Why Do Plants Need Humidity?
In order for a plant to stay healthy and fresh after it is harvested, it needs to maintain as much of its life-giving moisture content as possible. Considering modern day refrigerated storage conditions, this is extremely difficult. The more moisture a plant loses, the faster it will deteriorate. Since the rate at which a plant loses moisture (transpires) is directly related to the Relative Humidity (RH) of its storage environment, close attention should be paid to the RH of produce and floral storage rooms.
What is Relative Humidity?
Relative Humidity is the ratio of the actual amount of moisture in the atmosphere to the amount of moisture it can hold. So an RH of 100% means that the air can hold no more water (like on a rainy day) and an RH of 0% indicates there is no moisture in the atmosphere.
The properties of air are such that when it is dry, it has a tendency to pull moisture into it. So when the air in a storage room has a low RH it will extract moisture from produce that is stored there. This is where it becomes important to keep a high RH inside of storage rooms. Here's an example. A room that has an RH of 45-55% when it's empty will have an RH of 85-90% two hours after product is added. Where did the moisture come from? The product.
In refrigerated storage rooms, warehouses and containers such as coolers the average RH is about 55%. That's before plants are added to the environment. Since plants are made of about 98% water, an RH of 55% is like a dry sponge that absorbs as much water from the plant as it can. That is why it is essential to add humidity to your coolers. The closer the RH% is to the water content of the plant, the less water will be lost.
Photosynthesis is the process by which plants turn light energy into chemical energy (food) and is also the reason they transpire.
In order for carbon dioxide, a necessary component for photosynthesis, to be absorbed by the plant cell, the gas must pass through a solution. Since evaporation occurs wherever moisture is exposed to air, the plant must keep releasing water through its cells to absorb the carbon dioxide. In an effort to absorb as much carbon dioxide as possible, plants transpire from every square inch of their surface area; including leaves, stems and fruits.
The end result is that plants release more than 90% of the water taken in by their roots back into the air as water vapor. When the plant is growing in the ground this process is stressful but manageable. After harvest, when transpiration continues even though the fruit of the plant has no roots attached, the process will eventually take its toll. The plant (in most cases its fruit) will dehydrate and eventually become inedible.
