Plants absorb warmth from the sun throughout the day. Come dark, that heat slowly wanes. When temperatures drop at night, the condensing air around the plants becomes dew. If the temperature drops to 32 degrees F, the dew freezes on the flowers and leaves. While this type of borderline frost damages only a few leaves, colder temperatures kill less resilient vegetation. That means it's important to listen for freeze warnings in the spring and do whatever you can to protect the garden from harm.
Placing old sheets or blankets gently on top of the garden plants helps keep heat in the soil and protects the plant from frosty dew. For larger plants, tomato cages act as an alternative framework. Gardeners either place individual cages over plants followed by a layer of cloth that reaches to the ground, or they put the cages all around the perimeter of sensitive plants and hang a large piece of cloth suspended from the top down to the soil. Rocks anchor this larger sheet in place.
Empty flower containers protect against frost. Plastic ones are acceptable, but clay works more effectively, especially since plastic cracks from exposure to the cold. The pots chosen should offer the plant enough space so that no leaves touch the inside of the container when placed over top. The container goes upside down making a small house for delicate plants on the night of a frost warning. On the next day, the containers remain overturned until the temperature reaches above freezing.
Water insulates the soil and protects the plant roots from frost. When soil stays wet, it also remains warmer. For this method's success, water the plant's entire root system while the air temperature remains above 40 degrees F, while avoiding getting water on the flowers and leaves. This makes the soil release moisture, keeping the garden air a little warmer than it would be otherwise.
Plastic sheets make good garden insulation provided the plastic remains secured above the plants and hangs down around the entire parameter of the garden. Vegetation touching plastic easily sticks and freezes to the surface. Alternatively, placing the plastic in between plant rows covering as much soil as possible protects only the vegetation's roots. On average, both methods improve the garden's temperature by about 4 to 5 degrees.
Some plants react worse to frost than others do. Hibiscus, bay, geranium and peppers all easily damage when exposed to frost. That means waiting until frost warnings top in your region is the best way to protect your plants from harm. When personal schedules necessitate early plantings, it's safest to sow freeze-resistant vegetation. Examples include carrots, spinach and beets.
Container gardens offer space savings and flexibility. By putting flowers and vegetables into containers, a gardener can transport the plants wherever desired. When freeze warnings come, those containers move easily into a garage, enclosed porch or the house until the danger passes.