inches exposed. This “hilling” prevents greening. Side dress and “hill” again 2-3 weeks later. Hilling is crucial to establishing your crop because all tubers will form at the same depth as the seed piece or higher. By gradually building an ever-larger hill of soil around the plant, you are building the site for your potatoes to develop. Give them plenty of room between rows and build your hills wide and ample to maximize your potato harvest.

How Potatoes Grow

The plants, which are about 3′ high, send up long, pinnate leaves similar to tomato foliage. The tubers will develop in late summer, at the ends of underground stems. They are fairly close to the top 4-5 inches of soil.

Cultivating Potatoes

Keep weeds out of the potato patch with a very light cultivation, or use straw or leaf compost mulch. Gradually hoe soil toward the base of the potato plants, to prevent the roots from becoming sunburned. A second application of fertilizer is usually made 1 month after planting by side dressing in the row. Potatoes are almost 3/4 water, soil moisture is very important. Potatoes need about 1-2″ of water every week. Keep the soil evenly moist, and try not to let the soil completely dry out as this will cause sudden re-growth when watered, giving the tubers ears and noses, splits, or hollow heart. Let the water soak down to about 10-12″ each time. Cover plants if a hard frost is expected.

Storage Requirements
Spring or summer harvested potatoes aren't usually stored, but keep for 4-5 months if cured first at 60-70F for at least 4 days and stored at 40F. Dry fall-harvested potatoes for 1-2 days on the ground, then cure at 50-60F and a relatively high humidity for 10-14 days. Don't cure potatoes in the sun; they turn green. Once cured, store in total darkness in a single layer. Never layer or pile potatoes more than 6-8" deep.
Fresh
TemperatureHumidityStorage Life
55 - 60F90 - 95%5 - 10 months
Preserved
MethodTasteShelf Life
CannedFair12+ months
FrozenGood8 months
DriedGood12+ months

Harvesting Potatoes

2 1/2 – 4 months. The first young potatoes can be lifted out carefully, a few at a time, by merely pulling the soil away and replacing it for the remainder to develop. When the plants begin to dry and die down, the tubers will be ready. They can be left in the ground for a time but should be dug before a heavy frost. Dig on a bright, sunny day so the soil dries off the potatoes easily.

Laboratory experiments have shown that several aromatic herbs and their essential oils can suppress the sprouting of potatoes in storage and have antimicrobial activity against potato pathogens. English lavender, pennyroyal, spearmint, rosemary, and sage suppressed growth of potato sprouts, but oregano did not. English lavender was the most effective sprout inhibitor

Storage

For long term storage, keep potatoes in a cool (40 degrees F), dark place. Under the proper conditions, potatoes can last as long as 6 months. Light as well as warmth will promote sprouting and turn the potatoes green. Burlap sacks, netted sacks, slotted crates, or baskets are recommended for storing potatoes over winter. If your potatoes are stored at temperatures ranging from 33-40 degrees F, they will likely convert their starch into sugars, and will consequently taste slightly sweeter than normal. These potatoes will turn brown sooner when fried. You can take them out of storage and keep them in the warmth, but out of the light for a day or two and they will get some of their starch back. Storing potatoes at 50 degrees F will keep their starches intact. This is the ideal temperature if you want to fry the potatoes, make potato chips, or prefer the starchy taste. Ideally, humidity should be relatively high (80-90%). Low humidity is the main cause of shriveling during storage. Refrigerator storage works well, especially if you have a crisper that maintains humidity levels. For the most part, a refrigerator works hard at keeping the humidity levels down.

Potato Pests

  • Colorado potato beetle – A small yellow beetle with black lines down its back that produces one or two generations of havoc with potato crops. Control by handpicking.
  • Leafhopper – Causes foliage to go down early in the season, reducing yields.  Potato leafhoppers are fairly small, and difficult to see. It is important to catch them early. Scouting leaf undersides and axials is the best way to note their arrival and have time to treat before they build up. Organic pesticides are not particularly effective, but growers have had some success with combinations of neem extract and pyrethrins. Good foliage coverage is critical.

Potato Diseases

  • Blights and scabs – Grow resistant varieties and maintain proper pH (5-5.5).

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