frost

Annuals suffer when the temperature gets down to about 5 degrees and under. If it hits zero, they will most probably die unless in a VERY sheltered position, when a few might survive. I don't think that your idea of putting your sprinklers on is very helpful: how do you know at what time the coldest time of the night will be? It won't necessarily be at 5.45 a.m. Also, if you over-water them, the roots may well rot! Why don't you watch the weather forecast and cover them with fleece if frost is forecast?

I don't know what state you are from, but the concept you describe is used in Florida for citrus groves, fern nurseries and strawberry fields. On the night of a prolonged freeze (temp below 32 F for over 4 hours) sprinklers are left on all night. It causes a coating of ice over the foliage, holding the temp at 32 degrees. Whatever would survive at 32 F for a few hours will therefore survive the entire night. Even when temps drop into the 20's. Even fern and strawberry plants. But that is for a prolonged "hard" freeze. Frost is more easily handled by tossing the contents of ones' linen closet over the entire garden........

cont'd Frost does not require such drastic measures - simply toss the entire contents of ones' linen closet about in the garden.......