December 22nd, 2015 by UWBG Horticulturist
Boughs used as winter decoration are often from plants in the genus Ilex. Many Ilex, or holly species are dioecious, meaning that male and female reproductive organs are separated on individual plants. This trait promotes cross-fertilization which increases genetic variability, but can decrease seed-setting efficiency. Solitary individuals are unable to be pollinated, therefore it is necessary that male and female plants grow in close proximity or female plants will not produce berries.
Selected cuttings from the Washington Park Arboretum (December 15-28, 2015)
1) Ilex cassine var. mexicana
- This large, fast-growing evergreen is native to the southeastern coast of the U.S. as well as Mexico, Puerto Rico and Cuba.
- A healthy specimen can be found in grid 13-3W, just west of Lake Washington Boulevard.
2) Ilex verticillata ‘Red Sprite’
- This female, deciduous Ilex cultivar reveals large red berries when its leaves fall.
- Our best patch can be found along the path in the Joe Witt Winter Garden planted next to the male pollinizer, Ilex verticillata ‘Jim Dandy’.
3) Ilex opaca ‘Boyce Thompson Xanthocarpa’
- Evergreen tree that grows rapidly and assumes an attractive conical shape. As with most of the American Holly clade, this tree is cold hardy but not very wind-tolerant.
- Berries can be crimson-red, yellow or orange.
4) Ilex opaca ‘Emily’
- Found in the Pacific Connections Meadow plantings, this evergreen female boasts copious quantities of vivid red fruits, starting at a very young age.
5) Ilex serrata
- Located in the deciduous Holly clade on the west side of Lake Washington Boulevard, this holly spreads and suckers to form colonies.
- Small red berries are revealed in late autumn after the leaves have fallen.
December 11th, 2015 by UWBG Horticulturist
Conifer trees occasionally mutate into unusual forms, often slow-growing natural dwarfs. Thousands of these have been in cultivation for centuries. The Arboretum has only a few in its collection, sadly neglected in grid 37-1W – a corner of the Oaks area. Here are five examples:
Selected cuttings from the Washington Park Arboretum (December 1 – 14, 2015)
1) Chamaecyparis lawsoniana ‘Lycopodioides’
- Translated: “a form of Lawson’s false cypress that looks like Lycopodium” – a genus of club moss that’s said to resemble a wolf’s foot.
2) Chamaecyparis pisifera ‘Plumosa Nana’ Dwarf Sawara Cypress cv.
- Dwarf (nana), feathery (plumose), pea-bearing (pisifera) false cypress
3) Cryptomeria japonica ‘Bandai-Sugi’ Japanese Cedar cv.
- The cultivar name has been shortened recently to ‘Bandai’ because Sugi is the Japanese word for Cryptomeria, therefore is redundant.
- All parts of the flower are hidden in this genus, hence Crypto (hidden) meria (parts).
4) Picea abies ‘Gregoryana parsonii’ Norway Spruce cv.
- See Arthur Lee Jacobson’s Trees of Seattle for an explanation of the botanic name.
- Jacobson notes that only Lawson’s Cypress has more cultivars than Norway Spruce.
5) Tsuga canadensis ‘Hussii’ Eastern Hemlock cv.
- Because of people’s tendency to call all conifers “pine” or “fir”, botanists adopted the Japanese name for hemlocks – Tsuga. Does that sound too similar to ‘Sugi’?
November 23rd, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum, November 16 – 29, 2015
1) Arctostaphylus uva-ursi ‘Vancouver Jade’ Kinnikinnick or Bearberry
- Broadleaf evergreen and creeping groundcover with circumpolar distribution in northern hemisphere often found growing in association with Pitch Pine
- If there were still bears on Cape Cod, it would be a favorite food source for them.
- This cultivar, ‘Vancouver Jade’ is growing in containers outside the Graham Visitor Center.
2) Juniperus virginiana ‘Blue Coast’ Eastern Red Cedar
- A low growing, blue form of the Eastern Red Cedar
- Pioneer species found in mixed stands with Pitch Pine, reclaiming abandoned farms and grasslands
- Found growing under Pines in grid 36-4E, along nursery road
3) Morella pensylvanica Bayberry
Photo demonstrating the straightness of Arrowwood stems and their usage in making arrows
- Berries boiled to extract sweet-smelling wax used to make clean-burning candles
- Found growing in dry open sites along with Bearberry, Eastern Red Cedar and Pitch Pine
- Mass growing in Oaks Collection in grid 43-B
4) Pinus rigida Pitch Pine
- Rigid cone scales and stiff needles, hence its Latin specific epithet
- Used during days of wooden ships due to its resistance to decay
- Several young specimens in our Pinetum, grid 37-4W
5) Viburnum dentatum var. pubescens Arrowwood
- Large deciduous shrub with fruit a food source for songbirds
- Common name refers to Native American use of straight young stems as arrow shafts
- Old specimens located in southeastern Viburnum bed, grid 24-4W
October 20th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (October 19, 2015 – November 1, 2015)
1) Cupressus (Hesperocyparis) bakeri Modoc Cedar
- A moderately-sized coniferous tree with greyish-green scale-like foliage that is dotted with white resin. It is native to the Siskiyou and Sierra Nevada Mountain ranges. A slow growing tree, usually under 90 feet over many decades.
- Considered vulnerable to extinction in the wild in the medium term.
- Located in the Pacific Connections Garden Cascadia Focal Forest above the Chilean Gateway.
2) Euonymus myrianthus Evergreen Spindle Tree
- A member of the same family as burning bush, this large shrub was discovered in western China and introduced into cultivation by famed plantsman, E.H. Wilson.
- This plant has insignificant flowers in spring and bares conspicuous yellow fruit in fall, which persist well into winter.
- Located with the Asiatic Maples collection, north of where the upper and lower trails meet.
3) Notholithocarpus densiflorus var. densiflorus Tan Oak
- Native to the mountains from southwestern Oregon through central California.
- A natural source of tannin, Tan Oak bark was used in the process of tanning leather.
- This species is particularly susceptible to “sudden oak death” Phytophthora ramorum.
- Located in Pacific Connections Garden Cascadia Focal Forest above the Chilean Gateway.
4) Picea breweriana Brewer’s Weeping Spruce
- Native to the Siskiyou Mountains, this large coniferous tree is slow growing and adapted to extreme cold. The tough flexible branches are held horizontally, forming curtains of foliage. The stiff flattened needles are dark green with two white bands of stomata on the undersides.
- Located in the Pacific Connections Garden Cascadia Entry Garden near Arboretum Drive.
5) Magnolia grandiflora ‘Monlia’ Southern Magnolia
- A medium-sized evergreen tree to 50 feet, it has large green leaves with brown indumentum covering the undersides. Large fragrant white flowers in summer are followed by large upright fruit. The species is native to the southeastern United States.
- Located at the south end of the Graham Visitors Center parking lot.
October 7th, 2015 by UWBG Horticulturist
Selected cuttings from the Washington Park Arboretum (October 5 – 18, 2015)
1) Cedrus atlantica ‘Glauca’ Blue Atlas Cedar
- A large coniferous tree with vivid, glaucous blue foliage, making it easy to identify.
- Native to Algeria and Morocco on the Atlas Mountains, these specimens can grow up to 100 feet tall and beyond.
- Located in the Pinetum near the Lynn Street play area.
2) Cunninghamia lanceolata China Fir
- Members of the family Taxodiaceae, these trees are named after James Cunningham, who originally found C. lanceolata on the Island of Chusan in 1701.
- Cunninghamias are closely related to the redwoods (Sequoia), although the foliage is similar to that of the monkey puzzle tree (Araucaria araucana).
- Located in the Pinetum near the Newton Street entrance.
3) Picea engelmannii ssp. Mexicana Engelmann Spruce
- Conical tree with bluish-green to steel-blue needles.
- Native to the mountains of western North America from Alberta and British Columbia (where it attains its greatest size) and south to New Mexico and Arizona.
4) Picea pungens ‘Glauca’ Blue Colorado Spruce
- P. pungens is allied to P. engelmannii, differing in its glabrous shoots, and in its bluer, more pungently pointed leaves.
- Native to the Rocky Mountains and southern China.
- Located in the Pinetum.
5) Sequoia Sempervirens ‘Henderson Blue’ Coast Redwood
- Native to a narrow belt of the California coastline, where summer fogs off the Pacific Ocean are frequent and mitigate the seasonal heat and drought.
- Located in the Pinetum near 26th Ave. East and East McGraw Street.
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