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.

Summer hoophouse slideshow, starting sweet potato slips, Growing for Market March issue

I’m back from the West Virginia Small Farms Conference, where I gave three presentations, including this new one, The Hoophouse in Spring and Summer:

I ran out of handouts, and I know some people want to view the slideshow again, to catch the bits they missed. Before next Tuesday, I’ll upload The Hoophouse in Fall and Winter as well. Maybe even later today, if I get my more urgent tasks done first.


Yesterday I brought our seed sweet potatoes, which we’d selected and set aside at harvest-time, up out of the basement and into the greenhouse, to start growing them.  I wrote about growing sweet potato slips previously. The first step was to see if they float or sink. We save extra seed roots so that we can discard the less promising and still have plenty to grow. Sweet potatoes that float will grow better and yield higher. We had saved 100 roots for a goal of 320 slips. After removing a few rotten roots and discarding the sinkers, next I tested for white streaks, called sweet potato chimeras. I cut a small piece off the distal end (the string root end), not the stem end. The idea is to throw out roots with white streaks bigger than a pencil lead. I only found a few. It’s a genetic mutation that can occur at any time. Because sweet potato slips are clones of the mother root, if you propagate from chimeras you get more chimeras. I succeeded in my goal of having 80 good roots from each batch of 100. I set the cut roots in shallow bins in our germinating chamber to heal the cut surfaces and warm the roots ready for sprouting. In two weeks I’ll “plant” them in flats of compost and return them to the germinating chamber to start growing the slips. They’ll look like this:

Sweet potato slips growing in our germination chamber. Credit Kathryn Simmons

Sweet potato slips growing in our germination chamber.
Credit Kathryn Simmons


Meanwhile the March issue of Growing for Market magazine arrived, and I found a fascinating article about a new method of growing sweet potato slips, from Anthony Boutard and Caroline Boutard Hunt. They write first about “discovering” sweet potatoes and then deciding to grow them, ordering 20 varieties from the Sand Hill Preservation CenterTheir propagation method involves cutting each slip into one-node pieces and growing a plant from each short length. This reduces the number of roots to set, which saves propagation space. The single-node cuttings are set in 50-cell plug flats, trimmed of their leaves and grown in the greenhouse for only two weeks before planting out in the field. This reduces the time caring for the young plants by a lot, which once again saves greenhouse space. They say “The resulting crop is better quality because all of the resulting tubers grow from a single node instead of several, concentrating the production. Better yet, there is absolutely no drawback to the technique, at least in our experience to date.” And then, this lovely sentence “Certainly no reason to keep it within the family.” I love the way small farmers share information and tips!

Amusingly, they refer to the method I have written about as “traditional sweet potato slip production”! When I was starting out propagating our own, I followed advice to use cold frames, which clearly doesn’t work in Virginia in March and April. I couldn’t figure how those methods could produce enough slips in time unless a huge number of roots were used to start them. I found out that growers were actually using electrically heated beds. I tried a soil heating cable but it was nothing like warm enough. I searched for more advice and found the Southern Sustainable Agriculture Working Group the previous year had an Organic Farmer Network, who were exchanging tips. Someone, I think Ellen Polishuk of Potomac Vegetable Farms, answered others’ questions about growing sweet potato slips with something like  “I just grow them in flats.” That was a lightbulb moment for me – I knew how to grow things in flats! It didn’t seem like it was the traditional method at that time, but it certainly worked, so I adopted it and spread the word.


GFM-March2015-cover-300pxFor this issue of Growing for Market, I wrote about West Indian Gherkins as a trouble-free alternative to regular pickling cucumbers. We’re growing them in our hoophouse this spring, on a trellis net.

Andrew Meffert continues his series on greenhouse nightshade crops for colder climates. This month he provides part two of his detailed work on greenhouse peppers: Pruning and training for maximum production all season.

Lynn Byczynski gives some leads on finding and enjoying farming podcasts, while we are sowing seeds, potting up or otherwise engaged in manual not-mentally-demanding work.

Gretel Adams offers information about weed control in cut flower fields, and of course, it’s equally useful for vegetable fields! Crop planning to rotate crops with different growth habits and timing; neighboring up crops that will have similar cultivation requirements; using the most suitable tractor cultivation equipment; co-ordinating spacing of crops to fit the different equipment (including hands!) to be used for sowing and cultivating. It all adds up to efficient weed control, and maximizing yields from the space.

The lead article is by Lynn Byczynski, and provides a warning about a shortage of hybrid kale seed for the second year running. This has been caused by an increased demand for kale (yay!), a widespread case of black rot disease (boo!) and the fact that the biennial nature of brassica seed production means it takes two years to ramp up seed production.

There are some great new OP kales out there. We have our eyes on Olympic kale, available from High Mowing Seeds.

Olympic kale. Credit High Mowing Seeds

Olympic kale.
Credit High Mowing Seeds