Growing Irish Potatoes - March 10, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County
Irish potatoes are easy to grow in the home garden. Many varieties are available: heirloom, russet, yellow, white, red, blue. Within each of these classes, you may find early, late, storage, chippers, etc. The greatest thing about them: given the proper soil preparation, planting date, irrigation, and cultural practices, they all should grow and produce well in your backyard garden.
To start your potato patch, select an area where other crops in the nightshade family (tomatoes, peppers, eggplants) were not grown in the previous year. Next, decide how many pounds of potatoes you would like to harvest. Five pounds of seed potatoes will yield between 45 and 70 lbs. of potatoes and will require a garden area of about 10 x 12 feet. Always order certified seed potatoes to avoid disease problems. Order at least two varieties and keep records of where each is planted. Think about planting both an early maturing and a medium or late maturing variety.
Potatoes are best grown in well-drained soil in full sun. Prepare your soil by double digging and incorporate at least four inches of compost to the bed. This requires digging a trench the depth of your shovel or spading fork that is at least 18 inches wide. As you dig, lay the soil adjacent to the trench. Put half of the compost in the bottom of the trench and spade it in. Then, mix the remaining compost in with the soil to the side of the trench while filling the trench in. The center line of the trench will become the row. The row centers should be about 30 to 36 inches apart.
After your potatoes arrive, store them in a cool dark place (50-60 degrees F). In a week or so, they may begin to sprout. Cut each seed potato into five or six pieces making sure there is an eye (or sprout) in the center of each piece. Soil temperatures should be about 50 degrees F at the time of planting (March and April).
To plant, dig a ten-inch trench in your row, place some phosphorus fertilizer at the bottom of the trench (about 1/8 cup of triple super phosphate or several handfuls of bone meal per ten foot row). Then add two more inches of soil on top of the phosphorus. This method of fertilizer application is called banding and it puts the phosphorus where it is most efficient: near the roots. Finally, plant the pieces, eye or sprout up, at the bottom of the trench and cover with another inch of soil. The spacing should be about 10 inches.
When the potato plants reach about six to eight inches, backfill the trench with about four inches of soil. The backfilling is called "laying-by." Repeat this process until you begin mounding up the soil in the middle of the row. This increases the amount of stem in contact with the soil which will increase yields. It also prevents green potatoes (these should not be eaten).
A side dressing of manure or nitrogen fertilizer early to mid-season may also increase yields unless you used manure that is slowly releasing nitrogen during the growing season. Irrigate your potatoes often to maintain constant soil moisture. Erratic irrigation stresses the plants and can result in dry pockets (hollow heart) inside the potatoes. Weeds should be controlled by manually pulling. Hoeing could damage your potato crop.
Watch for insects. Potatoes can get aphids, flea beetles, blister beetles, leafhoppers, and other pests. Areas of the garden known to have grubs should be avoided. Diseases can also affect potatoes. If treatment is needed, make sure that the measures are either non-toxic/organic or the pesticide used is labeled for use on potatoes.
Early potatoes can be harvested when they reach an edible size. Just poke around the soil and see how big they are to see. Some growers artificially kill the vines by breaking or cutting them off at the soil surface. Others let fall frosts kill the vines. Dig them gently to avoid damage and store in a dark location at 38 to 40 degrees F.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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