9 Tips to Prevent Mold in Greenhouse – Mildew Prevention

How to prevent mold in a greenhouse is one of the most common questions growers at all levels have. This is no surprise. Every grower has encountered mildew or mold problems at one point or another.

What Is Mold in a Greenhouse?

Mold is a generic name for a wide variety of fungal diseases. It includes some of the most common greenhouse ailments, such as botrytis (gray mold) and powdery mildew. These can be detrimental to your crops, inhibiting growth and eventually even killing the plants.

These molds exist everywhere in the world, making them difficult to avoid. Mold spores can enter the greenhouse through the air or the soil, or even on equipment or clothing.

However, mold spores don’t have a negative effect on plants. It’s only when they develop into actual mold that they start harming crops. So the key to preventing mold outbreaks is to prevent mold spores from developing into an actual disease. Prevention is also an essential part, and the first step of IPM (integrated pest management).

What Causes Mildew and Mold Growth in a Greenhouse?

Growth of mold only happens when mold spores experience the right conditions to develop into actual mold. Different types of molds have different requirements.

Most common greenhouse molds develop in the presence of water or excessive moisture in the air (high humidity). They’re essentially a moisture problem. This is contrary to a common belief that molds are an issue of indoor air quality.

Many people are familiar with mold development in their homes, such as in a damp basement or on ceiling tiles. Though the types of molds in a household aren’t the same as in a greenhouse, the underlying principle is the same.

Most molds in a greenhouse are humidity related, so this guide will focus on these varieties. However, it’s important to remember that not all mold acts the same. For example, black sooty mold is a result of insect activity and requires different techniques to manage.

9 Tips to Prevent Mold and Mildew in Greenhouse

Mold and mildew prevention is an important part of greenhouse cultivation. Preventing these diseases significantly reduces crop loss, cuts back on toxic sprays and fungicides, and improves your product quality.

Here are 9 tips to prevent mold in a greenhouse:

  1. Use Dehumidifiers to Control Humidity

Greenhouses generally create a hot humid environment. This is due to the plants’ constant transpiration, releasing water vapor to the air. Without proper treatment, the greenhouse environment will remain very humid, leading to mold development.

Traditionally, growers open windows or use exhaust fans to release this moisture. However, this method isn’t very efficient. By releasing humid air, you also release heat, which then requires reheating, leading to high energy costs.

A more efficient way to deal with greenhouse humidity, is with dehumidifiers. Dehumidifiers, such as DryGair, remove water vapor from the air using a cooling system to create condensation. This water can then be drained and reused.

This concept is similar to what happens in an air conditioner. However, dehumidifiers are designed for humidity control, rather than cooling. So they’re much more efficient at removing moisture than air conditioning.

By controlling humidity from inside, you gain full control over your environment, without having to rely on outdoor weather conditions. This makes dehumidification the leading method to deal with molds in today’s commercial greenhouses and indoor grow rooms.

  1. Prune and Keep Space Between Plants

Humidity isn’t just a macro, greenhouse-wide problem. It can also be an issue on a micro level.

As plants constantly transpire, they surround themselves with water vapor. In dense foliage, this moisture has no where to go, leaving a pocket of humid air around the plant. These pockets of humid air are called microclimates, and they’re a leading reason for mold development. Once it develops, it can easily spread to other plants.

So, preventing humid microclimates is critical for mold prevention. The best way to prevent this issue is to keep adequate space between plants and prune plants with dense foliage.

  1. Improve Airflow

Another way to prevent humid microclimates from forming is by utilizing airflow. When air flows through the leaves and between the plants, it disperses the moisture, lowering the relative humidity your plants experience.

There are different types of airflow used in greenhouses and grow rooms, including vertical and horizontal fans. However, while these fans may disperse microclimates, they may create uneven conditions in the space, due to their linear directionality.

A better airflow scheme is air circulation. This is a fanning method that circulates air in all directions at once, 360°. By flowing evenly in all directions, air circulation disperses moisture while also creating uniform conditions throughout the entire space. Uniform conditions lead to more even growth, and more uniform products.

  1. Irrigate Properly

While previous tips tackled humidity, this one addresses free water in liquid form. Wet plants are the biggest catalyst for mildew and mold development. So, it goes without saying that irrigation can have a big impact on the issue.

Fortunately, proper irrigation is simple to pull off, keeping your plants completely dry. It’s always best to water straight to the soil, avoiding any contact between water and the plants themselves. It’s also recommended not to overwater. Wet soil can also contribute to molds, especially root rot, which may be fatal for most crops.

Using efficient drip irrigation systems, for example, can easily solve improper irrigation, providing an extra line of defense against fungal diseases.

  1. Maintain Radiation

Radiation is seen as one of the best ways to prevent mold, and it can definitely play a significant role. Proper radiation, coming from either sunlight or supplemental grow lights, helps evaporate water. This assists in keeping your plants dry, and in drying wet soil.

However, it’s important to note that lighting can also increase humidity. Evaporated water is, in fact, moisture. Radiation also increases the plants’ transpiration rate, further increasing the amount of water vapor in the air.

So, radiation is crucial for mold prevention. But you should also be aware of the amount of moisture it adds to your facility.

Powerful grow lights are often combined with dehumidification to offset the extra moisture. This combination isn’t just helpful in preventing molds and other diseases, it also stimulates the plants. It simultaneously increases photosynthesis and nutrient uptake, ultimately improving growth and fruit development.

  1. Remove Infected Plants

Our previous tips focused on reducing the presence of water or high humidity. However, there is more you can do to help prevent mildew outbreaks, or from spreading once outbreaks occur.

Active mold outbreaks can spread quickly, especially in a closed and crowded growing facility. So, if you spot symptoms of mold, such as powdery mildew or gray mold, you should immediately remove the infected plants.

This may seem simple and intuitive, but unfortunately growers often neglect this. Removing infected plants as soon as possible can have a huge impact on managing mildew outbreaks and minimizing losses.

  1. Keep Soil Clean

Mold can grow on almost any organic material. Dry leaves and other debris that lands in the soil is a hotbed for mold development and other diseases. This is especially true when the soil is wet or damp, as it often is.

So, routinely cleaning your soil and removing debris can help prevent mold development. This is another simple action that can significantly improve the overall health of your greenhouse.

  1. Avoid Injuring Plants

The final tip on this list isn’t just important for mold prevention, but for the overall health of your crops.

Injuries cause plants stress, making them much more susceptible to all types of infections. Furthermore, open wounds act as an easy entry way to mold spores, pathogens, and even pests, leaving your plants vulnerable.

So, an important part of preventing mold outbreaks is to keep healthy, uninjured plants. Make sure to be careful when handling your crops and operating equipment in the greenhouse.

More Information on Greenhouse Mold Prevention

Preventing mold and mildew in the greenhouse can seem like an impossible task. However, if you incorporate all of these tips properly, you can significantly reduce outbreaks, almost completely preventing them.

For more information, or for a free consultation with our experts, please feel free to contact our team.