ProHort

Center for Urban Horticulture
University of Washington

Vol. 6, No. 3

Cooperative Extension
Washington State University

Summer 1988

LANDSCAPE

MAINTENANCE

SEMINARS

. . . for the landscape
professional

Cooperating: Center for Urban Horticul-
ture, University of Washington; Cooper-
ative Extension Service, Washington State
University; Edmonds Community College;
South Seattle Community College.

Landscape Power
Equipment

Date : Monday, July 25
Time : 9 a.m. to 12 noon
Location : Center for Urban
Horticulture

Instructor : Chuck Nolan

Proper equipment can save you time and
money. It can also help you do a nicer job.
Learn what’s new in landscape power
equipment — mowers, aerifiers, edgers, line
trimmers, blowers, etc. Emphasis will be
placed on the efficiencies of different types
of equipment. You will be provided with the
facts — pro and con — to choose the appro-
priate equipment for your specific needs.
Several pieces of equipment will be dis-
played and demonstrated.

Chuck Nolan has spent most of his life in the
landscape industry, first as a tree trimmer,
later as a golf course superintendent, and
for the past several years, as a representa-
tive of Northwest Mowers Inc.

PRO HORT Editorial Staff:
Dr. John A. Wott
George J. Pinyuh
Van M. Bobbitt, editor

Plant Parasitic Nematodes

Date : Tuesday, August 23

Time : 9 a.m. to 12 noon

Location : Center for Urban

Horticulture

Instructor : Dr. Fred McElroy

Nematodes can weaken plants, cause
dwarfing, and transmit plant viruses. Dis-
cover what nematodes are, how they are
spread, which landscape plants they can
affect, and what control strategies are avail-
able.

Dr. McElroy, owner of Peninsu-Lab in
Kingston, Washington, offers diagnostic
services to the forestry, agricultural, and
horticultural industries. He completed his
undergraduate work at Washington State
University and received a Ph.D. in plant
pathology /nematology from the University
of California at Riverside.

This seminar qualifies for three hours of
WSDA pesticide license recertification
credit.

Managing Soil
Compaction /Efficient
Irrigation

Date : Thursday, September 8
Time : 9 a.m. to 12 noon
Location : Center for Urban
Horticulture

Instructor : Dennis R. Pittenger

Understand how soil compaction occurs
and possible solutions for it. Find out when
and how to amend soils. Practical ap-
proaches for determining water needs and
irrigation schedules of landscape plants will
also be discussed.

Dennis Pittenger is the urban horticulture
specialist with the University of California
Cooperative Extension. He provides tech-
nical support for county extension advisors
and members of the landscape industry. His
main interests are landscape irrigation and
soil management, species selection, and
tree management.

Parking

Free parking will be available for those
attending Pro Hort seminars. Please
park in parking lot if space is available.

OTHER

EDUCATIONAL

RESOURCES

Turf Management Seminar in Belling-
ham. Update your knowledge of her-
bicides, fungicides, insecticides, and growth
regulators available to turf managers. Re-
view fertilizer formulations and the impor-
tance of proper timing of application. James
Chapman, manager of the commercial turf
department at the Chas. H. Lilly Company,
will present a seminar on turf management
chemicals and fertilizers on Saturday, Au-
gust 13, 9 a.m. to 12 noon, at Bellingham
Vocational Technical Institute. This pro-
gram qualifies for two hours of WSDA
pesticide license recertification credit. The
registration fee is $12.50 before August 5
and $15 after. For details, call Van Bobbitt,
Center for Urban Horticulture, 545-8033.

An Inside View of How Plants Grow:
Practical Plant Physiology. August
26-28 at the Center for Urban Horticul-
ture. In this seminar, Dr. Barbara Smit, as-
sistant professor at the Center for Urban
Horticulture, will show you how plants
really work — how they photosynthesize,
how they use nutrients, how they react to
stress. A $75 registration fee, which must be
received by July 25, includes instructional
materials, refreshments, Friday evening re-
ception, and Saturday lunch. Registration
forms may be obtained at the Center for
Urban Horticulture. This is part of the
American Rose Society’s national seminar
series which is designed to provide ad-
vanced training to rosarians and other horti-
culturists.

International Society of Arbori-
culture’s Annual Conference. August
14-17, Vancouver, B.C. This outstanding
educational program will include speakers
such as Dr. Alex Shigo and Dr. Richard
Harris, author of Arboriculture — Care of
Trees, Shrubs, and Vines in the Landscape.
The registration fee, which must be received
before July 15, is $190. To request a regis-
tration packet, call (217) 328-2032.

Edmonds Community College Horti-
culture Courses — Summer 1988. Inte-
grated Pest Management, Monday and
Wednesday evenings, July 11-27; Ad-
vanced Plant ID, Tuesday and Thursday
evenings, June 28-August 18; Summer
Propagation, Thursday afternoons, June
30-July 28. 771-1679.

Lake Washington Voc Tech Horticul-
ture Course — Summer 1988. Land-
scape Irrigation: The Basic Nuts and Bolts,
Tuesday evenings, June 28-August 16.
828—5627.

South Seattle Community College
Horticulture Courses— Summer 1988.

Plant Materials for the Northwest, Tues-
days, 5-9 p.m., June 21-August 9; Plant
Propagation Workshop, Wednesdays, 9
a.m.-3 p.m., June 22-August 10.

764-5336.

ARTICLES

Is Chemical
Defruiting
Practical in the
Landscape?

Dr. James R. Clark
Center for Urban Horticulture
University of Washington

In the past few weeks, the question of de-
fruiting landscape trees has arisen a number
of times. The inquiry usually centers upon a
method to reduce or eliminate the produc-
tion of unwanted fruit. The situations usu-
ally involve a litter problem, i.e., staining a
paved surface, accumulating in hard-to-
clean areas, serving as a weed source. In the
absence of fruitless cultivars of many woody
plants, the questioner wants to know of
methods to solve the problem.

One possible approach is the use of chemi-
cal materials to either prevent fruit produc-
tion or to induce premature fruit drop. This
technique is utilized in the apply industry,
where crops are routinely thinned, chemi-
cally and by hand. Harris discussed several
chemical alternatives and possible ap-
proaches in Arborculture — Care of Trees,
Shrubs, and Vines in the Landscape. How-
ever, to my knowledge, the actual use of

such techniques in the landscape has been
limited.

Several reasons may explain this. First,
there is a general concern about pesticide
use in the landscape by clients. Second, the
demand is small — it is a speciality market.
Third, the information base about chemical
defruiting is relatively limited.

Regarding the available information on
chemical defruiting, the following facts
seem important:

1. The 1987 Pacific Northwest Weed Con-
trol Handbook recommends the use of Eth-
rel or Florel for defruiting. The active ingre-
dient in both chemicals is ethephon.

2. The Florel label reads: . .will reduce or
eliminate undesirable fruit from apple trees,
crabapple trees, carob trees, and olive
trees.” I spoke with the Washington State
Department of Agriculture about this label,
and the initial reaction of Mary Toohey was
that an applicator could not use Florel on
any tree species but the four mentioned.

3. Atrimec is another plant growth regulator
labeled for the “suppression of flower and
fruit formation. ” It is labeled for use on olive
(Olea sp. ), and glossy privet ( Ligustrum lu-
cidum), multiflora rose (Rosa multiflora),
and Japanese holly (Ilex crenata). Thanks
to Duncan Murphy of AAA Spraying in
Seattle for providing this information.

4. Sevin has also been suggested as a possi-
ble chemical defruiting material. It has been
used as a thinning agent in commercial ap-
ple orchards. However, it is not labeled for
defruiting of landscape trees and shrubs.
When used in the control of tent caterpillars,
reduced fruiting has been observed.

If there are any other personal experiences
with these or other chemicals for use in
defruiting I would be very interested in
learning about them.

I think there is great potential for using these
materials to solve the problem of unwanted
fruit. But for now, it appears that the use of
chemical defruiting methods will be limited
to a small number of plant species due to
the label restrictions of the chemicals avail-
able.

Plant Palette: Itea

ilicifolia

Timothy Hohn

Center for Urban Horticulture
University of Washington

Some plants seem to be relegated to the
shadows of horticultural awareness, shade
loving or not, with an unexplainable lack of
curiosity. Itea ilicifolia, though first intro-

duced to British gardeners in 1895, still re-
sides in relative obscurity there and is vir-
tually unknown in North America. Pitiful
neglect!

Described as a glossy, dark green shrub
covered with thin, pendulous inflorescences
of white flowers growing on cliffs along the
Yangtse River in Hupeh Province, China,
Dr. E. H. Wilson goes on to recommend
Itea ilicifolia, occasionally known as the
holly-leaved sweetspire, in th e Aristocrats of
the Garden, published in 1926. Not so
much an unknown plant, but an ungrown
one.

We have a single specimen of this particular
evergreen Itea in the Arboretum, although
we also have others of its deciduous Ameri-
can relative, Itea uirginica. There are 20
known species of sweetspire with most of
them inhabiting the subtropical and tropical
regions of Asia. They belong to the family
Grossulariaceae along with Ribes, Escal-
lonia, and others. Superficial inspection
may justify the common name “holly-
leaved, ” although it appears quite different
from other known members of the genus
and the family. The simple, evergreen
leaves are alternate, ovate, 2-4" long, and
do have marginal spines similar to holly, but
the leaves are not nearly so stiff. The flowers
appear in July on pendulous racemes up to
12" long! Each inflorescence has the ap-
pearance of a drooping pipe cleaner as they
dangle from the ends of the branches. The
flowers are not pure white, but tinged with a
slight, cooling touch of green. The fruit is of
negligible ornamental value.

The specimen in the Arboretum was
planted in 1952 and is now approximately
6-8' in height. The stems emerge from a
central crown and arch outward giving the
shrub a spread nearly equal to its height.
While hardiness ratings vary in the literature
from USDA zone 7 to no less than zone 9,
our plant has suffered only defoliation dur-
ing our occasional severe winters. It appears
unfettered by pest or disease problems.
This specimen produces a showy display of
flowers in the shade of big-leaf maple and
Douglas fir.

Pruning, though it can be accomplished
through old cane removal and heading
back in the early spring, is usually unneces-
sary. Plants should perform well in a moist,
well-drained soil of variable pH, in either
sun or shade. Plants in full sun will probably
require summer irrigation and mulched or
shaded root zones. Propagation by cuttings
taken from midsummer to early fall, treated
with 8000 ppm IBA-talc, and placed under
mist in a well-drained peat: perlite mix,
should show good rooting.

Itea ilicifolia makes a striking wall shrub with
its evergreen foliage and pendulous in-
florescences. One could easily consider it
the summer-blooming counterpart to

Garrya elliptica, the silk tassel bush which is
native to Oregon and California. The dark
green leaves are a perfect background for
showy companions, especially those with
distinctly horizontal or vertical lines which
contrast with the drooping pipe cleaners of
the Itea.

Itea ilicifolia can be seen in the Asiatic maple
section of the Washington Park Ar-
boretum— ask for specific directions at the
reception desk in the Graham Visitors Cen-
ter. Please let me know if you would like
propagules for establishing stock plants.

Low Water Use
Trees

George Pinyuh
Cooperative Extension
Washington State University

Scientific name

Acer ginnala
Acer glabrum

Acer saccharum
subsp.

grandidentatum
Acer negundo
Aesculus californica
Ailanthus altissima
Albizia julibrissin
‘Rosea’

Common name

Amur maple
Rocky Mountain
maple

Bigtooth maple

Box elder
California buckeye
Tree-of-heaven
Silktree

Aralia elata

Arbutus menziesii

Arbutus unedo

Broussonetia

papyrifera

Calocedrus

decurrens

Castanea mollissima
Catalpa speciosa
Cedrus atlantica
Cedrus deodara
Celtis australis
Celtis occidentalis
Celtis reticulata
Celtis sinensis
Cercis occidentalis
Cercocarpus
betuloides
Cercocarpus
ledifolius
Chrysolepis
chrysophylla
Cornus nuttallii
Cotinus obouatus

Crataegus spp.

X Cupressocyparis
leylandii

Cupressus glabra
Eucalyptus
niphophila
Ficus carica
Fraxinus oxycarpa
‘Raywood’

Japanese angelica
tree

Madrone
Strawberry tree
Paper mulberry

Incense cedar

Chinese chestnut
Western catalpa
Atlas cedar
Deodar cedar
European hackberry
Common hackberry
Western hackberry
Chinese hackberry
Western redbud
Birch-leaf mountain
mahogany
Curl-leaf mountain
mahogany
Golden chinquapin

Western dogwood
American smoke
tree

Hawthorn species
Leyland cypress

Arizona cypress
Snow gum

Common fig
Claret ash

Registration Form: Landscape Maintenance Seminars

Complete Series: Equipment, Nematodes, Compaction $31.50

Landscape Equipment $13.00

Nematodes $13.00

Soil Compaction/Irrigation $13.00

TOTAL: $

Group Rates:

Firms/institutions sending two or more employees per seminar. The rates are:

2-5 employees $10. 50/person 6 or more employees $ 9.50/person

To qualify for group rates: (1 ) firm’s registration must be received at least one week in
advance; (2) all registrants must be from the same firm; and (3) total registration fee
must be paid with one check or purchase order.

Firms using purchase orders must make prior registration arrangements.

Make checks payable to the University of Washington; no bank cards.

Portion of fees may cover refreshments and speakers’ expenses.

Receipts will not be returned by mail; they will be available at the door.

NAME

ADDRESS

CITY STATE ZIP

PHONE (DAY) PHONE (EVE)

Mail payment and registration to: Urban Horticulture Program, University of Wash-
ington, GF— 15, Seattle, WA 98195

For more information please call 545-8033.

Fraxinus

pennsylvanica cvs.

Ginkgo biloba
Gleditsia triacanthos
var. inermis
Ilex aquifolium
Juglans hindsii

Juglans spp.

Juniperus spp.

Koelreuteria
paniculata
Laurus nobi/is
Ligustrum lucidum
Lithocarpus
densiflorus
Madura pomifera
Morus alba
Morus nigra
Phellodendron
amurense
Photinia serrulata
Pinus spp.

Platanus x acerifolia London plane tree
Prunus laurocerasus Cherry laurel
Prunus lusitanica Portuguese laurel

Pseudotsuga Douglas fir

menziesii

Quercus chrysolepis Canyon live oak
Garry oak
Holly oak

California black oak
Valley oak
many other oak
species
Black locust

Green ash cultivars
Ginkgo

Thornless honey
locust

English holly
California black
walnut

other walnut species
Juniper species
Golden-rain tree

Mediterranean laurel
Glossy privet
Tan oak

Osage orange
White mulberry
Black mulberry
Amur cork tree

Chinese photinia
most pines

Quercus garryana
Quercus ilex
Quercus kelloggii
Quercus lobata
Quercus spp.

Robinia
pseudoacacia
Sambucus caerulea
Sassafras albidum
Sequoiadendron
giganteum
Sophora japonica

Sorbus aucuparia

Thuja plicata
Tilia tomentosa
Ulmus parvifolia
Umbellularia
californica
Zelkova serrata Japanese zelkova
For a more extensive listing of drought resis-
tant plants for the Puget Sound area, obtain
Low Water Use Plants, KC #125, from King
County Cooperative Extension, (206)
296-3986.

Blue Elderberry
Sassafras
Giant sequoia

Japanese pagoda
tree

European mountain
ash

Western red cedar
Silver linden
Chinese elm
Oregon myrtle

HomeocUmatic
Approach to Plant
Selection

Dr. Clement Hamilton
Center for Urban Horticulture
University of Washington

Landscape plants are most likely to perform
well in areas whose climate is most similar to
their native regions. This common-sense
proposition is gaining adherents once
again, as man-made landscapes in the Pa-
cific Northwest suffer the consequences of
last year’s severe (but not outrageously un-
usual) drought. It is no wonder that azaleas
need more summer watering than does
Gaultheria shallon, for instance; the latter,
native to our area, “expects” summer
drought, whereas an azalea from the south-
east U.S. is “accustomed” to plenty of sum-
mer rainfall.

Given that general principle, which some-
times goes under the heading “homeocli-
matic horticulture,” we in the Puget Sound
area can look to several regions in the world
for predictably successful plant material.
Our climate may be characterized as “cool
winter-rain,” that is, having a prepon-
derance of precipitation in the winter, rela-
tive drought in the summer, and cooler tem-

peratures than truly Mediterranean-type
climates. Our conditions are duplicated
broadly in (a) cooler parts of the Mediterra-
nean basin and (b) the lakes region in
south-central Chile. (Other winter-rain re-
gions, namely southern Australia and
South Africa, are generally too warm to
match our climate, even though several spe-
cies from these regions do well in our land-
scapes. )

Perusal of two lists of proven drought-resis-
tant trees, one compiled by George Pinyuh
(Washington State University) and one in
the Sunset New Western Garden Book, re-
veals a preponderance of species from
winter-rain regions. Several examples from
the cooler Mediterranean areas are Albizia
julibrissin, Cedrus atlantica, Ficus carica,
Tilia tomentosa, and several species of
Pinus and Quercus. Winter-rain western
U.S. has yielded many tough customers,
such as Aesculus californica, Sequoia-
dendron giganteum, and yet more species
of Pinus and Quercus. This is not to say that
all drought-resistant trees hail from winter-
rain regions — witness Koelreuteria pan-
iculata from eastern Asia — but rather that
these are indeed the logical places to look
first for the bests results.

Plants from Chile have not yet made great
inroads in Pacific Northwest landscapes;
that requires remedy, especially in light of

CENTER FOR
URBAN

HORTICULTURE

University of Washington, GF-15
Seattle, WA 98195

our climatic similarity with the “lakes re-
gion” between Valdivia and Puerto Montt.
To that end, I and a graduate student, Ms.
Sarah Reichard, recently spent two months
in that area conducting taxonomic and
plant materials research. We saw old favor-
ites Escallonia and Araucaria araucana
(female cones appear usually to break up
on the tree before they can fall and clobber
someone) as well as lesser known species
such as Drimys winteri, Desfontainea spin-
osa, and Eucryphia cordifolia. Some
areas — known as “nadis” — are charac-
terized by particularly poor drainage; this is
also a problem plaguing many street tree
sites. It was therefore gratifying to see that
one of the most common (and variable)
nadi plants, Embothrium coccineum, is also
one of the most successful street trees in
Puerto Montt. The many species of
Nothofagus, which North Americans have
inexplicably ignored, also have tremendous
potential for landscape use here.

Our work in Chile illustrates the essence of
the homeoclimatic approach: locate an area
with a similar climate and concentrate
especially on habitats with “urban-type”
stresses. This is one crucial step towards an
urban landscape with ever more appropri-
ate plants.

Nonprofit Org.
U.S. Postage Paid
Permit No. 62
Seattle, WA

SUMMER 1988