Sweet potatoes and leaf mulch

slowpoke_gardenerSeptember 5, 2012

I have worked harder prepping my garden this year than ever before. I tilled in more compost and manure, use more mulch, and harvested less. My early harvest was pretty good but went down quickly when the hot dry weather hit.

I mulched my sweet potatoes heavily soon after planting, which may have been a mistake. I felt that the ground had warmed plenty because of the warm early spring.

I dug under one plant this evening to try to find some potatoes because I was fearing that vines was mostly all I had because I could find no bulges in the ground or potatoes sticking out of the ground. I think it was a Centennial vine I dug under and only found 4 small potatoes. These plants were purchased slips and have been in the ground about 4 months.

I guess my questions are #1 do you members mulch your sweet potatoes, and how soon and how much? # how much can I blame on the rotten summer weather, although I did get better rain in July and August? #3 Is there anything I can do this late in the season other than just leaving then in the ground as long as possible?


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second question, why are my pictures showing up so large on my screen? I have been down sizing them on Photobucket but they still print large on my screen. I do have to blow the print up to see it, could that be why they are large? Are the pictures only showing large on my screen?


    Bookmark   September 5, 2012 at 2:47AM
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I believe you did well by mulching. But some years, especially these hot, dry years, sweet potatoes don't produce as much as normal. I've even seen years when one variety doesn't do well at all, and another does. I'd just wait, and try to maintain moisture in the soil.

Larry, wish I could help you with the pictures. But I don't know enough.

Tahlequah, OK

    Bookmark   September 5, 2012 at 10:19AM
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Okiedawn OK Zone 7


#1 I mulch early and heavily, putting 2-4" down as soon as I plant, and adding more as that decomposes and breaks down. #2 I believe it is the a combination of heat and drought. Sweet potatoes seem more bothered by a lack of moisture than by heat, at least up to a certain point. #3 Ignore them and don't give them any water or fertilizer and they should put more energy into forming tubers.

As with so many other gardening issues, this is a hard problem to figure out. I think your issues are related more to the heat than to anything else though. Cooler temperatures should help your plants form more tubers, and I've often wondered if decreasing daylength signals the end of the season is coming and maybe makes them form more tubers.

Sweet potatoes like poor soil but will grow in almost any soil. However, their production will vary with the kind of soil and how the crop is managed after it is planted. The crop, too, is at the mercy of drought and heat.

Too much fertility gives you too much foliage and too few potatoes, so be sure you don't enrich the soil too much and that you don't over-fertilize at planting time.

The late Dr. Sam Cotner, former head of Horticulture at Texas A&M University and author of "The Texas Vegetable Book" (now out of print), which is my gardening bible I refer to often (I should have it memorized by now) gives a top-notch description of how soil affects sweet potato output, and I'll paraphrase it here. Maybe something he says will provide some insight into what is going on with your sweet potatoes. He said these things about the relationship between soil and the sweet potato crop:

--Sweet potatoes can be grown on a variety of soils, as long as the soils are well-drained
--Sweet potatoes perform best in sandy loam
--Sweet potatoes grown in poor, sandy soils tend to produce low yields of smooth, high-quality roots
--Sweet potatoes grown in rich, heavy soils produce high yields of rough, poor-quality roots

Drainage plays a role too, and this is where I get into trouble because much of my soil doesn't drain well, so I am limited in where I can put sweet potatoes. If your soil has poor drainage, whether the soil is rich or poor, you'll tend to get sweet potatoes that are cracked or misshapen or have rough skin..or some combination of all of those.

Another thing I can think of that is not weather-related would be soil pH. Sweet potatoes do not perform well on soils that are very acidic or very alkaline. They do best on soils with a pH between 5.5 and 6.5. My unamended soil tests at 8.2 to 8.3 so in order to grow sweet potatoes I add peat moss to it instead of compost because peat moss is essentially "dead" and doesn't add a lot of fertility. It just makes the soil drain better and also lowers the pH because it is acidic. I save my good compost and manure for plants that like high-fertility soil. Why? Let me quote Dr. Cotner here: "Unlike most vegetable crops, sweet potatoes do not do better if high levels of organic matter are added to the soil." I know that this is a frustrating statement for a gardener to read because, in general, for most of the things we grow, adding high levels of organic matter gives us a better crop.

There is one more thing. When sweet potato beds are unmulched, the plants commonly root into the soil. (In good moist weather this is especially true.) This is bad. By rooting into the soil they are using energy to form more roots and more topgrowth. You want for them to put their energy into forming tubers. So, every week or two, take a garden rake and move around the sweet potato foliage, disturbing it enough that it cannot root into the ground.

I don't know if any of this helps. My gut feeling is that if you'll leave them alone from this point on and not water or feed them, they'll put more energy into forming tubers. I really think this year's heat is the biggest culprit, and the worst of the heat is about to go away unless the big cold front coming our way stalls out before it reaches us, and it is not supposed to do that.

I have the best luck with sweet potatoes when I plant them and then totally ignore them until it is time to dig them. I always do mulch early and, in fact, very soon after planting in order to keep the weeds from sprouting around the freshly-planted slips.

On my screen, your photo is pretty big, but you know that I don't take photos and post them so I can't tell you why it is showing up that big. I am sure someone who posts a lot of photos will be able to tell you though.


    Bookmark   September 5, 2012 at 10:27AM
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Dawn and George, thanks. Dawn I had not thought about the organic matter, but it seems that the per plant produce has dropped the past two years while my amendments have gone up. Also the weather the past two years has not been great.

I will try to post another picture. I will downsize to photobuckets smallest setting and see what happens.


If they does not work I may have to do something to the camera

Well, its still to large.

    Bookmark   September 5, 2012 at 12:00PM
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Hi Larry,

While I can offer absolutely no advice on your sweet potato issue, I can tell you that your first picture was actually a very good size on my puter. Your second pic came out too small for me to know what I was looking at...that is, if I hadn't seen the first;-)

Hope this helps

    Bookmark   September 5, 2012 at 4:20PM
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Ronni, thanks a bunch, I know very little about gardening, but I am dumber than a rock on using a computer. I must have something set wrong on my computer because they show up the same sixe on my computer. I use to down size to 96% and the picture would fit on my laptop screen. I have to magnify about everything to see it.

Thanks again, Larry

    Bookmark   September 5, 2012 at 4:52PM
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Both pictures look pretty good on my computer. A little big, but not CRAZY big. I sure could go for some sweet potato pie after all of this sweet potato talk.


    Bookmark   September 5, 2012 at 6:31PM
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Larry, We never look at our Sweet Potatoes until it's time to dig them, so I don't know what the problem with yours is. To me they look fine. And they have 5-6 more weeks to grow, so should be even better at digging.

Your first pic was 4&1/2 by 5 and looked real good. The second at 1 by 1&1/2 was too small to show up well.

    Bookmark   September 5, 2012 at 7:22PM
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Dorothy, thanks, I posted on the test forum and every thing worked as it should. The pictures on my screen above are much to large.

I am not the most patient person around and I have used more organic matter this year than ever before, partly because of my nematode problem. Other than insect damage the potatoes look as good or better than normal. It is unreal the amount of critters I have eating my garden.


    Bookmark   September 5, 2012 at 9:47PM
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