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  • SHORT-SEASON, HIGH-ALTITUDE GARDENING BULLETIN 861

    Herbaceous ornamentals:annuals, perennials, andornamental grasses

    INTRODUCTIONThe short-season, high-altitude gardening series was created in response to anoteworthy lack of information about designing landscapes and caring forgardens in the harshest of Idahos climates. This publication outlines steps forchoosing and caring for annuals and perennials in these short-season locales.

    By definition, herbaceous ornamentals are annual or perennial flowers and foliageplants that die back to the ground each fall. Ornamental grasses and bulbs arenot always classified as herbaceous, but will be included in this publication.

    Trees and shrubs form the backbone of landscapes, but herbaceous orna-mentals provide the beauty and accent that mark the difference betweenroutine and spectacular. They give a garden color, interest, and character. Inthe short-season, high-altituderegions of Idaho, our choices forhardy woody plants are severelyrestricted, making herbaceousplants more important than ever.

    Annuals are those plants that liveand bloom for only one year.They die at the end of the grow-ing season and must be replantedor allowed to reseed themselvesfor the following season. Theeffort and expense of replacingplants each year are major draw-backs to using annuals in the gar-den. On the positive side, annualsare unmatched in their variety,color, summer-long bloom peri-od, and adaptability. There is anannual plant for every situationin the landscape and this com-pensates for the extra effortinvolved in establishment.

    YOU ARE A SHORT-SEASON, HIGH-ALTITUDE GARDENER IF:

    You live in Idaho at an elevation above 4,500 feet, OR

    Your USDA hardiness zone is 4 or lower, OR

    You have a frost-free growing season of 110 days or less

    by Stephen L. Love, Kathy Noble, Stuart Parkinson, and Susan Bell

    CONTENTS

    INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1PLANT SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

    Hardy Annuals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Hardy Perennials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Hardy Bulbs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Ornamental Grasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

    CARING FOR HERBACEOUS & GRASS ORNAMENTALS . . . 9Planting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Obtaining Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Fertilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Controlling Pests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Providing Winter Protection . . . . . . . . . . . . . . . . . . . . . . . . 13

    CONTAINER GARDENING . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Container Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Soil Mixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Container Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Container Plant Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 15Container Plant Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    The colors of annuals and perennials comple-ment the form of trees and shrubs.

  • 2 SHORT-SEASON, HIGH-ALTITUDE GARDENING

    Annuals grow fast and bloom quickly so as to set seed andreproduce. Consequently, most need consistently good grow-ing conditions to be at their best.

    Perennials are defined as non-woody plants that live andflower for three or more years. Perennials, including bulbs andgrasses, provide one advantage over annuals in that theyneed not be replanted every spring. Some will last in the gar-den for only a few years while others provide decades of valueand interest. Many perennials are very hardy and can thrive insituations that present us with problems for other types ofplants. They are good candidates for adding color or interestto sloped areas, water conserving gardens, locations withpoor soils, and native plantings. The one disadvantage ofperennials is that many bloom for only a few weeks duringthe growing season. Overcome this deficiency by plantingperennials with complementary bloom periods to ensure thatsome plants are in flower at any given time.

    Herbaceous ornamentals can be used to achieve many effectsin the landscape. In addition to traditional beds, rock gardens,and borders, they can be used in window boxes, containers,and hanging baskets. This increases opportunities for main-taining color in a short-season, high-altitude landscape.

    PLANT SELECTIONSucceeding with herbaceous ornamentals in a short-season,high-altitude garden means selecting plants that can flourishin wildly fluctuating temperatures, cool nighttime tempera-tures, high light intensity, and poor soils. Another commonlimiting factor in Idaho gardens is untimely late spring andearly fall frosts. These harsh conditions decrease the numberof adapted plants that are suitable for planting in landscapes.However, there are still many beautiful species from which tochoose. If you are willing to put forth the extra effort, you canemploy season-extending methods to increase the selectionof plants that can be grown in Idahos harsh climates. SeeIntroduction to Short-Season Gardening in Idaho(http://info.ag.uidaho.edu/pdf/BUL/BUL0857.pdf) for adescription of these methods.

    As a rule, plants acclimated to USDA hardiness zones 2, 3 andin some regions, zone 4, will thrive in high-altitude growingconditions. They must also be able to remain attractive afterexposure to spring and fall frost. There are a sufficient num-ber of plants adapted to cold climates to allow creation ofany preferred garden style. Among hardy plant species, thereare those with round flowers, spiky flowers, early bloomers,and late bloomers. The bloom colors span the entire colorspectrum, and leaf color and shape are varied enough suchthat the design opportunities are limited only by imagination.

    Tables in this publication contain lists of annual and perennialflower species recommended for gardens in Idahos short-sea-son, high-altitude regions.

    HARDY ANNUALSFrost-tolerant annuals are irreplaceable in Idahos short-sea-son, high-altitude landscapes because they provide the bestoptions for season-long color. They also lend themselves toflexibility and allow you to creatively alter the landscapefrom season to season. Annuals are considered to be fullyhardy if moderate (not lower than 25F) spring and fall frostsdo not disrupt growth. Half-hardy annuals are those that arenot killed by light frost (down to 28F), but may experience adelay in growth and bloom. Most half-hardy annuals areadapted to cool climates but many also remain attractivethrough summer heat. Popular hardy and half-hardy annualsadapted to short-season, high-altitude Idaho gardens areshown in table 1.

    Adapted ornamental plants must be able to withstand spring and fallfrosts.

    Snapdragons are frost hardy. They start blooming early in the seasonand continue for a long time

  • HERBACEOUS ORNAMENTALS: ANNUALS, PERENNIALS, AND ORNAMENTAL GRASSES 3

    Table 1: Hardy AnnualsRELATIVE BLOOM

    SCIENTIFIC NAME COMMON NAME(S) HARDINESS PERIOD

    Achillea ptarmica Gypsy Yarrow FH Su/FaAgrostemma githago Corncockle FH Su/FaAnagallis monelli Pimpernel FH Sp/Su/FaAnchusa capensis Anchusa FH SuAngelonia angustifolia Angelonia HH Su/Fa Antirrhinum majus Snapdragon FH Su/FaArctotis hybrids African Daisy FH Su/FaArgyranthemum hybrids Marguerite Daisy FH Sp/Su/FaBidens ferulifolia Bidens HH Su/Fa

    Brachycome iberidifolia Swan River Daisy FH Su/FaBrassica oleracea Ornamental Cabbage FH FaCalendula officinalis Calendula FH Su/FaCalibrachoa hybrids Million Bells FH Sp/Su/FaCentaurea cyanus Cornflower, Bachelors Button FH Sp/Su/FaChaenorrhinum minus Dwarf Snapdragon FH Su/FaCleome sesquiorygalis Spider Flower HH Su/FaConvolvulus sabatius Ground Morning Glory HH Su/FaConsolida ambigua Larkspur FH Su

    Cosmos bipinnatus Cosmos HH Su/FaDianthus caryophyllus Carnation HH Su/FaDianthus chinensis Dianthus, China Pink FH SuDiascia spp. Twinspur HH Su/FaEuphorbia marginata Snow-on-the-mountain HH FolEustoma grandiflorum Lisianthus HH Su/FaGaillardia pulchella Gaillardia, Annual Blanketflower HH Su/FaGazania rigens Gazania HH Su/FaGodetia spp. Godetia FH Su/Fa

    Helianthemum hybrids Rock Rose HH Su/FaLantana spp. Lantana FH Su/FaLathyrus oderatus Sweet Pea FH Su/FaLimonium sinuatum Statice FH Su/FaLinaria maroccana Baby Snapdragon FH Su/FaLobelia cardinalis Cardinal Flower HH Su/FaLobularia maritime Alyssum FH Su/FaMimulus hybrids Monkey Flower HH Su/FaNemesia hybrids Nemesia HH Su/Fa

    Nemophila spp. Baby Blue Eyes FH Su/FaNicotiana x sanderae Flowering Tobacco HH Sp/Su/FaNigella spp. Love-in-a-Mist FH Sp/Su/FaOsteospermum hybrids South African Daisy HH Su/FaPapaver nudicaule Iceland Poppy FH SuPapaver rhoeas Shirley Poppy FH SuPetunia spp. Petunia HH Su/FaPhlox drummondii Phlox HH Su/FaPortulaca grandiflora Moss Rose HH Su/Fa

    Primula auricula Primrose FH SpRudbeckia hirta Rudbeckia HH Su/FaSchizanthus x wisetonensis Butterfly Flower FH Su/FaSenecio cineraria Dusty Miller FH FolSutera cordata Bacopa HH Su/faVerbena hybrids Verbena FH Su/FaViola cornuta Viola FH Sp/Su/FaViola wittrockiana Pansy FH Sp/Su/Fa

    Relative Hardiness designation: FH=fully hardy, HH=half-hardy. Bloom Season: Sp=spring, Su=summer, Fa=fall, Fol=grown for season-long attractive foliage.

  • Som

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