Well, the thicker and more insulating the better (but of course, you don't want to crush the plants underneath with the weight of it, use a support to keep it from doing that). And, it also helps a LOT to create a "dead air space" between the covering and the plants.

Don't feel too bad, there's been a lot of that going around my neck of the woods too. I don't really have anything to add to what Den said. Just a little encouragement.

One of the families I garden with somehow got a plastic bubble tarp. That has to be tops for thermal insulation per pound.

I have cages around my plants, and my seeds haven't sprouted. Is that enough support for blankets and dead air space? Is it okay to use blankets and sheets? I have a 400 square foot garden, so I might have to use both. Are tarps out then?

I'm sorry for all of the questions. I just really don't want to loose all my plants again so soon. They've only been in the ground for 3 days.

Thanks for the encouragement. I guess every experience is a learning one, huh?

You really don't want plastic touching the plants. Cloth is better. Newspaper works well, too.
Keski

Well, either would work for frost. The idea of putting something over your plants when there's a frost has nothing to do with keeping them warm, and everything to do with keeping the frost itself from forming on the plant. Just like parking your car under a carport keeps the frost off your windshield, any solid covering will keep the frost off your plants.

No simple throw is going to actually keep your plants warm by itself, they don't generate their own heat. At best it makes a very badly insulated structure that might keep it one or two degrees warmer inside than out, but probably not.

Long as the tarp isn't touching the plants (and hence they aren't touching something that is touching ice), it'll be fine.

I have been protecting tomatoes from fall frost for many years.
You can do down to the low twenties, for decades.

One thing is wet ground helps prevent frost, so if my hose is still hooked up I will soak the area around the plants I am trying to save. (I do this also for roses but do not cover roses in the late fall.)

Simply stay away from plastic unless you have a portable greenhouse, period.
The heavier the blanket or what ever you you use the better.
Do not let the cover crush the plants if they are small but I have covered potted flowers and simply throw the cover over them with no support and they survived just fine.

Mattress pads and car covers for me have been the most efficient, but I have used thin cloth sheets in layer if I am expecting sub 25 degrre temps.

Be wary of low spot frosts, i.e. cold air sinks into low areas and I have gotten up in the moring to see frost covering only small areas.
Now spring frosts are different from fall frosts and in spring frost there is little ground heat to offset frosts, i.e. it is the rising heat under the covers in the fall that actually defeats the frost.
If there is little warm air under the covers the heavier the cover to hold the heat in the better.

Remember heating-cooling only works by tranfer, addition or removal, of heat, not by transfer of cold.

Depending on how large your garden is, land scape fabric which can be purchased in rolls many feet wide, will work also.
Use the most flexible available.
You could put stakes in the ground to keep it off of the plants.
Just buy some wide enough so it droop over the edge along the sides.
Then you can pull it off, roll it up and save it for future use.

I try not to plant until the last frost date, then add a week.
I still have encountered an occasional light frost after that date. I usually tent the plants with whatever is handy at the time (sheet, tarp, blanket)or little "tents" of wood or cardboard to help them harden off, protect from the wind/cold and this year HOT!
I think the best thing is to look up your LDF (last date of frost), and/or planting dates on your County extention or Master gardeners web sites for your area. It sounds like you are planting a bit early for your area. Nancy

"I try not to plant until the last frost date, then add a week."

My last frost date was 4/15 they are calling for frost tonight! A week and 1 day! LOL

I started a lot of stuff early, green beans, okra, squash, corn, and planted tomatoes. We had not had a night below 50 in over a month and 1/2. We had a frost about 2 weeks ago. I lost a lot of tomatoes, which I covered with sheets, but everything else was fine.

Back to the OP, heavier is better. The tomatoes that survived were under some very thick bed sheets. The others were under thin bed sheets.

I'm headed out in a few minutes to put my "backup tomatoes" inside for tonight. They are huge and blooming. I started them March 1st and they have been outside, except the few nights of cold 2 weeks ago.

I've found cardboard is the best but often use sheets and blankets. Never use plastic.
I keep peppers and eggplants alive all winter, plus some hibiscus, so get to do quite a bit of frost prevention.
I love using big cardboard boxes for anything small enough to fit.
Also, if you can string lights, especially the old fashioned Christmas lights, along the plants, that can really help underneath the cover.

Lost all but 2 planted tomatoes last night, backups were inside. Corn is drooping but It will recover.

I had never thought of boxes, excellant idea.

Nursery pots can be put on top of your plants with something on top of them (secured so it doesn't blow off) to cover the drainage holes. We had a frost last night. It got down to 39. I didn't cover, because I missed the evening news. Nothing was bit, but there was some ice on the truck windshile. We have all of our veggies in pots on top of black nursery cloth. Maybe that was just enough heat to protect them? Our LFD is 4/1!

Excellent idea, not excellant.

Do not ever use a Toshitba lap top, they are cursed.
I can not type on this thing.

Some plants are a lot more cold-hardy, and some need the cool weather and do not mind light freezes. Look for early spring planting times appropriate to your zone like beets, peas, radishes, onions, spinach. Depending on where your zone 7 is some of these may need to have been planted earlier. The short maturities are nice to interplant. By the time radishes are done, zucchini is filling in (and they deter Squash Borers too).

Here is a link that might be useful: Vegetables for Early Planting