Introduction
Plant Selection
Hardy, Semi-hardy, Tender
Heat and
Drought Tolerant
Shade Tolerant Annuals
Fragrant Annuals
Ornamental Foliage
Climbing Annuals
Hanging Baskets
Cut Flowers
Planting
Starting Plants
Maintenance
Insects Problems
Disease Problems
Introduction
Plant Selection
Plant Dimension Characteristics
Specific Site Conditions
Classification by Bloom Periods
Perennials That Attract Wildlife
Planting
Starting Plants
Care and Maintenance
Introduction
Plant Selection
Planting Bulbs
Purchasing Bulbs
Care & Maintenance
Introduction
Plant Selection
Mature Size
Grasses for Specific Uses
Planting Ornamental Grasses
Obtaining Plants
Care & Maintenance
Introduction
Container Selection
Soil Mixes
Container Placement
Plant Selection
Plant Care
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Hardy, Semi-hardy and Tender Annuals
Hardy Annuals: These plants tolerate frost and cool
growing conditions. Many bloom in early spring or can be planted in
late fall to add color to the landscape. Hardy annuals are
irreplaceable for those who live in the cool, high-elevation areas of
Idaho, but can be good additions to the spring and fall landscapes in the
warmer valleys typical of southern Idaho. Popular hardy annuals
suitable for Idaho include:
| Common Name |
Scientific Name |
Regional Adaptation |
| Alyssum |
Lobularia maritime |
N, SW, SC, SE, HA |
| Calendula |
Calendula officicinalis |
N, SW, SC, SE, HA |
| Cornflower |
Centaurea cyanus |
N, SW, SC, SE, HA |
| Dianthus (China Pink) |
Dianthus chinensis |
N, SW, SC, SE, HA |
| Dusty Miller |
Senecio cineraria |
N, SW, SC, SE, HA |
| Kale (ornamental cabbage) |
Brassica oleracea |
N, SW, SC, SE, HA |
| Larkspur |
Consolida ambigua |
N, SW, SC, SE, HA |
| Pansy |
Viola wittrockiana |
N, SW, SC, SE, HA |
| Snapdragon |
Antirrhinum majus |
N, SW, SC, SE, HA |
| Sweet Pea |
Lathyrus oderatus |
N, SW, SC, SE, HA |
| Viola |
Viola cornuta |
N, SW, SC, SE, HA |
 Semi-hardy Annuals: These plants are not injured by
light frost events (down to 28° F). They can also tolerate cool
weather, although many are adapted to hot summer conditions and will bloom
all summer. Semi-hardy annuals can help extend the season and
provide color into the fall. Popular semi-hardy annuals suitable for
Idaho include:
| Common Name |
Scientific Name |
Regional Adaptation |
| Carnation |
Dianthus caryophyllus |
N, SW, SC, SE, HA |
| Cosmos |
Cosmos dipinnatus |
N, SW, SC, SE, HA |
| Gaillardia (Blanket Flower) |
Gaillardia pulchella |
N, SW, SC, SE, HA |
| Gazania |
Gazania rigeas |
N, SW, SC, SE, HA |
| Moss Rose |
Portulaca grandiflora |
SW, SC, SE |
| Petunia |
Petunia spp. |
N, SW, SC, SE, HA |
| Phlox |
Phlox drummondii |
N, SW, SC, SE, HA |
| Rudbeckia |
Rudbeckia hirta |
N, SW, SC, SE, HA |
| Salvia |
Salvia spp. |
N, SW, SC, SE, HA |
| Sunflower |
Helianthus annuus |
N, SW, SC, SE, HA |
 Tender Annuals: These plants cannot withstand any
frost an may not grow well during extended periods of cool weather.
Some of the tender annuals are actually perennials, but due to a lack of
hardiness will only survive one summer in Idaho. They can be planted
only after the soil has warmed in the spring and will die back after the
first frost of the fall, unless protected. These plants are more
suited to the warmer valleys of Idaho, although many can be planted in
cooler areas if desired for a short season of summer color. Popular
tender annuals suitable for Idaho include:
| Common Name |
Scientific Name |
Regional Adaptation |
| Ageratum |
Ageratum houstonianum |
N, SW, SC, SE |
| Amaranth (Love Lies Bleeding, Joseph's Coat) |
Amaranthus spp. |
N, SW, SC, SE |
| Begonia |
Begonia x tuberhybrida |
N, SW, SC, SE |
| Celosia |
Celosia cristata |
N, SW, SC, SE |
| Chrysanthemum (annual) |
Chrysanthemum carinatum |
N, SW, SC, SE |
| Coleus |
Coleus x hybridus |
N, SW, SC, SE |
| Geranium |
Pelargonium hortorum |
N, SW, SC, SE, HA |
| Impatiens |
Impatiens wallerana |
N, SW, SC, SE |
| Marigold |
Tagetes patula |
N, SW, SC, SE, HA |
| Nicotiana (Flowering Tobacco) |
Nicotiana alata |
N, SW, SC, SE |
| Verbana |
Verbena x hybrida |
SW, SC |
| Zinnia |
Zinnia elegans |
N, SW, SC, SE |
Key to regional adaptation notes:
N = Northern Idaho valley locations in USDA zones 5 & 6, Moscow to Sandpoint.
SE = Southeastern Idaho valley locations in USDA zones 3 & 4 from Rexburg to Pocatello. SC = South-central Idaho Magic Valley locations in USDA zones 4 & 5, Burley and Twin Falls.
SW = Southwestern Idaho Treasure Valley locations in USDA zones 5 & 6, Boise area (also Lewiston).
HA = High altitude (>5,000 ft) areas of central, southeastern Idaho and similar locations elsewhere.
Purdue University publishes a frost hardiness chart for
annual flowers. See this information at: http://www.ces.purdue.edu/extmedia/HO/HO-203.html
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