Annual Flowers

Last Updated: 06/20
by Cheryl Moore-Gough, Extension Horticulture Specialist and Rebekah VanWieren, Associate Professor of Landscape Design, MSU

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ANNUAL FLOWERS MAY SOLVE MANY

landscape problems. No other plants provide such continuous bloom. They fill voids in permanent plantings while young woody plants grow, offer flexible design options for myriad containers as added landscape interest, and provide inexpensive color and cut flowers in almost any soil.

Annuals are used in perennial plant beds to continue interest following early blooming bulbs and perennials. They can be transplanted or direct- seeded into the spot where tulip and daffodil blooms have faded, integrated into perennial plantings, or planted in front of woody, flowering shrubs to provide further interest through the season.

If you want plenty of cut flowers, devote a separate area of the garden to annuals, but be sure to coordinate it with the overall landscape plan.

 

 

Figure 1: Plant layout characteristics. Blocks of each annual planted in drifts. BY JOHNNY DOHNER

 

 

Planning the Flower Bed Garden

Integrating annual flowers into a planting bed or as a border planting in and of themselves can be an attractive element in the overall landscape. The following guidelines will help create a successful design. Flower beds can be any shape, but generally, curved bed lines look more natural and informal, while angular bed lines feel more formal. For plant placement, plant masses of individual flowers in “drifts” which gradually melt into each other (Figure 1). Graduate plant heights from front to back, and use lowest plants in front. Utilize a diversity of leaf and flower textures for dynamic interest across a space. No matter the chosen color palette (see below), repeating colors or plant species creates cohesion and balance within a larger-sized flower bed. When annual beds include perennials or woody plant material, massing the annuals together simplifies maintenance. Annual flowers may also be intermixed with perennials and woody plants to create a diverse plant community, where the annuals are used to fill gaps, as ground covers, and create aesthetic interest when other plants are still establishing.

Make the bed at least 3 feet but no more than 5 feet wide from front to back to allow for working the bed from its border. If it is deeper than 5 feet, plan stepping stones or a small path to allow access to the interior of the bed.

To be effective, each flower ‘drift’ should be large enough to be clearly seen from a distance. Use the “warm” or advancing colors (red, orange, yellow) in smaller masses to subordinate them; use “cool” or receding colors (blue, violet, green) in larger masses to contrast with the warm ones. The color wheel (Figure 2) will help you understand color use. Each cool color opposes a warm color. Colors across the wheel from each other are complementary and provide strong contrast. Adjacent colors are analogous, provide subtle color transitions, and occur more often in nature. If you don’t want strong accent, don’t arrange flowers with warm colors directly next to those with cool colors.

 

Planning the Flower Container Garden

Using annuals in container gardening is an excellent approach to adding landscape interest and focal points within a space, especially in areas with shorter growing seasons or where resources or space are not available for more intensive flower beds. Containers offer a myriad of design options, due to the wide range of available sizes, shapes, colors, and materials. When choosing the container(s), assess whether the container should stand out or blend into the overall landscape character. For example, bright-colored containers provide contrast and emphasis in comparison to more muted colors often in plant and building materials. The size of the container should feel balanced with the scale of adjacent structures, and also be manageable once it is filled with the weight of the growing medium. Plant materials should first be chosen based on growth habit and texture, before color.

 

Figure 2: Color wheel. BY REBEKAH VANWIEREN

 

 

Figure 3: Plant growth habits and texture diversity. BY JOHNNY DOHNER

 

Choosing plants with different growth characteristics creates a multi-dimensional, layered container design. Plants that are ‘fillers’ should have mounding growth habits to create planting fullness; ‘spillers’ are plants that spread or are vine-like to encourage plant growth outside and around the container; and, ‘thrillers’ are plants that grow upright or erect to provide additional height or ‘wow’ factor (Figure 3). A diversity of plant textures, through leaf and flower size and shape, gives flower containers dynamic interest and contrast between plant species. Finally, color considerations (see above) can be used to create cohesion or contrast within the container planting design. Utilizing leaf color instead of flower color is a powerful design tool, in addition to simply using a diversity of tones and hues of greens.

Containers should have 3–9 small holes on the bottom to accommodate water drainage, otherwise excess water holding can lead to lower oxygen levels in the soil and root rot. Use 12–24” depth of growing medium mixed for container gardening (potting soils are composed of many materials besides sand, silt, and clay found in natural soils). Upcycle materials, like plastic bottles, styrofoam, or foam board insulation to fill a portion of the bottom of large containers to reduce the overall amount, cost, and weight of growing medium. To reduce the mixing of these space-fillers and the soil, a small piece of weed-barrier fabric or several sheets of newspaper can be added before the growing medium. For watering recommendations, see below.

Color creates moods. Warm colors exhilarate and stimulate while cool colors relax the viewer. Let cool colors predominate in areas devoted to rest and relaxation. Warm colors command and direct attention to specific areas in the landscape.

You’ll find an example of an annual flower border with proper size and choice of plants in Figure 4. All flower borders, whether annual or perennial, are most attractive against a fence of neutral color or against a shrub background (Figure 4).

 

Starting Plants Indoors

Many annuals perform better if started indoors and transplanted into the garden. You can determine indoor planting time by finding the number of days from seed to flower on the seed packet. Table 1 includes some general information about planting dates for inside or outside sowing.

Many people plant seeds too early. This results in an oversized, leggy transplant that is susceptible to damping- off disease. Legginess is often caused by low indoor light levels and/or by too high a temperature. Let an electric fan blow air across the plants—the plant movement will help form stocky plants. You must coordinate the date of sowing with the average date of last frost in your location. Contact your local Extension office for the average date of last frost in your area. The right time to start seedlings also depends upon the species. Trial and error is the only way to determine a more precise time for a specific location and flower species.

Use a soiless seed germination mix (which often contains peat moss and perlite). Or, use a mix containing 50 percent loam soil, 25 percent peat moss, and 25 percent washed sand to start seeds indoors. If you use the soil mix be sure to pasteurize it to reduce the chances of seedling damping- off: Place moist soil into shallow trays and put these into a household oven at 180°F for 30 minutes. Use a probe-type thermometer to determine when all soil has reached the desired temperature. Microwave ovens can also be used to pasteurize soil. Determine the amount of time required by monitoring soil temperatures as described above for the regular oven. Purchased soiless mixes usually need no pasteurization.

Germination mixes should have a fine texture, screen if necessary. Fill pots or flats, and firm and moisten it before planting. Scatter seeds over the surface and cover them with mix to a depth equivalent to twice their largest diameter. Some seeds require light to germinate. This information will be included in the seed packet instructions. Label the seeded flats to maintain plant identity. Cover seeded containers with a plastic sheet to maintain relatively high humidity. Most seeds germinate well at temperatures between 50° and 80°F. Spiderflower (Cleome) and Petunia germinate better at warm temperatures (70°–80°F). Seeds of species that do better in cooler temperatures include African daisy (Arctotis), candy tuft (Iberis), bachelor button (Centaurea), clarkia (Clarkia), godetia (Clarkia), and larkspur (Delphinium). Remove the plastic sheet after the seeds germinate.

 

Figure 4: Color sequences and size considerations for an annual flower border. The back row (pictured top) features shrub or perennial planting integrated with annuals. The front rows (pictured bottom) feature annuals planted as border or to fill gaps while other plant material establishes. BY JOHNNY DOHNER

 

Bottom-water the seeded flats or pots by placing the containers in shallow trays of water and allowing water to move up through the mix. Watering from above can disturb or damage fine seeds or small seedlings.

If you initially used flats, transplant the seedlings to individual containers when they have reached the 2–3 leaf stage. Peat pots are popular but other containers with holes in the bottom work well also. Place the transplants in a greenhouse or a hot bed if possible. A shelving system with added “grow” lights works well. Be sure to harden-off the plants before transplanting them to the garden by gradually exposing them to our intense sun, dry air, and cooler nights over a 1- to 2-week period.

 

Setting out the Plants

Most annuals don’t require very rich soil, but they do need an adequate supply of nutrients. Work into the bed area a complete fertilizer at the rate of ¼ pound of actual nitrogen per 100 square feet. Using 5-10-10 fertilizer, 5 pounds of fertilizer per 100 square feet is the right amount. Also work in organic matter such as peat moss, compost or well-decayed manure to improve soil structure. Most annuals grow best at a soil pH of between 6.5 and 7.5. Attention to fertility now will help produce vigorous, healthy plants and blooms later on.

 

Suggested Annuals for Figure 4

 

Plant outdoors late in the afternoon on a cloudy day when soil is moist to help reduce transplant shock. Spacing depends upon the species. For example, giant zinnias are planted 18 inches apart, but alyssum only 6 inches apart.

Annuals that are direct seeded will need thinning before they become crowded. Failure to do this will result in overcrowding and spindly plants with few flowers.

 

Pinching

Removing the top growth of a plant is called pinching. This increases the number of blooms and forms a stockier, bushier plant. Some annuals that require this are Ageratum, Browallia, Calendula, Chrysanthemum, Petunia, Phlox, Dianthus, Salpiglossis, Schizanthus, Antirrhinum, Verbena and Zinnia. DO NOT pinch cockscomb, everlastings, poppies or stocks.

 

Aftercare

Hoe weeds to keep them from competing with flowers for water and nutrients. A mulch such as bark fines will decrease weed competition, conserve soil moisture, and lower high summer soil temperatures for better plant growth.

Water plants during warm dry periods to assure continuous plant development. Infrequent, deep waterings are better than light, frequent ones. At least the top 6 inches of soil should feel moist and cool. Use drip irrigation during flowering to prevent browning of the blooms by water puddling on them.

Remove spent blossoms (“deadhead”) to force a longer continuous bloom period and fertilize plants weekly with a water-based fertilizer according to label directions.

 

Fall Clean-up

Remove all annual plants from the bed after fall freeze to reduce the chances that disease organisms will be carried over into the next season and to discourage nesting rodents. Till or turn the soil to remove weeds and leave it in good condition for spring planting. If more organic matter is needed, add it during fall tilling.

 

Annuals that Reseed

Some annual species reseed themselves. If you want this to happen, leave the plants in place until the seeds have shed, then clean up the spent leaves and stems.

Browallia, Bachelor buttons, California poppy, Calliopsis, cornflower, Cosmos, four o’clocks, rocket larkspur, morning glory, Petunia, pinks, pot marigolds, snapdragon, spiderflowers, and sweet alyssum are some species that will reseed in a garden, sometimes to excess.

 

Acknowledgements

The author would like to acknowledge the original author of this MontGuide, Dr. Bob Gough, former Extension Horticulture Specialist.

 

Table 1: Ornamental and Cultural Characteristics of Annual Flowers

Plant Name	Uses	Color	Height	Bloom Period	Exposure	Planting Time	How Propagated	Limitations	Remarks
African Daisy Arctotis spp.	General	White, orange, steel blue	12–30”	July, August	Full sun	After frost	Seed or transplants	Will not flower well during hot nights	Has woolly leaves
Ageratum Ageratum spp.	General, edging, planters	Lavender blue, white, pinkish	3–10”	July to September	Partial shade	After frost	Transplants	Prefers warm climate	Deer resistant
Alyssum (Sweet) Lobularia maritima	Borders, edgings	White, purple, pinkish	9”	June to September	Partial shade	After frost	Seed or transplants, cuttings	Widely adapted	Can be invasive
Baby Blue Eyes Nemophila menziesii	Borders, pot plants	Sky blue with white centers	6–8”	May to September	Sunny to partial shade	Sow in flats in March	Seed indoors, plant outdoors after frost	Cut flowers do not last long
Bachelor Button (Corn Flower) Centaurea cyanus	Cut flowers	Blue, rose, white, mauve, purple	12–18”	Late spring, early summer	Full sun	Early spring	Seed	Cool nights needed for flowering	Can be invasive
Basket-flower Centaurea melitensis	Cut flowers, borders	Pink, purplish to white	24–60”	Late spring, early summer	Sunny	Early spring	Seed	Cool nights needed for flowering
Wax Begonia Begonia cucullata	Bedding plants, planters	White, Pink, Red	12–18”	Continuous	Partial shade	After frost	Transplants		Indoor plant also

 

Table 1: Ornamental and Cultural Characteristics of Annual Flowers (continued)

Plant Name	Uses	Color	Height	Bloom Period	Exposure	Planting Time	How Propagated	Limitations	Remarks
Blackeyed Susan (Annual Coneflower) Rudbeckia hirta	General	Golden-yellow petals with dark brown centers	24–36”	Summer and fall	Full sun	Early spring	Seed	Prefers warm climate	Can be invasive
Browallia Browallia spp.	General	Blue	9–30”	Late summer and fall	Full sun	After frost	Cuttings or seeds	Prefers warm climate	Several forms available
Calendula (Pot Marigold) Calendula officinalis	General	Yellow, yellowish to orange	18–36”	July to autumn	Full sun	Early spring	Seed	Rather dry soil. Does not like hot humid weather	Deer resistant
California Poppy Eschscholzia californica	General	Yellow, orange orange-red, red	12–18”	Summer	Full sun	Early spring	Seed	Light, sandy soil	Perpetuates itself by self- sown seeds
Candytuft Iberis umbellata	Flower borders	White, pink, mauve, purple, crimson,	10”	Summer to fall	Sunny	Spring	Seed	Needs well- drained soil	Good in cool climates
China Aster Callistephus chinensis	General, indoor decoration	Lavender, yellow center; rose, pink, crimson, white	18–30” Dwarf: 6–12”	August and September	Partial shade	After frost	Seed or transplants	Prefers cool nights	Thrives in fairly alkaline soils
Clarkia Clarkia spp.	General	Crimson, white to purple	12–36”	June and July	Sunny	Early May	Seed	Prefers cool nights
Cleome (Spiderflower) Cleome houtteana	General	our store, contact your county or reservation MSU Extension office, or e-mail orderpubs@montana.edu. Copyright © 2023 MSU Extension We encourage the use of this document for nonprofit educational purposes. This document may be reprinted for nonprofit educational purposes if no endorsement of a commercial product, service or company is stated or implied, and if appropriate credit is given to the author and MSU Extension. To use these documents in electronic formats, permission must be sought from the Extension Communications Coordinator, 115 Culbertson Hall, Montana State University, Bozeman, MT 59717; E-mail: publications@montana.edu The U.S. Department of Agriculture (USDA), Montana State University and Montana State University Extension prohibit discrimination in all of their programs and activities on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital and family status. Issued in furtherance of cooperative extension work in agriculture and home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Cody Stone, Director of Extension, Montana State University, Bozeman, MT 59717