What's Too Hot?

rustico_2009April 19, 2012

Now that I am tinkering with plastic mulch, I am wondering what is too hot? Soil under black plastic was in the high 80's today at peak.This was about 3 to 4 inches deep. That was about 10 degrees over air temp high. This would be for Watermelon, cucumbers, squash tomatoes, peppers and eggplant.

Anyway,hat tip to Jay for the tutorial a few threads back, thanks. It was easier than I thought.... Even without help.

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jrslick (North Central Kansas, Zone 5B)

Good question, I don't have an answer. I know that even under plastic, the soil temp can change with the weather.

I will ask around and see what I can find out.

Here is my latest laying plastic work.

Now I have one more tunnel to cover and lay plastic, 300 feet for sweet potatoes, 300 feet for Okra and then another 300 feet for peppers. I am debating about put it down for winter squash too. That would be another 1200 feet. Glad I bought that 5,000 foot roll!


    Bookmark   April 19, 2012 at 10:36AM
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I know heat loving plants can die in a black pot in a matter of hours here, even in the winter on a hot day.

The project in the picture is the one you direct seeded something into... or were going to? I did transplant around 100 peppers into plastic under low tunnels and agribon 19 and started summer squash seeds in holes in the plastic in another spot, no covering. I could probably just direct seed them but this is research.

Tomato transplants from about a month ago did really well with just row cover over hoops no plastic. They could go earlier with plastic mulch and poly on rain/hail days and at night.

The plastic mulch seems like it pays for itself in weed control alone. Then there is water preservation. I think I will be able to get two or three crops out of it in some instances. I hope it doesn't somehow bring a different set of problems?

    Bookmark   April 19, 2012 at 2:22PM
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jrslick (North Central Kansas, Zone 5B)

Yes I started cucumbers, zucchini, some watermelon and cantaloupe on April 1. The cucumbers and zucchini came up good, the melons about 50% germination. I know it was early, but I thought I would give it a shot. I lost some in a recent storm, from hail, but I will just replant and move on.

I am planting the remaining spots around May 1.


    Bookmark   April 19, 2012 at 2:45PM
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I look forwared to hearing your experiences as the season progresses and it gets hot.

Here in Texas I am thinking of using black plastic early on in the season to warm the soil and keep weeds back, but with later plantings using straw, leaves, etc to keep the soil cool.

When it gets really hot you might have to remove the plastic before the season is over. Then again cucs, squash, etc will shade the plastc by that point, keeping the heat down.

I suppose you work in plenty of fertilizer when preping the beds and use fertigation during the season?

I used plastic for my overwintered strawberries and it worked great.

In hoophouses, I envision using plastic mulch for early tomaotes then leaving the plastic on in the Summer to solarize the soil. The same plastic could be used the following year.

    Bookmark   April 20, 2012 at 2:01PM
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I'll keep you posted.You are right about removing or covering plastic with straw at some point.

Today the soil is almost 95F at 3-4 inches. Some of the lower transplant leaves are doomed, but the tops of the plants look o.k. We do not have a super hot climate like parts of the southwest. The hottest month average 90F for the high but it goes a little over 100F once or twice a year. As you know at 32 latitude the sun is intense.

I probably should open the row cover because is was like a sauna in there. Cucumbers are doing good, I took off the row cover and put cages on them yesterday and they are shading most of the area under the cages. The plants, Space saver and lemon cucumbers are about 20" long and have looked as good this stage than any cucumbers I have ever grown including those planted at the best times of the year.

I bought the kind of plastic that is white on one side and black on one side, with the idea of testing white for brassicas in the fall.

This is a new bed with 3 different sources of compost one being a super rich one I make for fertilizer. These beds will work without fertilizer for at least two crops probably more.

    Bookmark   April 20, 2012 at 5:26PM
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So far, everything grown using black plastic and row cover has done very well.My peppers and tomatoes are about 1.5 months ahead. Given our mild conditions it could be possible to improve on that with these basic methods and micro climates. Ground cherry plants are looking really good with plastic and row cover. All these plants do pretty good here eventually anyway.

It is very dry here even in winter ,except for when it is raining which is only a couple of days a month in winter, so the increased humidity has been a boon. I think I'll grow a lot of things under row cover(no plastic) just for the added humidity and animal protection. Spinach, beets and lettuce grew like I have never seen, both in speed and quality. Dino kale was nice under rows but leathery outside. We did have some bug problems in the low tunnels so I will have to figure that one out. Slight problem with earwigs and worse with scale and little winged things on some plants.

    Bookmark   April 30, 2012 at 12:01PM
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timmy1(6a ri)

You will not have a problem growing through black plastic...When the plant gets big enough, it will shade the plastic out anyway. Growing through clear plastic, now thats a lot hotter.

    Bookmark   April 30, 2012 at 8:27PM
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Just following up on this thread for suburbangreen.Based on this years newbie trials, I pretty much agree with timmy1 about plastic not needing to be removed if plants are going to cover it before it gets too hot. I got an early very uniform stand of of peppers and never removed the plastic. They were planted really close.On the other hand having them further apart would change the heating dynamics of the plastic over the season, maybe for better maybe for worse.

I didn't get a great stand of peppers on plastic, but I don't blame the plastic. The plants are very healthy but small. I experimented with putting the plants closer this year too,and I won't do that with bells again.

Next year the peppers that get planted on plastic early will be my normal distance and then I'll shade them as the season gets hotter.

Any other comments or lessons learned with plastic mulch?

    Bookmark   July 24, 2012 at 1:04PM
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Last summer when we had 90+ days in a row over 100 degrees many growers scrambled to find ways to keep their plants from cooking in the plastic. The best results that they spoke of @ the plasticulture conference was using a combination of surround & hay. I believe the surround sprayed on the plastic lower the soil temp 15-20 degrees & the hay lowered the temps another 5-10 degrees.
This yr our temps have been much milder than last. I have had more trouble with sunburn on my peppers in the plastic. I have 225 ft of peppers & once it got above 100 I picked 3 - 5 gal buckets of sunburned peppers in one day. Then picked a 3 gal bucket every day for about 2 wks. Now I hardly have any peppers left on my plants.

My concern is the temps as I am begining to plant for the fall. I was able to successfully germinate greenbeans in a row of white plastic, I will try to start some more beans in black plastic this weekend.
The biggest lessons I have learned this yr is spring pest are worse in the white plastic. I planted 200 ft of seedlings in black plastic with no signs of pest. 100 ft in white plastic was planted on the same day. Within 2 days I lost everything in the white! Once it warmed up I started 8 - 100ft rows of asparagus from seed in the white plastic. It has done amazing. I do have a few empty spots where pest attacked or they did not germinate. I plan to replant seeds where the bare spots are. The white plastic will also stay next yr to allow the asparagus to get established.

    Bookmark   July 24, 2012 at 1:30PM
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Wow!90 days over 100F!That's rough.Rougher than I have it. We don't have that heat. I don't think it has broken 100 for 3 years now, though 5-10 days each summer is the norm. The solar intensity is here due to latitude.

Sorry to hear about the sunburn peppers. That's an issue here too( San Diego County). About 25% get burns, only bell types though.

I'll use more plastic next year for weed suppression. I can't keep up hand weeding everything. Got to read up on the white stuff more. Maybe that would work better for plantings after June to keep weeds down without cooking roots.

    Bookmark   July 25, 2012 at 6:58PM
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i think if you used the surround on the peppers themselves (the actual fruit) it would reduce the sunscald losses. to me though it seems like there is a limited market for peppers.

    Bookmark   July 25, 2012 at 8:56PM
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Mark(Oregon, Zone 8)

An easy solution for sunscald on peppers is to lay a lightweight piece of row cover over the row. Not covered tightly which will increase the temps, but loosely to create some shade. Only problem is on windy days it could blow off if not tied on somehow. This works great for me in the hoop-house on peppers and tomatoes.

    Bookmark   July 26, 2012 at 1:26AM
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I am glad to know that, madronweb! I can jam a few conduit mini hoops in the ground over the peppers and clamp the row cover to them.

Peppers do o.k. here, randi.... nice bells do. I just grow a few others to liven things up. They are easy and don't take up much space in the garden or stand. Plus, we eat lots of them fresh. We also slice them or dice them and even do some roasting for recipes that take roasted peppers and then freeze them in these various forms.

    Bookmark   July 26, 2012 at 10:57AM
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