Harvesting, Curing and Storing Sweet Potatoes (A Visiting Professor feature)

Submitted by Ray Eckhart

Introduction
Sweet potatoes (Ipomoea batatas) are warm-season plants in the morning glory family (Convulvulaceae). The part we eat is the fleshy storage root of the plant, which is a little different than the regular Irish, or white, potato (Solanum tuberosum), a plant in the family Solanaceae. In that case, the part we eat is a fleshy underground stem of the plant, called a tuber.

Although sweet potato roots continue to grow until frost kills the vines, an extremely hard frost can cause damage to the ones near the surface. Chilling injury also results when soil temperatures drop to 50°F or lower, and this can result in internal decay in storage. The greatest danger from delayed digging is the risk of cold, wet soil encouraging decay. So the best time to dig is around the time of first frost in your area, or shortly thereafter. The vines can be clipped approximately 5 days before digging to improve skin-set or reduce the incidence of skinning the roots during harvest. To avoid exceptionally large sweet potatoes, a few hills should be dug in advance of the anticipated harvest date to determine the size of the sweet potato roots.

Puerto RicoFreshly dug sweet potato ‘Puerto Rico’

You can cook newly dug sweet potatoes right away, but their flavor, color and storage quality is greatly improved by curing at warm temperatures immediately after harvest. It is during the curing process that starch is converted to sugar.

Cure sweet potatoes by holding them for about 10 days at 80-85°F and high relative humidity (85-90 percent). Commercial producers have temperature and humidity controlled housing to guarantee good results, but for the home grower, they can be cured near a furnace or heat source to provide the necessary warmth. If the temperature near your furnace is between 65-75°F, the curing period should last 2-3 weeks. To maintain the required high humidity (85-90 percent relative humidity), stack storage crates or boxes and cover them with paper or heavy cloth.

CuringSweet potatoes curing

Once the sweet potatoes are cured, move them to a dark location where a temperature of about 55-60°F can be maintained, like an unheated basement, or root cellar. Sweet potatoes are subject to chilling injury, so don’t refrigerate them. Outdoor pits are not recommended for storage because the dampness encourages decay. Good results can be obtained by wrapping cured sweet potatoes in newspaper and storing them in a cool closet. Sweet potatoes can also be stored in sand.

Ornamental Sweet Potatoes
Have you ever wondered what, if any, is the difference between the ornamental sweet potato vines grown as a season-long ground cover, or, as “spillers” in container arrangements, and the vegetable we grow as food? The answer is – not much. They are just different cultivars of the same plant species, Ipomoea batatas. The ones we grow for food are selected and bred to produce large, uniform, good tasting roots, high in nutrients for eating, whereas the ones we grow ornamentally are selected for the striking shapes and colors of their leaves. Plant breeders introduce new variations every year. If you dig up the earth around your ornamental vines, you’ll find the same fleshy roots (different colors, perhaps) as the familiar ones we grow, or buy, for food. So, can you eat them? Well, technically, yes – but there’s no guarantee how they’ll taste. Most ornamental varieties are pretty bland. However, if you dig, cure, and store them as above, it’s possible they can stay viable until spring, when you can try to continue their growth for another season.

PropagationPropagating new plants (called slips) the following spring

References:
http://waynesword.palomar.edu/ww0804.htm
http://urbanext.illinois.edu/bulbs/bulbbasics.cfm
http://content.ces.ncsu.edu/ornamental-sweetpotatoes-for-the-home-landscape.pdf

Ray Eckhart is a former Penn State Extension Educator and avid home vegetable grower, with a weakness, bordering on obsession, for home grown tomatoes.

Infographic with a BIG grain of salt

Infographics can be great: They’re bright colorful ways to make sometimes complex concepts visual and easy to understand. Sadly, “easy to understand” does not necessarily equal “accurate” and they can also be extremely misleading.

Take this beautifully made image from National Geographic. It is an older image — first posted back in 2011, but it makes the rounds on social media from time to time, and popped up in my facebook newsfeed a couple days ago.

Look at it! Oh no! We’re loosing all of our vegetable genetic diversity!

Or not. First, it is comparing apples to oranges. This image looks a commercially available varieties in 1903 and compares it to the number of varieties in one specific center for preserving genetic diversity. What happens if we compare the same metric? If you look at the number of varieties in the National Seed Storage Laboratory, that was founded in 1958… so in 1903, at the top of the graph, the number for all these vegetables would be… zero. If you look at the present day, the current umbrella organization for all the US government funded efforts to preserve genetic diversity of crop plants is GRIN, (Germplasm Resources Information Network)  and if I do a quick search through that database using the keyword “tomato” I get… 9281 results. That is a pretty overwhelming improvement over 79 in 1983.

And what about commercially available varieties? To use tomato as an example again, in 1903, they found 408 varieties offered commercially. I just added up the varieties listed by just ONE seed company, Baker Creek Seeds, currently lists 287 different varieties of tomatoes. That is just ONE company. I have no doubt that if I added up all the varieties that are offered for sale in the giant pile of seed catalogs I get every spring it would be FAR more than the 408 on offer in 1903.

So… are we losing genetic diversity in our crop plants? Probably. There are lots of traditional varieties and land races that were never available commercially that have do doubt been lost, but to be honest, I think we’ve done a pretty good job at preserving the diversity. And certainly the USDA’s system of gene banks is an incredibly well run, impressive thing that deserves high praise indeed, for not merely preserving vast amounts of important genetic diversity but also working hard to characterize it and make it available to researchers and breeders so it can actually be put to work in the development of new and improved selections to try and feed the world.

So despite how colorful and easy to understand this infographic is, you don’t need to freak out about a massive loss of genetic diversity in our vegetable crops. Save that freaking out for all the wild species that have gone extinct or are about to go extinct thanks to habitat destruction and climate change world wide…

The great urban potato experiment

I don’t grow vegetables at home, mostly because I don’t have the space and partially because I don’t have the time. But I did want to try the potatoes-in-a-barrel method, which I also tried last year. But this year I planted about 6 weeks earlier (end of April) than I did the previous year (mid-June).  Here’s my mid-October harvests from both years:

October harvest  IMG_7560

Next year I’ll try planting even earlier. It’s not a huge harvest, but it’s fun to do, especially with kids. A richer media (like a green compost along with soil) might give you a better harvest.

If you want to try this yourself, here’s how to do it:

1) Use a plastic trash bin with holes drilled into the sides. Be sure to locate the barrel in full sun.

2) Put a layer of soil on the bottom, and add potatoes. (You can cut them into smaller portions, each with an eye, if you don’t have as many sprouted ones as I did.)

April planting 20143) Cover with soil and water well.

June 0554) As shoots and leaves emerge, continue to add soil or other media to the barrel, leaving the tops of the shoots and a few leaves exposed. I used a mixture of soil and composted wood chips. Water well.

June 0565) Continue to add media as needed, and continue to water through the season.

June 0106) When leaves begin to die back, you can dump the barrel onto a tarp and pick out your potatoes. Save the media for next year’s barrel.

R U nuts?

One of the things that comes along with having an extension appointment at a major university is I get lots of calls and e-mails from homeowners on a never-ending list of sometimes bizarre tree topics.  Technically, my extension responsibilities are related dealing with professionals; such as arborists and nursery and Christmas tree growers, but the ‘consumer horticulture’ calls still find me.  Last week I received a voice-mail message from an excited gentleman speaking at a decibel level somewhere between rock concert and jet plane take-off.  From the disjointed and rambling message I could tell the gentleman was elderly and maybe disoriented or had just had a few.  After identifying himself he indicated that he wanted to learn where he could find a “pine-nut tree”.  Although he didn’t give it, I knew the man’s location from his area code.  A legitimate response to such calls is to redirect them to the individual’s local extension office, but I hate getting the runaround as much as the next person, so I usually respond when it’s something I can help with and in this case I could.

I dialed the number and the gentleman picked up right away.  He sounded just as he did in the voice mail; gregarious, slightly rambling, and VERY LOUD.  His story, however, made me glad I called back.   His father had emigrated from Lebanon many years ago and he remembered how his dad had always reminisced about eating pine nuts in the Old Country.  For years he had wanted to plant a “pine nut tree” in memory of his dad.  The problem was every time he went to a nursery and asked for a “pine nut tree”, nobody knew what he was talking about.

 


Pine nuts. Photo: Paul Goyette – Wikimedia commons

 


Pinus pinea cone. Photo: Luis Fernandez Garcia – Wikimedia commons

 

I explained to him that the pine nuts his father cherished were from stone pine (Pinus pinea) trees, which are the pine nuts (pignoles) favored for making pesto.  In the US, the pine nuts that are sold commercially usually come from pinyon pine (Pinus edulis), which is native the southwestern US.  Unfortunately, neither of those trees will grow in the Upper Midwest, where he lives.  I pointed out that there are many other pine trees that produce edible nuts – the main reason those two species are widely used is because they produce very large nuts making them relatively easy to harvest.  In fact, there are about 20 species of pine that produce seeds large enough that harvesting the nuts is worthwhile.  Two pine species that produce edible nuts and grow well in our area are Korean pine (Pinus koraiensis) and Swiss stone pine (Pinus cembra).  I include both in my recommendations for alternative conifers for Michigan.  I gave the gentleman some information on nurseries in his area that I knew carried those trees and he was excited to have some direction on his quest to renew his father’s memory.

 


Korean pine (Pinus koraiensis) at the University of Minnesota Landscape Arboretum


Swiss stone pine (Pinus cembra) at Hidden Lake Gardens in southeaster Michigan.

Sidenote: The heartbreak of ‘Pine mouth’.

Have you ever experienced a bitter or metallic taste that persisted for days, even weeks, after eating pine nuts?  Then you’ve likely experienced Pine Nut Syndrome or ‘Pine mouth’.   The cause of the disorder is not completely known, but research by an industrious graduate student in the Netherlands suggests that nuts from certain pines; particularly an Asian pine, Pinus armandii, are most likely to cause the issue.  So, if you are a pine nut fancier, learn what you can about your source.  Pine nuts supplies can be cyclical since pine nut crops are often subject to biennial bearing.  Soaring prices during poor supply years provide incentive for inferior nuts to work their way into the market.

Label GMO foods? Sure, why not?

Lots of coverage in the mainstream media these days over various initiatives to label GMO foods.   I think GMO foods should be labeled; but not for the reasons you might think.

My personal opinion on GMO foods is that their benefits outweigh the potential downsides.  I think GMO foods should be labeled to make the public aware of how much of our food supply depends on GMO’s and the cost of not using GMO’s.  Obviously this will raise some social justice issues since wealthy people will have more opportunity to opt out of buying non-GMO products than the poor but it’s the same problem we have with organic already and it doesn’t seem to cause much of a stir.  My hope is that once GMO products are labeled we could get to the point where the main discussion on GMO’s focuses on the rational and scientific questions, not the irrational and emotional.  This weekend our Sunday paper included a quote from a local anti-GMO activist who tried to link the rise in obesity to increased use of GMO’s.  How about we’ve become too sedentary and we’re eating too much, period?  Or this from the “Health Ranger” Mike Adams: “Roundup herbicide devastates soils, rendering them contaminated and unable to produce healthy crops using traditional (or organic) farming methods. Once a farm plot is destroyed with Roundup, that farmer is forever enslaved to a chemical-based farming protocol.”   Hmmm… last time I checked farms could be certified organic after three years without synthetic chemicals.

Which is not to say I don’t have concerns about GMO’s; there are issues with any technology.  The largest questions I see, and the ones that are most difficult to answer, relate to unintended consequences.  One of the biggest selling points of Round-up ready technology, for example, is that it enables farmers to manage weeds with glyphosate, a relatively safe product in the world of industrial-strength herbicides, in order to reduce tillage and maintain crop productivity.  But as farmers use more and more glyphosate, they are also selecting for Round-up resistant weeds.  How long until glyphosate is no longer effective? Difficult to predict, but glyphosate resistance has already evolved in many weeds.

On the other side of the equation, the world’s population is projected to exceed 9 billion by 2050, with a disproportionate increase in the least developed countries.  As the need for food increases, land and water resources will become more limited and catastrophic droughts are likely to increase.  While it is easy to demonize industrial agriculture, it’s difficult to envision feeding ourselves and the world without the technology it has developed.

My Thoughts on 14 Foods…

Yesterday on Facebook I posted a link to a list put out by the Rodale Institute which takes a look at 14 things that you should never eat.  Some I thought were reasonable, and some I thought were a little nuts.  All in all though, it was an entertaining experience that made me think.

Here are my thoughts on the 14 foods.  Please feel free to disagree, and also realize that, while I am relatively familiar with the production of fruits, vegetables, and, to a lesser extent, staple crops like wheat, I’m not nearly as knowledgeable about meat and fish, and I’m certainly not a dietician.  So for most of these, you should take my opinions with a grain of salt.

Swordfish – I agree with Rodale simply because of overfishing concerns.  I am also concerned about the presence of heavy metals, but I do wonder how often someone would need to eat swordfish (and how much they would need to eat) to really endanger themselves?

Nonorganic strawberries – Well yes, strawberries are sprayed a lot, and if they’re grown organically they’re often sprayed a lot too – just with different things.  I certainly think it’s a good idea to wash anything that you buy from the store – no matter how it’s grown – with warm water before eating it, but I don’t see avoiding conventionally grown strawberries as substantially reducing risk – organic strawberries have their own set of risks (possible contamination and use of organic pesticides).  I do see a reason to buy locally grown strawberries – flavor!.

Diet Soda – I agree, because Diet Soda tastes like….well, I shouldn’t say it here.

McDonalds – I agree, not because of the GMO concerns, but instead because I’m opposed to the way that animals are treated in factory farms.  That said, I love my Big Macs way too much to give them up (Don’t bother calling me a hypocrite — I’ll just agree with you).

Canned tomatoes – I kinda-sorta agree, but mostly because I like fresh tomatoes, or tomatoes from a glass bottle.  I am somewhat concerned about BPA and would like to see more studies done on it, but I do not think that the danger is nearly as clear-cut as presented in this article.  My family and I really don’t eat that much canned produce simply because we’re not all that thrilled by how it tastes.

Bread – I don’t agree.  Certainly some people can have reactions to certain things in bread (like gluten) but the idea that modern wheat is some kind of lurking poison is a bit over the top.

Industrially produced hamburgers – Define industrially produced and I’ll tell you my opinion.  Then tell me exactly how I tell if a burger is industrially produced.  If it means I need to give up Five Guys….

Corn – I don’t agree, but I do love this line from the beginning of the article “Today’s corn plants are more like little pesticide factories with roots.”  It conjures a cool dystopian image in my head.  Look, every plant produces chemicals to defend itself from predators.  It’s true, we gave corn a new one by using genetic engineering, and now we’re able to grow corn by using fewer insecticides, almost all of which are much more potentially damaging to us and the environment than the Bt we’ve put into corn.

White chocolate – Umm – I don’t know what to say about this one.  I like it and I don’t see anything in the write up that convinces me it’s bad.

Artificial Sweeteners – I agree.  I can’t stand the flavor and I’ll admit to having headaches which have coincided with ingesting certain artificial sweeteners.

Sprouts – I think that sprouts are generally safe, but there’s no denying that there have been some instances recently where sprouts were found to be contaminated with one disease or another.

Butter flavored microwave popcorn – Sure, popcorn with real butter tastes better, but I like this stuff too – that said, I am concerned about the factory workers who suffer from popcorn lung as noted in the article.

Food Dyes – I agree, if only because fruity pebbles and the like look so scary!

Chain restaurant ice cream – Um…no — I love ice-cream any way it comes.

The Strawberry, And What Do You Do For An Encore?

 

Once upon a time, a long time ago (around 1714), a spy, posing as a merchant, was dispatched from France to Chile to investigate the defenses which the Spanish had installed there.  While there, he also had the opportunity to see some truly amazing plants, but he was most impressed by the strawberries.  Strawberries of one sort or another are native throughout most of the world, but most are just little bitty things.  They may taste good, but you’ve got to get quite a few of them together to make a decent snack.  These were mega-bruisers.  Five or six could fill a small plate.  The name of this spy was Amedee Frezier (which is a variation of the word for strawberry).

Anyway, being a top-notch spy, he managed to get his hands on six strawberry plants and make away with them back to France.  Sacrificing fresh water needed by both himself and his shipmates to ensure that the plants made it safely across the ocean, he finally arrived in France with his precious cargo, no doubt very proud of himself.

There was only one problem.  These strawberries never produced much fruit.  Still, the plants were pretty enough, so they were kept at various botanical gardens across Europe and propagated using the runners which they naturally produce.  But the scientific community never could figure out how to make them produce fruit on a regular basis.

Enter Antoine Duchesne, a great scientist of the 18th century.  Duchesne figured out that the problem that the Chilean strawberries were having was that they were female.  Sure, they had fruit when Frezier saw them, but when he brought them to Europe they were never placed near male strawberry plants to provide pollen.  So Frezier mated the Chilean strawberries with male strawberries native to Europe and Bang!  There were the big beautiful strawberries that Frezier had seen in Chile.  And in 1764 he presented a bowl of them to King Louis XV.  Duchesne was seventeen at the time.  I wonder, was the rest of his life a letdown?

Planting Edibles in Cities

The snow has just started falling and I’m already thinking about what I’m going to be planting next spring.  Most of my plantings won’t be at my own house, they’ll be out in the cities of St. Paul and Minneapolis.  We’ll be looking at all kinds of fun stuff like growing trees in various new types of containers, adding compost to planting holes in different circumstances, and even pruning methods.  But one of the big things that we’re starting to look at are new trees for the urban environment.  Cities have always spent time considering what they plant, but with the emerald ash borer ravaging the Midwest, now they’re thinking even harder.  And because of the local food movement, suddenly the cities are at least considering trees like apples and hazelnuts on a trial basis (sure, there are some places that use them here and there, but they’re less than common).  Of course, if this movement stalls, the cities would be upset at having so many “messy” plants around (that’s their big concern about edibles right now), but I don’t think it will.  I’m actually pretty optimistic about using fruits and nuts on public property.  Sure, some plants will fail because they get too many diseases or insects, or because they’re weak wooded, but some will make it too.  I think hazelnut has a great chance in the right place (it would be too bushy for most boulevards….).  Do any of you have a favorite edible that you think might work well in a city?  Let me know, maybe we’ll try it!

Closing the loop

Just a short post today as I am participating in an Extension planning meeting for most of the day.  One up-side to the meeting is we are meeting and having lunch at Brody Dining hall here at MSU.  If you’re around my age and attended college in the 80’s, the thought of eating at a dormitory dining hall might elicit memories of a hair-netted cafeteria lady glopping amorphous slop on your tray next to the mystery meat of the day.  Boy, how times have changed.  Today, the quality of dining hall food is point of competition for universities angling for students.  The Brody dining center is set up like a food court, daily choices for students include a fresh salad bar, southwest food, sushi, made to order pizza, home-style comfort food, even kosher food.

The dining halls are also part of MSU’s sustainability initiative.  Food wastes from the dining halls are collected and sent to an anaerobic digester and composted at the MSU Student Organic Farm.  The compost is used at the recently completed Bailey hoop-houses on campus to produce salad green and herbs for use in the dining halls, providing a closed-loop system.  Is the food produced in the hoop-houses going to make the dining halls completely self-sufficient?  Probably not in the foreseeable future.  But they do provide a good opportunity to promote horticulture.  The project has generated numerous press articles and there are posters around the dining hall highlighting the project.  In an age when many bemoan the public’s disconnect between farm and fork, the Bailey GREENhouses remind students, especially those that might not think about it otherwise, where their food comes from.

An unwanted bonus in your urban chickens

Longtime reader Ray Eckhart sent me a NYT story on urban chicken eggs and lead contamination.  As I’ve mentioned before on this blog, urban gardeners should have their soils tested for lead, arsenic, and other commonly found heavy metals before they plant edibles.  Chickens that are allowed to peck and scratch in metal-contaminated soils will pass that unwanted load on to you via their eggs.

So test your soils!  It costs a bit of money, but then you know exactly what’s lurking in there.  If your soils have significantly high levels of lead or other contaminants, you can still raise chickens as long as they don’t roam your garden.