A Simple Way to Get High Yields of Potatoes

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A good harvest of potatoes

It's no secret that I love growing veggies - potatoes in particular - so it upsets me that so many people are getting sad results when they try growing potatoes in novel ways. I just spent an evening watching videos of people who planted potatoes in various enclosures, grew beautiful plants, and then harvested two handfuls of small, knobby potatoes.

It was not their fault, because this is what usually happens when potatoes are given growing conditions that are much warmer and drier than would occur under normal circumstances, normal being the consistent cool, moist conditions six inches (15cm) underground. I learned this twenty years ago, when growing potatoes in towers made from old tires became a passing fad. The soil-filled black tires heated up so much that the plants lost interest in making potatoes (I harvested five), which never happens in my garden.

Potatoes in bags

The Problem With Growing Potatoes in Containers

Indeed, researchers in tropical climates have found that when soil temperatures rise above 75°F (25°C), potato plants signal their roots to stop making tubers. Instead, the plants may rev up other reproductive strategies, like developing more fertile flowers, or popping out little green potato-like organs on the main stem. Daytime heating of roots is one reason why potatoes grown in above-ground containers may fail in warm summer climates. Potatoes can take warm air temperatures, but when the roots warm up too, productivity plummets.

A second problem with growing potatoes in towers, pots or bags is the dwarfing effect caused by the containers. The plants sense that they are growing close together, which makes them produce numerous small tubers rather than a few large ones. Large containers or broad bins relieve this crowding a little, but consider: When the Master Gardeners of San Francisco, CA (a potato-friendly climate) compared the productivity of ‘Carola’ potatoes grown in beds, bins, bags and pots, these are the numbers from the final weigh-in:

Growing Method Average Yield Per Plant
Mulched raised bed 2.38 lb (about 1 kg)
Wire bin 0.70 lb (0.32 kg)
Plastic pot 0.62 lb (0.28 kg)
Potato bag 0.58 lb (0.26 kg)
Burlap bag 0.25 lb (0.11 kg)

You can follow this link to see the thoughtful work done by Canadian garden blogger Isis Loran, but spoiler alert she has not found a potato growing method to rival the hill-and-mulch method, which involves simply growing potatoes in the ground, and mounding loose soil and mulch around them each time you weed. "I loved that I could just rake up or hill up more soil & straw as the plants got bigger. It was much easier in my opinion than trying to add soil to the pallet container or rolling up the burlap bags," Loran writes.

Potatoes growing in an open-sided container

Loran gardens in a cool maritime climate like that of the British Isles, where potatoes tend to prosper no matter how they are grown. Research by the Royal Horticultural Society has found that variety does make a difference when growing potatoes in containers. When 21 different varieties were grown in 40-litre (16-inch diameter) green plastic potato bags, these varieties were the strongest producers: ‘Casablanca’, ‘Golden Nugget’, ‘Sharpe’s Express’, ‘Maris Bard’ and ‘Lady Christi’.

The story is the same in the US. In Wisconsin, potato lovers involved in the Kenosha Potato Project have found that ‘Calrose’ and ‘Charlotte’ tend to produce larger potatoes than other varieties when growth in soft-sided pots or bags.

How to Mulch Potatoes

Any biodegradable mulch is a good mulch for potatoes, though once-popular straw can be a problem because of price and pesticide contamination. I use both grass clippings and weathered leaves since that is what I have, and I especially like the way leaf mulch keeps the potatoes’ root zones cool, moist and free of weeds. A recent research project from Rutgers University showed that plants produced prettier, more uniform tubers with leaf mulch, and it’s fine to combine materials when mulching potatoes, for example by layering leaves with grass clippings. The important thing is to keep a light-blocking blanket of organic material between the shallowest tubers and the sun.

Potatoes mulched with leaves

The best time to start mulching potatoes is when the plants are ankle high and in need of their second weeding. Use a sharp hoe to nip out weeds, and then mound loose soil around the plants so the crown of the plant becomes snugged in with an additional two inches of soil. Then start layering on the mulch, and keep adding more until the plants begin to fail.

At this point you can feel around beneath the mulch for some tender new potatoes, and start harvesting all of the potatoes from your most advanced plants. As I pull individual plants, I often move the mulch to the centers of neighboring plants that are still growing and in need of as much mulch as I can muster.

When it comes to growing potatoes, the simplest method is the best.

Barbara Pleasant

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Comments

 
"Thanks Barbara, this was super insightful for me. I have a yard where only container gardening is possible and I've tried potatoes in bags for the last two years with disappointing results. Good to know that it's not the variety I tried... Bags just aren't their thing. "
Allisen Souza on Friday 8 May 2015
"I'm so glad I saw this as I was going to try bags this year. Now I might just dig another area and do more research on growing them in raised beds. =)"
Amanda on Sunday 10 May 2015
"Great timing! I was about to start mine in bags (again though last years yield was poor and now I know why). So, seeing as I have the cloth bag specifically for potatoes, what else would LIKE growing in it that would be a good use of all the soil/space? Suggestions?"
Dani on Tuesday 12 May 2015
"Dani, plants that like warm roots are good candidates, like tomatoes, peppers, and eggplant, and possibly basil and New Zealand spinach. "
Barbara Pleasant on Thursday 14 May 2015
"I have been having trouble with some kind of worm so I am trying the bags outside the garden to try to get potatoes with out channels and other damage created by them. "
Cathy Muskus on Friday 15 May 2015
"Wonderful article - I'm growing potatoes for the first time this year using the hilling method in a raised bed. I had a few tubers left over and didn't want to throw them out so will by planting them in a few white containers (that hopefully reflect some of that heat?) - I'm not expecting a lot from the container plants, especially after reading this article - our climate in Southern Ontario does get hot during the summer - but I'll treat it as a bit of a mini experiment. I have another suggestion for Dani - it's a bit late in the season (around here, anyhow), but another suggestion for her bag would be sweet potatoes which, unlike regular potatoes, REALLY enjoy the heat "
Margaret on Sunday 17 May 2015
"Barbara, So would you suggest that I bury my Yukon Gold and Nicola pots?"
Jerry on Monday 18 May 2015
"Jerry, burying the pots will help you get some potatoes, but they will be small because of the containers....Cathy, those may be wireworms, the larvae of click beetles. They can be caught and collected by placing bait, in the form of a handful of well-soaked beans, placed in the bottom of a 6-inch deep pit, covered with a board. "
Barbara Pleasant on Monday 18 May 2015
"Barbara, how often do the bait traps for wire worms have to be checked and refurbished? Sounds like a great idea for my sweet potato patch!"
jerry on Tuesday 19 May 2015
"Jerry, it will take several days for traps to attract the wireworms, so I'd say no more often than once a week. Cut up raw potato, carrots, and other tempting foods can be used as bait -- just be sure it's in a deep, cool hole that is well shaded."
Barbara Pleasant on Wednesday 20 May 2015
"I am happy to hear this, as I am still growing potatoes in the ground. I hill my plants with garden soil which is probably why I get blight (my plants die early, but I still get a crop to last the winter) but when I have used straw as mulch, mice move in and gnaw on the potatoes. "
Patsy Alford on Thursday 2 June 2016
"This disregards the space involved with planting. At 15" between plants and 30" between rows (main crop), 100 sq. ft. would be needed for 16 seed potatoes. 2 seed potatoes in each of 8 x 12" square bags would take up 8 sq. ft. At the harvest you suggested you would need 12 and a half times the space for 4 times the crop."
Ronald Maxwell on Saturday 5 November 2016
"Yields from seed potatoes in bags can also be increased by providing the best conditions. Mix equal parts ericaceous and John Innes No 3 compost to give a ph of 5.75 as potatoes prefer acidic soil. (A lower ph makes take up of nutrients difficult). Mix equal parts blood, fish and bone with kelp for fertilizer."
Ronald Maxwell on Saturday 5 November 2016
"The methods here are really helpful. I live in inland San Diego so I wait for cool fall and winter to plant my potatoes. However, my early fall plantings were devastated by white fly left over from summer (it has been warm). I did just cut the tops off at the soil line, hoping... I treated most of my garden plot by solarizing with black plastic. Wondering if I should solarize my potato patch too? "
Linda West on Saturday 12 November 2016
"please is sweet potatoes suitable for bag growing? thought some one spoke concerning this thanks"
sunny on Friday 10 February 2017

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