warming soil for early planting ?

mandolls(4)March 20, 2011

I have some raised beds that I want to try covering with frames of greenhouse plastic and extending my growing season (last frost here is May 31st)

Right now the beds still have 6-10 inches of snow accumulation, but it is 50 and raining this weekend so I should have access soon.

Is it a good idea to lay black plastic down for a week or so to warm up the soil? I am only planting cold season vegetables - broccoli, cabbage, peas, lettuce spinach, radish. I am hoping to get them in the ground by mid April (though that may be pushing it).

Will the plastic potentially cook the beneficial in the soil? Does this sound like a good idea?

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dan_staley(5b/SS 2b AHS 6-7)

Done all the time. I use a film from Johnny's.

Dan

    Bookmark   March 20, 2011 at 12:57PM
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tcstoehr

The farmer in my neighborhood uses plastic occasionally on his vegetable fields. Right now for example he has clear plastic on this rhubarb field:

Notice how much bigger the plants are where the plastic is.

    Bookmark   March 20, 2011 at 1:30PM
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DrHorticulture_(Z3 Central Saskatchewan)

If it's after the snow disappears, I would be more inclined to use clear plastic.

    Bookmark   March 20, 2011 at 1:30PM
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mandolls(4)

I would use the black plastic directly on the soil - for a couple of weeks to defrost everything, then use a clear plastic to cover the beds after planting. I already have both, so its not an extra expense.

I assumed the black plastic would attract the heat from the sun better than clear and warm it all up faster.

    Bookmark   March 20, 2011 at 3:07PM
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jolj(7b/8a)

Everyone is right in the above posts.
But it is only fair to tell you that sometimes plastic mulch can be a pain to remove.

    Bookmark   March 20, 2011 at 6:15PM
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dan_staley(5b/SS 2b AHS 6-7)

But it is only fair to tell you that sometimes plastic mulch can be a pain to remove.

True dat. I should have done some today, but was successful in finding something more fun to do with the kid.

Dan

    Bookmark   March 20, 2011 at 7:26PM
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wayne_5 zone 6a Central Indiana

Clear plastic should warm the soil more than black plastic.

    Bookmark   March 20, 2011 at 7:38PM
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Kimmsr(4a/5b-MI)

If the research done at several universities can be believed clear plastic applied to soils in the sun will warm that soil sooner because the suns rays will strike the soil. If black, or other opaque colors are used, the sun heats the plastic which in turn heats the soil through heat transfer. White or silver colored plastic reflects the suns rays and does not contribute any warming affect.
Since plastic is made of non renewable resources we need to question if using them in an organic garden is really acceptable.

    Bookmark   March 21, 2011 at 6:28AM
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mandolls(4)

Thank you all for the feedback. I am surprised to hear that the clear will warm the soil better than the black. I was thinking black because of people using it for solarization of soils, and gallon jugs used as heat sinks in cold frames are painted black as well.

Kimmer - the roll of black plastic that I have (6ml) was given to me by a friend who had lots left over from a roofing project, so it is better to use it than throw it in a landfill. Are there actually modern organic gardeners who use no plastics of any kind in their practice? I'm not sure I could operate without 5 gallon buckets, cell trays, plastic pots or hoses.

    Bookmark   March 21, 2011 at 9:15AM
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wayne_5 zone 6a Central Indiana

Mandolls, The reason for black objects in coldframes is that the black absorbs heat [good in coldframes]. White reflects heat away [good in certain instances]. And clear lets the heat pass through to the soil [good in soil warming and solarizing instances.

Kimmsr. I reuse many times many of the plastic pots and IRT plastic mulch.

    Bookmark   March 21, 2011 at 1:43PM
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dan_staley(5b/SS 2b AHS 6-7)

The reason I use dark film (from Johnny's) is if you aren't careful with the clear plastic, it can get too hot. You solarize the soil in summer with clear plastic.

Dan

    Bookmark   March 21, 2011 at 2:50PM
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mandolls(4)

OK - Thanks for straightening me out. That's why I asked.

Clear plastic it is.

Thanks!

    Bookmark   March 21, 2011 at 4:05PM
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wayne_5 zone 6a Central Indiana

I only use and recomend clear plastic on the soil for early spring and for cold and wet conditions into some of May.

    Bookmark   March 21, 2011 at 4:35PM
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jolj(7b/8a)

Yes clear plastic heats better in the day, but any solar nut from the 60"s & 70"s can tell you. Black plastic holds the heat at night, that is the reason everyone uses BP.

    Bookmark   March 24, 2011 at 10:29PM
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