English gardeners are renowned for their extravagant perennial borders. Look at most gardening books published “across the pond” and you’ll find photos of long, colorful tapestries – delphiniums, lupines, Himalayan blue poppies and primroses – the likes of which are difficult if not impossible to grow anywhere the climate is hot, humid, wet or freezing.
But Ruth Rogers Clausen, a horticulturist trained in England, has lived and gardened in the U.S. for decades. She knows the best of both gardening worlds.
Clausen is the author of several gardening books and gives lectures across the country about what to grow and how to grow it. She knows which perennials tend to be deer-resistant, which ones bloom for long periods, which ones will rot in a wet winter and much more. It’s based on nearly 50 years of gardening experience.
In her latest book, co-written with Thomas Christopher, “Essential Perennials: The Complete Reference to 2,700 Perennials for the Home Garden” (Timber Press), Clausen provides an exhaustive look at some of the most popular plants, along with notes about their hardiness, deer-resistance, placement, care and much more.
We talked by phone to Clausen recently at her home in Easton, Md. The following is an edited conversation.
Q: Your first book on perennials (“Perennials for American Gardens”) was published 26 years ago. What’s changed since then?
A: It’s quite different. The new one is much more up-to-date with newer cultivars in the marketplace. One example is Brunnera (perennial forget-me-not). There used to be a plain green one and a variegated one. Now there’s ‘Emerald Mist’ and several others. There are new plants coming out all the time and it’s very exciting. I wrote the book with Tom Christopher, who used to be a student of mine at the New York Botanic Garden in the ‘70s. (Christopher was also a longtime columnist at Horticulture magazine and has designed residential gardens for 40 years.)
Q: With all the new plants available for sun and for shade, how do you choose?
A: When I look at choosing a perennial, I consider several things. I want something that’s not going to spread a lot. It should flower a lot – will it bloom six to eight weeks? Those three-day wonders – perennials that only bloom for a few days – are not so much help to me in my garden. And it shouldn’t need staking. I also consider what the foliage is like. Does it hold up or will it look bad if the season is too wet or too hot or too dry? This is especially important for urban gardeners with limited space. Homeowners are not going to try a plant again if it fails the first year.
Q: What are some newer perennials that impress you?
A: Geums! I saw the natives growing in Glacier National Park (Montana). Two new cultivars are ‘Koi’ and ‘Mai Tai.’ ‘Mai Tai’ is exquisite, just a gorgeous color of apricot and peach. The Heucheras – coral bells – are very popular and there are new ones being developed every year. They have wonderful foliage. I like Heuchera ‘Green Spice’ and there’s a very new series called ‘Little Cuties’ – I’ve grown both ‘Sweet Tart’ and ‘Blondie.’ Mukdenia ‘Crimson Fans’ is quite new and has great color for a ground cover.
Q: The book includes deer-resistant perennials. What are some of your favorites?
A: In my garden, a fence isn’t practical and it would deny the deer the watering hole. I planted a lot of aromatic plants like yarrow and lavender with a strong fragrance. I also plant ferns and things with milky sap like dogbane and milkweed that they won’t go for. Heucheras are often on a “no-deer” list, but they’ll go for the green-leaved ones regularly. Baptisia, Hakonechloa grass and Ligularia are good ones, too, but one person’s deer herd is different from mine. There’s nothing that will keep plants absolutely safe except barbed wire.
Q: Any words of caution for novice gardeners?
A: Sometimes we have to be a little careful. Just because a plant is new doesn’t mean it will be hardy in your area. The testing for most of the new plants is extensive, but some plants bred in the Pacific Northwest, for example, may not be a hardy as those bred in the East. And look for perennials that bloom beyond spring. I look for plants that bloom in late June and July and in October and November. I was born and raised in England and my grandmother used to grow rock cress (Arabis caucasica), but there’s a new one called ‘Little Treasure’ that’s nice. But everything doesn’t have to be new. Don’t abandon old plants that still perform well in your garden.