Hi Lynette, this is a very good question. Another of our local collectors uses frost cloth every winter to protect his many hibiscus and says it works well for him. My mother has used them on her hibiscus and also adds a string of outdoor Christmas lights under the blankets to add several more degrees of warmth.
Frost cloth or blankets, sometimes called row covers by farmers that use them a lot, are not magic solutions but do add several degrees of protection on winter nights. I recommend the heaviest ones offered, that claim up to 10 degrees of protection, because they last longer and because hibiscus need every degree of warmth possible in winter.
The way they work is to trap heat that comes up from the ground during the night. It is IMPORTANT to drape the cloth so that it touches the ground all around the plant. Do not bunch it up around the main stem because that limits the heat that it can trap. The ideal way to use it is to have a frame to drape it over so that it becomes a mini greenhouse but I don't think many people actually do that.
You can buy this type of material at many places. Amazon.com and e-Bay have it, local nurseries sometimes have it, and many nursery and greenhouse supply companies have it such as
http://www.greenhousemegastore.com/Plant-Protection-Fabrics/products/1039/The heavier fabrics are rated at least at 3 ounces and 10 degrees of protection. I read somewhere that Home Depot and other box stores have it but not the heavy stuff that is likely to work better.
Frost cloth is sold in big rolls. Some companies cut it into different size pieces. Don't get the ones that are only 3 feet wide unless all your plants are very short. It would work on the 6 inch pots we sell but not on anything bigger. Remember, it has to touch the ground all around the plants so allow for enough size so that it can do this.
If anyone else has experience with using shade cloth, please share it.
Charlie
