How to Grow Basil in Greenhouse – Ideal Growing Conditions

Basil is one of the most popular herbs in the world. Growers of all sizes grow it across the globe. From home gardeners, through greenhouses, to large-scale indoor production facilities.

Basil is a warm weather crop. However, commercial growers grow it year-round, under controlled conditions. While basil may grow successfully in basic plastic greenhouses, many producers grow basil in advanced greenhouses, or even indoors. It’s also an extremely popular crop in hydroponic systems and in vertical farms.

This guide will cover the optimal basil growing conditions, regardless of production technique. These conditions are relevant for all basil varieties, including sweet basil, lemon basil, cinnamon basil, thai basil, etc.

What Are the Optimal Basil Growing Conditions?

In most of the world, basil is a summer crop, enjoying warm temperatures. However, basil is relatively easy to grow and will grow outdoors as long as there isn’t risk of frost.

Many growers grow basil plants in the ground or in soil. In this case, it’s best to use a well draining soil, while maintaining moist soil.

Another popular method of growing basil is in hydroponic systems, such as NFT or floating panels. In this case, you place the basil roots in water instead of soil. Growers add liquid fertilizer to the water, providing the nutrients the plants need.

When it comes to harvesting, it’s best to harvest basil leaves when plants reach around 6 inches in height. Home growers can harvest fresh basil as necessary, leaf by leaf. However, commercial growers usually allow the basil plants to grow larger. They then harvest the entire plant at once, before flower buds develop.

What Is the Ideal Temperature for Basil Cultivation

Controlling the temperature is one of the simplest ways to improve basil cultivation. By simply growing under a cover, you can increase temperatures, providing better conditions for your basil plants.

However, growing in a controlled greenhouse environment lets you further optimize conditions and maximize both yield size and quality.

As a warm season crop, basil plants grow easily in temperatures above 10°C (50°F). As long as there’s no danger of frost. They do, however, thrive in higher temperatures, with the ideal range being 26-32°C (80-90°F).

Basil seeds germinate best in temperatures of 24-29°C (75-85°F). In order to maximize the growing season, you can germinate seeds indoors during the end of winter or early spring. This allows seedlings to grow and develop true leaves before season. You’ll then be ready to plant your basil right when it starts warming up.

Alternatively, growing indoors or in a greenhouse can allow year-round cultivation and germination under ideal, controlled conditions.

Ideal Temperatures for Basil Production:

  • Basil growth – 26-32°C (80-90°F)
  • Seed germination – 24-29°C (75-85°F)

What Is the Ideal Humidity for Basil Cultivation

One of the most important factors for controlled environment basil cultivation is humidity. Like any crop, basil plants have a preferred relative humidity level, or VPD range.

When humidity is too high, or too low, your basil plants won’t be able to thrive. Outside of the optimal humidity range, basil develops and produces leaves at a slower rate. It’s also more susceptible to diseases and molds, and may even shrivel and die.

Both low and high humidity have a negative impact on basil plants. Low humidity leads to stress and causes the plant to close their stomata in order to stop transpiring and retain water. This slows down growth, as transpiration plays a crucial role in transporting nutrients through the plants.

Similarly, high humidity makes it difficult for the plants to transpire. When the air becomes saturated with water vapor, it simply cannot hold more moisture. This too slows down growth and leaf development.

Additionally, high humidity is a key factor in disease and mold development. It may cause outbreaks of some of the most common basil diseases, such as gray mold or basil downy mildew.

For basil cultivation, the ideal relative humidity range is around 70-85% RH. In terms of VPD (vapor pressure deficit), that’s 0.65-1.0 kPa.

Ideal Relative Humidity and VPD for Basil Production:

  • Relative humidity – 70-85% RH
  • VPD – 0.65-1.0 kPa

How to Maintain Optimal Humidity in Basil Greenhouses

As humidity plays a big role in greenhouse and indoor basil cultivation, it’s important to be able to control it.

In any closed agricultural environment, humidity always pushes upwards. This is due to the plants transpiring and releasing moisture to the air. Without a solution to reduce humidity, it’ll inevitably reach 100%. This leads to diseases and molds, or simply stunts growth and leaf development.

Ventilation and Heating Is Inefficient

The traditional method of reducing humidity is ventilation combined with heating. This method is simple. Growers release humid air through ventilation or by opening windows. They then keep heating continuously to make up for the lost heat and maintain ideal temperatures.

However, heating and venting is extremely inefficient. Constant heating to make up for the heat loss requires a lot of energy and has a very high cost.

Additionally, this method is often ineffective. If the weather outside is cold, cloudy, rainy, or humid, you may not see a reduction in humidity inside. This leaves growers with no solution to humidity, and inevitable mildew or other disease outbreaks.

Active Dehumidification Provides the Ideal Solution to Humidity

Active dehumidifiers, designed for horticultural settings, such as DryGair, provide the ideal solution for humidity control.

DryGair systems use an internal condensation technique to actively extract water vapor from the air. They then release it back to the greenhouse or grow room at the ideal humidity level. This means that you can avoid ventilation all together and fully control growing conditions from inside the space.

Of course, by closing and insulating the space, you both maintain ideal growing conditions, and retain heat inside. This cuts heating costs by an average of 50%, while providing full coverage against humidity. It also provides an optimal line of defense against common diseases.

Additional Tips for Commercial Basil Production

Improve Climate Control and Create an Active Climate with Air Circulation

Airflow is a crucial part of climate control in any greenhouse or grow room. The moving air helps disperse the humid pockets of air surrounding the plants. This improves growth by stimulating transpiration.

It’s important to note that not all types of airflow are equal. Directional fans, including both horizontal and vertical fans, create a gradient of airflow. This leads to different plants experiencing different conditions, depending on their location in the space.

Air circulation, as opposed to directional fanning, creates a circular airflow pattern. Circulation provides the same benefits as any fan, without the negative effects of linear airflow.

A proper air circulation mechanism doesn’t just stimulate plants by moving air. It also creates uniform conditions in the space. This means all plants experience the same, ideal growing conditions.

It also ensures that plants in far corners of the greenhouse don’t experience high humidity. Which often leads to mold outbreaks that can spread throughout the space.

DryGair dehumidifiers come equipped with a patented air circulation module to provide full humidity control, airflow, and uniform conditions.

Use Thermal or Energy Screens to Save Energy

Another way to boost your basil cultivation, while saving on heating costs, is using energy screens. As a warm weather crop, basil plants especially benefit from screens.

Thermal screens, sometimes called energy screens, help insulate the greenhouse and retain heat inside. As such, you can use them to maintain higher temperatures in the space, while heating less.

Many modern greenhouses take things further and install multiple screens. This improves insulation even more, providing more heat retention and higher energy savings.

Dehumidifiers and screens are a perfect combination. You can combine the two to further improve production and reduce costs. The dehumidification system controls humidity from inside the space, allowing it to remain fully closed and insulated with screens deployed.