A greenhouse is a structure designed to enclose a growing space, allowing for precise management of the internal environment throughout the year. This controlled setting extends the growing season and protects plants from harsh external weather conditions like frost, heavy rain, or excessive wind. Maximizing the harvest depends on the grower’s resources, climate control technology, and the specific intent behind the structure. A successful operation begins with a clear understanding of the environmental conditions that can be consistently maintained.
Determining Your Greenhouse Goals
Selecting plants requires an evaluation of the physical space and the level of environmental control achievable within the structure. Growers must assess available square footage and vertical space, which influences the choice between vining crops needing trellising and compact, bush-type plants. Understanding the local climate is also important, as it dictates the necessary investment in heating, cooling, and ventilation systems to prevent overheating or freezing.
The primary purpose of the greenhouse must be defined before any seeds are sown. A structure intended for year-round food supply requires a different setup and rotation schedule than one used simply for starting seedlings early in the spring. For instance, a heated greenhouse can simulate a tropical climate, while an unheated one acts primarily as a sophisticated cold frame, extending the season only on the shoulder seasons. The structure’s capabilities serve as the first filter for plant selection.
Heat-Loving Crops for Maximum Yield
Greenhouses excel at cultivating plants that require consistently high temperatures and a long, stable growing period. Indeterminate tomato varieties, which continue to grow and produce fruit throughout the season, thrive in this environment, favoring temperatures between 70–85°F (21–29°C). For optimal fruit set, these self-pollinating plants often require mechanical assistance, such as vibrating tools or shaking the plant, to ensure pollen transfer, a process typically performed by wind or insects outdoors.
Peppers, including both sweet and chili types, also benefit from stable heat, performing best when temperatures are maintained in the 70–85°F range. This consistent warmth prevents blossom drop, a common issue when outdoor temperatures fluctuate widely, thus increasing fruit yield. Cucumbers are another high-yield option, demanding warmer temperatures, ideally between 75–85°F, and a high-humidity environment. These vining plants are perfect for vertical growing systems, where they can be trained up trellises to maximize cubic space.
Eggplants require similar conditions to tomatoes and peppers, appreciating stable warmth to develop their fruits. Hand pollination—using a small brush to transfer pollen—is beneficial for eggplants, ensuring a high rate of fruit development. The controlled setting also allows for the consistent application of nutrients, such as potassium-rich fertilizer during the fruiting stage, which supports a large, sustained harvest.
Cool-Season Crops and Herb Production
The greenhouse structure can extend the harvest of crops that prefer cooler conditions, particularly during autumn, winter, and early spring. Many leafy greens, such as spinach, kale, and Swiss chard, thrive in unheated or minimally heated greenhouses, producing leaves even when outside temperatures are near freezing. These hardy crops often increase natural sugar production when exposed to colder temperatures, improving flavor and texture. The optimum temperature range for robust growth is around 50–60°F, with a minimum of 40°F.
Root vegetables, including carrots, radishes, and beets, can also be successfully grown in the ground or in deep containers within a cool greenhouse. The protected environment shields them from hard freezes and keeps the soil workable, allowing for a continuous supply throughout the colder months.
Herb production is well-suited to the greenhouse setting, offering a continuous supply of fresh flavor year-round. While basil prefers warmer temperatures similar to tomatoes, popular herbs like mint, cilantro, and parsley tolerate the cooler, moderate temperatures of a less-heated space. Maintaining temperatures between 65–75°F allows for frequent harvesting, and the enclosed space helps prevent pests that can rapidly defoliate these tender plants.
Propagation and Exotic Plant Options
Beyond direct food production, the greenhouse is invaluable for plant propagation, allowing gardeners to multiply their stock and get a head start on the outdoor season. Starting seeds indoors provides tender seedlings with the consistent warmth and humidity necessary for successful germination. This environment is particularly beneficial for heat-sensitive seeds that require soil temperatures higher than 70°F to break dormancy.
The greenhouse is also the ideal environment for asexual propagation techniques like taking cuttings, where a piece of the parent plant is rooted to create a genetically identical clone. For difficult-to-root woody plants, bottom heat, often provided by a heating mat, encourages rapid cell division and root formation, increasing the success rate. High humidity levels maintained in the propagation area help prevent unrooted cuttings from drying out before they develop a functional root system.
For hobbyists, the controlled climate opens the door to cultivating exotic and tropical species that could never survive the local climate outdoors. Dwarf citrus trees, for instance, can be grown in containers and protected from frost, allowing them to bear fruit consistently. Specialized plants like orchids, carnivorous plants, and certain succulents require precise humidity and temperature ranges that only a regulated greenhouse can provide.