I grow tomatoes in fabric containers that are 20 inches in diameter. A few years back, I got some of the red plastic mulch that is supposed to enhance their growth. I cut it so I had a disk that exactly fit in each pot. Although they had holes in them so water should go through, I had a mess every time I tried to water. The water would pool on top or wash the mulch to the side. I had to pile rocks on the outer edges to keep the stuff from crumpling and floating around.

If you could install drip irrigation under the mulch and pile some other kind of mulch on top to keep it in place, your plan might work.

plastic mulch "rings," like you mention, are fine. But I would never use CLEAR. Black is fine and will heat up the soil nicely.

The reasons I wouldn't use clear is 1) weeds 2) TOO much heat -- clear plastic is actually what one uses to solarize the soil for diseases. Bringing the temps up to well over 135F during the summer.

I've moved my way to natural mulches though. Feeds the soil and regulates temps(hot and cold) to extend seasons.

Perhaps try a large black plastic container as an experiment. They work great for me to get a leg up on my late maturing varieties of peppers.

Kevin

Dh was recently talking to a co-worker who gardens and he stated that he kept his eggplants in wall-o-waters the entire season and I will likely be trying that this year. The nights are cool here so these give the benefit of the warmth in the vening but are open at the top for venting excess heat.

There has been many discussion on HOW to extend growing season. One method is to do it from the FRONT END, ie spring. I have been studying this seriously myself.

The primary reason for retarded germination and growth is more SOIL temperatures than AIR temperatures. So the challenge is to keep the soil warm. Plants like warm feet but don't mind cool head.

Normal ground temperature (~ 4 ft below surface) range from 50F to 60F in most places on Earth. This is without solar heating and winter cooling.

For most garden vegetables (once they have germinated) a 60F soil temperature is a good start.
A clear plastic cover can help in two ways: (1) by trapping solar heat ( greenhouse principle) and reducing heat loss to the space in (the form of heat wave) at night. For this reason and purpose , clear plastic is superior to all other kinds. A thin layer of dry fluffy straw or leaves just under the plastic can have an improved greenhouse effect.

The "ring" idea, is good for potted plans. It can also be a useful tool where you get too much rain. In the ground , I would cover the whole bed. Once it warms up you can remove the plastic.

Thanks for the thoughts -- I'm going to try it!

I prefer to use natural mulch that I can mix with the soil later. It serves three purposes of keeping down the weeds, keeping in the moisture, and improving the soil. Plastic only serves the first two purposes so you have to add compost later. I use two types of mulch on my veggies: 1) I lay out mowed grass clipping in the sun until they are dry and then place them around my plants; 2) I get free composted leaves from the Fairfax, VA county transfer center which I put around my plants. After the growing season I mix it into the soil. Around my fruit trees I use shredded limbs.