NC Cooperative Extension Resources

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Extension Horticulture Specialist
Horticultural Science

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.

Common name Genus Bloom Period Frost tolerance Light Drought tolerance
Table 1. Bloom period, frost tolerance, light preference, and relative drought tolerance of bedding plants.
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.

Name Color Name Color
Table 2. Heat and humidity tolerant bedding plants.*
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 HIL-551, Bed Preparation and Fertilization Recommendations for Bedding Plants in the Landscape). 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 HIL-551, Bed Preparation and Fertilization Recommendations for Bedding Plants in the Landscape, 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.

Sensitive Intermediate Resistant
Table 3. Bedding plant sensitivity to air pollutants.*
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.

Comments Planting pattern Inches between rows of plants (Y) Inches between plants within rows (X) Estimated number of plants per 100 square feet
Table 4. Estimated number of plants to fill 100 square feet of bed area at various spacings.
For square spacing, the distance between plants within rows (X) equals the distance between rows (Y)

Square (See image)

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 (See image) 3.46 4 1,039
5.20 6 462
6.93 8 260
8.66 10 166
10.39 12 115

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

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

For triangular spacing, the distance between plants within rows

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

Recommendations for the use of agricultural 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 North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural 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 regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

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Last modified: Dec. 18, 2014, 3:42 p.m.