Updating an Historic Garden

By: Glenn Withey Charles Price

Glenn Withey and Charles Price have been resident curators of Seattle’s Dunn Gardens since 1997. Avid plantsmen with a passion…

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Charles Price and Glenn Withey have been resident curators of Seattle’s Dunn Gardens since 1997. Avid plantsmen with a passion for…

More From This Author
A Rhododendron yakushimanum hybrid with soft brown indumentum on the undersides of the leaves, which apparently makes the plant more resistant to the various mildews plaguing the rhododendron collection. Authors’ photographs

A Rhododendron yakushimanum hybrid with soft brown indumentum on the undersides of the leaves, which apparently makes the plant more resistant to the various mildews plaguing the rhododendron collection. Authors’ photographs

Living in a garden that has been around for over ninety years definitely has its challenges. When the two of us moved into the curators’ house at the Dunn Gardens, twelve years ago, our initial plan was to stay on for only a year. Little did we know . . .

It has been a pleasure, albeit at times vexing, to work within a historic garden. What was once a ten-acre, summertime retreat for Arthur Dunn’s family, designed by the Olmsted Brothers in 1915, has, over the years, become three year-round residences, occasionally open to the visiting public, covering a little over seven acres.

Edward Dunn, Arthur’s second son, was instrumental in arranging for the gardens to be preserved. Ed was a distinguished horticulturist who loved rhododendrons and their companion woodland plants. He was also an inveterate plant junkie, as we like to call people who cannot “just say no” to a new plant.

The woodland garden in spring, rhododendrons stealing the show beneath a canopy of trees, both deciduous and evergreen

The woodland garden in spring, rhododendrons stealing the show beneath a canopy of trees, both deciduous and evergreen

A Woodland Garden

When we began to work in Ed’s portion of the garden, the springtime rhododendron show in his woodland garden was spectacular. Before long, however, a disease that had run rampant among many of the rhododendrons began to show its cards. Whereas the “old” powdery mildew left a whitish coating on the leaves, this “new” form of mildew (several species of Microsphaera) left the foliage blotched and disfigured—until the leaves fell off. Ed had planted his seedlings closely and seldom returned to space them appropriately. The crowded beds stifled air circulation and exacerbated the mildew problem.

One treatment option was to spray with any of several fungicides that would help control the mildew. The drawback to this approach was that, once begun, the program would never really end; we would have to continue spraying indefinitely. More importantly, we wanted to avoid the use of potentially toxic chemicals in the garden. There were also several organic methods recommended, but all of them entailed more effort than we were willing to devote to the project. We did spray for years with a specially made “soil soup,” but could see no measurable results. In the end, we opted for “Darwinian gardening”—survival of the fittest—and simply eliminated the most susceptible plants from the garden.

We also thinned the tree canopy, as there was an excess of shade and a distinct lack of air circulation. Decisions to remove certain trees were fraught with controversy. While we both love trees, we also believe that every plant has to earn its keep. The garden has been around for almost a century, and our outlook is to consider the second century, not just the near future. A carefully thinned canopy will remain healthier, longer than will an overcrowded canopy where many of the trees struggle to hold their own. After all, the garden is not a natural forest.

When it came time to add new rhododendrons, we selected those whose leaves are covered with indumentum—a fuzziness, usually on the leaf’s underside. We observed in the Dunn collection, and confirmed with fellow enthusiasts, that such foliage seemed to offer much more resistance against this insidious disease. After almost a decade, we have had no problems with the mildew causing significant harm to plants with indumented foliage.

The shade of so many large trees can be a challenge when adding new plants to a woodland garden. As beds are cleared of invasive weeds, we try to add plantings that offer interest throughout the year. For the health of both the existing trees and the new plants, we prefer to start with smaller-sized plants. As tempting as it may be to bring in specimen-sized shrubs, we have found that these larger plants rarely settle in and thrive in the way a smaller plant does. Tree roots have the advantage of being there first, and they easily usurp most of the water in the soil. Perhaps, over the course of a decade, if one faithfully watered a specimen-sized plant, it might send out enough roots to successfully compete with its towering brethren, but it is seldom worth the effort.

A portion of the woodland garden, with pink Rhododendron ‘James Barto’ above blue Omphalodes cappadocica and Primula ‘Blue Cowichan’; dark, sinuous shoots of Disporum cantoniense ‘Night Heron’ in the foreground

A portion of the woodland garden, with pink Rhododendron ‘James Barto’ above blue Omphalodes cappadocica and Primula ‘Blue Cowichan’; dark, sinuous shoots of Disporum cantoniense ‘Night Heron’ in the foreground

Starting Small

So, for us, four-inch to five-gallon plants work best around mature trees. Though we miss the instant impact that larger plants would offer, the smaller plants settle in much more quickly and cost less per plant. Of equal importance is the risk of soil-borne diseases taking advantage of the existing trees. The garden soils are rife with Armillaria, Phytophtora, and Verticillium. The bigger the planting hole needed, the greater the risk of damaged tree roots, thus opening avenues for infection. Several grand trees have succumbed to these diseases during our tenure, and the last thing we want to do is to encourage more such problems.

While a vast majority of the new plants have taken hold and thrived, there have been some failures, even when starting with smaller material. Along one woodland walk, where Douglas-firs tower overhead, we once added an assortment of mop-headed hydrangeas. Transplanted into the garden from two-inch-diameter pots, they grew into resplendent plants. Even though their roots had spread out, we could never give them enough water in the drier period of late summer. A deep weekly drenching became necessary, raising concerns that the Douglas-firs were receiving too much water at the wrong time of year. Eventually, we removed the hydrangeas; we are still pondering what to replace them with for a late summer “zing” in the area.

Asian saber ferns (Polystichum neolobatum) emerge froma long-established mat of Cyclamen coum in full flower

Asian saber ferns (Polystichum neolobatum) emerge froma long-established mat of Cyclamen coum in full flower

Woodland Ephemerals

Ed loved woodland ephemerals and planted many throughout his portion of the property. Some grew into congested clumps. Among them were trilliums, many of which had grown undisturbed for decades. In talking with trillium enthusiasts, we learned that they could be successfully divided in late August or September. When we dug up a clump of red-flowered furrowed wakerobin (Trillium sulcatum), the mother plant yielded over forty divisions. To ensure their success, we potted up the divisions, over-wintered them with protection, and planted them out in the following spring. Other plants that divided well included Hepatica, Uvularia, and Galanthus. Of these, hepatica has been slow to recover, whereas the others did not miss a beat.

We increased other plants by seed. We added more of Ed’s choice Cyclamen hederifolium, along with C. coum. Our philosophy is that one can never have too many cyclamen, as their foliage adds so much during the bleaker months of the year. [See Pacific Horticulture, October 2008] The variation in leaf patterning is fascinating; it is rare to find a homely plant. (Our finest plants have been grown from seed obtained from Ashwood Nursery in the UK.)

We have also hybridized selected forms of both trilliums and Pacific Coast iris, grown them on from seed, and planted them in the garden. Trilliums take about seven years from sowing to first flowering, so raising them from seed is definitely a project of love—or madness (depending on one’s point of view). We have been selecting the trillium seedlings for fragrance, size, color of flower, and quality of foliage.

The native iris hybrids, derived from Iris douglasiana, I. innominata, and others, provide more immediate gratification, often flowering within two years of being pricked out of the seed pot. The color range and markings have been improved with each generation. We have had some serious problems with iris rust, so any seedlings that show evidence of the disease are rogued out immediately. It will take a few more years before we have large enough swaths to make a real impact in the garden, but we are well on our way. If there were a signature plant in the garden, we would say it is our native fawn lily (Erythronium revolutum). Ed collected seed of it in the wild, and also obtained it from fellow gardeners. Among those in the garden, he noticed that slugs did not eat the ones with mottled leaves, preferring instead those with plain green leaves. The resistant plants were then scattered throughout the garden by Ed, Doug Bayley (a past curator), Roger Lackman (the head gardener), and now by us. The effect, in spring, is magical.

The perennial border has been enlivened with the gold-and-green striped foliage of Japanese forest grass (Hakenochloa macra ‘Aureola’) contrasting with the nearly black foliage of Actaea simplex ‘Hillside Black Beauty’; pale blue annual love-in-a-mist (Nigella damascena) adds summer sparkle

The perennial border has been enlivened with the gold-and-green striped foliage of Japanese forest grass (Hakenochloa macra ‘Aureola’) contrasting with the nearly black foliage of Actaea simplex ‘Hillside Black Beauty’; pale blue annual love-in-a-mist (Nigella damascena) adds summer sparkle

The Perennial Border

In one part of Ed’s garden was a perennial border, which had been planted in the 1950s. By the time we arrived, it was in need of a major renovation. By their nature, perennial borders are high maintenance, and weeds can be the biggest problem. In Ed’s border, wild morning glory (Calystegia sepium) and couch grass (Elytrigia repens) had seeded in amongst the perennials. Other noxious plants were most likely intentionally planted: star-of-Bethlehem (Ornithogalum umbellatum), lords-and-ladies (Arum italicum), Spanish bluebells (Hyacinthoides hispanica)—all of them bulbous or tuberous—and several kinds of Oxalis.

We have also found that lesser celandine (Ranunculus ficaria) has quickly gone from desirable to invasive, in the Pacific Northwest. We are a lot more careful, nowadays, when experimenting with new plants in the garden to avoid unleashing new weeds into the environment.

The border reclamation began by salvaging worthwhile perennials, bare rooting them to eliminate any weeds, and potting them up. In an ideal world, we would have allowed the perennial border to lie fallow for two years, during which time we would have employed a variety of measures to eliminate any dormant weeds. Of course, the ideal and the practical collided. Everyone realized that the public could not wait two years for the perennial border renovation, so we gave it our best effort to eradicate the weeds. We mostly succeeded, but the three bulbs or tubers are still active, albeit on a much reduced level. It keeps us on our toes, as we can never ignore the weeding for long.

Native fawn lilies (Erythronium revolutum) cover the ground in early spring, in front of a buttercup winter hazel (Corylopsis pauciflora) in bud

Native fawn lilies (Erythronium revolutum) cover the ground in early spring, in front of a buttercup winter hazel (Corylopsis pauciflora) in bud

Extending the Season

Tweaking the plantings has made the border more appealing throughout the year. We added three cultivars of Hydrangea paniculata: ‘Limelight’, ‘Angel’s Blush’, and ‘Ruby’. By elevating the main framework of these shrubs three to five feet off the ground, we have been able to maintain the mass of perennials beneath and in the foreground, while gaining additional flowers at eye-level. To provide further color and flowering during summer and fall, we added cultivars of rose-of-Sharon (Hibiscus syriacus): ‘Aphrodite’, ‘Blue Satin’, ‘Diana’, and ‘Minerva’. These new sterile selections flower longer than older cultivars since they do not produce seed.

We use various annuals to keep the border looking as fresh as possible in late summer through early fall—often the most pleasant time to be outside in the maritime Northwest. For winter interest, we tucked in several kinds of boxwood (Buxus) that we are training into “gumdrop” shapes of varying sizes. We opted for boxwood, as it can take the intense competition from the surrounding perennials and won’t die out from being too shaded.

There are still many areas of the garden to tackle, and some of the earliest renovations are ready to be refreshed. Because the garden is listed on the National Register of Historic Places, we have to be careful to preserve what is historic when adding sympathetic new plantings. It’s a challenge that we enjoy. From the beginning, the two of us have worked with the garden conservation committee, composed of members of the EB Dunn Historic Garden Trust who share a love of the property’s horticultural heritage. A garden of this size and complexity can definitely be a “black hole” when it comes to time and money. Without the assistance from a key group of supporters, we would never have achieved as much as we have.

The Dunn Gardens is fast approaching its century mark. With continued thoughtful management, there is no reason why it should not survive for at least another hundred years.

Great white drifts of snowdrops (Galanthus nivalis) carpet an open portion of the woodland garden, along with clumps of pink Cyclamen coum

Great white drifts of snowdrops (Galanthus nivalis) carpet an open portion of the woodland garden, along with clumps of pink Cyclamen coum

If You Should Like to Visit…

Dunn Gardens are open for guided tours, by appointment only, from April through July and from September through October. Call 206/362-0933, send an email message to info@dunngardens.org, or visit www.dunngardens.org for information about tours, events, volunteer opportunities, and memberships. The gardens are located at 13533 Northshire Road NW, Seattle, WA 98177. They are about ten miles north of downtown Seattle. Directions will be provided.