Greenhouses are structures used to grow plants in a controlled environment, providing protection from the elements while promoting healthy growth. Greenhouses come in various sizes and designs, from small, portable units for home gardeners to large, commercial structures for professional horticulturists. They are made from materials such as glass, polycarbonate, or plastic to allow sunlight in while maintaining temperature and humidity levels. Shopping for greenhouses online provides a range of options, allowing you to find the right greenhouse for your gardening needs and available space.