Ruibal’s Plants Uses Supplemental Lighting To Speed Flowering

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Petunias that were grown under deep red/white LED lamps flowered 10 to 14 days earlier than plants grown under natural daylight.

When the weather gets warm, nearly everyone is itching to get outdoors. When the weather gets warm weeks earlier than normal, consumers and landscapers start their spring activities earlier, too, and that means they want their plants sooner.

The weather this spring really was unseasonably warm. The National Climatic Data Center (NCDC) reports that the United States experienced the warmest spring ever. The NCDC monthly climate report for May indicated that “with the warmest March, third warmest April and second warmest May,” 2012 had the warmest spring on record and the warmest year to date. The NCDC also indicated that this spring’s nationally averaged temperature of 57.1°F was 5.2°F above the long-term average.

These balmy temperatures inspired consumers to begin planting flowers. Unfortunately for eager gardeners and garden center owners, growers were not prepared to handle the early demand for spring color.

Customers Want Color Early

Matt Ruibal, vice president of Ruibal’s Plants of Dallas, Texas, normally receives requests for early flowering spring annuals, but this year’s demand was even greater than usual.

“Here in Dallas, whether they’re our landscaper or retail customers, they’ll buy plants in March if they’re blooming,” Ruibal says. “It’s that instant gratification mindset. They don’t like to wait for the plants to bloom, especially if their pansies are on their last legs. Many people have early season parties in March, and they want to have color for their yards.”
Ruibal says one of his main concerns during the first three months of the year is the need to have blooming petunias before March.

“With the naturally short day lengths during that time of the year, that is very hard to do,” he says.

According to Ruibal, it typically takes three weeks to get petunias to bloom in August when the daylengths are longer. A three-week turnaround would be perfect for getting the crops retail-ready in the spring, but the shorter days prevent this from happening. The good news for Ruibal and other growers is that supplemental lighting may mimic the effects of long, sunny days.

“If we start petunias in week two or week three in the spring, it takes 10 weeks to get them to bloom. We wanted to cut that time down to get them to a six-week crop if possible. That was our main reason for looking at using lights to get an early season petunia crop to bloom early,” Ruibal says. “Petunias that are started in week nine and week 10 can bloom in six weeks just using the natural day length. By extending the day length using lights with the early season crop, we thought we could reduce that bloom time from 10 weeks down to six weeks.”

Consider Cost

Based on the cost for the bulbs and the installation set up, Ruibal decided to trial LED lamps over other lighting alternatives.

“The cost for other light fixtures, such as high-pressure sodium lights, was easily 10 times more expensive than the LEDs,” he says. “The operating costs are also lower with the LEDs. They are very inexpensive to run compared to other grow lights.”

Ruibal said the LEDs were also easy to set up using standard light sockets.
“The standard sockets can be bought at Home Depot for less than $5 each. We wired the sockets with Romex for our trials. It was a very simple, cost effective way to install them.”

Testing Supplemental Light

Working with Hort Americas, an LED lighting supplier for the horticulture industry, Ruibal set up a trial to determine if supplemental light could speed up petunia flowering. Ruibal hadn’t done any previous supplemental light trials. The costs involved with installing the light fixtures were considered prohibitive for the 15,000 flats of petunias that he produces.

The light treatments included three different Philips GreenPower LED flowering lamps (deep red/white/far red, deep red/white and far red), TCP compact fluorescent lamps and the natural daylength. The far-red LEDs were used in combination with the compact fluorescent lamps.

All of the lamps were turned on for seven weeks beginning at the time of transplant. The lamps were turned on at midnight and off at 7 a.m.
Approximately 250 flats of petunias were grown under each light setup. All of the petunias were from the Dreams series and included the cultivars ‘Dreams Midnight,’ ‘Dreams Pink,’ ‘Dreams White’ and a mix.

Bloom Time Shortens With LEDs

“The plants flowered 10 to 14 days earlier, and that was pretty much across the board regardless of the flower color,” Ruibal says. “Petunias under the full spectrum LED lamps with deep red/white/far red LEDs, and the combination far red LED and compact fluorescent lamps flowered about five days earlier.”

Based on the results of the trial, he opted to use the deep red/white LEDs because these LEDs were found to be the most effective. Ruibal is planning to do another larger lighting trial for spring 2013 to confirm this year’s results.

“For the trial next spring we will increase the deep red/white LEDs from three tables to about 30 tables,” Ruibal says. “For the other lights the trial will stay the same. We will use two tables each for the full spectrum deep red/white/far red LEDs and the combination far red LEDs and the compact fluorescent lamps.”

PGRs Help Control Plant Stretch

One thing that Ruibal noticed with the petunias grown under the lights was a slight stretch in plant growth.

“There definitely is some stretch with the lights,” he says. “It wasn’t out of control. But there was a need for a growth regulator to keep the plants more compact. We made one application of Sumagic.

“Next year we might finish them with a late Bonzi drench. The PGR treatment will add a little more expense, but if I can get the plants to flower two weeks earlier, then that added expense would be worth it for us.”

Supplemental Light For Mandevillas

Based on the results that Ruibal got with the use of LEDs on petunias, he is considering trialing the lamps on other crops, such as a light study with mandevilla next year.

“We produce 1-gallon and 3-gallon mandevilla,” he says. “We can’t get them to bloom early like the Florida growers can. We can get them to a salable size by mid-April; we just can’t get them to bloom until mid-May.”
Ruibal brings in finished mandevilla from Florida during the first to second week in April.

“The ones that we grow don’t start flowering until mid-May,” he says. “If we can get those flowering by mid-April, we could cut a month off of the production time.”

Ruibal would eventually like to add lights to his propagation house.
“Although we haven’t done anything yet, that is definitely something we are considering,” he says. “During the early part of the spring season, our propagation house is completely full. Anything we can do to move the plants out two to three days sooner would definitely help us to get more turns out of the house. The lights would be used to speed up the rooting of
vegetative cuttings.”

David Kuack (dkuack@gmail.com) is a freelance technical writer in Fort Worth, Texas.
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