Sweet potatoes are grown from “slips,” (pieces of stem with a few leaves), grown from a mother root, not from seeds or replanted roots. We used to buy bare-root slips for transplanting, because we didn’t know how to grow our own, and had heard it wasn’t easy. We have been growing our own for many years now, and prefer the flexibility and reliability it gives us. We did make several mistakes initially, so I can warn you about what not to do. We have a system that we really like, and I have learned a few other methods that I will also tell you about, including one I helped out with the past two years, growing them in a hoophouse.
Disadvantages of buying sweet potato slips
- You need to specify a shipping date months ahead, then hope for good weather and no shipping delays.
- You might have late frosts, spring droughts, or El Niño wet springs, and climate change is only adding to the uncertainty, but slips that arrive in the mail need immediate attention.
- You have to get them all in the ground promptly, and do your best to keep them alive (because they arrive wilting).
- Some amount of drooping (transplant shock) is normal.
Advantages of growing your own sweet potato slips
- You can delay planting if the weather is all wrong (frost, drenching rain, heatwave)
- You can grow them big and plant 3-5 nodes underground, giving more chance of survival if there is a late frost, or an early drought.
- You can plant them in stages rather than all on one day.
- You can grow extra and keep them on hand to replace casualties.
- The sturdy plants get off to a strong start – the transplants don’t wilt – a big advantage where the warm season is on the short side for a 90- to 120-day plant.
- You have more self-reliance and less money going out.
How not to grow sweet potato slips
I made several mistakes learning to grow slips. You don’t have to repeat my mistakes! My first error – following directions written for much further south (in pre-internet days), was to try growing slips in mid-January in central Virginia. Dismal fight against nature! Likewise, I was puzzled by talk of using cold frames. Ours were freezing cold at that time of year.
Next, I set up a soil warming cable in a cinder-block-enclosed bed on the concrete floor of our greenhouse. This is how I discovered most soil warming cables have thermostats that switch off the heat at 70°F (21°C). I just couldn’t get the soil warm enough.
Three Successful Methods of Growing Sweet Potato Slips
- Twin Oaks slips-in-flats method
- Boutard single node cutting method
- Hoophouse or caterpillar tunnel bedding method (Twin Oaks)
Twin Oaks Slips-in-Flats Method
I’ve written about this before, so I’ll just give you a link to open another page.
Starting Sweet Potato Slips discusses pros and cons of growing your own slips, and describes our “slips in flats” method, which I learned from Hiu Newcomb of Potomac Vegetable Farms. Here is our Worksheet we use to stay on track with that task.Sweet Potato Plan 2022
The Boutard single node cutting method
Anthony Boutard and Caroline Boutard Hunt wrote an article about single node sweet potato propagation (which they learned from John Hart of Cornell) in Growing for Market in March 2015. They farm in Oregon and New York respectively.
Both the slips-in-flats method and this one start at the same time, planting roots in damp compost in a warm greenhouse. I corresponded with Anthony Boutard about our respective methods. He pointed out that the slips-in-flats method needs a lot of warm space to grow the slips, at a time when warm space is at a premium. Our method does take us from early March to mid-May.
The single node cutting method uses only 10-20% of the number of mother roots compared to the slips-in-flats method. It uses tiny plants in plug flats, saving on greenhouse space, and only needs 18 days between cutting the slips and planting in the field. The smaller plants can experience less transplanting shock than larger plants. On the other hand, I do not think they have the resilience that multi-node plants have, for example if a late frost strikes.
When these plants grow in the field, their root production is from the single node. This can lead to fewer, but very large tubers, an advantage or a disadvantage, depending on your goals. Better in climates with a short warm season than in hot places, although digging after a shorter growing period would be possible in warm climates.
This method can be used to grow more plants from purchased cut slips, which is very helpful if you are growing a rare heirloom with limited propagation material available. Plant the bought slips in the greenhouse and grow them on until you can make cuttings.
Like the slips-in-flats method, this one buys time if the weather turns bad and you need to back pedal on your planting out date.
To prepare single node cuttings, cut a slip from the mother tuber and cut off about ¼” (6mm) above a leaf node (the swollen point where the leaf emerges). In the leaf axil is a bud which will grow a shoot, and just below the bud is a ring of cells that can grow roots. You can trim back the leaf stem, or leave the leaf on. Make the second, lower, cut just above the next node down. You can make several cuttings from one regular slip.
50-cell plug flats work well to grow the cuttings. Push the lower end of the shoot cutting at an angle into the cell, creating an even V with the leaf stem. If a cutting is too tall to fit your cell plugs, you can cut more off the lower end. The new shoot will then grow upwards easily from the bud in the leaf axil.
Keep the trays warm and moist, and plant out after only 18 days, into well-prepared damp soil, with drip tape in place. Delaying planting for 10 days or so is not a problem.
This post includes a discussion of the Single Node Method, in an article in Growing for Market magazine by Andrew Schwerin from NW Arkansas. In warm climates, only use this method if you want really big tubers!
The Hoophouse Bedding Method
I learned this method from my friend and colleague River Oneida, who grew slips for Southern Exposure Seed Exchange. He planted up 4 beds 45’ (14 m) long with three rows/bed in a single-layer hoophouse and grew an average of 4000 slips/week, for a 6 week sales season (24,000 slips), with a peak and bell-curve ends of the season. Caterpillar tunnels could also work.
Store your saved roots at room temperature. From March 1 onward: start the sweet potatoes sprouting indoors in stages, as heated space permits, at 85°F (29°C), and high humidity. Remove any rotting potatoes. When each potato grows ¼” (6 mm) sprouts, take it out of the heated space and replace with new ones. Put the ¼” (6 mm) sprouted ones at room temperature to slow them down for batching with later ones.
In March: Cover the bed area in the hoophouse with a single layer of clear plastic, and kill any weeds that pop up. Four weeks before shipping starts (on April 1 in central Virginia), prepare the beds in the hoophouse. Dig out a flat-bottomed bed 1” (2.5 cm) deep, and set the sprouted sweet potatoes an inch (2.5 cm) apart in rows. One or two sprouts are enough. If possible, don’t bed unsprouted roots
Spread some compost, not lots. Replace the soil you dug out, on top of the sweet potatoes. Add soil from the aisles, putting 1”-3” (2.5-7.5 cm) of soil on top of the potatoes. Not more. Set out drip tape and irrigate regularly.
After bedding, stab holes in the plastic every 4” (10 cm) for respiration. Check regularly, opening the plastic on warm days once slips are visible. In mid-April or whenever you see slips emerging, remove the plastic in the daytime, but put it back for frosty nights Add more soil later to cover exposed tubers if needed. Regulate temperature if you want a faster or slower rate of production.
Some slips will be ready from the 3rd or 4th week of April onwards. If too many slips are ready at any point, pull and heel them in outdoors. Remember to water.
I first wrote this up for an article for Growing for Market magazine, and have included it in my updated slideshow, at the end of this post. It’s a great method for people growing lots of slips (for instance, for sale). It could also be used for smaller amounts, by occupying a corner of a hoophouse growing other crops at the same time.
More Posts on Sweet Potatoes
I have written a lot on sweet potatoes at all stages from propagating our own slips, growing them all summer, and harvesting. My posts include:
Transplanting Sweet Potatoes (biodegradable plastic; deterring deer)
Sweet potato harvests over the years (2020) summarizes my writing about harvesting, including Harvesting Sweet Potatoes (2016); Sweet Potato Harvest (2015) and again (2015) and earlier (2014) and in 2013, 2012
What Makes Sweet Potatoes Sprout (during storage)
I also have a blog post for Mother Earth News Organic Gardening blog, about growing sweet potatoes. And I have several articles in Growing for Market, which you can access online if you have a Full Subscription.
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