master the garden

part one botany basics: plant life cycles
Currier Hall, Newhalem, WA photo l. fowler
plant life cycles

There are three classifications of plants based on the number of growing seasons required to complete their life cycle: annual, biennial, and perennial

Annuals complete a life cycle in one season providing continuous bloom – going from a seed to producing seeds within that growing season. For most annuals, they are planted in spring and bloom in the summer – completing the cycle when cool temperatures arrive in fall. There are a few annuals that germinate in the late summer. A few, known as winter annuals, germinate in summer and fall, are dormant in winter and grow during the following spring and summer. Winter annuals also include plants the germinate in summer and perform throughout the colder months eventually going to seed in early spring. For he most part, annuals, unless they reseed themselves, will not grow a second year.

Some perennial plants are treated as annuals if they are not cold hardy in the northern climates but are perennial in the warmer southern zones.

Annuals are often grouped as hardy, half-hardy, and tender, referring to when they can be sown outdoors and their tolerance to early spring and fall frost or winter temperatures.

Hardy annuals include plants like pansy, ornamental kale, and dusty miller. They can withstand cold soil and frosts, may be sown in fall and are winter hardy depending on the severity, and are ideal for cool weather gardens.

Half-hardy annuals include plants like petunia and alyssum. They can withstand a limited amount of cold temperatures and light frost but if sown to early – even a light frost can kill them.Intense summer heat can cause these annuals to decline. They prefer cooler fall temperatures and and may revive with growth and bloom.

Tender annuals include inpatients, vinca, and zinnia that cannot withstand freezing temperatures. They should be sown outdoors only after danger of frost has passed and seeds for tender annuals are often sown in greenhouses then transplanted. the usually grow and bloom well in the summer heat.

During this period the plant germinates, grows, matures, blooms, produces seed, and dies.
OSU Extension

Knowing (summer, winter) weed life cycles is important in controlling the weed.

Biennial plants require all or part of 2 years to complete the life cycle. They require a dormant period, often induced by cool temperatures, between plant growth and blooming. Biennials are usually sown in spring, producing vegetative structures and food storage organs during the summer, set seed, and die during the following fall.

The plant overwinters and then produces flowers, fruit, and seeds.
OSU Extension

Sometimes bolting occurs when biennial plant starts are exposed to a cold spell before being planted in the garden.

When extreme environmental conditions exist, a biennial plant can go from seed germination to seed production in one growing season. This phenomenon is referred to bolting.

Perennial plant can live for more than 2 years and are grouped into two categories: herbaceous perennials and woody perennials.

Herbaceous perennial have soft stems that usually die-back to the ground in winter and new stems grow from the plants crown each spring.

Woody perennials, trees and shrubs, have wood stems and can withstand cold temperatures.

OSU Extension

glossary of terms

Anther – The pollen sac on a male flower

Apex – The tip of a root or shoot

Apical dominance – The tendency of an apical bud to produce hormones that suppress growth of buds below it on the stem

Axil – The location where leaf joins the stem

Bolting – plants produce a flowering stem in a natural attempt to produce seeds as a means of survival when under stress.

Cambium – A layer of growing tissue that separates the xylem and phloem and continuously produces new xylem and phloem cells

Chlorophyll – The green pigment in leaves that is responsible for trapping light energy from the sun

Chloroplast – A specialized component of certain cells; contains chlorophyll and is responsible for photosynthesis

Cold hardy – generally measured by the lowest temperature a plant can withstand

Cortex – Cells that make up the primary tissue of the root and stem

Cotyledon – The first leaf that appears on a seedling. also called a seed leaf.

Cuticle – A relatively impermeable surface layer on the epidermis of leaves and fruit

Dicot – having two seed leaves

Herbaceous – vascular plants that have no persistent woody stems above ground

Epidermis – The outermost layer of plant cells

Guard cell – Epidermal cells that open and close to let water, oxygen and carbon dioxide pass through the stomata

Internode – the space beween nodes on a stem

Meristem – Specialized groups of cells that are a plant’s growing points.

Mesophyll – A leafs inner tissue, located between the upper and lower epidermis; contains chloroplasts and other specialized cellular parts (organelles)

Monocot – having one seed leaf

Node – an area on a stem where a leaf, stem, or flower bud is located

Ovary – The part of a female flower where the eggs are located

Petiole – The stalk that attached a leaf to the stem

Phloem – Photosynthate-conducting tissue

Pistil – The female flower part; consists of a stigma, style, and ovary

Respiration – the process of converting sugars and starches to energy

Stamen – The male flower part; consists of an anther and a supporting filament

Stigma – The top f a female flower part; collects pollen

Stoma (pl. stomates, stomata) – tiny openings in the epidermis that allow water, oxygen, and carbon dioxide to pass into and out of a plant

Style – The part of a female flower that connects the stigma to the ovary. Pollen travels down the style to reach the ovary, where fertilization occurs

Transpiration – the process of losing water (in the form of vapor) through stomata.

Turgor – Cellular water pressure; responsible for keeping cells firm

Vascular tissue – Water, nutrient, and photsynthate-conducting tissue (xylem and phloem)

Vegetative structures – The vegetative (somatic) structures of vascular plants include two major organ systems: (1) a shoot system, composed of stems and leaves, and (2) a root system

Xylem – Water and nutrient-conducting tissue

suggested reading

Botany for Gardeners, Capon, B – 2bd edition (Timber Press, Portland, OR 2004)

Plant physiology, Salisbury, F.B. and Ross, C.W., 4th edition (Wadsworth Publishing Company, Belmont, CA, 1991)


  1. Oregon and Washington Master Gardener Handbook, 2008

self test

  1. Describe annual.

They lived briefly….they germinate grow bloom and go to seed in one year because they die at the end of this cycle they must be replanted the following season

2. Describe volunteer seeds.

Many annuals come up on their own from previous years seeds but they can be ready by reappearing from seed so prolifically

3. What is a biennial?

A plant that requires two full years to complete the growth cycle and die after the roots but do not flower the second year they flower and go to seed their garden uses are closer to those of annuals and perennials but many are cherished components of perennial gardens

4. What is a perennial?

Unlike annuals and biennials perennial plants live year after year trees and shrubs are woody perennials mature garden park and arboretum landscapes often are composed mostly of woody perennial plants

5. What is a hardy perennial?

They live through the winter in the ground Reviving from their crowns in Spring they send up new shoots often through the remains of the previous year’s dead stems leaves and flowers

6. What is a tender perennial?

They will not survive outdoor winter conditions even with protection they must be lifted before Frost stored and replanted after danger freezing weather passes

7. Define bulb

Composed of a thin flattened stem surrounded by fleshy dried Leaf faces called scales roots grow from the basil plate….onions garlic narcissus tulips and lilies are examples of plants that form bulbs. slicing an onion vertically and observing the interior gives you a good look at a bulbs anatomy

8. Define corms

Have solid interiors developed from swollen stems if you cut one you see homogeneous mass inside roots form at the base some examples of plants that form corms are crocus watsonia and gladiolus

9. Define tubers.

Are swollen modified underground stem they have a basal plate where roots originate tubers come in various shapes.

10. Define tuberous roots.

Composed of root tissue. Dahlias and tuberous begonias are examples of plants with tuberous roots

11. Define rhizomes.

Rhizomes are specialized stems that grow horizontally at or just below the soil surface. Iris, lily of the valley, and bamboo have rhizomes

12. Define self sowing annual.

A plant that comes up each year from the previous year’s seeds examples include: bachelor buttons California poppy, Cosmos

13. Define short-lived perennial.

A plant that lives only a few years before requiring replacement. Example: delphinium

14. Define half hardy tender perennial

A plant that won’t survive outdoor conditions during the winter. Examples include: Dahlia, gladiolus, fuchsia, tuberous begonia, and geranium

15. List advantages of annuals over perennials

Long bloom season – prolific bloom lower initial costs more suitable for containers use and changing color schemes and quick growth

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