The dirt on geraniums has nothing to do with their everlasting popularity, their bright and cheery blooms, or their fancy and fussy leaves. Those geraniums that are ubiquitous in window boxes throughout the summer months are exceedingly disease-prone and require a lot of special care in production.

In the past two years, millions of geraniums were destroyed under orders of the U.S. Department of Agriculture after they were linked to diseased cuttings imported by a California grower. The cuttings were infected with a bacterial disease, ralstonia solanacearum, that is on the government’s bioterrorism list and is a potential threat to crops such as potatoes, tomatoes, and peppers.

Karl Batschke, production director at Oglevee, Inc. in Connellsville, Pa., the country’s largest geranium producer, said his company’s farms have never had a disease problem, but he said the outbreak “doesn’t help the industry as a whole.”

In the late 1970s, Oglevee developed a rigorous scientific process to eliminate bacterial and viral pathogens that had in the past threatened to destroy the geranium industry. The process is designed to prevent disease among the 30 million annual cuttings the company produces in the United States, Kenya, and Mexico and ships on to wholesale growers, who produce tens of millions more for the consumer market.

According to Oglevee, the process has become nearly standard throughout the industry and has allowed the development of geraniums that are far more vigorous, free-flowering, and disease-resistant than those of the past.

Although geraniums have been around for more than 200 years, probably the most popular was the “Martha Washington” geranium,referred to today as regal geranium or pelargonium x domesticum. Today’s regal geraniums bear little resemblance to the Martha Washingtons likely grown by your grandmother.

Regals are an upright geranium with stiff, deeply toothed, pleated leaves and large, rounded blooms that come in a multitude of colors aside from the standard rosy red: bicolor white and dark purple, hot pink, raspberry, lavender, salmon, burgundy, and many more. Regals bloom heavily in the spring and sporadically in the summer and fall.