Published on 09/08/97

'Ebb and Flow' System Can Cut Greenhouse Costs

What would you call a system that could grow better greenhouse plants, prevent groundwater contamination and cut labor costs at half the cost of water and fertilizer?

Marc van Iersel, a University of Georgia horticulture researcher, calls it "ebb and flow."

"Instead of having all the water and fertilizer that the plants don't use immediately go out on the ground, we can recycle it and use it another time," van Iersel said. "This can save up to 50 percent of the water and fertilizer."

Van Iersel's research labs are at the Georgia Experiment Station on the Griffin campus of the UGA College of Agricultural and Environmental Sciences.

Georgia greenhouses produced plants worth $95 million in 1996. That's nearly double the 1991 value of $49 million. The value of greenhouse plants has steadily risen each year, and experts expect that trend to continue.

In most commercial greenhouses, van Iersel said, growers apply water by hand with a hose or with overhead sprinklers. Excess water runs out of the greenhouse, along with any fertilizers mixed in.

"That risks contamination of groundwater and creeks that can cause algae bloom and other problems," he said.

With van Iersel's automated ebb-and-flow watering system, though, growers don't let the extra water run off. They collect it in holding tanks and use it again.

The system pumps water and fertilizer onto watertight tables holding germination trays or young plants. Growers leave the water on the table for a time, then collect the excess water in tanks. Later, they pump it back out for the next watering.

Workers can't overwater with the system. And every plant gets the same amount of water and fertilizer. That's hard to do by hand.

Ebb and flow helps grow healthier, more evenly sized plants that are all the same quality. "Home gardeners will get a better plant," van Iersel said.

There is a downside for greenhouse growers. Installing the system can cost about $120,000 in 10 acres of greenhouses. Van Iersel said the cost can be recouped in three to five years with savings in labor, water and fertilizer.