A greenhouse is a controlled environment structure that uses transparent coverings like glass or plastic to trap solar radiation, converting light into heat that warms the interior air. Understanding how to manipulate this environment is the first step toward successful cultivation. This guide provides foundational steps to help new users successfully set up and manage their controlled growing space.
Site Selection and Basic Setup
Selecting the correct placement for a greenhouse is crucial. The primary consideration is maximizing light exposure, which means siting the structure away from tall trees or buildings that cast shadows. In the Northern Hemisphere, orienting the longest dimension of the greenhouse east-to-west is recommended to capture optimal natural light, especially during winter months when the sun is lower.
The ground beneath the structure must be level and stable to prevent collapse or drainage issues, sometimes requiring a slight grade away from the foundation to manage runoff. Proximity to utilities, such as water and electricity, is a practical consideration for long-term use. Easy access to a water source simplifies daily watering, and electricity is necessary for powering fans, heaters, or automated vent systems.
Mastering Internal Climate Control
The greenhouse’s operational mechanism revolves around managing temperature and airflow. Ventilation is the most important element of climate control, preventing the air temperature from rising to damaging levels, typically above 27°C (80°F). This is achieved by opening vents, doors, or windows to exchange warm, humid interior air with cooler, drier exterior air.
Beginners can choose between manual vents or automatic openers that use a temperature-sensitive piston to expand and contract, opening and closing the vent without needing electricity. During peak summer heat, active measures often become necessary, such as using exhaust fans to move the entire volume of air every one to three minutes. Circulation fans should also be used to prevent stagnant air pockets and ensure consistent temperature and humidity.
Shading is another essential cooling technique, often implemented via shade cloth or paint applied directly to the glazing. Shade cloths are available in various densities, typically blocking 30% to 70% of sunlight, which reduces the heat load. Balancing shading with light requirements is important, as excessive shading can cause plants to become weak and unproductive.
Humidity management is closely tied to ventilation, as high moisture levels promote fungal diseases like powdery mildew and Botrytis. Opening vents and using fans helps move moist air away from leaf surfaces, preventing condensation and spore germination. In dry climates, increasing humidity can be beneficial and is done by misting the air or damping down, which involves wetting the floor and hard surfaces.
Supplemental Heating
For colder periods, small electric heaters can provide supplemental heat to maintain nighttime temperatures, particularly for tender plants.
Essential Greenhouse Growing Techniques
Plant care within a greenhouse requires specific techniques adapted to container growing. The choice of growing medium is distinct from garden soil, with most commercial mixes being soilless and containing components like peat moss, perlite, and vermiculite. These materials are selected to provide high porosity and good water retention while ensuring adequate aeration for the roots.
Watering practices must be precise, as the limited volume of a container makes plants highly susceptible to both drought and overwatering. Watering early in the day is recommended, giving the leaves and soil surface time to dry before evening temperatures drop, which reduces the risk of fungal issues. Automated systems like drip irrigation are highly efficient, but hand watering allows a beginner to monitor individual plant needs and soil moisture levels.
Fertilization schedules must account for soilless mixes providing little to no inherent nutrition. Container plants require soluble fertilizers delivered through the water, with the formulation often chosen based on the desired growth habit. Fertilizers containing a higher proportion of nitrate nitrogen help keep plant growth compact, while those with more ammoniacal nitrogen can stimulate rapid growth. Growers should regularly monitor the growing media’s pH level, as it can fluctuate.
Extending Your Growing Season
The primary advantage of using a greenhouse is the ability to manipulate the timeline of the growing season. Beginners can use the warmer, sheltered environment to start seeds several weeks earlier than traditional outdoor sowing dates. This head start allows for the cultivation of varieties with long maturation periods, such as tomatoes, peppers, and eggplants.
The controlled setting is also invaluable for overwintering tender plants that cannot survive frost or cold temperatures. Plants like geraniums or citrus trees can be stored inside, protected from harsh winter conditions.
Before planting greenhouse-raised seedlings outdoors, a process called hardening off is necessary, which gradually acclimates the plants to harsher outdoor elements like wind and direct sunlight. Seedlings are initially sheltered, then slowly exposed to the outside for increasing periods over a span of two to three weeks. This gentle transition prevents sun scorch and transplant shock, ensuring the plants develop the sturdier structure needed to thrive in the garden.