Growing Sweet Potatoes in My Northern Garden

A Deliberate Agrarian Special Report

Dateline: 20 October 2011

I grew this amazing 3-lb Beauregard sweet potato in my garden this year. It was one of the easiest things I've ever grown.

Sweet potatoes are rarely grown by gardeners in the northern latitudes. Fact is, I’ve been gardening for nigh unto forty years and it was only three years ago that the idea of growing sweet potatoes here in Central New York State seriously entered my mind. It was then that a friend of mine showed me some sweet potatoes he had grown. They were huge, beautiful specimens of the Ipomoea batatas and I was duly impressed. That was when I determined that I should grow (or, at least, try to grow) sweet potatoes too.

As is so often the case when I get it into my head to do something new, a couple years (or more) may elapse before I finally get around to actually doing it. Some further incentive along the way helps. The incentive for me to finally grow some sweet potatoes came earlier this year when I read This Article in Mother Earth News magazine. 

The author, Ken Allan, of Ontario, Canada is an authority when it comes to successfully growing sweet potatoes in the north. Mr. Allan wrote a whole book on the subject. Sweet Potatoes For The Home Garden : With Special Techniques For Northern Growers is a book that every gardener who loves sweet potatoes and desires to grow them should have in their personal library.

The Book

 

Ken Allan's 200-page sweet potato how-to manual was self-published in 1998. It is not available from Amazon.com and I’m sorry to say that it is not available from any U.S. garden catalogs that I am aware of. But it is available directly from the author (details at This Web Site), and that is where I got  my copy. If you get a copy of the sweet potato book, please let Mr. Allan know that you learned about the book from me.

Now that we have those introductory comments out of the way, I’d like to provide you with a select few quotes from Ken Allan’s book and tell you about my first sweet potato harvest.

The first thing we northern gardeners need to understand when it comes to growing sweet potatoes (I assume you southern gardeners already know this) is that they are not grown, cured, or stored anything like the more common solanum potatoes (a.k.a., “Irish” potatoes or, as the old farm almanac editors called them, “murphies”). Here’s a quote from the book:

“When an experienced gardener uses knowledge of similar crops as a guide to growing sweet potatoes, the reward is a small crop of small tubers which have little flavour and which spoil sometime before Christmas. The potential, when you do everything right, is to have a large crop of the best sweet potatoes you ever tasted, with the additional bonus that, in conditions that are easy for the average gardener to supply, they keep better than any other crop.

Indeed, quite aside from eating quality and nutritional value, longevity in storage is one of the best arguments for making sweet potatoes a staple in the home garden. If this is counter to what you have read or observed about sweet potatoes, it is because the storage requirements of sweet potatoes are not generally known.”

I ordered sweet potato “slips” from Burpee. I chose the Beauregard variety because I liked the name and the description said that Beauregard is a large, very orange sweet potato. Slips are nothing more than short lengths of leafy stems that sprout and grow out of sweet potato tubers placed in water. They are totally unremarkable little pieces of vegetation, and it was hard to imagine that they would ever amount to anything much.

Nevertheless, I followed the directions for planting as given in the Mother Earth News article (and in the book). In time, the little slips grew to a dense tangle of vines.
 
I hoed up close to the fledgling row of vines with my Planet Whizbang wheel hoe as they spread out and did nothing else with them all summer. I didn’t even water them when we had a lengthy dry spell. The vines grew lustily; they dominated and suppressed virtually all weed growth. Which is to say that sweet potatoes are very easy to maintain and grow in the garden. I added no fertilizer to my soil and there were no problems with insects.

Come the first light frost this month (October) some of the vines suffered frost damage and I went looking for “the book” to see what I needed to do next. There I read...

"Sweet potatoes should never be allowed to cool below 50°F (10°C) and preferably not below 55°F, either in the garden or later in storage. This fact may dictate harvest time. Soil temperature usually drops to 50°F at the time of the first frost. Sweet potatoes don’t mature, they just keep on getting larger until the weather gets cool. Since expansion of the fleshy roots is most rapid in late summer and early fall, harvest should be delayed as long as the weather holds. They won’t do any growing at 60°F or below, however, so for those of us in the north there is little to be gained in leaving them in the ground past the second or third week of September (unless they are protected by a cold frame or some form of rowcover)."

It was October 10th when I read that and I hastened to put my soil thermometer to use. I was concerned that my soil temperature would be less than 55°, but it was 60°.   I commenced to dig....

Digging potatoes by hand with a garden fork is always hard work but it’s always downright satisfying when you uncover a lot of good potatoes and, boy howdy—did I find potatoes!

This is what the sweet potatoes look like with some of the earth around them removed.

I harvested four bread trays of sweet potatoes like shown here.

I had read something about properly curing sweet potatoes and found the full story on this critically important (but little understood) process in Chapter 10 of Ken Allen’s book:

"Curing sweet potatoes involves holding newly dug tubers at a fairly high temperature and humidity long enough for important physiological changes to take place: the skin becomes impermeable to moisture; cuts and scrapes scab over; starch is converted to sugar. The higher the curing temperature, the shorter the curing period. Optimum conditions are 85° to 90°F and 80% to 90% humidity for five to seven days. If the temperature is reduced to 80° to 85°F then the curing time can be doubled."

So proper curing is essential to long storage and  Mr. Allan explains what exactly makes this so...

"What happens during curing is that a layer of suberin forms in the skin of the fleshy root, enclosing each tuber in its own little organic plastic baggy. In suberization, starch is converted to unsaturated fatty acids which combine with oxygen to make suberin, a remarkable mixture of waxy substances which allows the tuber to breathe but which holds in almost all of the tuber’s moisture. Suberin, in combination with wound priderm (which forms a corky layer over wounds), seals in  moisture and seals out rot-producing organisms, thereby protecting against infection. Cured sweet potatoes do lose moisture but the loss is very slow. A properly cured sweet potato can sit at room temperature in the open air for several months and lose scarcely any weight."

Proper curing is also absolutely necessary if you want a truly sweet tasting potato— a natural malt-sugar sweetened potato.

Allan stresses that curing should begin immediately upon digging and he offers several ideas for how and where to get your just-dug sweet potatoes properly cured. He states....

"Gardeners who don’t have a climate controlled room will have to use some ingenuity to provide the warmth necessary for curing, and there are almost as many solutions to this problem as there are gardeners."

A climate controlled room could be nothing more than a spare bathroom or big closet in your house with a heating source and thermostat. But I have a small house with no room to spare. So my solution to the problem was a small chicken coop that I undertook to make several years ago and never finished. It was out behind my workshop, along with several junk lawnmowers, bicycles and other such items. I cleaned the chicken house out, put a small electric “milkhouse heater” inside and powered it with an extension cord out the window of my shop.
 

A milkhouse heater just inside the sliding door of this small chicken house took care of the heat source for my makeshift sweet potato curing kiln.

One end of my new “curing kiln” was completely open and I covered it with several layers of painter’s drop cloths, held in place with spring clamps. I placed my potatoes in plastic bread trays, stacked them in the kiln, and monitored the temperature with a digital thermometer (it's a handy tool to have on the homestead).
 

I closed in the end of the "kiln" with dropcloths.

A view behind the drop cloths, into the "kiln."

 

My kiln worked very well. The temperature fluctuated between 85° and 105°. After seven days I brought the warm potatoes into our house.

 

Kiln-cured sweet potatoes about to go into storage. Each of those egg baskets is holding 45 pounds of tubers.

 

That old wainscot cabinet is in our living room, just off the kitchen, and not far from the woodstove, which is our only source of heat. The temperature can really fluctuate inside our home on winter days. Hopefully that cabinet will do the job.

I packed 110 pounds of sweet potato tubers into the bottom of the cabinet.
 

My 110-pound sweet potato harvest stored away.

 

We have not yet tasted the potatoes. I’m giving them another month to cure in the cabinet. After we cook some up I’ll report back here with the taste-test results.

If those sweet potatoes do taste good and keep good you can bet I will grow them again in next year’s garden. If I decide to grow the Beauregard variety again I won’t have to buy my slips. I’ll simply grow my own. It’s easy to do and full details are in “the book.”

Thank you Ken Allan!