Sunday, August 24, 2014

From the Inbox: Problems with Sweet Potatoes - Help!

Anyone have any advice for Lyda?

She writes:

"I started growing sweet potatoes a few years ago. My first experiment was a rather successful one. I purchased an oriental sweet potato from an Organic Farmers Market and just put it in the ground and watered it. Once it started to sprout I clipped off some cuttings ( I didn't understand what slips were at that point),  took off most of the leaves and  dug those cuttings into the soil in a corner of my yard covered in mulch. 5-6 months later I had a 5 gallong bucket full of Sweet potatoes. I thought I was in heaven and couldn't believe everyone wasn't growing sweet potatoes. Since that time I have been plagued with bad crops. After that first crop I dug some home compost into that corner of the yard and started again. The vines grew like crazy but eventually became infested with white flies. When it came time to harvest there really wasn't much in the ground. Just tiny little  or long skinny ones on the root. Last Spring I used some of those same small sweet potatoes to start slips from a jar. The slips grew great. The first ones were put into a grow bag in March, which in South Florida is pretty warm as you know. I also have some planted in raised beds and they are now completely infested with white flies. It was from that first bag that I harvested today. 

I have a few theories/ideas:

1. I have been told to start with Certified Seed Potatoes to get a good crop and mine were not. That same person said that you may get a good first crop but then successive generations from those potatoes will be small. This describes what happened to me. The first crop was good but then when I continued to use the potatoes grown from that original the crops were smaller and less bountiful. Maybe I should have ordered slips or purchased a new potato from the market to grow slips?

2. Starting from small potatoes....would that have anything to do with it. I just figured it didn't matter as long as I had a slip or cutting to start with.

3. I thought my 2nd crop was so small because I had mixed in compost that had Chicken Manure in it and the nitrogen caused me to get alot of vine growth but little potato growth. This would not be true of this year's crop because I got rid of the chickens 18 months ago and there is no longer any chicken manure in the compost that was added to the grow bags.

4. Does pruning the vines cause less potato growth. I have been trimming them back when they grow into walk ways etc. and adding the cuttings to the compost bin. I did not do that for the 2nd crop though and had the same result.

Any thoughts or knowledge would be appreciated. Feeling frustrated after waiting 6 months and thinking there were potatoes growing in there."

On #1, I've never worried about "certified seed" on sweet potatoes. I believe that's usually a white potato issue. My guess is that soil nutrition has decreased.

#2: It's never mattered for me. They're regularly started from slips without issue.

#3: Nitrogen could perhaps lower  root production, but I'm not sure why that would be a continuing issue this far in. Hard to know without an idea of how much nitrogen is still available. You could always plant a crop of corn to soak up some of what's left, if there is too much left.

#4: Yes. Cutting back growth lowers the photosynthesizing power of the plant. Less area for light gathering; less stored in the roots.

Whiteflies have never been an issue for me in N. FL, but they're definitely an issue down south.

Anyone else have ideas for Lyda?


At August 24, 2014 at 9:04 PM , Anonymous db said...

Living in Zone10A, I grow them all year is MY take on sweet potatoes:

1. The way I see it, you start with a tuber from a plant...then grow a sprout from that tuber, a sprout we call a slip. That slip is just the top half of a plant, the tuber being from the previous top. Since there are no seeds, just tops and tubers, isn't you slip the same plant as the one that produced the tuber? Isn't it asexual reproduction, yielding a "clone" of the original plant?? So if you start wit ha good producing plant (the kind EVERY farmer wants to grow in order to maximize yield, right?), you'll always have the same basic plant....Am I looking at this crossways??

2. Small potatoes just take longer to grow out...and have less stored energy for the plant if supports. All the tubers do is store energy for the plants. (and that may be the on...)

3. Nitrogen DOES increase leaf growth, but you should still get decent tubers...I don't believe this is your issue.

4. Pruning the leaves will slow the tuber growth. Tubers are the end product of a plant that is storing energy. With plenty of food, sun, and water, you should get lots of tubers. However, I prune mine back all the time...some leaves for my rabbits, and some leaves for my family to eat. They make a fantastic spinach substitute....

I have to agree with David, your soil may be taxed. But it may also be another issue. Do you water daily? Mine get water 3 times a day from a timed sprinkler. 15 minutes at 8 am, 5 minutes at 2pm, and 5 minutes at 6 pm. This seems to keep all of my plants from heat stress. Not saying it is the right thing to do, but I will say that it works well for me.

I also supplement my soil with rabbit manure regularly. Between the water and the soil amendments, I get tasty `taters all the time. I leave mine in the ground until I want to eat them, then dig up what I need. This means longer growing times for the tubers to develop. This also keeps a year-round supply, with no extra storage space needed :)

SO, soil amendments, plenty of water, and, as Ace Ventura said, "Just wait longer!"

Hope that helps...


At August 24, 2014 at 10:00 PM , Anonymous Andi said...

WOW. You really water three times a day?

At August 25, 2014 at 9:04 PM , Blogger Unknown said...

Are you growing in full sun? I've grown a lot of sweet potatoes all around the Central Florida area. The only time I've ever seen white flies in the leaves is when we are growing in too much shade. In full sun they never seem to be a problem. I don't have documented studies or anything like that to back up this theory, so It may just be a coincidence, but it's an observation I've made over the years.

At August 27, 2014 at 12:55 PM , Blogger Cj said...

As it was explained to me, a sweet potato does the best, in regard to fruit/tuber production, when it is stressed. If the weather is nice and you give them lots of water all summer long, you'll end up with very impressive vines and little fruit. However, just like with a butterfly, if you let the vines grow and get big, then cut back on the water, giving them just enough to not die, they will start to produce the tubers we all love.

The logic behind this is that the plant can propagate with either a vine or a tuber... if the vine is doing great, it will keep growing the vine. However, when the vine experiences stress and focuses on producing tubers, it stores up energy in that tuber for a later time when the weather is better. If the plant dies, the tuber is still there and grows a new vine when the preferred weather returns.

At August 29, 2014 at 8:59 AM , Anonymous Lyda said...

White flies are a huge problem here in South FLorida regardless of shade or sun. I can control them using either neem spray or organic insecticidal soap on smaller plants like peppers but for plants that grow leaves like sweet potatoes it becomes almost impossible once they really start growing vines. Half way through the summer I just gave up and gave it the "let's see what happens" approach. I don't want to grow anything that requires that much work. I don't think the flies caused the no potatoes issue. It seems there should have been something forming down there all the months before the flies really got our of control?

At August 29, 2014 at 9:02 AM , Anonymous Lyda said...

Good information about tubers. Makes sense. I didn't go out of my way to water the sweet potatoes but we were getting rain almost daily in South Florida this year. I will have to check my records for last year's crop.

At August 29, 2014 at 9:07 AM , Anonymous Lyda said...

I agree about the Nitrogen. I don't think that is the issue either. It's been too long since I applied the compost that contained chicken manure and the problem has occurred in areas that did not have this amendment. I do add worm compost and quality home compost to my bags and beds so I really don't think the soil is deficient. The same soil grows many other things. I have had the same result when I did not trim the leaves at all and there were still plenty of vines growing everywhere. I appreciate your comments about "clones" but still can't help but wonder about the stock I used. Several generations from the original store bought potato. Just to prove to myself one way or another I will start next year with new slips from a different source. It's the only thing that makes sense to me since I am getting the same different soils, different locations etc. Thanks for the input.


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