Did black plastic mulch fry my tomato plants?

10 years ago

I have a raised bed which gets afternoon sun from 2pm on. I know it's not optimal that they're in shade until receiving a direct hit by the highest heat of the day, but it's what I have to work with.

In the spring, I covered the bed with black (shiny) plastic to warm up the soil. When I planted, I left it in one section, and cut holes to plant.

I have lost 3 tomato plants. While they normally wilt significantly during the heat of the say, it was very severe this season on several of the plants. The very tips of upper growth (newest leaves) wilted extremely, but then did not perk back up when the heat subsided. Other branches turned yellow and the plants then failed.

When I pulled the most recent casualty today, it occurred to me that maybe the black plastic made the soil too hot.

I'm in central NC, where it has been hot, humid as can be (dew points in the 70's, temps in upper 80's, a few 90's). We have lo had several periods of high rains, but not constant. The casualties were: 2 Black Krim and 1 Mortgage Lifter.

I have never seen top new leaf wilt from heat, without recovery, like this in prior years, and I have grown there for at least 5 years. I don't see spider mites or any other lethal pests.

Any udeas about whether the plastic could have killed them? ( I pulled the rest of the pkastic up.)

TIA!

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Comments (4)

lionheart_gw (USDA Zone 5A, Eastern NY)
10 years ago
I use black plastic as a weed barrier (and mulch) with good success. Of course, I don't live in NC and things there could have different results from the same thing in another climate. Still, it can get pretty warm and humid here during the summer, and the plants are in the strong, full sun.

I just make sure to cut a good-sized hole and make sure the plants aren't touching the plastic when they are first put in the ground. Once the plants grow and get more leaves, they shade the ground around them, thus preventing the plastic from getting too hot. I've never had any plants wilt and die from the plastic. It doesn't seem that the plastic could raise soil temps that much (and that far down) to impact the plants, but that's just a guess.

There are certainly a number of diseases that can cause wilting, and those are often more prevalent in the South (or at least it seems that way). But lacking any disease that would cause wilt, you have to wonder about too much or too little water, or perhaps herbicide damage.

How did the roots look on the plants that you pulled? Did the roots look long and healthy? Did the soil seem to be waterlogged, as in standing water or even just wet muck?

If plants are wilting and turning yellow, you could consider either fusarium or verticillium, especially if they don't perk up and rebound from possible environmental stresses. There is a virus or two that could do that too, but it's impossible to tell based on a description.

A few pictures could help if you have some. One close up, one "full body" shot would help. More if you have them. :-)

Probably someone else from your neck of the woods might have more to offer, as they would be more in tune with your local growing conditions and any diseases that are common. Just trying to bounce some ideas around for now and get things started.

Anyhow, I'm sorry that you are having these issues. We put so much time and effort and planning into gardening that it's disheartening when something happens to the plants.
digdirt2
10 years ago
Can't say if it did or not but it is entirely possible.

In our zones soil temps under black plastic even if it is landscape plastic with all the vent holes can reach 120-150 degrees once the summer heat comes. And it doesn't drop off much.

That is why, when it is used, monitoring the soil temps and covering it with a thick layer of some type of mulch (I use hay) is recommended to control soil temps.

Dave
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This has always struck me as odd, since black plastic doesn't absorb a lot more sunlight than dark colored soil. But I guess it adds a layer of insulation, so that to the extent the soil warms up, it won't cool as fast. In that regard, any plastic would do. Clear would probably work as well as black. Fruit production starts to tail off for tomatoes when nighttime temps don't get much below 75F. Peppers and eggplants should do fine. But that's air temperature. Your plastic on the ground won't affect the air temperature, one way or another. To the extent you have plants growing on the black plastic, they'll shade it, and you won't get any ground heating at all. I mean, the idea is that once the plants are mature, the sunlight should hit THEM, not the plastic. I assume this plastic is perforated, so you can irrigate? You can just check the soil temp, and if it starts getting uncomfortably high, just throw some leaves or newsprint over it.
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lionheart_gw (USDA Zone 5A, Eastern NY)
10 years ago
"In our zones soil temps under black plastic even if it is landscape plastic with all the vent holes can reach 120-150 degrees once the summer heat comes. And it doesn't drop off much. "

Hey Dave, this is good to know, as some of us cold zoners plan on moving south for retirement, and it's best to learn this stuff beforehand.

Good idea about using hay on top of the black plastic. Up here it's not so important, although it could reduce the risk of frying leaves of baby plants that might come into contact with the black plastic.
luke_oh
10 years ago
I'm with Dave, I use the black plastic under my tomatoes and peppers primarily for weed control and to heat the soil early in the spring. After the plants take off when the soil heats up I use straw over the plastic. Some of my tomatoes are not staked and the straw gives them a dry bed to lay on. Luke

Did black plastic mulch fry my tomato plants?

Comments (4)

lionheart_gw (USDA Zone 5A, Eastern NY)

digdirt2

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lionheart_gw (USDA Zone 5A, Eastern NY)

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