ISO Advice about Growing Sweet Potatoes

pamchesbayOctober 11, 2012

I've been reading Larry's thread about his sweet potato harvest. I'm growing sweet potatoes for the first time, have questions about what to expect, and what I can do to improve my harvest.

Background: Last spring, inspired by stories I read in this forum about growing sweet potatoes, I contacted Gary at Duck Creek Farm. We discussed my soil and growing conditions (ideal for sweet potatoes, they are a big cash crop in this part of Virginia), I ordered 14 varieties. I decided to do trials to find out which varieties we liked, and which grew best here. Before the plants arrived, I made three 30-35' raised beds about 10-12" high, 10" wide, and 4' apart. I laid cardboard between the rows to suppress weeds and keep the vines from rooting.

On June 13, I planted about 100 sweet potato plants (thank you Gary!). I used newspaper and grass clippings as mulch. Within a couple of weeks, the plants were growing strong and sending vines out everywhere. Temps this summer were normal hot. We got some rain. Deer got into the garden once, ate all the sweet potato leaves. I panicked, hit the Internet, and read stories from other people with deer issues. The sweet potatoes recovered very fast.

On Sept 21, I pulled up a couple of plants (Bugs Bunny) and harvested 5 potatoes (1 was 1.25 lbs, 4 were 6-10 oz). The plants had lots of skinny roots so I decided to give them more time. Tonight, I cut the vines on five varieties (Centennial, Cordner's Red, Norton, Carolina Ruby, 8633) and looked for tubers. I found several large potatoes (over 1 lb). Most plants had a couple of small tubers, and/or long skinny roots, or lots of thin white roots and no tubers that I could find.

Since sweet potatoes are a new crop for me, I don't know what to expect. I have questions ...

- What is a good harvest?

- Do most of your plants make big tubers? How big? How many tubers per plant is good?

- Do many of your plants have long skinny roots?

- How much of a factor is the sweet potato variety?

- Should I have cut the vines back during the growing season?

- Would cutting the vines give the plants more energy to use in making tubers?

Tonight, I cut the vines off about half the crop, didn't get any potatoes from at least half the plants that had long skinny roots. Our first frost is usually mid to late November. Would you recommend leaving them in the ground for a few more weeks, or until we have frost warnings?

Sorry for the long post, but I wanted to provide all the info I could think of. ;-)

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Pam, I know nothing about growing sweet potatoes, but I will tell you what I have done. I have had 2 years when I got long skinny roots, and some plants had nothing but a bushy root system under them. Both of those years I had soil pretty high in organic matter, plus I water too much.
I have also noticed that I get poor quality roots when I let the plants get to dry for to long, they start growing again and split.

I have had pretty good luck keeping deer out of my potatoes by using an electric fence. I now just string one wire low enough to step over, I will say no more than 3 feet high. I had one deer jump over the fence this year and get a few leaves. I just tied another wire and ran it zig-zag over the potatoes so when the deer jumped the wire it would land on the next wire. That only happened one night, I expect something on the under side of a deer is very tender to electricity. Try not to make the fence look like something that the deer sees as a problem, you want it to walk up and touch it. I have even thought of pressing a little peanut butter into a screen and hanging it on the fence.

I also have my electric fence so I can lift the wire up to about 6.5 feet into another set of holders so I can walk in and out of the garden anywhere when the wire raised. If the wire is down low you run the risk of falling on it.
If you fall on one when it is on it makes your undies wet.


    Bookmark   October 11, 2012 at 1:49AM
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Okiedawn OK Zone 7

Hi Pam,

First, I'd just like to say that Gary is fantastic and his plants are the best. And, by the way, Bugs Bunny is one of my favorite sweet potatoes. So, even if this year you see mixed results, I strongly encourage you to plant sweet potatoes again in the future. I had to try them in several places in my highly variable garden soil before I found the area where they grew best. With mostly dense, slowly-draining clay, it was a real challenge, but in the sandier and lower fertility soil at the west end of the garden, I finally found a place where they thrived for several years. Sadly, shade from large trees outside the garden now has shaded out that area in terms of it being suitable for sweet potatoes, but I broke ground on new sandy/silty soil this past spring where I intend to plant sweet potatoes next year, and there are no trees nearby that can eventually shade out that area.

There are various reasons why sweet potatoes sometimes don't produce tubers. Look first to your soil for answers. Since sweet potatoes are a root crop, the success of the crop is strongly dependent on the soil and how the crop is managed. Soil and crop management impacts the size and shape of the tubers, their overall quality and the yield from the plants.

It is hard to generalize because some varieties seem more tolerant of clay soil than you'd think, but in general sweet potatoes will produce a crop in almost any soil as long as it is drains well. Sweet potatoes grown in poor sandy loam soils tend to produce low yields of smooth, high quality and sweet potatoes grown in rich, clayey, heavy soils will produce high yields of rough, often misshapen, poor quality roots.

Whether the soil is rich or poor, if it is slow draining and stays too wet for too long, it will produce sweet potatoes that are rough and misshapen and often have rough, somewhat unattractive skin. So, what we glean from all of that is (a) well-drained soil is essential and (b) you'll get the best crop from well-drained soil which is sort of 'medium' in texture and fertility---not too sandy but also not too clayey or too rich.

For me, it is easier to start with sandy soil and amend it with a moderate amount of organic matter to increase its fertility and to help it hold adequate moisture than to start with heavier clay that is harder to amend. In order to get good sweet potatoes from my clay soil I not only add organic matter but also sand. My clay is very dense and slow-draining to begin with though. There are many clay soils that have a good percentage of sand in them and they don't have to be amended that much for sweet potatoes. So, look at your soil and see if you think it is too sandy/low in nutrients or too rich but maybe also too dense and slow-draining. I've always felt like if I could just take a gigantic kitchen-style mixer and mix up the sandy soil from the west end of the garden with the heavy clay from the east end of the garden, I'd have perfect soil, particularly for sweet potatoes.

Usually when people grow sweet potatoes and get small, stringy roots/tubers or only stringy roots and no tubers instead of larger, fleshy ones, the issue is that the soil is too fertile. Sweet potatoes are one of the few crops that do poorly on very fertile soil. You also can get a low harvest if the vines root into the soil (or mulch) as they grow, which diverts attention to growing more, more, more vines and not so many roots.

I am not sure where your soil is on the pH scale, but sweet potatoes grow best in slightly acidic soils with a pH between 5.5 and 6.5. However, I grow them in soil that varies from 7.0 to 8.2 in pH, although that isn't ideal, and I'm constantly working to bring down my soil pH.

You didn't mention if you used any sort of fertilizer with the plants, but most sweet potatoes will need some fertilizer although not too much, although that's more true if you have a sandy soil or sandy loam than if you have clay soil. Clay soil usually has adequate fertility because it is high in minerals.

It is hard for me to define what a good harvest is because it varies wildly depending on the soil, water and even the variety. However, when you dig your sweet potatoes you should have several large sweet potatoes and also usually a handful of smaller ones underneath each plant.

In a good year with adequate soil moisture, sweet potatoes in our garden make a big crop. Some varieties produce more than others. How big they get is going to vary depending on the variety, when they were planted, how hot the summer was (if it is too hot in combination with low rainfall, the crop is smaller), etc. Often in very hot and dry summers the plants produce poorly or they are slow to form tubers and you have to give them more time than usual in the fall to size up their crop. While they are very heat-tolerant, they really aren't very drought tolerant. You find yourself walking a fine line between watering them enough to get good production while simultaneously not watering so much that your yield is poor. Knowing how much moisture they need in your specific soil and weather conditions is one of those things you really only learn from growing the sweet potatoes.

Does variety matter? Well, of course it does. That's why commercial growers only grow varieties that produce high yields. They have to get a certain amount of lbs. harvested per acre in order to make money. How much does variety matter? In good conditions, I don't know that it matters a lot. Several years ago I trialed a lot of sweet potato varieties from Duck Creek Farms and almost every single variety produced very well. They all were in the same area, in the same soil and received the same moisture. I didn't look at a single variety and say "that doesn't produce well, and I won't grow it again". I was pleased with all of them. For me, the place/time to make decisions about what variety to grow again comes down to which ones have the flavor and texture we like the most.

I don't know that cutting back the vines would help improve the yields, but my instinctive answer is that no, it would not. Remember that plant foliage serves as the photosynthesis factory that provides the plants with the energy they need to grow and produce. Any time you cut the foliage, you're reducing the amount of foliage available to conduct photosynthesis. I don't cut the foliage back at all. I am very careful about keeping the vines from rooting into the moist ground or mulch as they grow though. I generally use a rake (never my hands because we have venomous snakes) to gently move the foliage around every few days so it doesn't sit in the same spot on the ground all the time and start rooting.

In the year I grew all those Duck Creek Farms varieties, the foliage ran everywhere, including climbing the 8' tall fence and growing through the fence and into the flower beds on the other side of the fence on the west side of the plants. On the east side, the vines grew across the pathway and through the tomato beds and wanted to climb the cags, which I didn't allow them to do. They all produced great yields, so if too much foliage is a problem, then I wouldn't have gotten high yields. Centennial, by the way, was one of the best producers that year. I should qualify that statement by saying that if they are producing heavy vines on soil that is low to moderate in fertility, that seems normal. However, if they are growing excessive foliage in excessively fertile soil that is "too fertile" or had too much fertilizer added, that is a problem because they will tend to stay in a state of vegetative production and won't produce tubers as well. Once again, you have to grow sweet potatoes for a few years in order to learn what level of soil fertility produces the best yields. There is no easy answer to the question of how much fertility is too much, but you'll know it when you see it because you'll have excess vines and low yields of roots.

Often, we get impatient and want our sweet potatoes to be ready to dig when we are ready to dig them. We have to be patient and dig them on their schedule, not ours. To ascertain if the plants are ready to be dug, I dig gently in the soil around the roots---I start about 8-12" away from a plant and dig with a hand trowel. I dig in closer to the plant as I look for roots. When I find them, I look at them to see if they are sized up large enough yet. If they are, I go ahead and dig. Otherwise, I replace the soil around the plant, pat it down firmly and water to settle it back down around the roots. I usually won't dig them unless there are at least a couple of very large tubers per plant.

I have harvested in October some years, but in my specific growing conditions, I get the best yields if I wait until very early November and harvest a couple of weeks before the date of my average first freeze. The difference in harvest from an early October versus early November harvest is significant most years. I know this because sometimes I dig some in October and leave others of the same variety another month---as an experiment to see if it matters. One factor that might be important is the amount of heat/drought in the summer months. If rainfall was very scarce in July and August and we had excessive heat, I get lower yields so leaving them in the ground another month in autumn's cooler, milder and usually wetter weather gives them more time to produce more roots. It all hinges on the weather though, because if autumn brings very heavy rains very early in the season, I'd just as soon dig the potatoes I have because the very heavy rainfall for weeks on end can cause splitting and cracking.

By the way, I do not cut the vines until the day I harvest. When I am digging down into the soil to check the status of the plants and to see if the potatoes are a nice, usable size, I just move the vines out of the way and take great care not to break them off. Once the vines are gone, if you leave the potatoes in the ground, the plants' energy is going to go into trying to grow more foliage, not more roots.

Hope this helps.


    Bookmark   October 11, 2012 at 10:07AM
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Pam I will try to show you a picture of sweet potatoes that have had to good of care. This is the second year for this area in the south garden, and because of it being new I amended it a lot. I also have a water line running to this garden. Because of family health issues I left the irrigation tubes turned on and turned the water off at the outside faucet, thinking that each time my wife watered her flowers my sweet potatoes would also get a drink. I was gone a lot helping sick family members. As it turned out my wife watered her flowers more than I expected, which meant my potatoes also got more water than I had expected.

The picture will show long skinny roots and low yield.


    Bookmark   October 11, 2012 at 11:09AM
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We've grown sweet potatoes casually for several years. I say casually because we plant them, water when dry and wait til a light frost kills the vines to dig them. In the past we've grown sweets that weighed 5-6 lbs and single hills that produced 8-10 lbs. We don't like potatoes that big because there's just the two of us, but in a year when the deer left the vines alone we got that. Also got a harvest of almost 200 lbs from a 50 ft row. Larry posted the pic of the harvest that year. I think it was 2010. Our soil is medium clay, gardened for almost 30 years, but we never fertilize sweets. We do rotate them into the bed where the corn was in alternate years and always spread the chicken litter--with woodshavings--onto the corn beds every November. This year was so very dry that even with irrigation the vines didn't grow nearly as large as they usually do. The deer ate about half the row once, then we spread blood meal and hair to discourage them. We have not dug any yet since it hasn't frosted yet. I'll be back with a harvest report when we do.

    Bookmark   October 11, 2012 at 4:05PM
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Dawn, Larry, and Dorothy: Ya'll gave me an excellent education today!

Dawn - My soil is close to perfect for sweet potatoes. Soil is sandy, pH: 5.6, organic matter 6.1. (Soil is described as "weathered" in state publications).
Farmerdilla grew up in this area - he said "In my youth, sweet potatoes were commonly relegated to newly cleared land (Newground)."

Gary is great - he's patient and gave me helpful advice. He said "You are in the heart of sweet potato production country and all should do well in your area ... a good sandy loam suits them well."

I think you described my situation when you wrote: "Sweet potatoes grown in poor sandy loam soils tend to produce low yields of smooth, high quality ..."

I didn't add fertilizer. I watered early on, but only when soil was very dry. I read that you shouldn't water within two weeks of harvesting. Also read that sweets put on a lot of growth 3-4 weeks before the first frost. These are things you learn from experience.
Varieties: I used info you posted from your trials and trials from Duck Creek and Kerr Center to help me decide what to order from Gary. If I hadn't read your posts, I would never have learned about Bugs bunny! So far, Bugs Bunny is tied with Centennial and I'm just getting started.

RE: cutting the vines. I saw a photo of a man who trimmed sweet potato vines by riding around the growing area on a lawn tractor. I'll continue to experiment - they are easy to grow here, and they are such beautiful plants! We love sweet potatoes and eat so many, it's a wonder that our skin isn't orange. We have 3 dogs - they love sweet potatoes too!
Larry, you know that old saying, "A picture is worth a thousand words?" The photo you posted gave me a reality check. I'll post a couple of photos at the end of this message - you'll see why.

Dorothy, thanks for the common sense advice. If I got 200 lbs from 50' of row, I'd be over the moon!

I know which varieties are "early, mid-season, and late" but realized that this doesn't mean I have to harvest them according to a predetermined schedule. I don't want to grow 5-7# sweets either! The biggest in yesterday's harvest was close to two lbs - that's big enough. I think some of the larger sweets started life as two potatoes that grew together.

I was going to ask about crop rotation - you answered my question.

After deer got into the garden and ate the leaves, we gave our dogs summer haircuts - three 60+ pound dogs have a lot of fur that is now around the sweet potatoes.

Now for the photos.

1. Digging under first plant (Centennial):

2. Biggest potato from yesterday's harvest:

3. First day harvest - checked 15-20% of plants. I'll leave most of the plants in the ground until we get closer to a frost:

Thank you!!

    Bookmark   October 11, 2012 at 7:26PM
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jdlaugh(Zone 6)

I harvested the last four sweet potato plants from my garden yesterday, and got this batch of potatoes. They were grown from one potato I bought at the super market, so no idea of the variety. Some were foot-ball size! Not an overwhelming harvest, but not terrible. The vines did cover a big area of the garden, to the point of being annoying.

In previous years I used a compact variety from Duck Creek. I'm going that route again next year. They take up less space and give me more consistent, smaller potatoes that are a nice size for single-serve baking.

Those are Seminole pumpkins on the left.

    Bookmark   October 14, 2012 at 1:16PM
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