horticulture science lesson 80 choosing plants for the landscape

Horticulture Science Lesson 80

Choosing Plants for the Landscape

Horticulture Science Lesson 80

Choosing Plants for the Landscape

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Interest ApproachInterest ApproachIdentify a situation that calls for a shade tree. Ask the class to develop a list of things to consider in selecting a tree to fill the need. Do the same with a shrub. You might have a student who says it doesn’t matter which type. Another student might be surprised that selecting a plant requires any consideration at all.


Student Learning ObjectivesStudent Learning Objectives•Define the categories of landscape plants.

•Explain why plant names are important.


Student Learning ObjectivesStudent Learning Objectives•Evaluate the selection of plant materials for the landscape.


TermsTerms• cultivar• foundation plants• genus• groundcovers• group plantings• hardiness• hedge• ornamental grasses• ornamental tree


TermsTerms• plant-hardiness zone map• plant heat-zone map• screen• shade tree• shrub• shrub borders• species• specimen plants• tree


TermsTerms• variety• vines


What are the common categories of landscape plants?

• Plants are divided into separate categories based on their size, their growth habit, and their function in the landscape. – Knowledge of the different terms used for plants in

the landscape industry is necessary in selecting the right plants for a particular function.



• A tree is a single-stem, woody, perennial plant reaching a height of 12 feet or more. – It may be deciduous or evergreen. – Trees for the landscape industry

are often classified as shade or ornamental.

• 1. A shade tree is generally a large deciduous tree that provides shade.

• 2. An ornamental tree is a small to medium-sized tree selected for its decorative characteristics, such as flowers, bark, or fruit.



• A shrub is a multi-stem, woody plant that does not exceed 20 feet in height.

• Shrubs may also be evergreen or deciduous. – They are used for many purposes, such as for

hedges, for borders, and as foundation plants.



• Groundcovers are plant materials that form a mat less than 1 foot high covering the ground. – Groundcover may be woody or herbaceous.

• 1. Although grass is the most common groundcover, the term is also associated with plants such as English ivy, periwinkle (vinca), euonymus, and Japanese spurge (pachysandra).

• 2. Groundcovers help to tie the elements of a landscape together.


• Vines are woody or herbaceous plants that require some type of support. – They may climb on objects or creep along the

ground. – Some ornamental vines are Boston ivy, wisteria,

and clematis.


• Flowering annuals, biennials, and perennials are ornamental plants that add bursts of color to the landscape. – In the landscape industry, the term perennial refers

to a herbaceous plant with a life cycle of more than two years, grown for its display of flowers or foliage.


• Ornamental grasses are valued for their textures and colors that add interest to the landscape. – Some ornamental grasses are annuals, others

perennials.– Certain ornamental

grasses grow better in warm climates, others in cool climates.

Why are plant names important?

• Plants have two types of names: common names and scientific, or Latin, names.

• Common names of plants can vary from country to country and from state to state, sometimes even from one town to the next. A plant can have many common names.– Because of this, common names are considered

unreliable. – A plant is given only one scientific name. – The use of scientific names reduces confusion in

the industry.


• In 1753, Carolus Linnaeus (Carl von Linné), of Sweden, developed a binomial system of naming plants. – All plants today, including landscape plant

materials, are given binomial names. – The first of the two terms is the genus, and the

other is the specific epithet. – The advantage of the binomial system is that the

binomial name is recognized and used by horticulturists around the world.


• 1. A genus is a group of plants closely related to each other. – It may contain one or more species. – Botanists use mainly the flower structure to

distinguish one genus from another. – The genus is always written with an initial capital

letter and is either underlined or italicized. – It is the same for every plant in a particular

group. – For example, Quercus is the Latin name for all

oaks, whereas Acer refers to all maples.


• 2. A species is a group of plants with similar characteristics that make the plants distinct from other groups in the same genus. – The species name is written lowercase and is

underlined or italicized. – A species can pass distinct characteristics from

one generation to the next. – There are many maples in the genus Acer. – Some of these are distinct from the others. – Although all the maples carry the Acer genus, the

specific epithets differ. – For instance, the specific epithet for the red

maple is rubrum, and the specific epithet for the Japanese maple is palmatum.


• A group of plants within a species that show a significant difference from other plants in the species is termed a variety.

• This difference can be passed on to the next generation through sexual reproduction.

• 1. A variety follows the species name. – It is written lowercase and is underlined or

italicized.

• 2. A thornless variety of honeylocust is written as follows: Gleditsia triacanthos var. inermis or Gleditsia triacanthos inermis.


• A cultivar is a group of plants within a species that have a distinguishing characteristic. – However, unlike a variety, the only way to pass this

characteristic on to offspring is to propagate the plants by asexual means.

• 1. For example, the Crimson King Norway maple has a distinct maroon leaf color.– Seeds from a Crimson King Norway maple may or may not

produce seedlings that have the distinct maroon color.

• 2. The first letter of each word in a cultivar name is capitalized, and the name is enclosed with single quotation marks. The scientific name for Crimson King– Norway maple is correctly written as Acer platanoides

“Crimson King”.

What factors should be considered when selecting plant materials

for the landscape?

• A landscaper or gardener may encounter many different growing situations.

• Fortunately, there are hundreds of plants from which to choose.

• Selection of landscape plants requires the landscaper to take many factors into account.


for the landscape?

• Selection of plants for the landscape should be based in part on the appearance of the plants. – Superior plants have attractive qualities in each season of

the year.

• 1. Valued qualities include showy and possibly fragrant flowers, good-looking, healthy foliage in the summer, beautiful fall color and fruit effects, and winter interest created by the branching structure or bark.

• 2. Outstanding plants have symmetrical form or shape.

• 3. Plants should also be free of pest and disease.


for the landscape?

• Select plants that can tolerate the range of temperatures in the location where they are to be planted. – A plant’s ability to withstand cold temperatures is

referred to as hardiness. – Plant species have different levels of hardiness. – Heat also has an impact on the growth of plant

species. – Some plants are more sensitive to heat than

others.


for the landscape?

• 1. The U.S. Department of Agriculture has created a plant-hardiness zone map in which the United States has been divided into regions based on average annual minimum temperature. – These areas are called

hardiness zones.– Through research and observation, it has been

determined in which zones plant species can grow.


for the landscape?

• 2. The plant heat-zone map developed by the American Horticultural Society identifies regions based on the average number of days above 86° F (30° C).– At 86° F (30° C), plants

are unable to process water fast enough to maintain normal functions.

– At temperatures above 86°F (30°C), cellular proteins in plants are damaged.


for the landscape?

• Avoid using plants known to be messy. – Messiness comes from fruit, peeling bark, and

easily broken twigs that litter the landscape.

• 1. Trees tend to cause more problems associated with messiness than other landscape plants.

• 2. Messy plants add to the work required to maintain the appearance of the landscape.


for the landscape?• Choose plants that are resistant to disease and

insect problems. – Installing plants prone to pests is impractical. – Not only do the plants suffer, but labor and money may be

needed to address the problems. – Avoiding non-infectious diseases may be equally important.

• 1. Some plants sicken and decline if planted in soil that has a pH too high or too low for the species. – Most plants do well in soils with a pH from 5.5 to 7.0.

• 2. Other plants have a very low tolerance to air pollutants and should not be used in areas recognized as having high levels of air pollution.


for the landscape?

• A plant’s life expectancy, growth rate, and mature size must be considered.

• 1. Some trees, like oak, beech, and baldcypress, can be expected to live hundreds of years. – Others, including some types of

poplars, elms, maples, and cherries, have short life expectancies and begin to decline after only 15 to 20 years in the landscape.


for the landscape?• 2. Short-lived trees tend to be fast growing.

– Fast growth may be desirable in some situations. – However, fast growth is often associated with weaker wood.– Fast-growing trees are more likely to suffer storm damage.

• 3. One of the easiest things to forget about when selecting plants for the landscape is their mature size. – Plants installed landscape without consideration to their

mature size can outgrow their intended purpose. – Always design a landscape with knowledge of the mature

size of a plant.


for the landscape?

• The amount of moisture that the soil holds can be a limiting factor in plant selection. – Most plants prefer moist, well-drained soils. – Be sure to select plants that tolerate the type of

soil for a given site.


for the landscape?

• Shrubs serve multiple functions in a landscape.

• Their selection should be determined on the function they are to serve.

• 1. Specimen plants display outstanding form, texture, and color. – These particularly attractive plants can stand

alone and are used to add accent to a planting bed.

– When placed with other plants in a shrub grouping, a specimen should be planted so it can be seen and enjoyed as an individual plant.


for the landscape?

• 2. Group plantings consist of a number of different species of shrubs. – The individual plants are less important within

group plantings than they would be as specimen plants.

– The individual plants of each species should either be positioned to overlap each other slightly, forming a mass, or be placed with some space between the plants.


for the landscape?

• 3. A hedge is a planting of one type of shrub whose limbs intertwine to form a barrier. – A hedge may define space, tie

other landscape elements together, or screen views.

– Some hedges may be as tall as 20 feet.

– Others may be only 1 foot or so in height. – Hedges can be clipped for a formal appearance,

or they can be left unclipped for an informal, natural look.


for the landscape?

• 4. A screen is a solid mass of one type of shrub that serves as a living wall. – It effectively blocks views. – The ideal shrubs for use as screens

are tall, narrow, upright plants.

• 5. Foundation plants are shrubs placed around the foundation of the house.– They soften the corners, block the view of the

foundation, and help to tie the house to the landscape.


for the landscape?

• 6. Shrub borders are masses of many shrubs on the border of the property.– Shrub borders help to create the walls of the

outdoor living area, screen views, and serve as backdrops for flowering plants.

– Unlike a group planting, all the shrubs in a shrub border should be drawn on a landscape plan as touching or overlapping one another to form a single mass.


for the landscape?

• Other considerations when selecting landscape plants include safety, rooting habits, density of shade, and food for wildlife.

• 1. Avoid using plants with thorns that could present safety hazards in certain settings.

• 2. The roots of some trees grow at the surface of the ground, making it difficult to grow grass or other plants beneath the trees.


for the landscape?

• 3. Consider the density of the shade cast by the tree. – Some trees allow sunlight to reach the ground

and permit grass growth, while others create dense shade, making it difficult to grow grass or other plants underneath.

• 4. Certain plants produce edible fruit that attracts birds to the landscape.

Review/SummaryReview/Summary

•What are the common categories of landscape plants?

•Why are plant names important?

Review/SummaryReview/Summary

•What factors should be considered when selecting plant materials for the landscape?

horticulture science lesson 80 choosing plants for the landscape

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