Season extension

Season extension is a vital practice in agriculture. It allows farmers to grow crops beyond their natural outdoor growing seasons. This method provides extra time for harvesting. It can also be used to grow food during rainy seasons in certain climates. Most crops stop growing when daylight drops below 10 hours. Season extension helps bypass these natural limits. Growers use various tools to manage temperature and light. These methods ensure plants can thrive even when the weather is harsh.

Many techniques rely on unheated structures. These are often called cold houses or unheated greenhouses. They protect plants from freezing temperatures and drying winds. They also shield crops from frost, snow, and ice. These structures can extend the season for hardy vegetables into the fall. Sometimes they even last through winter until spring. If temperatures inside drop below 32 degrees Fahrenheit, supplementary heating might be used. This keeps the environment stable for the plants.

Some greenhouses use passive solar design to stay warm. These are called passive solar greenhouses. They use thermal mass to keep the air warmer on overcast days. They also stay warmer at night. Other advanced systems move heat from the ground to the greenhouse. These include ground-coupled heat exchangers and thermal chimneys. Some use thermosiphons or "climate batteries" to store ground heat. These methods provide energy without using much fuel. They represent an elegant way to manage heat.

Polytunnels are another common type of structure. They consist of curved frameworks covered in thin polyethylene plastic sheeting. There are two main sizes of these tunnels. Low tunnels are only 2 to 4 feet tall. A person cannot walk inside them and must lift the plastic to reach plants. High tunnels are much larger commercial buildings. They are tall enough for people to walk through easily. Some are even large enough to operate tractors inside. Some high tunnels use two layers of plastic. Air is blown between the layers to increase insulation. This process can reduce the amount of sunlight reaching the plants.

Row covers are lightweight fabrics used for frost protection. They can be placed directly on crops as floating row covers. They can also be placed over hoops or wires. These fabrics allow rain to pass through easily. They also allow plants to transpire, which means they can release moisture. This is different from plastic sheeting which holds moisture in. A row cover works by letting frost form on the fabric instead of the leaves. Outside covers must be clipped, pinned, or weighted down. Inside covers can simply be draped to the ground.

Smaller gardens often use temporary coverings for protection. These include glass cloches or newspaper cones. People may also use baskets, plastic bits, or mulches. Mulches like hay, leaves, or straw are pulled on and off daily. Mulch can also be applied directly to the soil. Organic mulches like straw or compost help retain heat. They can also add heat through decomposition. However, growers must be careful with animal manure. It can cause chemical or thermal burning. It can also introduce coliform bacteria. Using aged compost is often better because it is safer.

Soil management is another way to extend the season. Raised beds are areas where soil is piled higher than the surrounding ground. This soil can be more than a foot deep. Because the soil is loose and elevated, it heats up faster in the spring. This allows for much earlier planting. Hotbeds are another method using heat from compost. A mass of hot compost is placed under a thin layer of soil. The plant grows directly above the rising heat. Both methods help plants start their life cycles sooner. This maximizes the total growing time available to the farmer.