They work reasonably well for frost protection, and very well for insect and bird exclusion.

I've found that, overall, it pays to buy the thicker stuff -- less likely to tear, etc. Also lasts a bit longer.

Supports can be almost anything you cobble together - bamboo poles, concrete rebar, you name it. For most things, though, you don't have to support it -- it's so light you can just drape it over the plants with no problem. Depends on the exact plant you're growing.

If you are growing any plant with an apical growth pattern, you will need to hoop the fabric over the plants. I use 8 gauge galvanized wire cut to the right length. For plants with grow points nestled down below the leaves, laying the fabric over the plants work well.

Fabrics with heavy unit weights give more frost protection but less light transmission. Watch out for low soil temperatures. Once you put on the cover, the air temp with rise a few degrees or more but the soil takes a lot longer to warm than air. For me low soil temperature is often more significant than low air temperature. Plants can't take up as much moisture and nutrients from cold soil as they can from warm soil.

Where you expect to plant, you might start by putting down plastic allowing light in but keeping the heated soil from losing radiant heat. A week of these minigreenhouse arrangements make a difference in immediate soil temperature, at least in the upper half foot or so.

Last spring, the medium-heavy weight covers helped me put out cool-weather transplants like spinach and kale in April  held them down with rocks or rebar (no supports needed)  they helped with hardening off, sun acclimation, and wind protection. Just kept them there and the plants were doing very well when the covers came off a few weeks later.

I tried using lighter ones later in the spring for both hilled and trellised squashes, melons, and cukes but the hilled plants outgrew the covers very quickly, and the trellised ones seemed to suffer from the reduction in fresh air. Hand pollination (necessary after flowering), I found, is easier said than done, hard to keep up with, and tedious. As a bug shield for cucurbits, I think covers may be inferior to rotation and companion planting.

Didn't try them for eggplants, which got eaten up by flea beetles within hours of transplanting. I'd use them if attempting eggplant again.

Even if using covers for insect protection, I'd rotate crops, since any bugs that sneak in or arrive late in the season can emerge in spring under the covers!

I'm not sure if they're much use in fall, since the cool-weather plants were fine on their own and the warm-weather ones would be awkward to wrap and wouldn't last much longer in a freeze.

Here is a link that might be useful: Garden Quilt Covers

I like Reemay brand and I use the lightweight 'insect barrier' type. It's good for 10 degrees of frost protection yet light weight enough that it needs little if any support. It's available in various widths and lengths from several garden supply vendors and is listed in most seed catalogs too.

Dave

Here is a link that might be useful: Reemay Insect Barrier

All of the newer types are stronger than they used to be but they can rip. Anchoring well around the entire perimeter is essential if you even have moderate wind.

These fabrics are usually rated in oz./sq yard. .5 oz./sq.yd. is the lighter weight material; 2.0 oz,/sq. yd. is fairly heavy. For me the heavier material is reserved for the fall when plants don't need the light for growth. And since plants are sturdier in the fall I just drag a cover over them to protect the crop. I have reused the heavier fabric for 5 or more years, depending on the severity of the rips over time.

Dave, I think you are pushing the limit a little on the 10 degree figure. I can't even get that with double plastic layer on a greenhouse. And for insect protection if you have insects coming from the soil or residue beneath the cover you will still have insects. But I don't want to downplay the benefits of the row covers. They've paid for themselves many times over in my fields.

My experience with Remay - the lighter weight - involved cabbage butterfly exclusion last year. I was pleased with the results. I don't need the extra frost protection, in fact - our sudden, unexpected hot spells makes the selection important - as heat build-up can result if a heavier cover is used.

They were also used for bird deterrant over the strawberry beds. When the season was over, I stored them intact, and will definitely use them at the first sign of a white butterfly - (early enemy #1).

Don't know how much mileage I can expect, but they still look fine after the first season.

Bejay

Dave, I think you are pushing the limit a little on the 10 degree figure.

You may be right as I have never had to push it to that limit. It's just what the manufacturer claims for it. I have had to count on it for some 26-27 degree nites and had no problems.

As to the control of dirt/ground insect access with it, weed barrier and careful tucking of the Reemay around the base of the plants eliminates most of that for me. But even without that block you have eliminated all the air access and so cut the potential problems by 2/3. ;)

I can't even get that with double plastic layer on a greenhouse.

Air chamber double-wrap still doesn't give you 10 degrees? That's good to know. I realize you're way north of me and your greenhouses are quite a bit larger than my small 10x20' one so the cost might be prohibitive for you, but have you considered the bubble-wrap blankets? We bought ours from Farm Tek Supply at a good price and it's on its 5th year with only a few tears. With no or little wind I can get 20 degrees difference inside to outside temps with it. Just a thought. ;)

Dave

I'm in the same zone. As others said, row covers work fine but if what you are looking for at this point is protection from cold, you'll get a lot more of that with some plastic sheeting. I get a big roll of 10 foot wide 6 mil stuff from the big box store every few years. I support it on PVC tubing, which I get in 10 foot pieces, and place in to ground to make support hoops. THe plastic sheeting lasts a few seasons, then starts to fall apart from the UV. The PVC lasts for maybe 5 or 6 years, then it too gets brittle.

I also save old plastic milk jugs, fill with water, and put them under the cover, spaced around the plants. Evens out the temps; absorbs heat during the day, releases at night.

I have had these little greenhouses covered with snow and ice and the plants in them are perfectly happy, even tomatoes and cucumbers (I'm always trying to jump-start those).

I use row covers later in the season for some lighter protection from cold, but mostly for bug protection. Keeps the deer from eating stuff also. I usually get my row cover material from Johnny's.

Ken

I use several layers of row covers in late fall to protect late greens--lettuces, mustards, etc. My stuff held well into late December with temps in the low teens.

"..have you considered the bubble-wrap blankets?"

I got one better Dave on my smallest 15x40 GH.. a layer of bubble-wrap sandwiched between two 6 mil films with inflation on both sides. But the problem with long nights is that till 6 AM the inside temp isn't much different from outside temp if there is no supplemental heat. I've been watching a bucket of water inside the GH and when the morning temp is in the mid twenties there is ice. I have no plants in it yet this spring but a smaller catalytic heater does keep the temperature at a suitable range all night.

Ken, plastic sheeting can cook your plants if you don't cut slits in it to let heat out during the day. The nice thing about row covers is that they keep frost off the plants yet allow the excessive heat to escape. A commercial greenhouse is basically a plastic cover with a buffered airspace. The larger the greenhouse, the more buffering. However the daytime temperatures can soar over 120F real fast on a sunny day in any unvented, plastic covered system.

I am thinking about making a couple pvc/sheet plastic mini hoop houses myself. I hope to use them to extend the start of my season by around 2 weeks. Hopefully to help warm the top few inches of soil faster, then get beets, carrots, broc and cauli going outside in the garden earlier also. Will the plastic heat the air inside too much in April/early May here in Maine? I sometimes got to work at 6 AM, on other days I get home at 11 PM, so venting and sealing them willmay be problematic, unfortunately

I have tried row covers (the lighter weight ones) and found them worthless. The reason is springs in my area invariably involve high winds (at least one 70mph storm can be counted on and 20-30mph winds are common).

Based on other's experiences I would say they are worth a try, but do consider how windy your site is likely to be during their use and plan accordingly. If your site is windy you will be better off laying them over the plants and weighting it down as close to the ground as you can. Any kind of support that lifts it off the ground is going to catch more wind.

My first experience with row cover this Spring is good so far. Covered the broccoli plants and as I mentioned in another post, the plants seem to be thriving under there. I still check periodically for bugs,tho. I used enough cloth to cover the plants keeping in mind to make sure there was enough slack to take in account the growth of the broccoli. Then weighed edges down with small rocks. For the bok choy plants, I made a tent using two bamboo stakes that just happened to be in a "U" shape upside down tho (from a broken pot trellis),one on each end of the row; then a straight bamboo stick across the top. Then draped the cloth over this and weighed down edges with stones and dirt.

I find row covers most useful on squash. I cover the hills when the seed is planted and take the covers off when the first female flowers appear. By that time the SVB has departed for your gardens.
Also useful on such things as spinach, kale, broccoli raab, lettuce, to keep off flea beatles, cabbage butterflies and aphids.
And one piece wrapped around a teepee of pole beans defeated Peter Rabbit. It was secured with clothes pins.

I find I have much better germination when I use Remay like material laid directly on the soil over new seedings.
It seems to keep more moisture in the bed and warms the ground a little. Unfortunately, it also gives cover to the vole who eats a few of the protected sprouts. I've used the stuff for 20 years now with excellent results. Also use over eggplant against flea beetles and on hoops over new transplants. They can get big enough to survive bug attacks before I take the cover off. It's the number 1 beneficial product to come out in many, many years.