Keep it moving

Fans have long been used for climate control in greenhouses. Their benefits are well documented: Proper air movement helps regulate temperature and humidity as well as improves photosynthesis, nutrient uptake, carbon dioxide/oxygen replacement, stem strength and resistance to disease.

However, commercial greenhouse owners all too often allow their careful nurturing to come undone post-harvest. When plants are being stored and transported to market, they can spend days in warehouses and tractor trailers with poor temperature control. Due to the plants being in close proximity to each other, and excess moisture caused by the lack of natural wind and light, they are more susceptible to fungus and disease.

Fortunately, the same benefits that fans provide in greenhouses also work during storage, transportation and other indoor operations. Overhead fans, directional fans and ventilation fans can maintain a dry space with uniform temperatures and humidity levels, which reduce the spread of disease and maintain healthy plant function.

Increased air flow, decreased losses

All major growers and distributors suffer some small percentage of product loss during the storage and transportation phases. For example, Bell Nursery grows more than 100 million ornamental plants each year, but used to lose about 5 to 10 percent of plants stored at their Elkton, Maryland, warehouse. Most of the loss was due to Botrytis, a fungus blight that spreads and thrives in moist conditions.

The problem is that plants are exposed to less sunlight and less effective ventilation systems during storage than they would be in a greenhouse, which prevents standing water from drying as quickly. Rapid temperature changes and high humidity also cause condensation, which exacerbates the problem.

Bell used floor fans in an attempt to reduce moisture and cut losses, but the airflow was too weak to penetrate the dense foliage on the shelves. The fans also couldn’t reach the tops of plants on the 6-foot racks.

“The plants are potted, so getting that constant, unobstructed, vertical air movement through the leaves is really important to keeping the products healthy,” says facility manager Jim Patton.

Bell installed three 24-foot diameter overhead fans that produced facility-wide airflow that hit the plants from all angles. The installation resulted in a drier facility and a 75 percent decrease in product loss, Patton says.

Photo courtesy of big ass fans

Strengthening plants with wind

Traditional greenhouses and distribution centers aren’t the only indoor areas that can benefit from airflow. Blossoming interest in locally grown, sustainable food sources, as well as changing laws and societal attitudes regarding other types of plants such as hemp, are resulting in more plants being grown indoors on a larger scale.

Plants grown in such areas are subject to the same conditions as Bell Nursery’s warehouse — lack of light, lack of wind and moist conditions. In addition to product loss from disease, such conditions can also result in weak, spindly plants.

For example, FoodChain in Lexington, Kentucky, raises fish and lettuce in a symbiotic relationship in order to reconnect people with their food. The nonprofit grows 320 pounds of lettuce, 20 pounds of herbs and 150 pounds of tilapia monthly through a sustainable, symbiotic process: the fish waste is used to nurture the plants and the plants are used to filter water for the fish.

“Our plants don’t have the same stimuli as they would if they were growing outdoors, and one of those stimuli is wind, which most people don’t think of as being necessary for plant growth,” says Rebecca Self, FoodChain’s executive director. “In essence, we had an environment that was too cushy for the plants, so we needed to give them a little bit of resistance.”

Foodchain installed two wall-mounted fans to blow across the lettuce. The breeze “makes them stronger, a little more rigid and they grow better,” Self says.

The facility is kept hot and humid for the tilapia, so an 8-foot diameter overhead fan meant to cool employees adds a little more breeze for the plants as well. The result is stronger, crisper lettuce, which is served in a local restaurant next door.

Putting heat in its place

Warehouses and many spaces used for indoor growing are utilitarian structures. Typically, they aren’t adequately temperature-controlled or well-insulated. For delicate plants, a single unexpected temperature swing can be the difference between life and death. Fans —particularly large, overhead fans — can help maintain ideal temperatures and improve the effectiveness of heaters.

Fans reduce thermal stratification, which is essentially the layering of different air temperatures in a space, from hottest at the ceiling to coldest on the ground. Hot air rises, so when a cold snap blows in and the heaters kick on, it could be hours before the space becomes saturated and the warm air reaches the plants on the ground. Exactly how long depends on factors such as ceiling height, the effectiveness of the heaters and the level of insulation.

The quickest and most efficient way to destratify large, open facilities is with large overhead fans, which are able to push the warm air down quickly and mix the air to create a uniform temperature.

Conclusion

There is no way to totally eliminate post-harvest product loss, but fans can help reduce it by regulating and equalizing temperature and humidity, as well as drying moisture. Additionally, greenhouses and indoor growing operations can benefit from gentle air movement that mimics natural conditions, creating stronger plants.