Growing potatoes in the Willamette Valley

Growing potatoes in “towers” or structures designed to accommodate layers of growth is a popular Internet and garden site recommendation. The allure of getting pounds of potatoes in a small space leads people to try this technique.

The process as described is simple: build a structure (wood, wire, a pot, etc.) plant potatoes in the bottom, keep watered and fertilized, add soil as the plant grows and voila! Potato bounty!

The reality is often disappointing for some growers because towers are difficult to keep evenly watered. But if you use care and don't build your towers too high, potato towers are one way to save room in your garden.

How potatoes grow

Potatoes originated in South America, and breeding has resulted in hundreds of varieties that grow all over the world. There are early, mid- and late-season varieties that grow in almost every climate.

Seed pieces will produce a main shoot one to two weeks after planting. Rhizomes (a horizontal stem) begin to grow on the underground shoot at about the same time, so it is important to plant deep enough (at least 6 inches) to allow for the rhizome development. Rhizomes grow horizontally and thicken at the tip to form a tuber.

Tubers form between five to seven weeks after planting and occur at about the same time as flower formation. But some varieties never flower. The developing tuber competes with leaves and shoots for nutrients so it is important to supply adequate moisture and fertilizer during the tuber development and growth period.

Some potatoes make five to six close-set rhizomes off the main stem, which terminate in tubers that can be large because there are so few of them.

Other varieties grow over a longer season and can set potatoes further up the stem by producing new rhizomes, typically up to a foot above where the first rhizomes that form. These tend to produce relatively large potatoes and quite a few smaller ones.

Finding the right temperature

Potatoes are a cool-season vegetable but are sensitive to hard frosts. Cool, moist conditions favor the period when tubers are forming. The optimal range for shoot emergence is daytime temperatures of 68 degrees F to 72 degrees F. The optimal range for tuber formation is when the temperatures are in the 50- to 60-degree range. When night temperatures are above 68 degrees F, tuber set is reduced and above 84 degrees F, it is inhibited.

For growers in the Willamette Valley, daytime temperatures between 55 degrees F and 60 degrees F are the best time to plant. In the Eugene/Springfield area, this translates to late March-early April when average daytime temperatures are from 55–60 degrees F and night lows are from 36–39 degrees F. Rainfall at this time of year averages between 2–2.5 inches per month. This ensures an adequate moisture supply, but it's wise to plant in raised rows or raised beds to avoid rotting. You can cover the ground with plastic for a couple of weeks before planting to warm the soil and encourage it to drain well. Also, consider covering the emerging plants with a row cover (either Remay or plastic) at night to protect against insect attacks and frost.

For best results, choose a variety suited to grow locally. For growing in towers, choose a mid- to late-season variety (90–130 days or more.) Late-season varieties continue to send out rhizomes and form their tubers later so you get the “layered” effect in a tower. But this also means you need to pay very close attention to the watering and fertilizing needs of the plant during the higher temperatures of July and August. The wet/dry cycle of watering produces bumpy tuber formation. Potatoes like even, consistent moisture.

Getting a good start

Look for certified seed potatoes at local garden centers. One pound of large potato seed stock may yield up to 10 pounds, and one pound of fingerling potato seed stock may yield up to 20 pounds.

Cut the seed potato into egg-sized pieces with at least three or more eyes per piece. Allow the cut side to seal over (it will have a smooth, dry surface) then plant in well amended, well-drained soil. If planting in a tower or pot, place 6 inches of soil in the bottom then cover the seed pieces with 6 inches or more of soil. Space the seed pieces 12 inches apart. As the plant grows, pile more well-amended soil around the stem leaving the top 6 inches of the plant exposed.

If planting in a wire bin, pile straw, leaves or sheets of newspaper around the edges to keep the soil from falling through the sides. Try to keep the tower no higher than 2–3 feet as taller towers are difficult to keep evenly watered. Plants dry out more rapidly in the tower or pot method, so monitor the watering closely.

Potatoes will do better in slightly acidic soils around 6 pH. You may fertilize every two to three weeks with a balanced granular or liquid emulsion fertilizer. (NPK numbers roughly the same like 4-6-6.)

Harvest potatoes after the tops have died down. Dust the soil from the skins with hands and store in a cool, dry place.

Potatoes are broadly grouped according to the average number of days needed to reach maturity (when tubers reach an edible size.) Different growers will use different classifications. Here are a few:

  • Very early earlies (early, early summer) — 75 days
  • Early (early summer) — 90 days
  • Mid or maincrop ( mid-summer) — 110 days
  • Maincrop to late maincrop (summer into autumn) — 135-160 days

Varieties

Variety Days to Maturity Season Notes
All Red 100-120 Mid-late  
Bintje 100-120 Late Heirloom
Butte 100-120 Late  
Canela Russet 90-120 Late  
Carola 90-120 Late  
Catalina (true seed) 100-120 Mid-late  
Chieftain 100-120 Mid-late  
Desiree 95-100 Late  
Fingerling Salad 100-120 Late  
French Fingerling 90-120 Mid-late  
German Butterball 100-120 Late  
Gold Rush 90-120 Mid-late  
Green Mountain 100-120 Late Heirloom
Ida Rose 95-100 Mid-late  
Kennebec 100-120 Mid-late  
Kerrs Pink 100-120 Mid-late Heirloom
King Harry 100-135 Late Heirloom
Purple Peruvian 110-135 Late  
Purple Viking 100-120 Mid-late  
Red Sangre 100-135 Mid-late  
Rose Finn Apple 110-135 Mid-late  
Russet Burbank 95-110 Mid-late  
Russet Norkotah 95-110 Late  
Russian Banana 100-120 Late Fingerling
Yellow Finn 95-100 Late  
Yukon Gem 95-100 Mid-late  

Sources

Online sources of certified seed potatoes

Certified seed can also be purchased at local garden centers. Call for dates of arrival. Seed potatoes usually arrive too early for planting so need to be held until the time is right.

Previously titled
Growing potatoes in towers

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