Coping with seasonal changes

When the seasons change, so do growers’ environmental concerns. Even in the greenhouse, where some growers can control their surroundings, changes in the weather can greatly impact the growing process.

Changing light levels

According to Matthew Kispert, horticulturist at CropKing, growers should be cognizant of higher light levels at different points in the year. He recommends looking first at irrigation. Higher light levels can lead to some nutritional issues that proper irrigation methods can help prevent.

“When you are moving plant starts into a greenhouse they are going to go through a period of hardening off,” Kispert says. “Expect some slight initial wilting during periods of high light, especially if you are running irrigation [with higher] EC levels. As the light levels increase, the water demand on the plant is going to go up.”

As this happens, Kispert says growers should lower EC levels. In essence, lean the ratio of nutrients to water more towards water to prevent plants from becoming too stressed. He also says using shade curtains as the season progresses is one way to prevent excess light from hitting the plants.

According to Kispert, there are clear dangers to not properly managing light levels. For starters, he says more serious wilting and some burning are among the problems that can be caused by rising light levels.

“The growing point is the most sensitive part [of a crop],” Kispert says. “One, it’s the highest point on the crop and two, it’s the smallest amount of tissue, so it’s unable to move as much water out as older leaves can.”

Rising humidity

Kispert says high humidity is a more common issue for older plants in the fall than it is for newly planted crops in the spring.

“In the spring, you usually have the opposite problem where the greenhouse is too dry,” Kispert says. “Air temperatures tend to be cooler as well.” As a result, Kispert says it can be beneficial for growers to artificially raise humidity levels in the greenhouse until temperatures naturally rise in the summer. Doing this can prevent crops from being hit by both increased light levels and a dry, stressful growing environment in the greenhouse.

In the fall, Kispert says warmer temperatures outside paired with a larger canopy in the greenhouse means there is going to be more water in the air. Signs that humidity levels are too high include condensation on the walls of the greenhouse — which could then drip on plants and make the plants susceptible to certain fungal pathogens — and on the denser parts of the plants, including the fruit and stems.  Issues with pollination might also arise from high humidity. 

“If you’re growing a flower crop like a tomato, and humidity is high, pollination isn’t going to be as effective since the physical act of shaking the pollen from the plant is harder because the pollen is stickier,” he says.

Raising the temperature in the greenhouse prior to sunrise will also help to lessen condensation.

To combat high humidity levels, Kispert recommends dipping the temperature in the evening by rapidly bringing in cold air. This will effectively shut the plants down and halt transpiration. If this is done correctly, it can prevent condensation the next day.  Floor heat should be turned off earlier in the day as well to lower root temperatures overnight.

Signs that efforts are working and other concerns

Kispert says there are obvious signs growers should look for when determining if their preventative measures are working.

“The turgidity of the plant should improve. It’ll show less wilting and get more uniform growth,” he says. “You should be able to see fewer dramatic changes in the plant over a set period of days.”

He also says that there are specific times during the day when growers should be looking for different issues. Condensation, for example, is most visible during the first part of the day, so growers should check plants for it first thing in the morning.

“Ideally, there will be less of a dramatic change in the crop between morning and noon in the physical appearance of the crop,” Kispert says.

And for any pest and insect issues that could come up, Kispert recommends taking stock of what treatment options are readily available before each growing season and ordering products ahead of time. That way, if an issue does occur, treatment can begin with products on hand, without having to wait for an order to ship.

As the seasons change, so should your greenhouse settings and procedures. For more tips on how to accommodate these changes, including specific humidity guidelines, check out the CropKing blog here.

Photo: iStock