I assume you're going to be planting through the plastic, in which case you'd be better off going with the black.

Rodney

Thanks, Rodney. Actually, what I was intending to do is put the plastic down and leave it until planting time, usually the last week of May here in Minnesota (might be slightly earlier this year), then take it up. My tomato growing area is about 32 feet long and 6 feet wide. In this space I plant two rows of 14 plants each. The idea would be to get an early warm-up of the soil, encourage microbial action, worms, etc. Does this make sense?

Gary

It is true that clear plastic let more light/heat get in, but for the purpose of warming the soil early in the season, it also can let the heat out at night by radiation. Black plastic gradually heats up the soil and keep most of it. Clear plastic does/can more than warming up the soil. In a sunny hot day it can burn the plants roots.So it is a good temporary solarizer.

So here is what I do. : cover my raised bed from early Feb and keep it covered till August. When I want to plant, I cut a small circle for each plant and do the planting. This also prevents the beds from getting too much rain water. In warm climates probably you wont need the BP on after plant out or you put a layer of mulch on it . But in our cool PNW, and with my few hours an direct sun, it help to keep it on .

I will just add to this a bit of thermal physics. Black plastic gets hot, because it absorbs the sunlight. Yes, black plastic gets warmer than clear plastic does, but the stuff underneath it doesn't. In the case of black plastic, what is underneath it is not heated directly. It gets some heat from the black plastic. Probably less than half that energy hitting the black plastic. Clear plastic allows sunlight to penetrate and warm the soil directly. ALL the sunlight heats the soil. That heat conducts well to depth, so the soil will get more thoroughly warmed. Now clear plastic is pretty transparent to infrared light, so the warm soil at the surface will cool radiatively more than it would with black plastic, but the warm soil underneath won't, because it is insulated by the soil on top. Note that polystyrene is somewhat more opaque in the infrared than polyethylene, so from the point of view of allowing sunlight to warm the soil and keeping that warmth, the former is probably better, but either will heat the soil better than black plastic would.

So I agree with the U. Maine extension piece that clear plastic will warm soil better than black plastic would.

Thanks, dan., appreciate the additional information.

Gary

I do what seysonn does -- cover the gardening area with black plastic and cut holes for the plants. It really cuts down on weeds and everything grows the same. I've never done it to warm the soil in the vegetable garden, although in one of our ornamental beds we had a huge problem with thistle. We pulled the plants (mat juniper), which we wanted to get rid of anyway, then covered the area with black plastic for almost a year. Haven't had much of a thistle problem there since.

That makes sense. If soil warming isn't the highest priority, but blocking light to weeds is, black plastic is what you want. If soil warming is the highest priority, then one is better off with clear plastic. Both will help with moisture retention.

Clear plastic is ok BEFORE planting out any thing. Otherwise the soil can get too hot for the plants roots. JMO

Seysonn