Search Leads to Bulbs With Reliable Repeat
Customer photo of the Perennial Tulip Collection by Diane Rusin Doran of Glenelg, Md.
Without a doubt, tulips are the foundation of many springtime gardens. But gardeners often find that after two or three years of flowers, their tulips produce only leaves and then disappear entirely. Why don't tulips multiply and re-bloom like daffodils and crocuses?
The main reason is they don't like our climate or our soils. Tulips are native to the mountains of central Asia, where the soils are thin and rocky. Cool, wet springs are followed by hot, dry summers. In this type of environment, the bulbs stay bone dry throughout their summer dormancy period. When fall comes, and the rains begin, the bulbs' growth cycle begins anew.
In most regions of the U.S., there's enough rainfall to keep soils moist throughout the summer (or if there's not enough rain we keep the ground moist ourselves with irrigation). Tulips bulbs that spend the summer in moist soil, tend to split apart and are also susceptible to fungal diseases. To ensure a colorful display of tulips every spring, many home gardeners and most public gardens plant fresh tulip bulbs each fall. Though it's fun to choose new varieties and new color combinations every year, many gardeners would welcome the opportunity (and cost savings) if they could plant tulip bulbs once every five years, rather than each fall.
The quest for a truly perennial tulip began in earnest about 25 years ago at Michigan State University. Leo Vandervlugt, president of Dutch Gardens, was a graduate student at MSU, and part of the research team. "My family has been in the bulb-growing business for four generations," said Vandervlugt. "There was no question that my graduate work would have something to do with growing bulbs." Vandervlugt and his colleagues at MSU tested hundreds of tulip varieties, and found a number of them that re-bloomed the following year with no loss of vigor. "After blooming, most tulip bulbs split into a number of smaller 'daughter' bulbs," said Vandervlugt. "These smaller bulbs don't have the energy that's needed to produce a flower the following year."
"In our research," he went on, "we were looking for bulbs that didn't split after blooming. Bulbs that stayed intact for one, two, three or even five years retained the ability to re-bloom. By trial and error, we identified a few varieties that retained their primary bulb for quite a few years before splitting." Vandervlugt also found that if they grew the tulips in the production fields for seven years—one year longer than usual—they could produce an extra-large, 14-cm tulip bulb that was more likely to provide several years of bloom.
In Holland, research on perennial tulips is ongoing. Dutch growers are now producing several of the varieties that proved to be reliable in the University of Michigan testing. Dutch Gardens offers five of these perennial tulip varieties, as well as a Perennial Tulip Collection. These jumbo, 14-cm bulbs produce extra-large blooms in mid-spring on 20" to 24" stems. Color choices include red, white, pink, yellow, a red/yellow bicolor and the collection, which features all the colors.