Growers Seeking Disease-Resistant Geraniums
June 7, 2022 Geraniums are a go-to for any gardener, as they offer delicate blooms and vibrant color. As for growers, they choose geranium cultivars based on their botanical characteristics, such as their vigor and habit. Most importantly, growers look for cultivars that are disease-resistant.
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“Very high on my priority list is the shape and size of individual leaves, because this is key to both disease control and plant habit,” says Albert Grimm, Head Grower of Jeffery’s Greenhouses in Ontario, Canada.
Grimm says botrytis is a saprophyte, and it needs dead or dying tissue to grow on to get a foothold in a crop. Lower leaves abandoned by the plant make an ideal location for this disease to get started. Some geranium varieties expand leaf size under low light more dramatically than others, Grimm says. Larger leaves allow less light to reach into the canopy, and this increases leaf abscission and botrytis incidence in high-density crops.
His operation is in Canada, so the geraniums are being grown at cooler temperatures and experience cool temperatures at garden centers. For this reason, Grimm looks for varieties that are cold-tolerant.
Vigor, Timing Important to Growers
Dominik Neisser of Vivero Internacional is looking for the opposite. He grows geraniums in California, so he orders heat-tolerant varieties. He says an ideal variety is even growing with the same vigor and flower timing, and most importantly, is disease-resistant.
Neisser says his favorite variety to grow is PAC’s Darko Series because it has a good shelf life, timing, and spacing, in addition to minimal bloom shatter and high resistance to diseases and pests.
Some varieties may be easier to work with than others based on their growth habits and how easily they can be modified.
“On the regal pelargoniums, the Candy Series is very easy to vernalize and can be programmed very well for flower timing,” Neisser says of a geranium series from Ball Seed.
Looking toward the future, Neisser says scented geraniums are popular, such as the Aroma Series from Westhoff. He encourages other growers to keep an eye out for all the varieties on the market.
“Keep trying out alternatives and keep the door open for the smaller breeders,” Neisser says.
Annie Glaser, Grower and Production Manager for Foertmeyer & Sons Greenhouse Co. in Delaware, OH, says her favorite geraniums are from the Fantasia Series by Ball FloraPlant.
“Over the last few years, we have worked really hard on developing the perfect recipe. From direct stick to ship is about 11 weeks for our 12 cm crop. They handle plant growth regulators very well and almost six weeks to the day after our Florel application, they’re spiking and starting to bloom,” she says. “While we do apply a B-Nine/Cycocel tank mix, irrigation really comes in handy for control as well. From a production standpoint, Fantasias are great. The blooms hold with little to no shatter and the size and consistency is perfect for shipping.”
Glaser looks for varieties with uniformity in their growing habit and vigor. Compact varieties are also beneficial because there is rarely enough bench space in a greenhouse, she says.
She is keeping an eye out for ‘Super Moon Red’ geraniums from Selecta One, which have larger blooms and darker foliage. They also have a more defined zonation on the leaves, which Glaser says is an attractive trait.
“One thing I can’t recommend more is subirrigation. This allows the foliage to stay dry and greatly reduces the instances of botrytis and other foliar diseases,” she says. “Keeping the blooms dry once they’ve opened is imperative to shipping perfect geraniums.”
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