(gardening) Selecting and Planting Landscape Trees.pdf

NR-460

Selecting and Planting

Landscape Trees

Mike Kuhns, Extension Forester

and Larry Rupp, Extension Horticulturist

Second Edition

July 2000

INTRODUCTION

Trees and shrubs are a valuable addition to most property. Properly planted, well

maintained trees add beauty, wind protection, shade, wildlife habitat, visual

screening, and other benefits to the landscape.

Unfortunately, many landscape trees are not properly planted or cared for. In some

cases this is simply a matter of neglect, but in other cases the person planting or

caring for a tree is not properly trained. Recent research findings have led to

improved methods for planting and maintaining trees that are often very different

from traditional methods. In some cases we have found that traditional methods

have actually done considerable harm.

Planting techniques have received considerable attention in recent years. In-

creased awareness about tree root systems, soils, and the effects of planting on

both, have led to new recommendations on planting depth, soil amendments,

fertilization, and tree handling. In this publication we describe how to select a tree

and the most up-to-date techniques for planting landscape trees and for post-

planting care. Recommendations are based on research where possible, though

many questions about tree planting have not yet been answered by researchers.

We will update this publication as new information becomes available.

This second edition updates the first edition published in February 1995. Exten-

sive changes have been made to the tree selection guide, including the addition of

many new species and cultivar names for each species.

TREE SELECTION

In selecting a tree species or cultivar – a species is a particular type of tree, like a

Norway maple; a cultivar is a cultivated variety of a species selected for certain

characteristics, like a ‘Crimson King’ Norway maple – our goal should be to have

a tree well-matched to its planting site so it survives and thrives. The tree must

also achieve our goals for size, shape, function, and appearance and must be

affordable. Unfortunately, people usually only pay attention to visually obvious

characteristics like flower color, presence or lack of fruit, and crown shape or size.

Though such characteristics may be important, they usually have little to do with

whether the tree will do well on its planting site. Lack of knowledge of a tree’s

site-related needs results in disappointed tree owners and a lack of well-adapted

trees in our landscapes.

A tree’s site-related needs and its ability to withstand environmental extremes are

rooted in its native origins. All landscape tree species and cultivars were once

native to a certain climatic or geographic region or have been bred from native

trees. These native trees were well-adapted to their surroundings and these

adaptations usually carry over into the cultivated trees we see (with the exception

of some species like fruit trees that have undergone intensive breeding). For

example, though a white fir ( Abies concolor ) at a nursery may have been grown in

a nursery in bright sunlight, it still has its native characteristic of shade tolerance

that allows it to seed-in under the shade of a forest canopy. Cottonwoods ( Populus

species) are native to bare river flood plains which helps explain their preference

for moist soils and bright light. Though you may not know much about a particu-

lar tree’s native habitat, remember that trees have specific site requirements that

vary between species and cultivars. Matching your site conditions to a tree that

you like is the key to tree selection. Several factors that should be considered in

matching a tree to your site are described on the following pages.

SOIL CONDITIONS

Soil provides trees with physical support, water, mineral elements (sometimes

called nutrients), and oxygen for the roots. Certain properties, such as soil pH

(alkalinity or acidity), drainage, density or compaction, texture, salinity, and

structure affect a soil’s ability to provide these benefits to trees. Modification of

these properties at planting time may be possible and will be discussed later.

COLD AND HEAT TOLERANCE

Some trees are very cold hardy and withstand extremely cold temperatures, while

others are killed by a mild frost. In some cases a tree may be fairly cold hardy

while dormant but may become active too early in the spring and suffer damage by

a late frost. Other species may be able to tolerate very high temperatures and some

withstand both extreme cold and heat quite well. Plant hardiness zones indicating

average annual minimum temperatures have been developed by the U.S. Depart-

ment of Agriculture and are shown for Utah on page 11. A detailed map of these

zones for Utah is available from the Utah Climate Center at Utah State University

or at www.ars-grin.gov/ars/Beltsville/na/hardzone/ushzmap.htm.

SHADE TOLERANCE

A tree’s shade tolerance can vary from very intolerant to very tolerant and is

important if you have a very shaded or very open planting site. Shade intolerant

trees rarely do well in shaded areas. Though shade tolerant trees do best in at least

partial shade, some also do well in sunny locations.

WATER REQUIREMENTS

Some tree species are very drought tolerant and can grow in near-desert condi-

tions, while others need access to abundant water at all times. Many heat tolerant

species are also drought tolerant. In much of the populated area of Utah, including

the Wasatch Front, precipitation does not provide enough water for the needs of

many of the trees we plant. Irrigation is necessary on such sites in most years for

all but the most drought tolerant trees. However, trees also can be weakened or

killed by over watering

PEST RESISTANCE

Some tree species or cultivars are highly susceptible to insect or disease pests

while others are nearly pest-free. For example, Lombardy poplar ( Populus nigra

‘Italica’) is very susceptible to a stem canker and is almost certain to die within 5

to 15 years. Ginkgo ( Ginkgo biloba ), on the other hand, has few known pests and

is also very pollution tolerant. Serious, life-threatening pests like borers and

cankers deserve much more attention and concern than late-season leaf feeding

insects or other non-life-threatening pests. Stressed trees are often much more

susceptible to pest attack and damage.

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