It depends on how heavy the row covers are and how tightly you stretch them and which method you use to fasten them down.

With the heaviest frost blankets that give you approximately 8 degrees of frost protection, those are a bit 'heavy' and might weigh down very small seedlings, if pulled tightly across the bed. I hold them down with U-shaped metal staples and leave a bit of looseness so they can flutter lightly above the plants, but not so much they bounce up and down and beat the plants to death on a windy night.

With the lighter weights, they usually aren't heavy enough to hurt the seedlings unless the seedlings are very, very young and tiny and delicate.

I'm not sure any of the row covers would hurt corn, and covering emerged corn is very important because if the growing tip of each corn plant freezes, you'll have to replant in order to get a crop.

You can make hoops out of heavier gauges of wire and suspend row covers over them low tunnel style. You also can buy the hoops, but making them from wire or PVC pipe is simple. For more permanent hoops you might want to make hoops, if you use them, from electrical conduit. You then suspend the fabric over the hoops (not matter what the hoops are made of), weighing it down at the edges with something. I use either metal groundcloth staples or sometimes just place green metal fence posts or 2 x 4's on the ground hortizontally to hold down the edges. Sandbags are what Johnny's recommends...there's various ways to do it. You can clip the row covers to the hoops, or not.

I have several different weights of floating row cover and I use them only occasionally on a cold night, and I don't go to the trouble of putting up hoops just for one night. If a big cold spell threatened and I needed to cover up plants for an extended period of time, I'd likely put in hoops.

My most recent purchase of rowcover material was of the very lightweight floating rowcover used to protect plants from insects. Since that fabric will be used on a more long-term basis, I'll likely use hoops with it, but I haven't decided yet.

I've linked a page from Johnny's that shows some hoops supporting a heavyweight covering over some 8' x 4' raised beds. Of course, these are in a very cold climate, so they used heavyweight frost blankets plus greenhouse plastic over sturdy hoops. In our climate, unless your site is very exposed to the wind, you likely could just use wire hoops or let the floating row covers float. I just wanted to show an example of a hooped bed.

Dawn

Here is a link that might be useful: Low Tunnels at JSS

Kaiti, A good temp solution is to drive rebar into the edge of your bed on both sides, and bend small PVC pipe that will slip over the rebar on each side and form a hoop. You probably need one arch about every four feet. This way it is temporary and doesn't take much effort to remove it when you are finished with it.

I had some animal jump into my floating row cover and tear up two long pieces on the same night. It could have been a cat that became interested because it moved in the wind, but I have also had a possum in my yard so that is always a possibility. Last year I made a fitted cover to go down over an metal arched bed cover and I made it out of sheer curtain material. It was more durable but I think it blocks a little too much light to leave on for very long. In my case it was for protection from insects, but I have also covered plants with floating row cover, then at night tossed a tarp over them for extra protection from the elements. One year it was so cold that I filled one gallon jugs and 2 litre bottles with hot water and carried them outside and stuck under the "cover" and weighted it all down with bricks around the edges. It worked. I have never bought the heavy material, just the soft floating one. I want a greenhouse. LOL