ProHort

Center for Urban Horticulture Cooperative Extension

University of Washington Washington State University

Vol. 5, No. 1

Winter 1987

LANDSCAPE

MAINTENANCE

SEMINARS

. . . for the landscape
professional

Date : Thursday, January 29

Time : 9:00 a. m. -noon

Location : Center for Urban Horticulture

“New Construction Sites”

Thomas Berger, landscape architect,
Thomas L. Berger and Associates

“Nitrogen-fixing Plants for Infertile Soils”
George Pinyuh, extension agent, Washing-
ton State University

“Plants for Wet, Poorly Drained Sites”

Dr. Barbara Smit-Spinks, professor, Center
for Urban Horticulture

Bring your questions about these and other
problem areas for an exchange of ideas with
other landscape professionals.

Pesticides: Environmental
Concerns , Safety , and
Calibration

Date : Wednesday, February 25

Time : 9:00 a.m.-noon

Location : Center for Urban Horticul-

ture

Instructor : James Ely

Update your knowledge of the environ-

mental concerns associated with pesticide

usage. Review safety procedures and cal-
ibration techniques. This seminar qualifies
for 3 hours of W.S.D.A. pesticide license
recertification credit.

Mr. Ely is a horticultural pest control consul-
tant and former owner of A-l Spray Service
of Tacoma.

Learn how proper scheduling can make
your operation more efficient. Scheduling
insures that horticultural tasks are com-
pleted at the proper time, helps to distribute
the workload more evenly throughout the
year, and results in greater productivity. The
scheduling of both work activities and of
manpower will be covered.

Bruce McCormack is president of Blue Rib-
bon Landscape Management, past presi-
dent of the Washington State Nurserymen’s
Association, and an instructor of landscape
business courses at Edmonds Community
College.

OTHER

EDUCATIONAL

OPPORTUNITIES

South Seattle Community College
Horticulture Courses — Winter 1987.

Nursery Operations; Winter Plant I.D.;
Landscape Design; Pruning; Plant Dis-
eases; Landscape Seminar. Call 764-
5336.

Edmonds Community College Horti-
culture Courses — Winter 1987. Soils;

Conifers; Landscape Materials; Landscape
Design; Plant Propagation; Pruning; Small
Engine Repair; Tree Surgery; Japanese
Gardens; Landscape Bidding & Estimating;
Landscape Business; Greenhouse Studies.
Call 771-1679.

Lake Washington Vocational Tech-
nical Institute. Training is offered in nur-
sery and greenhouse operations. Call Don
Marshall, 828-5621 or 828-3311.

Washington State Nurserymen’s Asso-
ciation Annual Convention — January
8—10. Theme: “Back to the Roots.” Loca-
tion: Seattle Marriott, Sea-Tac. For more
information call (206) 863-4482.

Turfgo Northwest plans to offer periodic
seminars for their customers which will
qualify for pesticide license recertification
credit. Call 821-9867 for more informa-
tion.

Home Garden Pest Control Series For

homeowners and professionals who deal
with residential landscape pest control
problems. Each session will qualify for 2
hours of W.S.D.A. pesticide license recer-
tification credit.

I. Urban Integrated Pest Management

Thursday, February 19, 7 to 9 p.m.

II. Pesticides for the Home Garden

Tuesday, February 24, 7 to 9 p.m.

III. Common Insect Pests

Thursday, February 26, 7 to 9 p.m.

IV. Weed Identification and Methods of
Control

Tuesday, March 3, 7 to 9 p.m.

V. Common Diseases of Ornamentals and
Fruit Trees

Thursday, March 5, 7 to 9 p.m.

Location: Center for Urban Horticulture

Registration Fees: $10.00 per individual
session; $40.00 for complete series. See
Urban Horticulture Presents for details.

Cooperating: Center for Urban Horticulture,
University of Washington; Cooperative Ex-
tension Service, Washington State Univer-
sity; Edmonds Community College; South
Seattle Community College.

Managing Landscape
Problem Areas

Efficient Landscape
Maintenance Scheduling

Date

Time

Location

Instructor

Tuesday, March 24
9:00 a.m.-noon
Center for Urban Horticul-
ture

Bruce McCormack

ARTICLES

to provide plants more likely to thrive in
urban sites.

High Soil
Temperatures in
Urban Sites

Dr. Barbara Smit-Spinks
Center for Urban Horticulture
University of Washington

Tree roots in urban sites can be exposed to
unusually high temperatures. A report this
summer at the International Horticulture
Congress by M. N. Dana and W. R. Graves
from Purdue University examined the
range of root zone temperatures of urban
street, suburban street, urban nonstreet,
and native woodland sites. Sites monitored
were street level planting pits, raised plan-
ters, and roof-top planters. Temperatures
were measured twice from June through
October with a thermister probe.

Significant differences in temperatures were
found among the sites. The temperatures of
urban soils were typically several degrees
higher than less urban soils. Urban soil tem-
peratures may rise to lethal levels; high tem-
peratures ranged from 34-37°C
(93-99°F). In an extreme case, soil tem-
peratures near a utility steam line ranged
from 45.3-69.3°C (114-157°F).

In related work, root and shoot responses to
elevated root zone temperatures were mea-
sured for Acer rubrum, Cercis canadensis,
Cercis chinensis, and Gleditsia triacanthos.
Temperatures between 22-32°C
(72-90°F) were optimal for root extension,
while 32°-40°C (90- KMT) resulted in a
severe decline in root growth. G. tria-
canthos was more tolerant and root exten-
sion continued at temperatures several de-
grees higher than the other species.
Decreases in shoot height, fresh weight, and
root fresh weight were also evident at tem-
peratures greater than 30°C (86°F). The
provenance or source of the plants did not
appear to affect root responses to tem-
perature.

These studies illustrate the need to further
describe the nature of urban plant environ-
ments. They also suggest that variability
among species could be identified and used

W. R. Graves and M. N. Dana. 1986. Abstr.
#533, 602. Hort. Sci. 21.

Soluble Salts

George Pinyuh
Cooperative Extension
Washington State University

One of the most common problems associ-
ated with growing plants in containers, par-
ticularly indoors, is the buildup of soluble
salts in the growing medium. This situation
often results in the tips and margins of
leaves turning brown or black and dying. In
severe cases it looks as though the leaves
have been scorched. Plant wilting may also
be associated with the leaf burn, even after
the plant is watered and the soil is moist.
Sometimes a whitish crust on the soil sur-
face, on the rim of the pot, as well as on the
plant stems will be evident.

Blame for these maladies tends to be placed
on diseases, insects, or even low humidity,
but the cause more often can be traced to
the accumulation of soluble salts and other
toxic substances, like fluoride, in the con-
tainer soil. Sometimes underwatering or the
tendency to allow the medium to dry out
too much or too frequently is thought to be
at fault; this may be part of the problem, but
it’s usually not the direct cause for the leaves
burning.

If it’s not insects, diseases or low humidity,
but rather soluble salts, what are these salts
and where do they come from? And more
importantly, what can be done about it?

Most water supplies naturally contain a cer-
tain amount of dissolved salts in them and
the use of such water consistently can lead
to a buildup of these salts in the growing
medium. Fertilizers which must be applied
to provide the necessary mineral nutrients
to plants also consist of salts; in addition,
many water softeners use sodium chloride
in the softening process, and when such
water is applied to plants, the salts are in-
cluded.

Fertilizing is frequently at fault, especially
over-fertilizing. Plants in low light levels in
homes just don’t need as much in the way
of nutrients as do those growing in high light

intensities. Most indoor plants in Puget
Sound houses are, by definition, growing
under low light conditions, especially from
November to March. In many cases where a
plant is growing in less than 300 foot can-
dles of light through the year it may only
need fertilizing twice a year with, say, a
fertilizer containing 20% nitrogen. A 10%
nitrogen or less fertilizer will probably be
needed more frequently.

Recently purchased larger, foliage plants
that have been grown very rapidly in Cal-
ifornia or Florida with large amounts of fer-
tilizers and lots of water, often high in salts,
boron or fluoride, will begin to burn up
once they are brought home. The usual
reduction in irrigation leads to a higher con-
centration of salts in the soil. Even if the
roots are not killed by the salts, the greater
concentration of salt outside the roots pre-
vents the water from moving into the plant.
Sometimes the salt difference between the
medium and the root cells is so great, water
actually moves out of the plant into the
medium. This, of course, can lead to root
death, wilting, yellow leaves, burned fo-
liage, and, if nothing is done about it, to the
death of the whole plant.

Poorly drained potting soils are often at fault
because they tend to prevent movement of
water and dissolved salts through the pot.
Even when excess salts are leached out with
proper watering, if the bottom of the pot is
allowed to sit in this water, it’s pulled back
up, salts and all, by capillary action and the
salt concentration goes way up.

If enough water is not put on a plant each
time it’s irrigated, so excess salts can leach
out, a salt layer often accumulates midway
in the soil. This almost always happens
when plants are in pots with no drain holes
to allow excess water and leaching.

Consider the following to help deal with the
salt problem:

1. Leach all newly purchased plants (espe-
cially larger ones) with plenty of warm
water. Do this three times with half hour
intervals between water applications; all
water must be allowed to drain away. Re-
potting such plants in fresh soil is not a bad
idea.

2. This leaching process should be carried
out two to three times a year, especially on
salt sensitive plants. Many palms, spider
plants, dracaenas and avocados seem to be
salt sensitive.

3. Except for cacti and succulents, keep the
soil of most plants evenly moist. Don’t allow
them to dry to the point where the concen-
tration of salts in the medium goes up.

4. Do not overfertilize.

5. Do not allow excess water to be pulled
back up into the medium. Pour this away, or

elevate the bottom of the pot from the
saucer so it never actually sits in water.

6. Do not use softened water to irrigate
house plants or any plants, for that matter.
Sodium can be removed by the use of 1
tablespoon of gypsum per 6 inch pot before
leaching.

7. Fluoride, which also burns the leaves of
many containerized plants, is not very
teachable nor will it settle out or dissipate if
the irrigation water is allowed to stand be-
fore use. It will not go off as a gas. Use rain or
distilled water for very sensitive plants, or
keep the pH of the medium up at 6. 5 to help
tie up the fluoride.

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

Lessons from
Madrones

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

The University of Washington campus is
home to a fair number of madrone (Arbutus
menziesii) trees. In the past several months I
have made several observations about the
species.

A grove of large, old, established ma-
drones along 15th Avenue N.E. has been
in a declining state of vigor for several
years — heavy leaf drop, stem and
branch cankers, leaf necrosis, and branch
dieback. Though this grove received min-
imal foot traffic, it was underplanted with
summer-irrigated turf. No new madrone
seedlings were ever seen; perhaps they
were mowed off. Last year, though, a
program to correct the decline was initi-
ated. It consisted of two major compo-
nents: 1) discontinuing mowing; and 2)
halting summer irrigation under the trees.
As a result, a large number of seedlings
developed this year. Also, the decline of
the existing trees has not worsened.
Whether it will improve remains to be
seen.

That madrones respond in this way is not
surprising. In western Washington, near the
northern limit of its range, the species pre-
fers dry, exposed slopes. Throughout its
range the species is subject to rather
droughty summers. But more critical to this

situation is a subtle arboricultural concept —
mature trees established under one set of
environmental conditions often do not re-
spond well to a change in that environment.
Thus, a madrone accustomed to dry sum-
mers will not always tolerate the introduc-
tion of summer irrigation, which can change
soil temperature, aeration, and micro-
biology.

Landscape management on campus oc-
curs at all levels — intensive to “natural-
ized.” In many bed (non-turf) areas,
young madrones are growing. Undoubt-
edly seed-generated, these plants are
uniformly vigorous with no evidence of
the typical madrone problems; I marvel
at the quality. And these young ma-
drones occur in irrigated beds.

Why are these small plants so healthy? I
could argue that the combination of turf and
madrone is bad due to factors such as com-
petition and allelopathy. Yet, I believe it is
more related to the idea of an established
environment. Seedlings that germinate and
develop with irrigation seem to “adapt” to
those cultural conditions and do well (What
would happen to these trees if all summer
irrigation was removed?). Seeing such trees
only reinforces the positive qualities of
madrone as a landscape plant.

Why isn’t madrone planted in the land-
scape to a greater degree? Small plants
can be grown in containers. Young trees
grow vigorously. The majority of prob-
lems seem to occur on older trees on
disturbed sites.

I am told that madrone does not transplant
well — meaning that trees die shortly after
being moved. Is it a response to distur-
bance? Do they not regenerate a new root
system? Is it the timing of planting? Does the
culture in the nursery play a role? There are
more good questions than adequate an-
swers.

These observations about madrone offer
insight into the character of tree growth and
development in general — young plants of a
given species are almost universally more
responsive to changes in environment than
are mature trees. This must be appreciated
for the successful rentention of large plants
during construction, site development, or
transplanting.

Registration Form: Landscape Maintenance Seminars

Complete Series: Problem Areas, Pesticides, Scheduling $30.00

Landscape Problem Areas $12.50

Pesticides $12.50

Landscape Maintenance Scheduling $12.50

TOTAL: $

Group Rates:

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

2-5 employees $10. 00/person 6 or more employees $ 9.00/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.

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.

Non-Profit Org.
U.S. Postage Paid
Permit No. 62
Seattle, WA

CENTER FOR
URBAN

HORTICULTURE

University of Washington, GF-15
Seattle, WA 98195