You would have to be out there spraying water as soon as the critical temperature (around 27-28) is reached, and spray repeatedly until it warms to 29. Meanwhile the roses would be coated with ice (this is how the protection works) and would likely sustain structural damage rather than freezing damage.

not sure how this got double posted. Please let this one drop off the page. Thanks

Mary Lu, it was down to 28F. here last night. I didn't cover anything because it's been dry this week. My tomatoes, which are planted out, are a little darker green because of the cold but there was no frost so they didn't melt down like a frost will do to them. Roses, peonies, daylilys all came through fine and most of them are just sitting here in plastic grocery bags. If we get frost warnings I cover as much as I can and scootch things still in pots or whatever as close to the foundation as I can to help protect things. Cover what you can and pray for the best. Usually perennials that come up early do fine with a few light frosts. Pretty much like in the early fall. Best Wishes! MeMo

In some ways, frozen pipes are a bigger problem in the Southern US, where only occasional freezes happen, than in the North. One time after a cold snap and everyone in town had faucets running all night and half the day or had busted pipes, an associate of mine said, “You Yankees must have pipes freeze all the time”. I told her that up there they don’t put pipes where they freeze so easily. There are open crawl spaces all over the place with plumbing in the open. There are often pipes in attics over the insulation, especially in slab-built houses. Pipes are run through exterior walls. They freeze. They flood houses. They cause many expensive plumber calls. Running water freezes less readily than standing water in pipes for more than one reason. Yes, the water entering the pipes is warmer than what it will be sitting in the pipes. Yes, running water is less able to form crystals than standing water. Effectiveness of leaving faucets cracked open depends on a lot of variables, air temp, ground temp that determines water temp, and the velocity of the water. Blanket statements of leaving a faucet open will or will not keep your pipes from freezing are both too broad. It can be a good solution for a temporary situation, but not a good one for a vacation or seasonal vacancy. If toilet is supplied with vulnerable pipe, tie a string to the lever, toss the other end into the tank and flush so it holds the valve open enough to make flow. This is all based on simple logic and knowledge of the basic properties of water in solid and liquid forms. If you know that your plumbing is vulnerable, turn off the water if you can’t do anything else. At least, if the shut-off is effective, and many of them leak, you won’t find a flooded building on your return. Make doubly sure the faucet closest to the shut off is open when opening all the valves so the other pipes have less chance of refilling. If you can do a halfway decent job of draining the lines, and the shut-off is effective, you stand a better chance of less damage because you give the residual water room to expand. To get all the water out, you must drain all the local low points not just one low point. If you can’t, you might still get split pipes, but the probability is lower. The more water you can remove, yes with compressed air for instance, the better off you are. Sometimes you can get RV antifreeze (non toxic) into the pipes. Yes, you should put it in toilet bowls and traps. Vessels with straight sides and bottom are more likely to crack with contained freezing water than those with sloped sides (V-shaped or round), but freezing water can still crack the less vulnerable ones. Remember that in toilets, the trap is not exactly bowl-shaped. That tank is still a problem if the water shut-off is not totally effective and the tank refills. For a regularly-idle property the best way is to make sure the pipes can all be passively drained, the shut off works, a faucet specially placed at or near the service entrance is open and drains to a freeze-proof drain (in the basement). The fact is, with a poorly-designed plumbing system it is going to cost you to make it freeze-proof. The more security you want, the more it will cost and it is an exponential relationship. If you can buy a house that is that way right out of the gate and you like to leave it in freezing weather, you’ve been blessed.