The Garden Professors™

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.

Freshly 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.

Sweet 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.

Propagating 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.

You CAN grow it, but is it worth it?

As winter sets in here in Michigan, I’m seeing gardeners deploying winter protection. Like this, which I saw on a visit to Hidden Lake Gardens with some friends recently:

Well. Isn’t that attractive? Come around to the far side, and you see this:

Pinus contorta ‘Chief Joseph’ which is a stunningly beautiful conifer, green in the summer, this brilliant shade of gold in the winter. Sadly, those gold needles are also incredibly prone to turning a less brilliant shade of brown if exposed to too much winter sun and wind. Hence the ever-so-attractive sun-and-wind shade they’ve installed here.

Call me old-fashioned, but the point of a garden is to be pretty, and though you CAN wrap delicate shrubs in burlap or upend styrofoam cones over tender roses or even (yes, I’ve seen it) put little roofs over your hardy succulents to keep excess rain off of them, but is it really worth it? For me, if I have to put something ugly on my plants to keep them healthy, it isn’t worth it. In my garden, I’d lean towards something else I also saw on that visit:

Chamaecyparis obtusa ‘Crippsii’ No, it isn’t quite as stunning as the pine… but it will grow and not turn brown, with no fuss.

What about you? Are there plants you are willing to make your garden ugly to keep happy?

When trees can’t predict weird weather

Our normally mild corner of the country got hit early and hard with cold weather a few weeks ago. For several days straight, our home thermometer read anywhere from 22-25F. Now, Seattle routinely gets temperatures this low sometime during the winter. But this cold spell came very early – much earlier than our regionally adapted trees and shrubs were used to. The effect on our plants was significant.

Rhodies react to cold but tolerate the freezing temperatures

Trees and shrubs start getting ready for dormancy in the summer. They key in on the progressively shorter days and make biochemical preparations that are unnoticeable. When the first frosty evenings arrive, leaf color changes begin immediately. Chlorophyll, proteins and sugars are scavenged and stored in trunks and roots – we see leaves change from green to red, orange, yellow, and eventually brown. Slowly an abscission layer is laid down at the base of the leaf petiole, and when the layer is complete the leaf dies and falls.

But this year the trees weren’t ready. It got cold really fast, and green leaves died on the trees. And they are still there. Eventually these old leaves will fall, though some of them may stay on until spring.

Both the hydrangea in the foreground and the styrax in the back have retained their leaves after the cold snap.

What does this mean in terms of tree health? Well, it won’t kill them, but it does set them back in terms of food storage. A lot of the nutrients that were still in the leaves when they froze are lost to the tree. So there may not be as many reserves for winter root growth, or for spring leaf flush. Overall, we could expect to see less than normal growth in established trees and shrubs.

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…

You think YOU had a bad day…!?!

I'm itchy all over. — I’m itchy all over.

Just downloading some photos from the end of the summer, and found this. Rarely can I work up sympathy for a tomato hornworm (Manduca quinquemaculata). Though the moth is quite lovely, the caterpillars really did a number on my tomatoes (and two spindly eggplants) this year, and I recall joyously taking this photo in August.

However, I’ve had a rough Monday, and can kind of relate to being covered in Braconid wasp pupae. The larvae have chewed their way through the caterpillar, to spin their grisly cocoons of death (would have made a great post a couple of weeks ago) and dangle there in the breeze until emerging. I know it is nature’s way, but, dang.

Get a handle on your microclimates

Practically the first thing a budding gardener (at least in the US) learns is their USDA winter hardiness zone. Based on average winter low temperatures, hardiness zones have many flaws but are still a very useful tool in figuring out what plants can and cannot survive your particular winters.

Right after learning about winter hardiness zones, we generally hear about microclimates – the idea that small precise locations within our garden may be, sometimes significantly, warmer or colder (or wetter or drier) than the surrounding climatic norms. The most pronounced producer of microclimates in most people’s gardens is their house – the sunny southern and western walls in particular can be markedly warmer than the rest of your yard. If you have hills, you also get frost pockets in low lying areas and warm south-facing hill sides.

But just how much warmer ARE your microclimates? I used to live in a drafty, poorly insulated nearly 100 year old house which had VERY warm microclimates all around it because all the heat my furnace put out was rapidly leaking out into the outside world. Great for growing plants that normally wouldn’t take my winters, but oh, the heating bills! A modern, well insulated house leaks a lot less heat out into the garden. Over time in a garden, you can learn by trial and error just how far you can push growing tender plants in warm microclimates by planting things and watching them die or survive. But there is an easier and faster way to figure out your microclimates. Collect some actual data, getting firm numbers of how warm and cold different parts of your yard are.

I’m heading into the first winter in a new garden, and getting ready to deploy a handful of cheap mechanical min-max thermometers. I’m placing one out in the open, the others against the south wall of a shed and other places I think should prove to be warm microclimates. Out they go, and after particularly cold weather – or just in the spring – I can check the different minimum temperatures they’ve recorded. A few degrees differences isn’t worth worrying about, but get to 10 degree differences, and you are talking a whole winter hardiness zone warmer.

In addition to comparing different locations in my garden, I also like to compare the actual temperatures I’m recording with those from local official weather stations (to do that, just go to www.weather.gov, enter your zip code, and then click “3 day history” on the right side of the screen). The zone map is created based on readings from weather stations like these, and if your particular yard is consistently showing temps warmer or colder than the local official readings (provided, of course, your thermometers are accurate), you should adjust your winter hardiness zone accordingly.

Finally, a min-max thermometer is a great way to test various winter protection methods. Tender plants can be insulated with a thick layer of leaves or (my favorite) cut conifer branches or even styrofoam boxes. How well do these protections work in your garden? Tuck a thermometer in with the plant before you cover it and then, come spring, check the minimum temperature it recorded against what you saw in the open air. Again, a difference of 10 degrees Fahrenheit corresponds to a whole winter hardiness zone warmer, giving you real actionable information about what you might be able to over-winter with the help of different sorts of insulation.

It is worth reiterating that minimum winter temperature is only one of a myriad of factors that go into winter hardiness, moisture, duration of cold, health of plants, and even summer heat matter as well, but winter lows are important, and it can be easily and precisely measured. So why not get some numbers on it so you can have a better idea of just what tender plants you can get away with in your various microclimates? A few thermometers is a lot cheaper than putting out a bunch of rare perennials and having them freeze out on you.

Is it an Elmaple!

So let’s see here…someone planted a nice little Japanese maple outside a hotel, and everyone was happy. Then an elm started to grow next to it, and it looked pretty good. In fact, it looked better than the maple. So, what the heck? Let the elm grow and ignore the maple. And now….At what point do you decide which tree to sacrifice so that the other can live a reasonably healthy life? (Yes, there is a correct answer!)

A scary Halloween story

Those of you that have followed the blog for a while know that poor tree planting is one of my pet peeves. It drives me crazy to watch tree installers use backhoes to gouge out gigantic holes and then drop in the intact root ball, clay, burlap, twine and all. But this dig-and-dump method (or “cost effective practice” according to installers) of installing trees often dooms them (the trees, not the installers) to a slow and ugly death. So in honor of Halloween, let me share my latest horror story.

Twice a day I drive down this street in NE Seattle. I’ve long admired the row of dead street trees left to remind us all of our own mortality. A few of these Liriodendron have somehow survived though “survival” seems a generous term. They’re more like zombies, slowly losing body parts but somehow still functioning until someone puts them out of their misery.

One lone tree seemed to defy all odds. Until our latest windstorm, which revealed the cause of all this arboricultural agony.

That’s right, there’s the clay-covered rootball, still intact. Only one root has managed to escape into the native soil. There may be others on the opposite side, but by now (several years after installation) there should have been sufficient root establishment to prevent failure.

Several of us have written about bare-rooting trees before, and while there’s still not consensus on the practice I think we would all agree that the tree planting in this case was not acceptable. There are better ways, and yes they take more time (or “not cost effective” according to installers), but planting trees right mean fewer replacements later.

Scenes From A Zoo

The other day I went to a local zoo with my family. I’m not a big zoo lover. I hate to see animals in cages and kept from their natural wanderings and habits, but this zoo serves as a rescue, so I didn’t complain too much. As we were walking around I couldn’t help but notice the following container which I can only suppose once served as a food or water bin for one group of animals or another.

I really liked that quote. I wish I knew where it came from. Then, just a few minutes later, I saw this.

Hmmmm….now don’t get me wrong, I’d much rather see trees bound up and tortured than animals. But really, the natural world includes many different living organisms that interact with each other, and with us. Each is deserving of our care and respect. The way this poor tree is planted shows a complete disrespect for its life. Too deep — and it looks like more soil will be applied to fill the bed! This is just sad. Look, if we’re going to have zoos then let’s try to make them into places that celebrate the natural world.

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:

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.)

3) Cover with soil and water well.

4) 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.

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

6) 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.