A greenhouse is a building made mostly of glass or plastic, designed to trap heat and shelter plants. Inside, a grower can stretch the season, keep out pests, and control water and temperature more precisely than any open field allows.

The idea took hold in 17th-century Europe, when wealthy collectors built glasshouses for exotic plants. Dutch growers turned it into an industry. Today the Netherlands packs thousands of hectares under glass, and Spain's Almería region is a sea of white plastic. Greenhouses range from a home gardener's cold frame to industrial ranges the size of small towns.

What they make possible

• Year-round tomatoes, cucumbers, peppers, and lettuce
• Seedling production for transplanting outdoors
• Hydroponic and vertical growing systems
• Protection from hail, wind, and many insect pests

The trade-off is energy. Heating glass in a cold climate costs money and produces emissions. Modern designs use thermal screens, geothermal heat, and LED lighting to cut the bill.