What Is a Greenhouse?
Everything you need to know about outdoor greenhouses.
When it comes to gardening, you may be wondering exactly what a greenhouse is and how it works. These structures, originally referred to as botanical gardens, have been used by gardeners around the world for centuries. They create ideal growing conditions for plants while also protecting them – especially those that are delicate or out-of-season – from excessive heat or cold. If you want to invest in your own greenhouse garden, read on to find out what exactly greenhouses do.
What Is a Greenhouse?
How Do Greenhouses Work?
Benefits of Greenhouses
Types of Greenhouses
What Is a Greenhouse?
A greenhouse is a structure in which plants are grown and protected from the elements. They usually have walls and a roof composed of a predominantly transparent material such as plastic or glass, which allow light in to create a regulated climate ideal for cultivating a variety of plants. Historically, greenhouses date back to the Roman era, where gardeners developed early protective growing structures to cultivate crops year round. Today, there are several types of greenhouses that can be found in various sizes, ranging from small home greenhouses to large industrial structures used to grow crops.
In short, a greenhouse traps heat from sunlight to create a warm, controlled environment where plants can thrive. Here’s how it works:
Sunlight Enters Through Transparent Panels
Greenhouse walls and roofs are typically made from translucent material like glass or polycarbonate. These panels allow sunlight to enter while protecting plants from outdoor elements.
Light Converts to Heat
Once outside, sunlight is absorbed by plants, soil, and other surfaces. That light energy is converted into heat (infrared energy), warming the interior.
Heat Becomes Trapped
The greenhouse structure slows the escape of heat, creating a warmer internal environment than the outside air. This is known as the greenhouse effect.
Ventilation Regulates Temperature & Humidity
Because heat builds up quickly, ventilation is essential. Opening vents, windows, or using fans helps regulate temperature, control humidity, and promote airflow for healthy plant growth.
The Right Conditions Support Photosynthesis
With warmth, light, and proper airflow, plants can efficiently perform photosynthesis – the process that fuels growth.
Ongoing Care Is Still Required
While greenhouses provide heat and light, gardeners must still manage watering, fertilization, and airflow. Warmer temperatures can increase evaporation, meaning plants may need more frequent watering and nutrients.
Extended Growing Opportunities
With proper accessories like covers, propagation mats, and shade cloths, greenhouses allow you to start seeds earlier, extend the growing season, and protect delicate plants.
Tip!
Browse our guide on How to Use a Greenhouse for even more tips and tricks.
Benefits of Greenhouses
Greenhouses are most commonly utilized by home gardeners, botanists, and commercial plant growers to control the environment for their plants. Read on to explore some of their benefits:
- Enhanced Control: Greenhouses help overcome environmental challenges by giving you greater control over temperature, humidity, and growing conditions.
- Year-Round Protection: They allow for year-round plant growth by protecting plants from seasonal shifts and harsh weather.
- Extended Seasons: Greenhouses extend growing seasons, allowing you to cultivate plants in late winter or early spring.
- Seed Starting: Greenhouses can be used for delicate processes such as germinating seeds, providing the consistent warmth and humidity that seeds need to sprout successfully.
- Exotic plant cultivation: They can even be used to grow exotic plants that wouldn't otherwise survive in climates outside their natural environments.
Tip!
Need help choosing between each greenhouse option? Check out our guides – Types of Greenhouses and Your Guide to Greenhouse Sizes – for even more information.
Frequently Asked Questions
What is the purpose of a greenhouse?
The primary purpose of a greenhouse is to create a controlled environment where plants can grow regardless of outside weather conditions. This allows gardeners to extend growing seasons, protect delicate plants, and cultivate species that wouldn't normally survive in their local climate.
How does a greenhouse trap heat?
Sunlight passes through the transparent walls and roof, where it's absorbed by surfaces inside and converted to infrared energy (heat). This heat cannot easily escape through the insulated structure, causing temperatures inside to rise 20–30°F higher than outside.
What can you grow in a greenhouse?
You can grow virtually any plant in a greenhouse, including vegetables, herbs, flowers, tropical plants, and seedlings. Common choices include tomatoes, peppers, cucumbers, lettuce, and ornamental plants that benefit from controlled conditions.
Do greenhouses work in winter?
Yes, greenhouses work in winter by trapping available sunlight and converting it to heat. However, in very cold climates, supplemental heating may be needed to maintain optimal growing temperatures for certain plants.
