Potato Research, Mother Earth News Fair PA and Heritage Harvest Festival

Crates of potatoes in our root cellar.
Photo Nina Gentle

Potato Research on Harvest and Storage

Last week I mentioned that while researching potato yield figures, I found an interesting publication, The Potato Association of America, Commercial Potato Production in North America 2010. I’ve been reading that and learning more about potatoes. Here I’m going to focus on harvest and storage, because that’s the bit we’re currently challenged by. I also learned more about planting in hot weather, but that’s for another time.

Potato harvest.
Photo Nina Gentle

In England we planted in spring and harvested in October, waiting for the frost to kill the vines. In Virginia we plant in March and June, harvesting in July and October. We have grown Red Pontiac, Yukon Gold and Kennebec here, mostly. They all seem to be determinate varieties. I only just learned there are determinate (varieties with naturally self-limiting growth, generally “early” varieties) and indeterminate varieties (such as “Russet Nugget,” “Nicola,” “German Butterball” and “Elba”). The distinction is explained in Potato Bag Gardening. Growers using towers, grow bags, and cage systems want indeterminate potatoes, which continue to produce more layers of tubers on the stems as they are progressively covered with more soil. Growers wanting a fast reliable crop in the field mostly choose determinate types, which grow as a bush, then flower and die. The Wild Woolly Web does seem to have some contradictory statements about which varieties are determinate and which indeterminate, and some dedicated container growers make assertions not supported by experienced commercial growers. So Reader Beware! I trust Extension and here’s a link to their Ask an Expert page on potato types, and the University of Maryland Extension Home and Garden Info Center Potatoes.

June-planted potatoes in early September
Photo Kathryn Simmons

Whether the vines die naturally at the end of their lifespan, or they die of disease, or the frost kills them, or you kill them yourself by mowing or flaming, the potatoes will store better if you then wait 2-3 weeks before harvesting. The potato skins thicken up (becoming more resistant to scrapes and bruises) and the potatoes become higher in dry matter. Harvesting is easier if the vines are well dead. We generally bush-hog ours. Decades ago, in England, we had late blight in the middle of the season, and we cut the tops off and made a very smoky bonfire. (I wouldn’t participate in that much air pollution nowadays!) After waiting for a couple of weeks for the late blight spores to die, we dug the potatoes. The idea was to prevent spores getting on the tubers. As I remember, it all worked out OK.

If at all possible, harvest when the soil moisture is 60-80% of field capacity. Not too dry, not too wet. This reduces damage from scraping. If using a digger, don’t set it digging too deep, or too much soil will be damped on the harvested potatoes.

Tuber temperature will also impact bruise and rot susceptibility. Ideally soil temperature will be 45-65F (7-18C).  Because soil temperature lags 3-4 hours behind air temperature rise each day, in cold weather, try to harvest around 6 pm or a bit later. In hot weather, harvest in the morning.

When freshly harvested, potatoes are tender, breathing things. Avoid bruising, which is damage that does not break the skin, by not dropping potatoes more than 6” (15 cm), or throwing them towards a container. Don’t bang them to knock off extra soil.

When harvesting in summer, we stack the crates of potatoes under a big tree overnight to lose some of the field heat before moving them to the root cellar early next morning. Potatoes you take from storage can be no better than the quality of the potatoes you put into storage!

The first part of the storage period is the curing. The potatoes are still actively respiring, so they need a good oxygen supply. Failure to ventilate the cellar enough can lead to Black-heart, where the inner tissue of the potatoes dies and turns black. During the curing period, the skins further toughen up, and cut surfaces and superficial wounds heal over, enabling long term storage. The temperature should be as close to 50-58F (10-14.4C) as you can get. The lower end of the range is best for fresh eating (as opposed to junk food manufacture). Hotter temperatures will promote more rot, and age the potatoes faster, leading to early sprouting. Relative humidity should be 90%, but not 100%! If there is too much condensation, use a fan and open the cellar doors, when temperatures are closest to the goal. Curing takes 10-14 days.

Sorting potatoes .
Photo Wren Vile

We find that a single thorough sorting after 14 days can remove almost all of the storage problems that are going to happen. Not sorting at this point lets rots spread.

After the curing period, the potatoes become more dormant and do not respire so actively. They don’t need as many air changes as during curing, but if the cellar is too warm, you will need to aerate more. The temperature during the storage period should be 40-50F (4.4-10C), and closer to the lower end of the range is best. Constant temperatures or a steady decline is the goal, not dramatic fluctuations. Humidity should still be 90-95%, to keep weight loss to a minimum.

Potatoes have a natural dormancy of 60-130 days (depending on the storage temperature). After that period, they will start to sprout. Some plant extracts, including clove oil, can add 20-30 days storage, and will then need to be reapplied. I do not know anything about this myself, and do wonder how you remove the clove flavor from the potatoes!

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Speaking Events

I have two speaking events coming up in September
Mother Earth News Fair

2019 Mother Earth News Fair Pennsylvania.

September Friday 13- Sunday 15, 2019
Location: Seven Springs Mountain Resort, 777 Waterwheel Dr., Seven Springs, Pa. 15622

I am giving two 60 min workshops

Hoophouse winter lettuce: Green Forest, and Red Salad Bowl, two of our fifteen varieties.
Photo Wren Vile

Lettuce Year-Round on Friday 9/13 12.30-1.30 pm at the Grit Stage

This presentation includes techniques to extend the lettuce season using row covers, cold frames, and hoop houses to provide lettuce harvests in every month of the year. The workshop includes a look at varieties for spring, summer, fall, and winter. Pam Dawling considers the pros and cons of head lettuce, leaf lettuce, baby lettuce mix, and the newer multileaf types. She also provides information on scheduling and growing conditions, including how to persuade lettuce to germinate when it’s too hot.

Cool Season Hoophouse Crops on Saturday 9/14 3.30-4.30 pm at the Building and Energy Stage

Learn how to fill your hoop house with productive food crops in the cool seasons. Pam Dawling discusses suitable crops, cold-hardiness, selecting crops, calculating how much to harvest and how much to plant, crop rotation, mapping, scheduling, seasonal transitions, succession planting, interplanting, and follow-on cropping.

Book-signing at the Bookstore Saturday 4.30-5 pm. Buy new books at the Bookstore and bring your grubby used copies to be signed too!

Demos at New Society Publishers booth, of tomato string-weaving and wigglewire system for fastening hoophouse plastic to framework
Friday 3 -3.30 pm, 4.30-5 pm; Saturday 10-11 am, 1.30-2.30 pm; Sunday 9-10 am. 1-2 pm, 3.30-4 pm

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Heritage Harvest Festival, Monticello, Charlottesville, VA

September Friday and Saturday 21-22, 2019
Buy tickets online
Workshop with Ira Wallace
10:30 – 11:30 am Saturday in the Heritage Tent

Winter Gardening: No Tech to High Tech 

Learn tips on growing cold-hardy vegetables (not only kale!) out in the open and with varying degrees of protection from rowcovers, low tunnels, coldframes and hoophouses (high tunnels). We’ll consider crop choices, planting dates and harvesting so there’s always something to eat for everyone from winter market gardeners to small backyard growers. We’ll explain ways to maximize production with succession planting and follow-on cropping.

 No extra fee for the workshop, included with the price of general admission

Booksigning: SATURDAY, SEPT. 21st, 11:45am – 12:15pm, MONTICELLO SHOP TENT (WEST LAWN). Buy new books at the Bookstore and bring your grubby used copies to be signed too!

December view in our hoophouse, showing lettuce mix and turnips.
Photo Wren Vile

Sweet corn, potatoes and okra

Our first sweet corn of the season (Bodacious).
Photo Pam Dawling

Sweet Corn

We sowed our first sweet corn on 4/18, eight days earlier than usual this year, because we had auspicious weather. We look at the leaves of the white oaks to decide when it is warm enough for corn planting. The oak leaves should be as big as squirrel’s ears. Phenology signs like this are especially useful when the weather is extremely variable, which we are getting more of as climate disruption has got us in its grip.

Our first sweet corn sowing is always a bit of a risk. In fact we often prepare for this by sowing some corn seeds in styrofoam Speedling flats, the same day we sow the first corn planting outdoors. Read more about this seedling technique and transplanting corn.

Our third planting of sweet corn on the left, fourth in the middle, 5th (barely emerging) on the right.
Photo Pam Dawling

We’ve been harvesting sweet corn since July 2, which is two days earlier than our target start date, so we’re very happy. Initially, of course, we got smaller amounts, but we are now harvesting three times a week and getting good amounts. We are back up to 6 sowings this year, after we had to cut back for a couple of years. For a hundred people we sow an average of 1100 ft (335m) each time we plant, with each planting intended to last us 15 days (7 or 8 pickings). Our goal is sweet corn from July 4 to mid-October (our average first frost is October 20, a 13 year average from our own records).

Three varieties of sweet corn in one planting. On the left Bodacious; in the middle, red-flowered Kandy Korn; on the right, Silver Queen not yet fully grown.
Photo Kathryn Simmons

Each sowing includes several varieties (with different numbers of days to maturity) on the same day, so a planting will give us at least two weeks of delicious corn. In this photo from a previous year, you can see (from left to right): later-maturing Silver Queen, not yet at full height; red-flowered Kandy Korn; fast-maturing shorter Bodacious. Each plant is only going to provide two or three ears, so to have enough, and to have a continuous supply, it is necessary to plan ahead. See the Succession Planting section ahead.

Sowing sweet corn

We have switched to sowing corn with the EarthWay seeder, with a homemade next-row marker. This is much quicker than sowing by hand, but does rely on providing overhead irrigation consistently until the seedlings emerge. Another trade-off is that we get more weeds germinating in the (watered) aisles than we did when we only watered the furrows at planting time. Drip irrigation would be another approach.  So far we have not lost corn to crows, which was the reason we took to the handsowing-under-ropes method some 20 years ago. Back then we also sowed our fist corn with a tractor seeder, but we had to follow that with putting up ropes, or we lost it all to birds. Details of our hand-sowing method are in this post from May 2016.

Staying on top of weeds in the sweet corn

Once we get to late June, more of our time in the garden is taken up by harvesting (a sign of success), leaving less time for weeding. We have a system I like that helps us stay on top of sweet corn weeds. Each time we sow sweet corn, we hoe the previous planting (about two weeks old), thin the plants to one every 8″-12″ (20-30cm) in the row, and wheel hoe or till between the rows. We have two Valley Oak wheel hoes that we really like. The handle height is adjustable and they are available with different width hoes (and other attachments). Our tiller is a BCS 732 from Earth Tools BCS

Don’t let this happen to you! Weedy young corn.
Photo by Bridget Aleshire

We also hoe the rows of the corn planting before that one (about 4 weeks old), and till between those rows and broadcast soybeans (which we till in lightly). Soybeans will grow in partial shade, handle the foot traffic of harvesting, and provide some nitrogen for the soil. For the last corn of the season, we undersow with a mix of soy and oats. After the harvest ends, we leave the patch alone, and the oats survive the first frosts (which kill the corn and the soy) and go on to be our winter cover crop for that plot. When it gets cold enough, the oats do die, and the plot becomes an easy one to bush hog and disk in the early spring for our March-planted potato crop. I like that opportunity to eliminate one round of disking, and to get a winter-killed cover crop established

As we harvest corn we pull out any pigweed that has somehow survived our earlier efforts. I learned at a Sustainable Weed Management workshop, that pigweed puts out its seeds in one big bang at the end, so pulling up huge pigweed is worthwhile, if it hasn’t yet seeded. (Actually you can see it for yourself, but before the workshop I hadn’t noticed!) Our soil has improved over the years, so it is now possible to uproot 5ft (1.5 m) pigweeds. Sometimes we have to hold the corn plant down with our feet, but we do almost always succeed in getting the weeds out, without damaging the corn.

Succession Planting for Sweet Corn

In Sustainable Market Farming I have a chapter on succession planting, and my slideshow on Succession Planting is one of my most popular ones. You can watch it right here.

I posted on Mother Earth News Organic Gardening blog about Growing Sweet Corn for the Whole Summer. You can read it here:

Growing Sweet Corn for the Whole Summer – Organic Gardening

Our sweet corn sowing dates and harvests from those plantings are

  1. 4/26, harvest 7/9 (with a few ears from 7/4)
  2. 5/19, harvest 7/24
  3. 6/6, harvest 8/8
  4. 6/24, harvest 8/23
  5. 7/7, harvest 9/7
  6. 7/16, harvest 9/22

Avoid mixing types of corn.

There’s a confusing aspect of hybrid corn varieties: There are several genotypes, and if you inadvertently plant a mixture of different types, it can lead to starchy unpleasant-flavored corn. Also don’t plant Indian corn, popcorn or any kind of flint or dent corn within 600′ (180 m) of your sweet corn. For this reason we grow only sweet corn in our garden. Ignore those cryptic catalog notes at your peril!

Dealing with raccoons, skunks and curious cats in the corn

We have trapped (and then killed) raccoons in our corn most years, and the past few years we’ve tried deterring them with nightly radio broadcasts. We have the large live mammal traps, and we found for raccoons, we needed to stake the trap down to the ground. I followed suggestions from Joanna Reuter of Chert Hollow Farm, staking the traps down and smearing peanut butter high on the stake in the back of the cage. Well, the first morning I caught a small, very white skunk! I let it out carefully. The next morning I caught the same skunk again. And the third morning, again. You can read more about how I let the skunks out. I’ve also caught some of our cats by accident.

Raccoons don’t seem to like Silver Queen as much as Kandy Korn, maybe because the husks are tighter and harder to rip off. Actually I like Kandy Korn better than Silver Queen too.

Okra

Cow Horn okra flower and pod.
Photo Pam Dawling

We have started harvesting our okra. It’s a little later than it might have been because we had to replant. The first planting had leggy seedlings due to not enough light soon enough in their lives. Then we planted it out with novice helpers, and they didn’t plant them deep enough. The feeble stems couldn’t take it. We made an attempt to hill them up to give more protection to the stems. Another mistake we made was over-watering. When we pulled up some of the dead plants for our postmortem, they reminded me of retted flax stems – the fibers were still there, with the soft tissue rotted away. This is why I think the problem is that we over watered rather than under-watered.

This year we are trying Carmine Splendor, a red okra from Johnny’s, as well as our usual favorite Cow Horn from Southern Exposure.

Cow Horn okra pods.
Photo Bridget Aleshire

We like Cow Horn for its tall plants, high productivity and the fact that the pods can get relatively large without getting fibrous. They are still tender at 5-6″, which is the size we used to harvest at. Some years we have attached a card to the handles of the pruners we use for this job, with a life-size drawing of a 5″ pod. This helps new crew get it right.

We do find it very hard to convince our cooks that we have specially chosen this “commune-friendly” variety so they don’t have to deal with fiddly little okra pods when cooking for 100. We’ve had to compromise and harvest at 4″. Hence the venturing-out to another variety, accepting people are hard to convince about Cow Horn!

We grow a 90′ row, with plants about 18″ apart in the row. This is enough for the hundred of us (some people never eat okra despite the cooks’ best efforts!)

Carmine Splendot okra plant.
Photo Pam Dawling

Carmine Splendor is a 51 day (from transplanting) F1 hybrid, with sturdy 5-sided pods that are deep red when small. I haven’t tasted them yet.

Potatoes

June-planted potatoes emerging from mulch in mid-July.
photo Pam Dawling

Our June-planted potatoes are starting to come up through the hay mulch, and we need to walk through and free the trapped shoots. This means we walk through investigating the spots where we expect there to be a potato plant but we don’t see one. If we find a trapped shoot, we open up the mulch to let the plant see the light. We do this same job with garlic in late November or early December.

This week we are harvesting our March planted potatoes. I just dug 30lbs for tonight’s dinner. Yes, lots of diners! The rest of the crop will be harvested using a digging machine on Thursday.

We harvested our March-planted potatoes 21 days ago, and we are in the process of sorting them and managing conditions in our root cellar to cure the potatoes and help them store well.

Crates of potatoes in our root cellar.
Photo Nina Gentle
Click here for our Root Cellar Warden” instructions from last year.

Dormancy Requirements of Potatoes

We are researching the dormancy requirements of potatoes in an effort to store ours so they don’t sprout when we don’t want them to!

What I know so far about dormancy is that potatoes need a dormancy period of 4-8 weeks after harvest before they will sprout. So if you plan to dig up an early crop and immediately replant some of the potatoes for a later crop, take this into account. Get around this problem by refrigerating them for 16 days, then chitting them in the light for 2 weeks. The company of apples, bananas or onions will help them sprout by emitting ethylene.

To avoid sprouting, keep the potatoes below 50F (10C) once they are more than a month from harvest, avoid excess moisture, and avoid “physiological aging” of the potatoes, caused by stressing them with fluctuating temperatures, among other things.

Tobacco Hornworm pupa

Just had to add this, which I dug up yesterday. These brutes are about 2″ (5 cm) long. They are heavy and they move slightly. Also, check out the comments on the last post and be sure to see SESE’s Ken Bezilla’s Instagram of a hornworm in black light.

This is the pupa of the tobacco hornworm.
Photo Pam Dawling