UPSIDE DOWN POTATOES

“That’s no way to grow tatters — they’re upside down!”

What Is It?  Conventional potatoes (Solanum tuberosum) are grown under the soil surface, usually 8 to 12 inches below grade.  Upside down potatoes are planted on or above ground.

History:  Surface planting dates back to 16th century Europe when small farmers had to grow food without the aid of draft animals or manure fertilizer.  Digging by hand was hard work; growing potatoes on top of the ground was much easier.

Tillage:  Conventional farm equipment is not needed to grow upside down potatoes.  The soil is not plowed, harrowed, or cultivated.  If desired, weeds or cover crops may be mowed to facilitate planting.  For household or market gardens, only the most simple hand tools are required:  A lawn rake for collecting leaves and a hay fork or stable fork for spreading mulch.

Crop Rotation:  To avoid spreading disease, do not plant potatoes following any crop in the botanical family Solanaceae:  Tomatoes, potatoes, peppers, eggplant, tobacco, petunias, or ground cherries = husk tomatoes = tomatillos (Physalis pubescens).  Avoid ground where lawns, meadow, or cereal crops have grown recently as these soils contain wireworms that will tunnel into developing potato tubers.  Do not plant potatoes on soil treated with lime or wood ash; potato scab flourishes in alkaline soils.  For best results plant potatoes following clover or other nitrogen-fixing cover crop.

Plant Spacing:  3 feet between rows (69 rows per acre) x 1 foot between plants (208 plants per row) = 14,352 plants per acre.  For equidistant spacing, 20 to 21 inches between plants is recommended for optimal yield.  If smaller potatoes are desired, increase plant density to 15 inches equidistant spacing or 2 feet between rows (104 rows per acre) x 9 inches between plants (277 plants per row) = 28,808 plants per acre.  High density plantings (8 inch equidistant spacing = 98,000 plants per acre) produce very small “baby” potatoes ideal for soup, stew, or steaming.

Seeding Rate:  23 pounds of potato sets (cut tubers) per 208 foot row = 1,600 pounds per acre.  Up to 46 pounds of whole (uncut) seed potatoes per 208 foot row = 3,174 pounds = 1.6 tons per acre.  Ideal sets or seed potatoes are egg-sized, have 2 or 3 eyes = buds, and weigh approximately 1.75 to 3.5 ounces.  Remember to cure potato sets in a warm, dry, airy place for at least 7 days so cut surfaces can heal.  Uncured sets will rot.

Greening Seed Potatoes:  Place cut potato sets or whole seed potatoes in bright, diffuse light at 60 to 70 degrees Fahrenheit for 6 weeks prior to planting.  Potato skins will turn green and buds will start to grow.  “Greened” potatoes grow faster and are more resistant to rot and insect pests.

Organic Fertilizer:  On soils of average fertility, potatoes grown following a clover cover crop will not require supplemental plant food.  For weak soils, apply 1 to 2 pounds of compost or composted manure per plant = 7 to 14 tons per acre.  (Deposit a forkful of compost in a small mound then place a seed potato on top of the compost).  Alternatively, broadcast 1 ounce per square foot = 2,700 pounds per acre of a general purpose organic fertilizer (2 parts weed seed meal or cottonseed meal + 1 part phosphate rock or bone meal + 2 parts greensand, granite dust, or potash rock = 5 parts by weight).

Chemical Fertilizer:  Provide synthetic fertilizers according to soil test recommendations; chemical nutrients are best dosed in small amounts throughout the growing season, ideally dissolved in irrigation water.  The average potato crop requires 9 pounds of nitrogen, 12 pounds of phosphorous, 8 pounds of potassium, and 0.50 pound of zinc per ton of expected yield.

A 40,000 pound crop = 20 tons of potatoes needs 9 x 20 = 180 pounds of nitrogen, 12 x 20 = 240 pounds of phosphorous, 8 x 20 = 160 pounds of potassium, and 0.50 x 20 = 10 pounds of zinc per acre.

For household or market gardens, apply 3 pounds of 10-10-10 (10% nitrogen + 10% phosphorous + 10% potassium by weight) or other general purpose fertilizer per 100 square feet = 1,300 pounds per acre.  For best results broadcast fertilizer in 3 split applications:  1 pound at planting, 1 pound when vines are 2 feet long, and 1 pound when potatoes flower.

Irrigation:  Potatoes need 1 to 2 inches of water weekly for best growth and highest yield.  Ample moisture is especially important when plants are flowering as this is when tubers form.  Drip irrigation is recommended to keep leaves dry.  Dry vegetation is necessary to prevent foliar diseases.

Mulching:  If soil is light and well drained, potatoes can be placed directly on the soil surface then covered with 8 to 12 inches of leaves, straw, spoiled hay, or similar mulch.  If soil is heavy or poorly drained, apply 8 inches of leaves then place sets or seed potatoes on top of the leaves = plant above the soil surface.  Cover planted potatoes with 8 to 12 inches of leaves, straw, or similar organic material.  (Apply mulch generously as it will settle to approximately half of its original volume).  On ground of average fertility, potatoes will obtain all of the nutrients that they need from the topsoil and rotting mulch.  If soil is poor, fertilizer can be broadcast directly on the mulch or soil surface.

Planting Date:  Potatoes require a long, cool growing season.  Maximum tuber formation occurs between 60 and 70 degrees Fahrenheit.  Tubers will not form if soil temperatures exceed 80 degrees Fahrenheit (which is why deep mulches are so important to keep earth cool).  In temperate climates potatoes are usually planted 5 to 6 weeks before the average last frost in spring.  In subtropical climates plant potatoes immediately weather turns reliably cool.  In cool climates, time planting so potatoes mature 3 to 4 weeks before average first frost in fall.  In warm climates, plant potatoes in the “cool” season so that tubers can be lifted before weather turns hot.

Fall Planting:  In areas with mild winters, potatoes can be fall planted, usually after the first hard frost = killing frost.  Fall planted potatoes remain dormant over winter then resume growth early in spring.  Fall planting has numerous advantages:  Early emergence allows potatoes to outgrow most weeds, and plants make most of their growth when water is abundant and temperatures are cool.  Fall potatoes normally out-yield crops planted in spring or early summer.

Disease Control:  Potato diseases are best avoided by long rotations (7 years is ideal).  Slightly acidic soils prevent scab from growing on potato tubers.  If necessary, adjust soil pH with agricultural sulfur:  Broadcast 1 to 2 pounds of sulfur per 100 square feet = 500 pounds per acre (for sandy soils), 1,000 pounds per acre (for loams), or 2,000 pounds per acre (for clay soils).  If earth is especially cold, wet, or heavy, dust potato sets or whole seed potatoes with powdered sulfur before planting.  To help prevent foliar diseases keep potato plants dry by watering with drip irrigation hose laid directly on the soil surface.  Control potato blight by spraying foliage with microfine wettable sulfur.

Insect Control:  Upside down potatoes rarely have insect problems unless the plants are over-fertilized or grown in vast monoculture fields.  Pests are best avoided by growing potatoes in narrow strips (not more than 4 rows wide) with unrelated crops planted on each side.  Potatoes grown in weedy fields do not often require insecticides because weeds provide food and habitat for beneficial predators.  Thin clumps of weeds to single plants spaced approximately 3 feet apart = 5,000 weeds per acre.  Widely spaced weeds do not appear to slow potato growth or decrease yield.

Potato Bugs:  Colorado Potato Beetles (Leptinotarsa decemlineata) are the most troublesome pests of potatoes because they reproduce quickly and rapidly develop resistance to chemical insecticides.  Beetles are best controlled with floating row covers of spun-bonded polyester, or use an approved organic insecticide.  Synthetic pesticides provide uncertain control unless different classes of chemicals are rotated with each spray application.  Following are specific control recommendations:

>>>  Potato beetle populations are rarely suppressed by a single control method.  For effective results, multiple control measures are required.

>>>  Potatoes have considerable tolerance to most insect pests.  1/3 of a potato plant’s foliage can be consumed by insects before yield declines.  Potato plants are most vulnerable when flowering as this is when tubers form.  For highest yields, concentrate control efforts to protect flowering crops.

>>>  For efficient control of potato bugs, monitor pest populations regularly.  1 potato beetle per plant is the approximate economic threshold for cost-effective pest management.  2 beetles per potato plant is a significant infestation that requires immediate pesticide application or other control measure.

>>>  Crop rotation is a primary defense against potato bugs.  Plant tomato family crops together as a group and rotate field as far away as possible from previous season’s location.  Eliminate nightshade (Solanum ptychanthum) and ground cherry = husk tomato = tomatillo (Physalis species) as potato beetles eat these weeds.

>>>  Potato bugs prefer plants grown with chemical fertilizers.  To reduce crop damage, use organic plant foods.  Manure is the most effective fertilizer for controlling potato bugs.

>>>  Lady Beetles (Coleomegilla maculata) are major predators of immature potato bugs and their eggs.  To attract lady beetles plant flowers around and between potatoes and other tomato family crops.  Lady beetles eat pollen and nectar when potato bugs or other prey are scarce or absent.  (If flower seed is not available, plant weeds to provide food for beneficial insects).

>>>  Azatin is an “insect growth regulator” = a synthetic juvenile hormone that prevents young potato bugs from maturing into adults and laying eggs.  Spray crops weekly to break the potato bug’s reproduction cycle.

>>>  Beauveria bassiana is a pathogenic fungus that kills potato beetles.  Spray fields after each rain or every 7 to 10 days, preferably in the morning or evening when temperatures are cool and leaves are damp.

>>>  “BT” = Bacillus thuringiensis variety tenebrionis is a natural bacterial disease that kills Colorado potato beetles.  Apply every 7 to 10 days as necessary.

>>>  Neem Seed Oil (Azadirachta indica) is a natural insect repellent that makes potato leaves taste bad.  Spray fields weekly to prevent potato bugs from feeding.

>>>  Pyrethrin is a short-lived contact insecticide that can be applied up to day of harvest.  Originally extracted from the Pyrethrum Daisy, pyrethrin is available in both natural = organic and synthetic forms.  Apply pyrethrin only as needed to control severe potato bug infestations.

Weed Control:  Upside down potatoes do not require herbicides or mechanical cultivation.  Weeds are controlled by thick layers of mulch that prevent unwanted plants from obtaining light.  If a weed pokes up above the surface, pull it by hand or smother it with a forkful of mulch.  Alternatively, just let the weeds grow; weedy fields rarely require insecticides.  Thin clumps of weeds to single plants spaced about 3 feet apart = 5,000 weeds per acre.  Widely spaced weeds will not harm tuber quality or yield.  Note:  Remove tall weeds from under floating row covers to prevent potato beetles from laying eggs on crop foliage.

Harvest:  Potatoes are best left undisturbed until they are fully mature, about 120 to 140 days after planting.  Gather main crop = storage potatoes 2 to 3 weeks after the vines yellow and die back naturally in the fall.  New potatoes may be harvested when the plants start to bloom.  Harvesting upside down potatoes is simple:  Just pull aside the mulch and pick the tubers off the ground.  No digging is required!

Potatoes are best harvested when the soil and weather are dry.  Newly lifted potatoes have tender skins that are easily damaged.  For highest quality, handle tubers gently and set them on the soil surface to cure for several hours.  Exposure to air and sunlight will dry and toughen skins.  Well cured potatoes are more resistant to bacterial and fungal infection during storage.

Yield:  Potatoes grown underground normally yield more than tubers planted on the soil surface.  However, surface grown tubers are of much higher quality:  Clean, well-formed, and damage free.  Significant losses occur when underground potatoes are harvested; one quarter of the crop may be bruised, chipped, cut, split, or punctured.  Upside down potatoes rarely have harvest damage.

On unfertilized, non-irrigated fields, potatoes grown on the soil surface yield approximately 1 pound per plant = 14,000 pounds or 7 tons per acre.  Expect about 200 pounds = 3.5 bushels of potatoes from a 208 foot row.  Note:  1 bushel of potatoes = 60 pounds.

Irrigated, fertilized potatoes grown on the soil surface yield 2 to 3 pounds per plant = 28,000 to 42,000 pounds or 14 to 21 tons per acre.  Expect approximately 400 to 600 pounds or 7 to 10 bushels per 208 foot row.

Non-irrigated, unfertilized potatoes grown above the soil surface = on 8 to 12 inches of leaves typically show a yield increase of 3 to 5 ounces per plant over potatoes grown on the soil surface.  Expect approximately 8 to 9 tons per acre or 4 to 5 1/2 bushels per 208 foot row.

Irrigated, fertilized potatoes grown above the soil surface = on 8 to 12 inches of leaves usually show a yield increase of 11 to 15 ounces per plant over potatoes grown on the soil surface.  Expect about 19 to 27 tons per acre or 9 to 13 bushels per 208 foot row.

>>>  The average potato plant sets 20 or more tubers but develops only 5 to 10 potatoes.  (The rest of the tubers are absorbed by the plant).  These values remain relatively constant regardless of whether potatoes are grown under the ground, on the soil surface, or above the soil surface.  Growing conditions must be ideal for a plant to yield more than 10 tubers.

>>>  Fall planted potatoes grown on the soil surface typically yield 9 to 14 ounces of tubers per plant (without irrigation, fertilizer, herbicides or insecticides).  Set small = 2 ounce seed tubers on the ground then cover with with 8 inches of leaves.  Let weeds grow wherever they rise above the mulch.  Expect about 2 to 3 bushels per 208 foot row — 4 to 6 tons per acre.

Storage:  On well-drained sandy soils potatoes can be stored in the field or garden.  Cover rows with a 1 foot thick layer of straw to keep soil from freezing.  Alternatively, use hay bales or bags of leaves to insulate potatoes.  Harvest potatoes only as needed; tip over bales or move bags aside, lift potatoes, then replace insulation to keep soil warm.

Potatoes keep better if they are cured before storage.  Curing toughens and thickens skins so tubers can better resist rot and bruising.  Handle tubers gently and place in a dark, well ventilated barn or garage for 2 weeks.  Ideal curing temperature is cool but not cold = 60 to 65 degrees Fahrenheit.  After curing, move potatoes to a deep root cellar for long-term storage.

Root Cellars:  Large amounts of potatoes are best kept in a frost-free root cellar that is dark, cold, and well ventilated.  Ideal storage conditions are 38 to 40 degrees Fahrenheit and 85% relative humidity with good air circulation.

A traditional root cellar built 15 feet underground maintains 50 to 55 degree Fahrenheit temperatures year round.  This is sufficient to hold tubers 3 to 9 months, depending on variety.

A small root cellar is easily made by burying a garbage can up to its lid.  Gently fill can with potatoes, close lid, then cover with hay bales or bags of leaves to prevent freezing.  (Potatoes can be cushioned with dry sawdust or wood shavings, straw, peat moss, rice hulls or similar materials.  Apply packing materials loosely around each tuber as can is filled).

How To Build A Potato Clamp:  If a root cellar is not practical, store potatoes in a clamp above ground:  Start with a 6 to 8 inch layer of brush for aeration and drainage.  Gently pile potatoes on top of the brush then cover tubers with a 1 foot thick layer of straw, leaves, or similar organic material.  Cover mulch with turf, burlap, or landscape fabric to keep wind from blowing away insulation.  Alternatively, shred mulch before application; shredded materials will not blow away. For convenience, potato clamps can also be constructed from bales of straw or hay.

Cost Per Acre:  It costs approximately $5,700 to grow an acre of upside down potatoes in Butler County, Pennsylvania (40.8606 degrees North Latitude, 79.8947 degrees West Longitude).  Figure on spending about $1,100 per acre for labor; $2,000 per acre for variable expenses; and $2,600 for machinery, deer fencing, and irrigation systems.

Would You Like To Know More?  Please contact the Author directly if you have any questions or need additional information about growing upside down potatoes.

Eric Koperek = worldagriculturesolutions@gmail.com

About The Author:  Mr. Koperek is a plant breeder who farms in Pennsylvania during the summer and Florida during the winter.  (Growing 2 generations per year greatly speeds development of new crop varieties).

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