Pots of potatoes - Common Ground

ON THE GARDEN PATH by Carolyn Herriot

The potato (Solanum tuberosum) is one of the most diverse food crops in the world and was first domesticated by humans 10,000 years ago. Potatoes originated in the Andes, but only arrived in North America with the Irish settlers.

The potato is best known for its carbohydrate content; a medium potato has approximately 26 grams. Potatoes provide vitamin C, vitamin B6, potassium, magnesium, phosphorus, iron and zinc. The nutrients of the potato are evenly distributed between the flesh and the skin so it’s best to eat them unpeeled.

potato flowers

Potatoes are easy to grow and highly productive; a 30-foot row can yield up to 60 pounds. One pound of seed potatoes can provide up to 10 pounds or more. It is highly recommended to start with commercial, certified, disease-free seed potatoes, but, having said that, I grew some great russets using certified organic potatoes from the produce section and they volunteered again last year!

Planting tips

Dig a shallow trench running north/south to provide plants with the maximum exposure to sun. Line the trench with uncontaminated wood ash and granular seaweed, which provides potash for good yields.
Plant seed potatoes 3” deep and 12” apart in the trench.
Cover with a layer of compost or topsoil.
Although potatoes like well-fed, manured soil, don’t over-manure, as this leads to scab.
Do not lime soil where potatoes will be grown; they prefer acidic pH 6.0-6.5.
Keep potato tubers dark to prevent exposure to sunlight, which turns them green, bitter and mildly toxic. Do not bury the tubers too deep, as potatoes naturally grow close to the surface.
Keep developing tubers covered by earthing-up against stems when plants are 6” tall, avoiding the leaves. Repeat every 6” of growth. Applying protective mulches also locks in moisture, which benefits growth.
To get the longest harvest, plant one early variety (Epicure, Caribe), one mid-season variety (Yukon Gold, Red Pontiac) and one late variety (Russet, Yellow Banana).

Ideally, small tubers, the size of a hen’s egg, are planted uncut. Larger tubers should be cut in pieces with at least two, but no more than three, eyes. Leave cut pieces overnight to form a callous, which will help prevent them from rotting in cool soils. the minimum soil temperature at time of planting should be 6°C (45° F), but potato tubers should be planted no later than the end of May.

You can enjoy an early harvest of new potatoes two months after planting by ‘grabbling’ with your hands under plants, without disturbing them. For the main harvest, cut the stem cleanly with a knife, just above ground and leave the tubers in the ground for two weeks before lifting so the skin has a chance to harden. Store potatoes (protected from rats) in burlap bags or paper sacks in a cool, dark, frost-free place. Stored tubers need ventilation or they may sweat and rot; check periodically for spoilage.

Problems with potatoes

Earwigs turn potato leaves into lace, but they don’t affect the growth below ground.

Late blight (Phytophthora infestans) can affect potatoes, particularly in cool summers. Tops blacken and the potatoes perish. To prevent blight, follow crop rotations, avoiding sites where Solanaceae, tomatoes, peppers and eggplants have grown before.

Wireworms are lured by potatoes and they especially cause problems in newly established gardens where sod has been removed. Nematodes are an effective biological control.

Colorado potato beetle can be a pest. Companion planting with marigolds and garlic are said to repel this beetle. Try side dressing with neem seed cake as a systemic insecticide.

Scab (Streptomyces scabies) adversely affects cooking quality, though not yield or storage. It shows up as brown, rogh ‘corky’ spots on tubers. Avoid fresh manure.

Carolyn’s new book The Zero Mile Diet – A Year-round Guide to Growing Great Organic Food (Harbour Publishing) will be released April 2010.www.earthfuture.com/gardenpath

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