Special Report: Combining Spring Bulbs and Perennials

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Perennials anchor our landscapes, but it can take quite awhile before the blooms of some types appear each season. Having interesting leaves—especially early in the growth period—helps quite a bit (heck, some perennials are grown just FOR their leaves, especially by folks who are 'blessed' with abundant shade). But what if the flowers of a different plant were to ride above those leaves early in the season, and then magically disappear just before the perennial's flowers show up? That's what happens when you drop the right Spring bulbs into the right kind of perennial.

For the past four seasons, Dr. Bill Miller, director of Cornell University's Flower Bulb Research Program, has been doing just that; testing combinations of bulbs and perennials to see what looks the best for the longest period of time. And now the results are in: A list of the 15 most successful combinations has just been released by Cornell and the Netherlands Flower Bulb Information Center.

The timing is perfect! Dr. Miller and his team used existing perennial beds to test their combinations, and the time for you to plant Spring bulbs in your perennials (or anywhere else) is coming up soon—around Halloween in the far Northern regions and between Halloween and Thanksgiving in the rest of the country (at least where there's enough of a winter chill to make Spring bulbs happy).

"We didn't plant any new perennials for these studies", stresses Dr. Miller, "so people can take a look at our results, figure out which kinds of bulbs would be best to interplant in the perennials they already have in their landscape, get the bulbs in the ground and see the results immediately next season.

"Of course, our main goal was to find pairings where the growing perennials would allow the bulb's flowers to be fully seen, and then hide the fading leaves of the bulbs after the flowers are done." This, of course, solves the oldest problem with Spring bulbs—allowing their leaves to collect the solar energy necessary to fuel the following year's flowering without having to look at those leaves as they become less and less attractive.

One of the perennials that provided the best foundation for this task was Rheum (pronounced "re-um", with a long 'e') palmatum, a large leafed cousin of rhubarb. It hit the Top 15 twice, working well with white anemones and white hyacinth. "The leaves of the Rheum species we used are really red early in the season, and look great underneath the white bulb flowers," says Dr. Miller.

Penstemon is another perennial that can work with two kinds of bulbs—in this case, hyacinth or daffodils. "We used 'Husker Red' penstemon because its early leaves are a wonderful dark purple; but you could drop any full-sized daffodil or hyacinth into any leafy penstemon and get good results," says Dr. Miller.

"Same with oriental poppies and phlox," he continues; "I'm confident that any full-sized daffodil will look good coming out of just about any Oriental poppy or phlox. And any of the so-called "black tulips" like 'Queen of Night' should look great growing out of almost any sedum, although dark leafed sedums add the most dramatic accent to those deep purple tulips. Asters and ornamental alliums also combine well in general."

As do geraniums and tulips, it turns out. "We tested 'Don Quichotte' and 'Splish Splash' tulips with 'Claridge Druce' Geranium, and both worked well—as would any full-sized tulip." And the sight of 'Ballade' tulips growing out of 'Mayflower' geraniums led to pure horticultural poetry in the final report {Quote}:"The early geranium foliage makes the tulip blooms look as if they are floating in a sea of green." Who says researchers got no soul?

Hiding fading bulb leaves is job #1, of course, and all 15 combinations achieved that goal—with most of the pairings blooming in sequence, and thus creating a longer show in that one spot. But the researchers also praised a few pairs that bloomed at the same time, like daffodils and Pulsatilla (an anemone cousin sometimes called the 'Pasque Flower') and tulips with bleeding heart. ("We used the 'Parade' variety," notes Dr. Miller, "but any big red tulip will work well in bleeding heart".)

Other good 'foundation perennials' include yarrow, Potentilla, Lamb's Ear, and bugbane—a perennial with a long history of use as an insect repellant (its scientific name, Cimicifuga comes from the Latin word for bedbug). It's a useful family of plants; another member of the genus is the famous women's herbal remedy, Black Cohosh.

Here's a link to the complete '15 Best' list—with sequential photos of the plants as they blend together early and late in the season.

Here's a longer list of 44 successful bulb and perennial combos from Cornell.

And to some bulb and perennial planting tips, so you can get your combos right the first time.

Now, the specific varieties used by the researchers are named in each combination, and you're more than welcome to seek out the exact same bulbs (if you can find them). But since you'll be working with your existing perennials, Dr. Miller suggests you use the results as more of a general set of guidelines.

"Look at our sequential photos to see how the leaf textures and colors of the plants compliment each other throughout the season, note the required heights of each plant and then put in the kinds of bulbs you think might work well with your perennials" he says.

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