September 5th, 2015 by UWBG Horticulturist
How some trees react to high winds.
A broken Acer macrophyllum (Big Leaf Maple) stem located at the east end of Loderi Valley in the Washington Park Arboretum
1) Pseudotsuga menziesii Douglas Fir
- The detritus lying on the ground following a wind event in the Pacific Northwest provides ample evidence of how P. menziesii defends itself against wind.
- The wood of P. menziesii is brittle and can snap. When a strong wind acts on a Douglas Fir, the tree sacrifices small pieces of foliage to shed the wind’s energy.
2) Thuja plicata Western Red Cedar
- In contrast to Douglas Fir, Western Red Cedar limbs are fibrous and tenaciously strong. Long, bendable limbs whip and swing in the wind, but rarely break.
- The wind’s energy is transferred to the trunk and the cedar relies on its massive girth and extensive root system to keep it upright.
3) Populus trichocarpa Black Cottonwood
- In growth, P. trichocarpa sacrifices strength for speed.
- Just to the northwest of our Overlook Pond, a massive black cottonwood demonstrates how weak wood tends to shatter under stress.
4) Salix spp. Willow
- Often growing in wet bottomlands, the roots of willows can be shallow mats that are relatively easy to peel up when a strong wind levers a tall tree.
5) Acer macrophyllum Big Leaf Maple
- The wood of Acer macrophyllum is strong but heavy. The massive, reaching limbs can shatter mid-limb when wind pulls on the sail-like leaves.
- A recent example is located at the east end of Loderi Valley just above Arboretum Drive, although many of our big-leaf maples are festooned with “storm stubs.”
August 23rd, 2015 by UWBG Horticulturist
Selected cuttings from the New Zealand Forest in the Pacific Connections Garden at the Washington Park Arboretum (August 17 – 30, 2015)
Native to New Zealand (and Australia, Asia, and Africa). Flowers are sweetly scented and seeds are coated with a sticky substance giving the plant its name, pitch-seed.
All plants below can be seen growing in the New Zealand Forest in the Pacific Connections Garden.
1) Pittosporum eugenioides Lemonwood
- New Zealand’s tallest Pittosporum, P. eugenioides can reach 40 feet.
- Its yellow-green leaves with curly edges have a strong scent of lemon when crushed.
2) Pittosporum divaricatum
- Divaricating (stretched or spread apart) branching patterns and small juvenile foliage protect this plant from beaked predators.
- As the plant gains height, adult foliage emerges safe from predation.
3) Pittosporum patulum Pitpat
- Endemic to the South Island of New Zealand.
- Pitpat has been on the IUCN Red List as endangered since 1999.
- IUCN stands for: International Union for Conservation of Nature.
4) Pittosporum ralphii Ralph’s Kohuhu
- Thick leathery, undulating leaves sport dense white tomentum on the underside.
- Hermaphroditic flowers give way to orange-yellow seed capsules and black seeds.
5) Pittosporum tenuifolium ‘Tom Thumb’
- This purple-leaved cultivar of P. tenuifolium is a dense, slow-growing evergreen shrub with a rounded habit.
- You can find this plant in the newly-renovated courtyard of the Graham Visitor Center.
August 14th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (August 3 – 16, 2015)
1) Clematis afoliata
- Native to the dry, eastern side of New Zealand.
- Now growing in our New Zealand Focal Forest.
- Eventually becomes a wiry mound with fragrant spring flowers.
2) Hakea epiglottis
- Native to Tasmania and growing outside our Education Office.
- Hakea needs sun and dry, infertile soil.
- The round “stems” are true leaves despite their appearance.
3) Phyllocladus aspleniifolius
- Another Tasmanian native, this tree prefers moist lowlands. Its “leaves” are actually modified stems called “phylloclades”.
- A related species, Phyllocladus alpinus is native to New Zealand and is growing in our New Zealand gardens.
4) Ruscus aculeatus Butcher’s Broom
- The “leaves” of Ruscus and Danae are called “cladodes”: a subtle and not clearly defined difference from “phylloclades”, but still modified stems.
- Ruscus aculeatus and Ruscus hypoglossum are both growing in the Witt Winter Garden.
5) Danae racemosa Alexandrian Laurel
- Danae and Ruscus are members of the Asparagus family.
- Danae is native to Asia Minor and is growing in our Winter Garden.
- Ruscus is native to the Mediterranean region.
August 6th, 2015 by UWBG Horticulturist
If this year’s hot and dry summer is a climate change omen for Seattle and the greater PNW, then here’s the tree of our future: Lagerstroemia spp and its many hybrids and cultivars. Commonly known as crapemyrtles, these trees are tolerant of hot and dry summers and offer appeal throughout the seasons. They have lustrous foliage and large colorful flowers in the growing season (spring and summer); in the dormant season (fall and winter), the foliage and bark provide interest.
‘Sioux’ is a National Arboretum Fauriei Hybrid crapemyrtle introduction from the 1950s that produces an abundance of large, bright pink flower clusters during summer. Its foliage is the darkest green of any crapemyrtle and turns to a handsome purple color in fall. The bark is tan in color and the twigs have a reddish color. See National Arboretum link below for more information on the Fauriei hybrids.
Common Name: Sioux Crape Myrtle
Location: Center for Urban Horticulture, west end of Douglas Greenhouse parking lot
Origin: National Arboretum Introduction. Name registered May 1, 1992.
Height and Spread: 12′-15′ tall; 8′-10′ wide. Multi-stemmed small tree, large shrub
Bloom Time: Summer, extended out as long as temperatures remain warm.
Specimen at CUH
July 12th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (July 6 – 20, 2015)
1) Itea ilicifolia Holly-leaved Sweet Spire
- Native to western China
- Evergreen shrub growing up to 16 feet tall and 10 feet wide
- Bears fragrant racemes of greenish-white flowers in late summer and fall
- Located west of the Magnolia Collection near the south end of the Asiatic Maples
2) Lomatia myricoides Long-leaf Lomatia
- Native to New South Wales in southeastern Australia
- One of the hardier members of the Proteaceae
- Honey-scented white flowers are much visited by bees in summer
- Located across Arboretum Drive from the New Zealand Focal Forest
3) Pterocarya stenoptera Chinese Wingnut
- Native to China
- Deciduous tree to 70 feet or greater, with a trunk diameter as large as 8 feet
- Located west of Azalea Way, north of Loderi Valley
4) Quercus vacciniifolia Huckleberry Oak
- Native to western North America, mountains of the Sierra Nevada and southern Cascade Range
- Leaves and acorns are an important food source for birds and mammals within its native range.
- Located atop the rockery at the east end of the trail above the Gateway to Chile
5) Rehderodendron macrocarpum Mu gua hong
- Native to Mt. Emei, Sichuan Province, China
- Small deciduous tree 20 to 30 feet tall, related to Styrax
- Located east of Azalea Way on the north end of the Rhododendron Hybrid bed
June 15th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (June 8 – 21, 2015)
1) Cornus controversa Giant Dogwood
- A rounded deciduous tree bearing spreading, tiered branches and alternate, elliptic leaves, C. controversa can potentially reach 40 feet in height. White flowers are borne in large, flattened cymes in early summer. Following the flowers, masses of deep red fruit develop, changing to blue-black.
- Native to China, the Himalayas and Japan, C. controversa is less cold tolerant than our native dogwoods. This specimen is located along Azalea Way near the Hybrid Bed.
2) Kalmia latifolila Mountain Laurel
- A dense, bushy shrub with glossy, dark green leaves and large corymbs of cup-shaped flowers, Kalmia latifolia is native to North America. Thought by many to be our country’s most beautiful flowering shrub, it is the state flower of both Connecticut and Pennsylvania.
- This specimen is located along the lower trail, near Rhododendron Glen.
3) Quercus robur ‘Concordia’ Golden English Oak
- A standout specimen amongst the late spring flush of green, Q. robur ‘Concordia’ offers us bright yellow young foliage which will eventually turn color in the fall.
- It is located on the east side of Azalea Way near the Woodland Garden.
4) Pterocarya stenoptera Chinese Wingnut
- A large spreading tree with long pinnate leaves and winged green fruit produced in pendent spikes up to 12 inches in length. Wingnuts are a member of the plant family Juglandaceae.
- This specimen is located at the south end of the nut flats, just west of Azalea Way.
5) Staphylea pinnata Bladdernut
- A deciduous shrub up to 15 feet high, S. pinnata is known for its curious bladder-like fruits in late spring and early summer. This specimen is located amongst the True Ashes, west of Azalea Way.
June 12th, 2015 by UWBG Horticulturist
An Osprey nesting pole was installed yesterday in Union Bay Natural Area (UBNA). Located near Carp pond in the SE corner of UBNA loop trail. UW Athletic Dept funded the project when it was realized Osprey were being attracted to nesting in ball fields’ lighting across the way. Hopefully now, people will be safe from falling branches and Osprey will have more appropriate digs to settle into.
Jim Kaiser, consulting wildlife biologist and owner of Osprey Solutions, was hired to do the install. Jim has installed over 300 Osprey nesting poles in the PNW. He is one of the most knowledgeable biologists on Osprey and has quite a fascinating and experienced repertoire in creating new homes for them.
For more information on Osprey and their nests, please visit:
Osprey fact sheet
Attaching nesting platform to pole
Erecting Nesting Pole
Looking south along UBNA loop trail
May 15th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (May 11-24, 2015)
1) Cytisus x praecox ’Luteus’ Warminster Broom
- This broom is a hybrid of C. multiflorus and C. purgans and is located on Arboretum Drive in the Legume Collection.
- Many of the brooms are blooming now or soon to bloom, including the pineapple broom, Argyrocytisus battandieri, whose fragrance earned it its common name.
2) Erica arborea var. alpina Tree Heath
- While non-alpine tree heath can reach heights in excess of 20 feet, the alpine variety is the “short” one, reaching only 10 to 15 feet.
- Alpine tree heath has white flowers versus light-gray, and the scent is reminiscent of honey.
3) Hydrangea luteovenosa Sweet Hydrangea
- In full bloom now, this semi-trailing Hydrangea is located on the Ridgetop Trail in Rhododendron Glen.
- Though widely distributed in western Japan, this species of Hydrangea is critically endangered in Korea.
4) Rhododendron ‘Snow Lady’ x Rhododendron degronianum ssp yakushimanum
- Hybrids are often created to blend two or more outstanding traits from two separate taxa into one single plant, e.g. flower color and leaf indumentum.
- There are several areas in the Washington Park Arboretum, including Azalea Way, Loderi Valley, Rhododendron Glen and the Puget Sound Rhododendron Hybridizers bed, showcasing many hundreds of hybrids of Rhododendron.
5) Syringa reflexa Nodding Lilac
- The buds of Syringa reflexa start out a rosy–red before opening to pink and eventually fading to almost white.
- The specific epithet “reflexa” refers to the nodding habit of the flower heads.
- Lilacs are located throughout the Washington Park Arboretum, though many are found just south of the Woodland Garden along Azalea Way.
May 1st, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (April 27 – May 10, 2015)
Opening Day crew races through the Montlake Cut, and the 1936 USA Olympic gold in rowing may never have happened without these following trees:
1) Thuja plicata Western Red Cedar
- UW’s world-renowned boat maker, George Pocock followed the lead of Native Americans and used this Pacific Northwest giant for the hulls of his Pocock Classics.
- The skin is made from a single plank of 3/32″ thick cedar and offers a combination of stiffness and springiness that eliminates the need for the extra weight of a hull.
2) Pinus lambertiana Sugar Pine
- Keels of Pocock’s boats were made from this soft, even-grained Oregon native.
- Sugar pine has very low shrinkage when it dries, so hull warping and cracking was kept to a minimum with this choice wood.
3) Xanthocyparis nootkatensis Alaska Yellow Cedar
- Cheeks (two lowest timbers at the head rails) and washboards (thin planks fastened to the side to keep out water) were made from this honey-colored wood.
- Pocock was especially fond of the way Xanthocyparis aged with Thuja plicata.
4) Picea sitchensis Sitka Spruce
- Hand-carved seats and gunnels (uppermost plank in a hull) were made from these giants from Vancouver, BC.
5) Picea engelmannii Engelman Spruce
- Oars used in rowing competitions are made from Engelman Spruce.
- The oar consists of three bonded pieces made from one single plank of Engelman spruce split to make mirror-imaged sides, and another piece is cut for the center.
Resources: http://www.pocockclassic.org, http://shipwrightjournal.blogspot.com
April 19th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (April 13 – 26, 2015)
1) Acer cissifolium Vine-leaf Maple
- A three-leaf maple native to Japan.
- The extraordinary racemes of tiny flowers give the tree a cloud-like appearance.
- Located in the Asiatic Maple Collection.
2) Acer rubrum Red Maple
- This popular street tree is native to eastern North America.
- On this sample the petals have fallen, leaving the elongating peduncles and their tiny, immature samaras.
- Located in grid 3-5E on Arboretum Drive.
3) Cornus florida Flowering Dogwood
- Named for its showy bracts.
- Native to the eastern United States.
- These cuttings are from ‘Royal Red’ near the south end of Azalea Way and from an unlabeled white cultivar near the north end.
4) Cornus nuttallii Pacific Dogwood
- A west coast native named for Thomas Nuttall– a British botanist and explorer.
- Natural seedlings are scattered throughout the Arboretum.
- This is the provincial “flower” and floral emblem of British Columbia.
5) Cornus nuttallii x florida ‘Eddie’s White Wonder’
- So named because it was one of a few survivors of a flood at Henry Eddie’s nursery near Vancouver, B.C.
- It is a hybrid of Cornus nuttallii and C. florida.
- Several specimens are growing along Azalea Way.