One hard frost can severely damage or kill even the hardiest of annuals. All the time, money and energy put into caring for your annuals can be salvaged by avoiding frost in the first place. Some frost protection can be put together from household items while more extensive procedures may take some foresight and special materials. Either way, the amount of money spent to protect your flowers is surely negligible when compared to the time and effort spent on growing them.
Water your annuals thoroughly before nightfall. Water droplets will be released during the night, keeping the air slightly warmer.
Push two wooden stakes into the ground on either end of your bed of annual flowers. Be sure they are roughly at the same height.
Place a plastic tarp or bedsheets over the stakes to create a tent over your annuals. This will insulate the flowers and keep frost off their leaves. Do your best to prevent the fabric from touching the leaves or petals as it may freeze and damage the plants once removed.
Stretch tarp or sheets all the way to the ground and place rocks or heavy sticks on their edges to keep in place.
Remove covering after the frost to prevent overheating and assess any damage.