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A hot cap is a tool which is used to protect tender plants during cold weather. Hot caps fall under a family of tools known as “season extenders” because they can be used to extend the growing season, especially in areas where this period may be short. In addition to insulating plants from cold temperatures, hot caps also protect them from marauding birds and small animals, giving them a better chance to thrive to a larger size which will allow them to withstand garden pests.
Hot caps can be made from heavy translucent paper or plastics, and they are readily available in many gardening supply stores. Gardeners can also make their own with plastic sheeting or old plastic milk jugs. In all cases, the hot cap needs to be installed just above the ground to permit some air circulation, because otherwise the temperature inside could get extremely hot, and the plant might wilt or suffocate due to lack of adequate circulation.
Some gardeners use hot caps to prepare the soil for planting. In this case, hot caps are placed over the soil to encourage it to warm up for around a week before planting, and once seedlings are established, the hot caps may be reinstalled until the seedlings are bigger, or until the weather is more favorable. A hot cap can also ease the transition from greenhouse to the outside world in the case of especially fragile plants, allowing more temperature control in the outside world.
In gardens where pests tend to be common, it is a good idea to firmly stake hot caps so that they cannot be dislodged by wandering deer, rabbits, and other visitors such as cats. The hot cap can also act as a deterrent because a collection of these devices will make the garden more difficult to navigate, and therefore less enjoyable for animals to browse for snacks in. Additional deterrents such as mesh fencing, scarecrows, and electric fences can also be used to make the garden more inhospitable to unwanted guests.
Using a hot cap will not prevent plants from being frostbitten if the temperature takes a sudden plunge. The best way to quickly and cheaply prevent frost damage is to simply throw some old bedsheets over tender plants in the early evening. The bedsheets will trap the residual warmth from the day and act as a layer of insulation to reduce the risk of frost damage. Other frost-prevention products are also available, for those who find the bedsheet lacking in elegance or style.