Selection and Use of Stress-Tolerant Bedding Plants for the Landscape

 

HIL #552 Revised 8/99 -- Author Reviewed 8/99
Douglas A. Bailey, Professor
Department of Horticultural Science
College of Agriculture & Life Sciences
North Carolina State University

What is Stress?
Each of us are subjected to stresses and pressures every day in our home, work, and living environment; plants are no different. Unfortunately, there is no "stressless" environment, and there is no totally stress-resistant bedding plant. Each site has its stress level and each plant has its tolerance level. There are steps that can be taken to reduce or avoid stress in the landscape. However, no program can prevent all problems, and the key to successful landscape color using bedding plants is to match the particular site with specific plant species. But before you can select plants to use, the site should be accurately analyzed and characterized, and preparations should be made to minimize stress conditions that may occur.

Characterization of the Landscape Site
A site analysis for bedding plants should include

  1. temperature averages for the color season,
  2. amount of sunlight received daily,
  3. rainfall averages and average intervals between rains, and,
  4. soil characteristics such as drainage and moisture retention.

Each of these components should be further defined prior to plant selection.


Table 1. Bloom period, frost tolerance, light preference, and relative drought tolerance of bedding plants.

Common name
(genus)

Bloom Period

Frost tolerance

Light

Drought tolerance

Ageratum
Ageratum

Summer

Tender

Full sun

Moderate

Alyssum
Lobularia

Spring to early fall

Tolerant

Full sun to partial shade

Low

Aster
Callistephus

Summer to early fall

Moderate tolerance

Full sun to partial shade

Low

Begonia
Begonia

Late spring to early fall

Tender

Full sun to heavy shade

Low

Blanket Flower
Gaillardia

Summer to early fall

Tolerant

Full sun

Moderate

Browallia
Browallia

Summer

Moderate tolerance

Full sun to partial shade

Low

Calliopsis
Coreopsis

Summer

Moderate tolerance

Full sun to partial shade

Moderate

Candytuft
Iberis

Late spring to early summer

Tolerant

Full sun to partial shade

Low

Calendula
Calendula

Summer to fall

Tolerant

Full sun to partial shade

Low

Celosia
Celosia

Summer to early fall

Tender

Full sun

Moderate

Coleus
Solenestenon

Late spring to fall (foliage)

Moderate tolerance

Partial to heavy shade

Low

Cornflower
Centaurea

Summer

Moderate tolerance

Full sun to partial shade

Low

Cosmos
Cosmos

Spring to early fall

Moderate tolerance

Full sun

Moderate

Dahlberg Daisy
Dyssodia

Summer to fall

Moderate tolerance

Full sun

High

Dahlia
Dahlia

Summer to fall

Tender

Full sun

Low

Dianthus
Dianthus

Spring and fall

Very tolerant

Full sun to partial shade

Low

Dusty Miller
Senecio

Spring to fall (foliage)

Tolerant

Full sun to partial shade

Moderate

Geranium
Pelargonium

Late spring to early fall

Tender

Full sun

Low

Globe Amaranth
Gomphrena

Late spring to early fall

Moderate tolerance

Full sun

High

Gloriosa Daisy
Rudbeckia

Summer

Tolerant

Full sun to partial shade

Moderate

Hypoestes
Hypoestes

Summer (foliage)

Tender

Partial to heavy shade

Low

Impatiens
Impatiens

Late spring to early fall

Tender

Full sun to heavy shade

Low

Lisianthus
Eustoma

Midsummer to fall

Tender

Full sun

High

Lobelia
Lobelia

Summer

Tolerant

Full sun to partial shade

Low

Marigold
Tagetes

Late spring to fall

Moderate tolerance

Full sun

Moderate

Melampodium
Melampodium

Late spring to early fall

Tender

Full sun

Moderate

Nicotiana
Nicotiana

Summer

Tender

Full sun to partial shade

Low

Ornamental Pepper
Capsicum

Late summer to fall

Tender

Full sun

Low

Pansies and Violas
Viola

Early spring, fall, and winter

Very tolerant

Full sun to partial shade

Low

Petunia
Petunia

Spring to early fall

Tolerant

Full sun to partial shade

Moderate

Phlox
Phlox

Spring to early summer

Tolerant

Full sun to partial shade

Low

Portulaca
Portulaca

Summer to early fall

Tender

Full sun

High

Salvia
Salvia

Early summer to early fall

Tender

Full sun

Low

Sanvitalia
Sanvitalia

Early summer to fall

Tender

Full sun

Moderate

Snapdragon
Antirrhinum

Spring to early summer, fall

Very tolerant

Full sun to partial shade

Low

Spiderflower
Cleome

Summer to early fall

Tender

Full sun

Moderate

Treasure Flower
Gazania

Late spring to fall

Tolerant

Full sun

High

Verbena
Verbena

Late spring to early fall

Moderate tolerance

Full sun to partial shade

Moderate

Vinca
Catharanthus

Late spring to fall

Tender

Full sun to partial shade

Moderate

Zinnia
Zinnia

Late spring to early fall

Tender

Full sun

Moderate

Temperature. Very few species look attractive and flower profusely from early spring through late fall, and rotational planting for continuous color should be considered (Table 1.). Cool-season flowers such as dianthus, snapdragons, and pansies can be used early in the season. It is possible to extend the flowering season of cool-season annuals by placing them in a protected location, shaded from direct sunlight from 12:00 to 4:00 PM. Heat-loving flowers such as gaillardias, portulaca, sand verbena, and vinca do not begin to flower until early summer and should be used for summer color and high temperature situations. Heat tolerance is an advantageous characteristic, and bedding plant trials can offer cultivar suggestions to landscapers interested in plant performance in high temperatures (Table 2). Another temperature consideration is frost tolerance (Table 1). Avoid early planting of tender plants to prevent frost damage. Tender species also will be the first to be killed from frosts in the fall.


Table 2. Heat and humidity tolerant bedding plants.*

Name

Color

Name

Color

Bronze-leaved Begonia
Impatiens, Continued

'Brandy'

Pink

'Dazzler Blush'

Blush

'Whisky'

White

'Accent Bright Eyes'

Blush

'Espresso White'

White

'Super Elfin Blue Pearl'

Lilac

'Vision'

Red

'Accent Lilac'

Lilac

'Bingo Red'

Red

'Dazzler Burgundy'

Burgundy/Purple

'Espresso Rose'

Rose

'Super Elfin Violet'

Burgundy/Purple

'Bingo Rose'

Rose

African Marigold
Green-leaved Begonia

'Perfection Gold'

Gold

'Prelude Pink'

Pink

'Perfection Orange'

Orange

'Viva'

White

'Voyager'

Yellow

'Prelude White'

White

French Marigold

'Varsity Scarlet'

Red

'Red Marietta'

Single Red

'Scarlanda'

Red

'Orange Boy'

Double Orange

'Eliza'

Rose/Salmon

'Bonanza Orange'

Double Orange

'Ambra'

Rose/Salmon

'Bounty Gold'

Double Gold

'Rum'

Bicolor

'Early Queen Sophia'

Double Bicolor

Geranium

'Hero Harmony'

Double Bicolor

'Pink Orbit'

Pink

Petunia

'White Orbit'

White

'Pink Carpet'

Pink

'Ringo White'

White

'Eterna Pure Pink'

Pink

'Pinto Red'

Red

'Pink Madness'

Pink

'Pinto Rose'

Rose

'White Carpet'

White

'Hollywood Rose Pink'

Rose

'Celebrity White'

White

'Pinto Salmon'

Salmon

'Eterna Vivid Red'

Red

'Hollywood Star'

Bicolor

'Rose Madness'

Rose

Impatiens

'Rose Carpet'

Rose

'Dazzler White'

White

'Deep Rose Pearls'

Rose

'Impulse White'

White

'Coral Madness'

Coral

'Impact Rose'

Rose

'Velvet Picotee Improved'

Bicolor

'Novette Deep Rose'

Rose

'Electra Blue'

Blue

'Dazzler Coral'

Coral/Salmon

'Eterna Lilac'

Burgundy

'Impact Coral'

Coral/Salmon

'Supercascade Lilac'

Burgundy

'Impulse Salmon Orange'

Coral/Salmon

'Purple Pirouette'

Double Purple

'Accent Rose Star'

Star

Vinca

'Spotlight Mix'

Mix

'Peppermint Cooler'

Upright White/Red Eye

'Impulse Carmine'

Carmine

'Grape Cooler'

Upright Pink/Rose Eye

'Impact Carmine Rose'

Carmine

'Rose Carpet'

Prostrate Rose

'Accent Deep Pink'

Pink

Adapted from Armitage, A. 1988. 1988 heat tolerant annuals for the landscaper. Greenhouse Grower 6(13):54,56.

Light. Light and temperature are closely related, and plants listed as preferring lower light may tolerate more sun, if temperatures are moderate. When evaluating light exposure, note the duration and intensity of light the site receives. Four hours of full sun during the morning is much different than four hours of afternoon sun. Also, in a shaded location, the degree of light filtration can vary. In general, if the site receives more than 3 hours of unfiltered midday sun, it should be treated as a "full sun" site, with respect to plant selection (Table 1). "Partial shade" can be defined as receiving unfiltered morning sun, but shade during the afternoon hours, or moderate shading throughout the entire day. A "heavily shaded" site would receive very little direct midday light and less than 60% of the sun's intensity during the remainder of the day. A mismatch of plant and light can lead to reduced flowering, leggy growth habit, burning of plants, and stunting of growth.

Water. Water stress in North Carolina covers both extremities of the spectrum, even for the same landscape site. Bed preparation is essential for avoiding both moisture excess and drought conditions (See Horticulture Information Leaflet No. 551). For most situations, supplemental irrigation will be required at some point during the growing season. For minimal irrigation sites, select "drought tolerant" species (Table 1). The best insurance against excessive moisture is proper bed preparation and sufficient drainage. Keep in mind that the majority of over watering problems, assuming a well-prepared site, occur from too frequent irrigations rather than too much water applied at any one time. If supplemental irrigation is in place, apply enough water at every watering to assure complete bed coverage. Also, an irrigation schedule should take into account rainfall and be adjusted appropriately to be most effective.

Soil Characteristics. Plants depend on the soil for water, anchorage, and nutrients. Frequent heavy rains in combination with poorly drained beds will reduce plant performance and increase the chances of root rot problems. On the other hand, beds with excellent drainage combined with little water holding capacity could require irrigation as frequently as every other day. Nutrient deficiencies and toxicities are common in the landscape, although they are easily avoided if proper steps are taken. Do not guess at fertility levels--take a soil test and send it in for analysis. Follow proper bed preparation guidelines given in Horticulture Information Leaflet No. 551 to avoid water, pH, and nutrient stress situations. Again, stress prevention and avoidance is much easier than relying on stress tolerance.

Air Pollutants. Some landscape sites, especially in highly urbanized areas, are subjected to significant levels of air pollution. The most damaging of these pollutants are sulfur dioxide (SO2), ozone (O3), and peroxyacetyl nitrate (PAN). Symptoms of SO2 injury include necrotic (dead) spots between the major veins, where the tissue turns light tan and papery in texture. The most common symptom of exposure to O3 is the formation of tiny, light-colored flecks or spots on the upper surfaces of affected leaves, similar to spider mite damage. PAN injury is expressed as silvering, glazing, bronzing, and sometimes death of the lower leaf surfaces. Bedding plants do exhibit relative sensitivity and tolerance to these materials (Table 3), and if pollutants are a problem, plants should be selected accordingly.

 

Table 3. Bedding plant sensitivity to air pollutants.*

Sensitive
Intermediate
Resistant
Sulfur Dioxide

Aster

Coleus

Dianthus

Castor Bean

Begonia

Cosmos

Nasturtium

Chrysanthemum
(most varieties)

Centaurea

Geranium

Zinnia

 

China Aster

Marigold

 

 

Chrysanthemum
(some varieties)

Poppy

 

 

Ozone

Ageratum

Fuchsia

Impatiens

China Aster

Aster

Marigold

Verbena

Chrysanthemum
(most varieties)

Begonia

Pansy

 

Chrysanthemum
(some varieties)

Petunia

 

Geranium

Salvia

 

Lobelia

Dahlia

 

 

Ornamental Pepper

Peroxyacetyl Nitrate (PAN)

Aster

Ornamental Pepper

 

Begonia

Dahlia

Petunia

 

Calendula

Fuchsia

Salvia

 

Chrysanthemum

Impatiens

Snapdragon

 

Coleus

 

 

 

Gaillardia

 

 

 

Pansy

 

 

 

Periwinkle

*Adapted from Rogers, M.N. 1976. Air pollution, p. 441-481. In: J. Mastalerz (ed.).
Bedding Plants, Prentice-Hall, Englewood Cliffs, N.J.

Program for Stress Reduction
Successful colorscaping accepts there is no perfect planting site and builds upon given parameters. Steps to follow include:

  1. Site analysis for temperature, light, water, and soil characteristics.

  2. Proper adjustment of beds to reduce/prevent nutrition and water stress.

  3. Selection of proper plant species for specific sites, including rotation of plants for specific time periods.

Paybacks include more attractive color, less maintenance requirements, and more satisfied clients.


Table 4. Estimated number of plants to fill 100 square feet of bed area at various spacings.

Comments

Planting pattern

Inches between rows of plants (Y)

Inches between plants within rows (X)

Estimated number of plants per 100 square feet

For square spacing, the distance between plants within rows (X) equals the distance between rows (Y)

Square
4
4
900
6
6
400
8
8
225
10
10
144
12
12
100

For triangular spacing, the distance between plants within rows and between rows both equal X and the distance between rows (Y) equals 0.886 times X

Triangle
3.46
4
1,039
5.20
6
462
6.93
8
260
8.66
10
166
10.39
12
115

 


Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact an agent of the North Carolina Cooperative Extension Service in your county.

Published by the North Carolina Cooperative Extension Service


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