Modern greenhouses can range from gigantic, tree-housing glass and steel habitats to miniature, backyard DIY set-ups. Solar radiation passes through the transparent membrane and is absorbed by the floor and plants within. Since air is not able to escape, the thermal energy is trapped within the greenhouse, raising the ambient temperature. These are often ventilated in order to prevent temperatures from rising too high, and to reduce extreme humidity. Windows can also be opened and closed in order to release trapped heat. Light is usually provided directly by the sun, but LED lights can be installed if extra light is required. If these core elements are in place, a greenhouse can function properly:
Core Parts of a Greenhouse:
Temperature Regulation
- This will depend on the kinds of plants you’re growing, and what type of greenhouse you’ve installed. During the summertime, safe temperatures range between 60- and 85-degrees Fahrenheit. In the winter, the lowest temperatures can drop somewhere around 45 degrees Fahrenheit -- however this is not ideal for hot or warm greenhouses. For most plants, the best place for them to grow is somewhere between 60- and 75-degrees Fahrenheit. It still may be a good idea to research your plants' particular desires beforehand.
- Warmth in a greenhouse is primarily fueled by the sun. This can come directly from the sun’s rays, from the warmth of the Earth itself, or by storing thermal energy in so-called ‘thermal batteries’. If temperatures get too hot, cooling periods are accomplished through ventilation. This can be a series of fans, or merely cracking a few windows to let the breeze inside.
- One of the easiest and oldest ways to construct and insulate a greenhouse involves one or more earthen walls. A sunken or partially sunken greenhouse can be built by carving into a hillside, or through excavating a few feet so your greenhouse foundation can rest underground. Within the earth, the molten core and packed soil maintains a fairly stable temperature underneath the first few feet of dirt, regardless of the temperature on the surface. A greenhouse nestled within or beside this exposed soil has access to the earth’s internal heat. Warm air inside the greenhouse has less space to escape, and the heat from the earth itself has an opportunity to transfer to the greenhouse directly.
- If additional heat is needed, electric or gas heaters are also viable options. However, heat will need to be circulated through the air by fans, or another form of ventilation system, to ensure that it’s properly distributed. This way, each plant is adequately warmed, and there is no hot vs. cold side to your greenhouse that complicates the growing process.
- Equipment can be used to make this process easier to monitor and maintain. There are some obvious answers here, like a temperature sensor. This can range from a simple thermometer, all the way to an automated process which monitors the ambient temperature and adjusts the ventilation system remotely. A temperature alarm can be installed which issues alerts for any potentially dangerous drops or gains in temperature. Some advanced types of temperature alarms can be accessed remotely from your computer or phone.
Sunlight
- 6 hours of sunlight is the average minimum that most plants need to be happy. Just like all other factors, this differs between plants, and may need to be adjusted accordingly.
- How much light can enter your greenhouse, and for how long, is determined by several factors: your location, the material of your greenhouse panes, the season, and any overhanging deciduous trees that may provide shade during the day. Pay attention to how light distributes itself throughout the greenhouse. Equally diffused light allows for every hungry leaf to get its fair share. Additionally, the light reflecting and bouncing back into the open space means every side of the leaves are exposed to sunlight.
- The placement of your greenhouse will change how much sunlight is able to reach it throughout the year. This depends on your location in relation to the equator. Those in the Northern Hemisphere are better suited with a greenhouse situated as far southeast as possible. This provides the most access to light, especially in the morning. Morning light avoids the shadows found during high noon and is usually the most helpful for plant growing.
- Not all shade is a negative. If direct sunlight is burning your plants, or if things are simply getting too hot, shadows cast by leafy trees can provide some relief. This is likely most effective on the west side of your greenhouse, so that morning light can access the building freely. During the green seasons, light is diffused through foliage, protecting vulnerable plants. In the Winter, bare branches allow the maximum amount of light to penetrate when it's most needed.
- If you have particularly light-hungry plants, or if you live in a place where sunlight is hard to come by, additional light might be a necessity. LED grow lights come in a variety of shapes, sizes, and prices. Artificial light comes with its own set of benefits. It may come as a surprise to learn that the actual color of the light has a large effect on how well it suits plant growth. Light with a heavy red quality is typically best for hungry plants. LED lights can also be installed and automated to maximize the amount of light applied each day. There is no waxing or waning of quality light during different times of day or seasons, and leafy trees or neighboring houses’ shade is no longer a concern.
Moisture and irrigation
- The amount of water you’ll need to access will grow with the size of your greenhouse and the size of your garden aspirations. It’s always a fair option to manually water your plants, whether via a personalized watering can or a large soda cup you’ve kept around forever. However, for happier plants, and less work in your day, an automated irrigation system may be the right choice.
- One of the simplest and most space-efficient choices comes in the form of either irrigating mats or trays. Both are porous materials, placed underneath the plants and pumped full of water in order to maintain enough moisture. Water is drawn up into the root system until the soil is saturated. This directs thirsty roots downward, creating a deeper, more stable root structure. Since water is being pulled upwards only when it’s needed, there’s less opportunity for overwatering, or excess runoff.
- Overhead sprinklers are fairly easy to install and can be very efficient if used in tandem with some form of moisture regulation. Sprinklers and spigots can be attached to timers in order to automate the process and ensure that the plants never become too dry. Water spraying from overhead, however, means that moisture isn’t directly applied to the root zone. Water drips down from leaves and stems to reach the soil. It’s difficult to ensure that this process is applied uniformly, and waste from runoff can become a concern.
- Drip irrigation is one of the most popular choices for hobby and industrial greenhouses alike. Drip piping, or drip tape, is placed within each plant’s container, directed at the root zone. Water is added incrementally and doesn’t spend time collecting upon or dripping down foliage. Since excess or standing water increases the chance for diseases and pests, this is a healthy choice for most plants. A drip irrigation system is not usually a large investment, but it does cost more to install and maintain than your mom’s watering can.
Ventilation and Air Circulation
- As a greenhouse collects heat inside, the temperature will continue to rise until there’s a way for it to escape. In the early years of greenhouses’ conception, vents would be accomplished by carving out small holes in the walls of the growing room, or by simply opening a few windows to create a cross breeze. The glass and steel greenhouses of the late 19th and early 20th century often had vents installed in their roofs. As polyethylene and plastic greenhouses have become more common, roof-attached vents have accordingly become more difficult to install. This has primarily been replaced through ventilation systems equipped with fans. These fans are installed at either end of the greenhouse, pulling in air from one side, and pushing it out the other.
- Not only is proper air circulation essential for temperature regulation, but it also has a direct impact on the health of your plants. Plants need fresh air, specifically CO2, in order to photosynthesize and grow. Constantly circulating new air means that no plant is left struggling to breathe and eat well. Additionally, a gentle breeze hardens and stabilizes the plant’s root and stem structure, creating more hardy and durable crops.
