The Reusable. 18" diam. x 18" high Wall O Water plant protector, absorbs heat from the sun during the day and releases it at night. This provides an even greater benefit than simple frost-protection covers that do not store heat.
You fill the tubes of these self-standing plant protectors with water, and they provide additional heat, allowing you to plant earlier and harvest later.
Should the weather drop to freezing temperatures, the wall o water becomes even more effective. Acting as an igloo around the plant, the frozen Season Starter releases even more heat, which protects the plants down to 16°F and even melts snow.On hot summer days, the wall o water, is just as powerful in protecting your plants. It absorbs solar heat and moderates the temperatures inside, keeping plants cooler and protecting them from overheating.
I have found that Walls of Water are useful for extending the growing season for tomatoes, peppers, eggplant and other warm-season vegetables.
I bought mine at Ace Hardware, and I am sure you will be able to find them at your local hardware store or garden center.