Growing Annuals

Learn to Identify, Grow and Use Annuals 

Annuals are plants which are able to grow from seed to mature plant, flower and produce seed all within the space of one year. They are horticulturally valuable crops, grown commercially as cut flowers, as seedlings or as colourful pot plants. In home gardens, public parks and other places, annuals are grown widely all over the world, primarily because they can provide a quick and spectacular, often colourful display. Annuals can help to keep gardens or parks looking their best, by filling gaps between perennials or by disguising the messy foliage of bulbs as they seasonally die-off.

Lesson Structure

There are 8 lessons in this course:

1. Introduction
   • Review of the system of plant identification, physiology, information sources
   • Types of Inflorescence
   • Choosing Flowers for an occasion
   • What flowers last longest as cut flowers
   • Care of cut flowers
2. Culture
   • Planting, staking, mulching, watering, feeding, pruning, etc
   • Review of more commonly cultivated annuals
3. Propagation
   • Methods of propagating annuals.
   • Seed sources
   • Sowing Seed
   • Greenhouses and other propagation aids
4. Hydroponic growing of selected varieties of annuals.
   • Annuals in hydroponics
   • Understanding hydroponic systems
   • Culture of selected annuals in hydroponics -Aster, Carnation, Gerbera, Stock etc
5. Pest & Disease
6. Irrigation
7. How to Grow Annuals
   • Growing in Greenhouses (shade houses or other controlled environments)
   • Growing in Flower Beds
   • Types of bedding systems
   • Judging flowers
8. Harvest, Post Harvest & Quality.
   • Harvesting
   • Deterioration of flowers
   • Shelf life
   • Post harvest treatment

Each lesson culminates in an assignment which is submitted to the school, marked by the school's tutors and returned to you with any relevant suggestions, comments, and if necessary, extra reading.

Aims

• Discuss the classification of annual flowering plants through the plant naming system.
• Discuss culture requirements of annuals.
• Propagate annuals.
• Explain methods of hydroponic culture in relation to annuals
• Identify pest and diseases of annuals
• Describe various types of irrigation systems and the water requirements of annuals.
• Describe various greenhouses and related equipment available.
• Determine procedures for the handling of annuals during and after harvest.
• Design annual flower beds.

Growing Tips for Selected Annual Flowers

Ageratum (Ageratum spp.)

Plant winter or early spring, space at 15-25 cm, varieties vary in height from 15 to 45 cm (A. conyzoides is a weed in some areas) with blue to lavender flowers. Likes most soils, sun to light shade, moist soil; protect from strong winds.

Alyssum (Lobularia maritima)

Excellent edging plants, 5-15 cm tall, space 10-20 cm apart, masses of tiny blue or lilac to white flowers completely cover foliage. It is very quick growing and produces excellent specimens within a few weeks. This plant prefers full sun and good drainage.

Amaranthus

Young plants susceptible to fungus, need full sun, rich soil but don't feed too heavily (liquid fertilizers can burn), avoid disturbing roots (e.g. by cultivation)

Antirrhinum (Snapdragon)

Seedlings susceptible to damping off and insects, best in milder weather (can die in heat), prefers alkaline soil (add lime if adding compost or organic mulch). They are particularly susceptible to rust diseases (detected by small pale spots underneath leaves which become redder eventually erupting into brown pistules). They make good cut flower. There are many varieties varying in colour from yellows and whites to pinks and reds. There are tall, intermediate and dwarf varieties from around 1 m to 20 cm in height.

Humidity in tropical zones may cause sever fungal problems due to the hairy foliage of the snapdragon.

Chinese Aster

Best planted late spring or summer for autumn/winter flowers, fungal wilt and viral disease a problem in hot weather (burn affected plants and don't replant asters into a bed previously affected by wilt). Asters prefer alkaline soil.

• Callistephus chinensis 'Ostrich Plume' is an old favourite which displays very good resistance to the wilt disease. It is early flowering.
• C. chinensis 'Dwarf Queen' is another early flowering annual aster but only reaches 25cm.

Begonia (Bedding)

This is B. semperflorens (Fibrous rooted) Green or copper tinted leaves, white to red flowers; most grow to around 15 cm tall (some to 30 cm), best in high organic soil, well drained, full sun to part shade. Excessive overhead irrigation tends to collapse the plant.

Calendula (Pot Marigold)

Yellow to orange flowers, 20 to 50 cm tall, excellent cut flower; it does well in poor soils and full to part sun. Pinch out growing tips of seedlings to encourage bushy growth. Calendula does well in most climates including sub tropics (but not wet humid tropics). They are relatively short lived in the hot humid summers of the tropics and subtropics. For this reason they are best planted in late autumn to spring.

Celosia

Hardy, disease resistant, brightly coloured annuals. Celosia must have a well drained soil and plenty of sun. They grow well in pots or the ground, spaced 20-25 cm apart.

• C. cristata (syn. C. argentea var. cristata) (cockscomb) - flower heads vary in size and shape making uniform displays difficult.
• C. cristata "Thompson's Magnifica" (Prince of Wales feather) - flowers deep red to yellow, space 25 cm apart.
• C. cristata var. pyramidalis (flame of fire) - medium height.

Cosmos

Fine foliage, brilliant coloured flowers, adapt to most soils, prefer sunny slightly sheltered site and dry soil, overfeeding can make plants too tall and leggy risking breaking in wind.

• C. bipinnatus - varieties vary from 1-2 m tall, very hardy graceful plant, may be damaged by strong winds, flower colours white or pink to shades of red, purple and orange.
• C. sulphureus - yellow, orange or scarlet flowers; generally smaller plants than C. bipinnatus

Helianthus (Sunflower)

Adapts to most conditions if water supply is good, but prefers friable, fertile well drained soil. If seed is allowed to develop it often attracts birds. The brightly coloured large flower heads is the main reason it is grown.

Helichrysum (Strawflowers or Everlastings)

Hardy plants for full or filtered sun need well drained, moist soil (not too wet or too dry), good as cut or dried flowers. Pinch out terminal buds to increase bushiness.

There are a number of helichrysums, both perennials and annuals, which will grow in warm climates.

H. bracteatum - plant seed or seedlings at 15-30 cm spacings in spring, to 1.5 m tall, multi coloured flowers.

Lathyrus (Sweet Pea)

Needs full sun, protect from wind, fertile moist soil. Sow seed in autumn or winter. Sweet pea offer scented flowers in a wide range of colours. They are good as cut flowers. Sweet pea dies back in hot weather. A climbing support is needed to keep flowers and foliage off the ground.

Limonium (Statice)

Plant autumn for winter/spring flowers - flowers can be used cut or dried, flower colours mainly blue to pink and yellow; they prefer full sun and moist soil, few pests.

Lobelia

Sun or semi shade; moist to wet fertile organic soil, water during dry weather; pinch tips out of young plants to encourage bushiness.

• L. cardinalis - to 1 m tall, tall spike of red flowers. Two forms available - green or red foliage.
• L. erinus - to 15 cm tall, creeping plant, blue, pink or white flowers, good in baskets or as a border.

Marigold (Tagetes spp.)

Marigolds may grow and flower most of the ear in tropics and sub tropics. Bacterial wilt can sometimes be a serious problem (you can use sterilized soil to control this problem); marigolds readily self seed.

• T. erecta (African Marigold) - to 1 m tall, brittle plants, need wind protection, large yellow to orange flowers, best in autumn
• T. patula (French Marigold) - dwarf varieties 15-30 cm tall; smaller flowers yellow to orange/brown, plant in summer.

Petunia

Grow and flower well all year in tropics and sub tropics if supplied with ample water. Plants rarely last more than 6 months - but if pruned after flowering, it is possible to extend the life of petunias to almost 12 months (in warmer climates). New perennial petunias need protection from extremes in humidity. Annual petunias are available in many colours from white and pink through to reds and lavender, singles and doubles. Good in beds, baskets or tubs. Prefer fertile well drained but always moist soil. Grow in full sun to half shade.

Phlox

Phlox needs rich moist well drained soil; Plant in late winter or early spring for spring and early summer display. Humidity may be a problem causing fungal diseases.

Portulaca

Very hardy, low creeping plants, succulent like foliage, multicoloured flowers occur throughout hotter months, (suits tropics or sub tropics), prefers full sun, sandy soil

Schizanthus

S. pinnatus (poor man's orchid) - Very hardy in sub tropics but prefers filtered sun, fertile moist friable soil. Susceptible to various diseases in tropics, protect from strong winds. Poor man's orchid may self seed.

Viola

Viola requires the roots to be kept cool and moist. Mulching the soil will help the roots cool and moist. Viola is relatively hardy but prefers moist fertile and alkaline loam. Aphids may sometimes be a problem. They can be grown successfully in the sub tropics but are more difficult in the tropics due to the heat/humidity.

Zinnia

Plant in winter or spring; zinnia prefers fertile alkaline soil out of the wind. They come in a large variety of flower colours; Zinnias are very heat tolerant if well watered.

• Z. angustifolia (syn. Z. elegans) to 30 cm tall, long flowering
• Z. elegans "Lilliput" varieties excellent cut flowers
• Z. haageana (Mexican zinnia) to 60 cm tall -flowers yellow shades 

WHY STUDY ANNUALS?

Annuals are grown mostly because they are quick to establish and very colourful.
These are plants that can sometimes be criticised as being expensive to maintain, because they can be short lived and may need replanting every six to twelve months. They are nevertheless grown widely because the benefits largely outweigh the costs.

When you study this course your knowledge and understanding of annuals will multiply.
You will see possibilities for using them that may not have occurred to you before; as container plants, in garden beds, for vertical or roof gardens or as indoor plants.

You will learn to select the best annual for each situation you encounter; and your knowledge of how they can be used will expand - for potted colour that can be moved around the garden; as a cut flower to be taken indoors or as a stunning bedding display in any situation from full sun to shade and dry soil to wet.