Breeding Sweet Potatoes (turning them into a seed grown annual)

[reed]

It was about two weeks ago when I discovered those first two volunteers, now I'm up to five that I've transplanted into pots and yesterday found three more.

Yesterday I planted thirty seeds, way less than I've done in the past but much more in line with what I can really handle. Planting two or three hundred seeds direct in the ground has really been a waste. It told me that it can now easily be done with my seeds, and that the germination rate has vastly improved over the years, but I wasn't able to take good care of or properly evaluate them all. I'm sure many that might have been excellent plants were simply lost.

Fifteen of the seeds I planted were from my ornamental line, about half from the one I'm calling Ms. Bloom and were self-pollinated from flowers that opened after the plant was brought in last fall and pollinated by me shaking the flowers. Self-pollination won't happen with sweet potatoes without some help because the flowers generally point up and the anthers are down in the bottom, below the stigma. There is something tasty to bees in the bottom of the flower, so the pollen gets moved to the stigma as they squeeze past on their way in and out. The rest of those fifteen seeds were from the Ms. Bloom and the one I call Tries to Climb but they were developing capsules when I brought them in, so I don't know where the pollen came from. The original Tries to Climb did not tolerate indoor conditions as well as most and is just now recovering nicely, I may have to change the name because it IS climbing, just like a pole bean. The other fifteen seeds were from the 2023 semi-isolated culinary elite line.

I planted them in trays this year instead of direct seeding, as I transplant and grow them in pots anyway, and I already know that my seeds can easily be direct seeded and produce a crop in 100 days or less. That 100 DTM from seed has been a big focus of selection over the years. That's a huge difference between sweet potatoes and potatoes. With sweet potatoes I get more seeds and something to eat from seed.

The culinary roots I put in wet sand to clone are doing well and I'll be transplanting the slips into their pots over the next few days.

All of this is a bit later than I usually do it. In my climate I'm sure I could wait as long as the first of July to set out clones of my short season sweet potatoes, or for that matter probably any sweet potato. I don't think the term "mature" means the same thing with sweet potatoes as with most other crops. They "mature" to the point of producing seeds in around forty days or even less, many start blooming even sooner than that. "Mature" as far as storage roots is just whenever they are big enough to be worth eating, they don't get "ripe". Eating size happens in probably not much more than fifty days, it's just that the longer they are in the ground the bigger they get.

I started them later this year and I'm going to harvest them sooner. I've always left them as long as possible in order to harvest more seed but waiting almost till frost precludes having warm weather for the roots to cure and increase the sugars. Since I'm also now sure that they vines will finish maturing seeds, even if the roots have been removed, there little to be lost by harvesting in late September while the weather is still consistently warm.

I'll see how things go this year but I'm thinking of offering two to three thousand seeds from the culinarily line for sale, and basically retiring from the project other than for my own use. I'm going to continue with my ornamental line and eventually hope to offer them as clones or sell them and my rights to them, also in their entirety. Three thousand seeds in the hands of someone with the facilities and manpower to do so can easily produce a large number of new, genetically unique individual varieties. If just two hundred superior plants were selected for continued breeding the possibilities are vast. 

No matter which line is moved to a new owner they all contain the genetics to restore seed production to any sweet potato that can be forced into bloom. The culinary line just comes ready to eat, so to speak, where the ornamental line might take a few, or several years of selection like I did.

I would prefer that they stay in the public domain but that is not a requirement. If in the event that money talks, I'm prepared to listen, and I have all the documentation and breeding pedigree to go with them. 

[reed]

Prepping a large area for planting corn yesterday, I found five more volunteer sweet potatoes. This is a spot where sweet potatoes have not been for four years. Laying there for years before sprouting sort of confirms my theory that what is believed to be low germination rate of sweet potatoes isn't that something is wrong with the seed. It's just that without artificial intervention like nicking the seed coat or soaking in acid they just sprout when they get around to it.

In my seeds I planted I only have around 25% germination. I think that's because it's been too cloudy and wet. In years past I've noticed that when planted in a bed or trays a few come up right away and those that don't seem to like drying out. Whenever they dry out, as soon as it gets wet again more sprout, this can go on in cycles for weeks. I've had them set around dried out all summer only to sprout in August or September. I've always selected for those that sprout faster and more predictably and not kept most of those that sprouted later. This year it's been constantly wet and cloudy, so they have never dried out, nor had a lot of hot sunshine. Still between the volunteers and those I planted I have exceeded the number I actually have room for, so I'll watch them a bit longer before selecting the ones I want to keep. 

[Richard Watson]

Last summer I put the whole seed tray in the freezer for three weeks and had a couple more seeds pop up once back outside again, doing the same thing as drying out I suppose. 

[reed]

Last summer I put the whole seed tray in the freezer for three weeks and had a couple more seeds pop up once back outside again, doing the same thing as drying out I suppose. 

Could be I reckon. Being a tropical species I'm a bit surprised they can lay in the ground for years and survive all the freeze/thaw and wet/dry cycles that happen in that time. I bet in a drier climate they might be able to lay dormant in the ground for a very long time.

[reed]

Sweet potatoes are doing really well this year. It's been hot and very dry with only about 1/4 inch or so of rain in the past five weeks, but I've been regularly watering the sweet taters. I think they like my keeping the water in a big tub for a few days to reduce temperature shock of pouring ground temp water on what is probably 100 plus degree soil.

Even with regular water those with dark colored leaves wilt a bit in the hottest part of the day but I don't think it really hurts them. It makes me wonder, and I have some reason already to believe that sweet potatoes don't really need full sun all day, at least not in a hot climate. I think they might do just as well or even better with mostly just morning sun. Morning too, is when they bloom and when the bees are most active.

My more uniform pots and soil mix seems to be working well too. Now if there are differences in growth or production, I'll be more sure it's genetic.

I don't have a good scale, so I took some that I harvested last October to work and used the postage scale to weight them. They averaged 8 ounces, which I think is a very nice size. Before, in a 3-gallon pot I've seen a range of two or three to six or seven that size per pot.

This year in 7.5 gallon pots and with consistent soil I should be able to get a good idea of production. If anything, I hope I end up with more that size rather than larger ones. 

**Note on production in small pots. It is critical that the bottoms of the pots with drain holes are buried a bit in the ground and that the pots are never moved once feeder roots have exited into the ground. So, they are not actually growing in just in the pot. The "clump root" trait is also critical, so you don't end up with empty pots with taters in the ground under them. All of my clones have that trait, I hope those started from seed this year do to.

[Richard Watson]

Thats a good thought about the water temp on hot days, I going to think about how I could set up a system, an iron bath might be an idea, before fulling with water I could spread Butynol over it surface so as to help heat the water.

[reed]

I have a big Rubbermaid stock watering tank sitting in the garden. I fill it from the municipal water and let it sit in the hot sun for a day or two. Water is about 55 F out of the tap but just one day in the sun warms it much closer to the temp of the soil in the pots. Also gives some time for a lot of the chlorine to evaporate. I don't really know for sure if temperature shock is an issue just seems like it might be. Using my watering can also lets me be sure each plant gets the exact same amount.

[reed]

Sweet potatoes flowering is really picking up right now. I'm starting to pay attention to differences in size and color of the flowers.

Another thing I've noted is, and it's not cut in stone, that seed started planted plants seem to start blooming sooner than cloned plants. I wonder if that is somehow related or maybe over time, part of the process of them forgetting how to bloom and make seed. My clones are in full bloom now but some of the seed grow plants have been doing it for a month. Haven't seen quite as many bumblebees as usual which is a bit worrisome but lots of little bees are visiting and capsules are starting to form.

Here are some photos showing variation in flowers. The dark one is the darkest I've even seen.


Darker color flower on a 2024 volunteer


Mid range color on the plant "Miss Bloom" sprouted in 2022


Lighter color on a 2024 seed grown plant

[Richard Watson]

That first photo is quite a colourful flower

[reed]

I don't think the color and size of flowers really matters much but it's fun to see.

[reed]

I've just now started collecting sweet potato seeds and finding some capsules that have already shattered and dropped seeds. It's been an odd year in several ways, and I hadn't even kept the paths clear around the pots. It's all cleaned up now and I've started the process of removing lots of old leaves, which makes finding the seeds a lot easier. The plants themselves being grown in pots aren't affected by the neglect and tall weeds in the paths and they are looking great. Since I was careful to make sure soil mix and conditions were consistent this year, I should be able to see any differences in production between the various plants.

I think there are nine volunteer plants that came up early enough that I quickly prepared pots for them and added them to the patch. They all look great too with two especially interesting ones with dense bushy growth and lots of seeds forming. Volunteers are all over the place this year with new ones coming up even now. A couple that ended up being left where they sprouted are just as big and vigorous as those I planted.

After making the slips this spring I just pitched the old roots on top of an unused tub of soil where the just kept making more slips. We plated some of them in two spots in the garden. One in quite a bit of shade and one at the other end in full hot sun. They are all from the same two clones and those in the shade, even without any watering all year look fantastic. Those in full sun and also without watering look ok but are about 1/2 the size of the shade ones. The primary patch is in full sun but has been watered regularly. I've thought before that sweet potatoes might be happier in some climates with a bit of shade, and this seem to support that. Makes it easier to take care of because you don't have to be so attentive to watering.

I think that selecting for the clump root trait and bushy habit along with growing in pots is the way to go with sweet potatoes because it makes harvest so easy. Although they are every easy to trellis so a larger vine, as long as it has clump root does fine too. A tree branch with some side branches stuck in the ground works fine. I'm also more and more convinced that the pots don't have to be really large. I've had good harvests in 3-gallon pots and those I'm using this year are 7.5 gallons.

I have roots from last year that are still good to eat so I know that they easily store for a full year without much effort. I took some to work and used the postage scale, and they averaged about 8 ounces. That's the range I'm hoping for because each one makes for a nice serving. I'll see if the improved conditions this year makes bigger roots or more roots, I hope it makes more. I'll find out in another month or so.

I had resolved to take lots of pictures and videos this year, and I have taken some but haven't processed and sorted them yet. I'll definitely be taking lots of the harvest and the whole patch is more much photogenic now that the paths are cleaned up. 

 
   

[Ohio Alex]

This year I trialed a bunch of random varieties I've found at grocery stores. One variety, whose identity I'm not sure of [either standard beauregard or Jersey] seems to have self pollenated and is developing a seed capsule. I'm hopeful I can collect it before it shatters.

[reed]

seems to have self pollenated and is developing a seed capsule. I'm hopeful I can collect it before it shatters.

Some are more prone to shattering than others, but you don't have the wait until danger of that. Once it gets to full size and starts to yellow a bit you can clip the stem and take it inside and put the cut stem in a little water. I do that often in late season when frost is likely. Probably a third of my total seeds each year mature inside like that with no apparent ill effect.

[reed]

Something that I have never understood is how a species such as sweet potatoes or garlic loses its ability to make seeds because people started cloning it instead. I've observed something over the last few years that makes me wonder about it even more.

My clones that are three or four years old still flower and make plenty of seeds, but they aren't perfectly consistent. Two plants slipped from the same root may not produce seeds at the same rate or start doing it at the same time.

I plant in a mixed polyculture so it may be that one is next to a highly compatible neighbor and another one isn't but that doesn't explain the other thing I see. That is often times a new seed grown plant makes a huge number of seeds its first year and just lots of seeds its first year as a clone.  The first-year seed grown plants don't sacrifice anything in favor of seeds, they grow just as big and make just as many sweet potatoes as the clones.

The decreased seed from the clones isn't all that dramatic but it makes me wonder how many years or decades it would take until they do stop making seeds. Obviously, it isn't a universal thing because some the heirlooms I started with had been cloned for a long time and still managed to make some seeds, just not as many as the younger clones.   

I doubt I'll ever know the whole story on why these plants do what they do but fortunately I don't think it really matters all that much. It's just an interesting phenomenon that I've observed. 

[reed]

I haven't done much as far as posting photos this year, so I made this little video to catch up.