Black plastic mulch

[smallblueplanet]

I'm gonna have another go at growing melon in the greenhouse, and I was wondering about planting thru black plastic mulch.

Has anyone ever used black plastic as a mulch for growing stuff like melon or toms thru?

[rustylady]

No, never used it. If you are growing in the greenhouse are you intending to grow in a border or in a pot? Black plastic can be used to suppress weeds, or to increase soil temperature, but I have never heard of anyone using it in a greenhouse.

[smallblueplanet]

We grow in our greenhouse borders - I've only seen black plastic used on melons in a polytunnel, but I've only just started looking.

[smallblueplanet]

Could be that clear plastic mulches are better than black plastic.

The soil temperature under a plastic mulch depends on the thermal properties of a particular material in relation to incoming solar radiation. Black plastic mulch, the predominate color used in vegetable production is an opaque blackbody absorber and radiator.

Black mulch absorbs most ultra-violet (UV), visible, and infrared wavelengths (IR) of incoming solar radiation and re-radiates absorbed energy in the form of thermal radiation or long-wavelength infrared radiation.

Much of the solar energy absorbed by black plastic mulch is lost to the atmosphere through radiation and forced convection. The efficiency with which black mulch increases soil temperature can be improved by optimizing conditions for transferring heat from the mulch to the soil. Because thermal conductivity of the soil is high relative to that of air, much of the energy absorbed by black plastic can be transferred to the soil by conduction if contact is good between the plastic mulch and the soil surface.

Soil temperatures under black plastic mulch during the daytime are generally 5° F higher at a 2-inch depth and 3° F higher at a 4-inch depth compared to those that of bare soil.

In contrast, clear plastic mulch absorbs little solar radiation but transmits 85% to 95%, with relative transmission depending on the thickness and degree of opacity of the polyethylene. The under surface of clear plastic mulch usually is covered with condensed water droplets. This water is transparent to incoming shortwave radiation but is opaque to outgoing longwave infrared radiation, so much of the heat lost to the atmosphere from a bare soil by infrared radiation is retained by clear plastic mulch.

Thus, daytime soil temperatures under clear plastic mulch are generally 8 to 14° F higher at a 2-inch depth and 6 to 9° F higher at a 4-inch depth compared to those of bare soil.

Clear plastic mulches generally are used in the cooler regions of the United States, such as the New England states. Using clear plastic mulch will require the use of a herbicide, soil fumigant, or solarization to control weeds.

Welcome to the Center for Plasticulture at Penn State

[starwatcher]

I have not yet grown anything this way but have used black plastic sheeting to control weeds on my beds, watch out for slugs sbp it certainly attracts them. I am thinking of growing maincrop spuds this way to break up the soil on OH'S plot which we are just clearing, my only reservation being the slug problem.

[smallblueplanet]

Thanks starwatcher - I think maybe I'll stick to outdoor mulching. I wonder if you use clear plastic whether the slugs wouldn't like it/be able to hide?

(Just have to hope its hot enough to cook 'em! )

[starwatcher]

slugs not liking clear plastic, interesting thought sbp Hows your wilkos cold frame I haven't used mine yet

[Burnzie]

I use black and white plastic with the white side up to reflect light back up on to the leaves.

Burnzie

[smallblueplanet]

.....Hows your wilkos cold frame I haven't used mine yet

Didn't get one in the end, worried about the strong winds we get here - gonna try and make one .