Growing for Market, Sweet potato propagation and yields

The April issue of Growing for Market is out! For those of you growing sweet potatoes, Andrew Schwerin from NW Arkansas has written an interesting article. I’ve written about starting sweet potato slips before and I have a slideshow that includes three methods of  starting your own slips.  He and his wife Madeleine grow 1500 feet of sweet potatoes each year, a third of their growing area.

I was interested to note their reasons for growing so many sweet potatoes (apart from the obvious fact that they can sell that many). Sweet potatoes are not a big moneymaker in terms of the space occupied. Here at Twin Oaks we pondered similar issues this winter when deciding which crops to grow.  We worked down a list of 25 factors, deciding which were important to use. We chose our top handful of factors and then worked down a list of crops we might grow, awarding points (or not!) for each factor for each crop. This helped us narrow down what to focus on this year. And yes, we are growing sweet potatoes! I wrote about this in Growing for Market in February 2017.

These growers listed the following factors as their reasons to grow sweet potatoes:

  • Sweet potatoes produce well in our soil

  • They aren’t troubled by intense summer heat

  • Extensive vines will smother most weeds

  • Few pest or disease issues

  • Most of the labor is in early October, between intensive harvests of summer and fall crops

  • They store long-term for steady sales through the winter

Sweet Potato harvest at Twin Oaks. Photo McCune Porter

They like Beauregard, and wanted to try using the single node cutting method, as advocated by Anthony and Caroline Boutard – see my Sweet Potato slideshow for details. Initially they were excited about the single node cutting process, as their roots produced exponentially more growing shoots each week. OK, maybe exponential is a bit of an exaggeration, but it gives the sense of it. Because they had so much propagation material, they started making 5-node slips, rooting clusters of cuttings in pots of compost, 3 nodes in the soil for roots, 2 nodes above ground.

Some of their single node cuttings failed to thrive, both in the trays and in the field, so they developed a 2-node cutting system instead, and also used their five-node slips. And so they had a trial of three sweet potato cutting methods, with plants in different 100 ft beds. In the past (using the regular slips method) they have averaged yields of 500-600 lbs of sweet potatoes per 100 ft bed, with a range from a poor 250 lbs to a few successes with 1000 lbs/bed. Of course, yield is not the only important feature of a market crop, although understandably it has a high profile for those growing 1500 row feet for sale.

At harvest, they found that their single-node sweet potato plants were producing a couple of hundred pounds per 100 ft bed. The 2-node beds produced about 500 pounds per bed, of relatively few, very large (6 – 20 lb) sweet potatoes. The plants with 3+ nodes in the soil gave more reasonable sized potatoes. They tend to get jumbos, so they have started planting closer (10″) to tackle this – not many customers want jumbos.

In his article in Growing for Market,  Anthony Boutard pointed out that single-node cuttings do produce fewer tubers which are larger and better formed. This is a big advantage for growers in the north, but less so in the south. The Arkansas growers have found that the 2-node cuttings are even better at this tendency in their location, which is much further south than Anthony Boutard’s farm.

Beauregard sweet potatoes saved for seed stock.
Photo Nina Gentle

Other articles in this month’s Growing for Market include Managing a cash crisis
How to climb out of the hole by Julia Shanks, the author of The Farmer’s
Office. Farmers deal with a very seasonal cash flow, and may well have gone into farming with good farming skills but not good business skills. Julia writes about four rules for getting out of a financial hole.

  1. Quit digging (don’t incur any more inessential expenses).
  2. Keep the dogs at bay (communicate with your creditors about how you plan to pay, and how you plan to keep producing the goods).
  3. Climb out (increase revenue in as many ways as possible).
  4. Get your head out of the sand (don’t panic, face realities, be proactive).

She goes on to list 10 ways to protect yourself from getting in such a hole again.

Sam Hitchcock Tilton has an article about cultivating with walk-behind tractors, ie, weeding and hoeing with special attachments. There are some amazing walk-behind
weeding machines (manufactured and homemade) throughout the world. There
is an entire style of vegetable farming and scale of tools that have been forgotten, in between tractor work and hand growing – the scale of the walk-behind tractor. The author explains how commercially available tools can be adapted to work with a BCS or a carefully used antique walk-behind tractor.

Mike Appel and Emily Oakley contributed Every farm is unique, define success your own way. Money is not the only measure. Quality of life, family time, and personal well-being are up there too, as are wider community achievements. Farming is equal parts job and lifestyle, and the authors recommend having a strategic plan for yourself and the farm, which you update every couple of years to pinpoint goals and the steps you need to take to reach them.

Cossack Pineapple Ground Cherry
Photo Southern Exposure Seed Exchange

Liz Martin writes about husk cherries (ground cherries) and how to improve production of them, to make a commercial crop viable. Who would have guessed that hillling the beds before planting can make harvest so much easier, because the fruits roll down the sides?

Judson Reid and Cordelia Machanoff wrotea short piece: Fertility tips and foliar testing to maximize high tunnel crops, and Gretel Adams wrote about  Scaling up the flower farm. Many of the ideas also apply to vegetable farms.

Growing for Market article about sweet potatoes; zipper spiders

GFM_August 2014_coverThe August Growing for Market magazine is out, including my article about growing sweet potatoes. There is (of course!) a whole chapter in my book about sweet potatoes, and I’ve written previously in GfM about harvesting, curing, selecting roots for growing next year’s crop, and storage (September 2007). And also about starting sweet potato slips and planting them in spring (Feb 20007). And the harvest (twice) and starting the slips are covered in my blog too.

This time I wrote about growing the sweet potatoes out in the garden or field: varieties, crop requirements, when to plant, making ridges, using biodegradable plastic mulch, stages of development (roots first, then vines, then potatoes); and pests and diseases.

Also in this GfM is a good article by Joanna and Eric Reuter of Chert Hollow Farm (who I’ve mentioned before., when they decided to drop organic certification). They write about their 12 or so varieties of garlic and how they market them for specific uses such as roasting, eating raw and sauteeing.

The editor, Lynn Byczynski, writes about her son’s wedding and the flower arrangements she made for the big day. Chris Blanchard writes about Gardens of Eagan farm in Minnesota. Once owned and operated by Martin and Atina Diffley, it is now owned by the Minneapolis Wedge Food Co-op. It has expanded and now hosts a few satellite farms which help supply all the broccoli the Wedge needs. Eric Plaksin of Waterpenny Farm (not too far from Twin Oaks), writes about when he broke his foot, and makes suggestions to help other farmers be (somewhat) prepared for adversity, so it’s manageable. And lastly, Gretel Adams writes an inspiring article about growing bulbs and corms for cut flowers.  A good read all round!


And, on a different topic: Does anyone know if zipper spiders eat hornworms?

Zipper spider on tomato plant.  Credit Wren Vile

Zipper spider on tomato plant.
Credit Wren Vile

We get tobacco hornworms on our tomato plants. Outdoors, they usually get parasitized and do little damage. But the mother of the parasites doesn’t fly inside the hoophouse, and in there we sometimes have to handpick the hornworms. These things get big! And are hard to squash! This year we have lots and lots of these zipper spiders, and few hornworms. I never seem to find zipper spiders eating, but they must, because they grow fast. Anyone know what they eat?

Starting sweet potato slips

Growing sweet potato slips from roots planted in flats of compost.Credit Kathryn Simmons

Growing sweet potato slips from roots planted in flats of compost.
Credit Kathryn Simmons

The weather outside is still full of rain, but I’m optimistically starting growing our own sweet potato slips. Surely it will dry out by May?

Sweet potatoes are related to morning glory, in the genus Ipomoea. They are not yams, even though they are often called yams! True yams are a tropical species of tuber (genus Dioscorea). Sweet potatoes are roots, not tubers, and will not even cross with yams. So forget yams. Unlike white potatoes, which have the annual plant sequence of vegetative
growth, flowering and dying back, sweet potato plants would continue growing forever if the weather was warm enough.

The mystique of sweet potato slips

Sweet potatoes are not grown from seed or from replanted roots, but from “slips,” which are pieces of stem with a few leaves, grown from a mother root. We used to buy bare-root sweet potato slips to plant, believing growing our own would be very tricky. The collapse of our supplier and our desire to have organic plants (plus a need to reduce our expenses one year), pushed us into growing our own. We had some problems initially, so I can warn you about how not to do it. Now we have a system we really like, and we’ve found several advantages of homegrown slips over purchased ones.

With purchased slips, we had to specify a shipping date months ahead, then hope the weather sprites would be kind. We had to jump to when the plants arrived, and get them all in the ground pronto, to keep them alive as best we could (because their roots needed moisture). We accepted as normal a certain amount of drooping. We can have late frosts, spring droughts or El Niño wet springs, and climate change is only adding to the uncertainty. With homegrown slips we can delay planting if that seems wise; we can plant them in stages rather than all on one day. The transplants don’t wilt. We can grow them big and plant them with three to five nodes underground, giving more chance of survival in heat or frost. We can keep some spares on hand to replace casualties. The sturdy plants get off to a strong start, which could be an even bigger advantage further north where the season of warm-enough weather is on the short side for a 90–120-day plant. And we are self-reliant — we never have to spend money on them.

Timing

Figure out your ideal planting date and work back to find your starting date. Planting is usually done about two weeks after the last frost. The soil temperature should reach at least 65°F (18°C) at 4″ (10 cm) deep on four consecutive days. For us, that’s around May 12. It takes eight weeks to grow the slips, and the roots produce more slips if conditioned for two weeks (or even four), before you start to grow slips. So start ten to twelve weeks before your planting date. We now start March 1. Here’s where I made my first big mistake — following directions written for much further south, I tried to start growing slips in mid-January. Dismal fight against nature!

Testing (Optional)

If you want to get the best yields from your mother roots, first test the roots in a bucket of water — the ones that float are said to yield better and produce better-flavored roots. Next, test for viral streaking — also known as color breaks or chimeras, where paler spots or radial streaks appear in the flesh — and discard roots with pale spots or streaks wider than a pencil lead. Cut a thin slice from the distal end of each root — the stringy root end, opposite the end that was attached to the plant stem. All the sprouts will grow from the stem end, so don’t cut there! If you can’t tell the difference between the ends, you can ignore this step and plan not to propagate your own slips for more than a couple of years (so the virus load doesn’t get too high). Or if you are a home gardener dealing with a small crop, you could keep the slips from each root separately and cut up the mother root before planting and then discard the slips from streaked roots.

Conditioning (Also Optional)

Put the chosen roots in flats, boxes or trays, without soil, in a warm, moist, light place for two to four weeks. Ideal conditions are 75°F–85°F (24°C–29°C) at 95% humidity. This can double or triple the number of sprouts the root will produce in a timely manner. We use our germinating chamber, which is an old glass door refrigerator heated by a light bulb. See the photo above. Conditioning after testing allows the cut surfaces to heal before they are covered by compost. The environment for sprouting the roots is similar, so you can probably use the same location.

Sprouting

Set up a place with light, humidity and ventilation at 75°F–85°F (24°C—29°C) and with about 12″ (30 cm) of headroom. Plant the selected roots almost touching each other, horizontally in free-draining light potting compost in flats or crates. Water the boxes and put them to sprout. Once again, we use our ex-fridge germinator. Using boxes is much more manageable than having the roots loose in a big coldframe. Indoor spaces are much easier to heat than the great outdoors! Boxes can be insulated and put on a bench at a decent working height, with lights or heat lamps over them. Keep the compost damp, and if your planting medium is without nutrients, give liquid feed occasionally once sprouting starts. For small quantities of slips, it is possible to sprout the potatoes half-submerged in water, either in trays of water or by suspending a sweet potato impaled on toothpicks, resting on the top of a glass of water. For larger quantities I recommend our method.

Cut sweet potato slips put in water to grow roots.Credit Kathryn Simmons

Cut sweet potato slips put in water to grow roots.
Credit Kathryn Simmons

Cutting and spotting the slips
After 5–7 days, the roots will begin to produce slips. Ideally, wait until the slips are 6″–12″ (15–30 cm) tall with 4–6 leaves beginning, then cut them from the root and stand them in water. If necessary, cut them a bit shorter. Some people pull or twist the slips from the roots, but this could transfer diseases by bringing a small piece of the root with the sprout. I cut the slips daily, bunch them in a rubber band and stand them in a small bucket of water. The slips will grow more roots while they are in water for several days, which seems to be an advantage. Once a week I spot (plant) the oldest, most vigorous slips (with good roots) into 4″ (10-cm) deep wood flats filled with compost. The spotted flats require good light in a frost-free greenhouse and sufficient water. If you are two weeks away from your planting date and are short of slips, you can take cuttings from the first flats of slips that were spotted, to make more. The slips planted in flats become very sturdy, allowing flexibility about planting dates and a longer slip-cutting season. About ten days before planting, start to harden off the flats of slips by reducing the temperature and increasing the airflow. It’s also possible to skip the spotting stage and transplant the slips outside directly from the water, but I don’t think this is as good as spotting them into flats of good compost for a few weeks.

Once a week we plant the rooted slips in flats.Credit: Kathryn Simmons.

Once a week we plant the rooted slips in flats.
Credit: Kathryn Simmons.

From Sustainable Market Farming, (c) Pam Dawling, New Society Publishers 2013