Plant Life Cycle

Every plant goes through a life cycle that takes it from a tiny seed, through growth and flowering, to producing the next generation of seeds. For some plants the whole cycle takes a few weeks; for others (like giant redwoods) it stretches over thousands of years. But the basic stages are almost always the same: germination, growth, flowering, pollination, fruiting, and seed dispersal. Then the new seeds land somewhere new and the cycle starts again.

  • Main stages6Germination, growth, flowering, pollination, fruiting, dispersal
  • Fastest life cycleapprox. 6 weeksArabidopsis (a lab favourite)
  • Slowest100+ yearsSome palms, agaves and the Puya raimondii
  • Annual plantsLive 1 yearThen die after setting seed (e.g. sunflowers, beans)
  • Biennial plantsLive 2 yearsGrow leaves year 1, flower and die year 2 (carrots, parsley)
  • Perennial plantsLive many yearsMost trees and shrubs

Stage 1: Germination

A seed lying in the soil is essentially a tiny baby plant in a protective shell, plus a packet of stored food. When the conditions are right (warm enough, moist enough, sometimes light enough), the seed germinates. Water soaks in, the seed swells and bursts open, and a tiny root pushes down into the soil. Soon afterwards, a shoot pushes up to the light. The new plant is now called a seedling.

Different seeds need different triggers to germinate. Some need to be soaked in water. Some need a period of cold (which is why some flower seeds only come up after winter). A few need to be partly burnt in a fire before they will sprout, an adaptation to plants that live in fire-prone habitats.

Stage 2: Growth

The young plant grows by adding new cells at its tips and in its layers. Roots push deeper into the soil, leaves expand to catch more sunlight, and the stem gets taller and thicker. Most of the plant's energy at this stage comes from photosynthesis in its newly opened leaves.

How fast a plant grows depends on its kind. Bamboo, the fastest-growing plant on Earth, can grow over 90 cm in a single day. A giant redwood adds maybe a few centimetres of height a year, but keeps doing it for over 2,000 years.

Stage 3: Flowering

When the plant is mature enough, it starts producing flowers (in flowering plants), cones (in conifers) or spores (in ferns and mosses). This is the start of the plant's reproductive stage. Flowers are designed to make and exchange the male and female cells (pollen and ovules) that the plant needs to produce seeds.

Stage 4: Pollination

Pollination is the transfer of pollen from a flower's male parts to its (or another flower's) female parts. Most flowering plants rely on insects (especially bees), birds, bats or sometimes the wind to do this work. Once a pollen grain lands on the right female part (called the stigma), it grows a tube down to fertilise an ovule, just like a sperm fertilising an egg in animals.

Stage 5: Fruiting and seed development

After fertilisation, the ovule starts developing into a seed. Each seed contains a tiny embryo plant plus a packet of stored food (often starch or oil) to fuel its first weeks of growth, all wrapped in a protective seed coat.

At the same time, the flower's ovary tissue grows into a fruit around the seeds. The fruit can be juicy and sweet (apple, peach, grape), to attract animals; dry and papery (dandelion seed); spiky (burr); explosive (witch hazel); or even waxy and floating (coconut). Each kind of fruit is a different strategy for getting the seeds away from the parent plant.

Stage 6: Seed dispersal

A plant cannot grow well right underneath its parent (too much competition for light and water), so plants have evolved many ways to disperse their seeds:

  • Wind: dandelion parachutes, sycamore helicopters, lightweight orchid seeds.
  • Animals (in stomachs): berries and other fruits get eaten; tough seeds survive the journey through the gut and emerge later, often with a built-in pile of fertiliser.
  • Animals (on fur): burrs and sticky seeds hitch a ride on passing fur or clothing.
  • Water: coconuts float across whole oceans; some river plants release seeds that float downstream.
  • Explosion: some seed pods burst open under tension, flinging seeds metres away.
  • Fire: some pinecones only open in the heat of a forest fire, releasing seeds onto freshly cleared ground.
Fact Some seeds can wait an extraordinarily long time before germinating. In 2005, scientists successfully grew a healthy date palm from a seed that had been recovered from Masada, an ancient Israeli fortress. The seed was around 2,000 years old. The young palm was nicknamed Methuselah. Even more impressive, in 2012, Russian scientists grew a small flowering plant from a seed found in the frozen burrow of an Ice Age squirrel; that seed was around 32,000 years old.

Annuals, biennials and perennials

Plants run through their life cycle on very different schedules.

  • Annual plants complete the whole cycle in one year: they germinate in spring, grow through summer, flower and set seed in autumn, then die. Most garden vegetables (beans, lettuces, sunflowers) are annuals.
  • Biennial plants take two years: in year 1 they grow leaves and a root; in year 2 they flower, set seed and die. Carrots, parsley and some onions are biennial.
  • Perennial plants live for many years, flowering and setting seed every year. Most trees and shrubs are perennial. So are most wild flowers.
Did you know? The Bolivian plant Puya raimondii may have the most dramatic life cycle of any plant. It grows for 80 to 150 years as a giant rosette of spiky leaves, then flowers just once, sending up a 10-metre tall flower spike with thousands of white blossoms. After that single spectacular flowering, the plant dies. Each Puya raimondii in the wild has only one big moment in its whole life, but what a moment.
Deeper dive: how seeds know when to germinate

Seeds are surprisingly smart about timing. A wild seed lying on the ground does not just germinate as soon as it falls; it waits for the right conditions. Otherwise it might sprout in autumn just before winter killed it, or in the middle of a drought when there was no water. So seeds use a range of triggers to detect a good time.

The most basic trigger is water. A dry seed cannot germinate. Once a seed is soaked, internal enzymes activate, the seed coat softens, and growth begins. This is also why most desert plants only germinate after a heavy rain.

Many seeds (especially in cold climates) need a period of cold before they will germinate, a process called stratification. This stops them sprouting in autumn or warm spells in winter, and ensures they wait until spring. Some seeds need light to germinate; others need darkness. Some need to pass through an animal's gut, which both transports them to a new location and partly digests the seed coat. A few species need their coat to be cracked by repeated freezing and thawing, or even by fire (the heat melts a waxy seed coat).

The most extreme strategy is just to wait. Many seeds can survive for decades or centuries in the soil, biding their time until conditions are right. A forest cleared by a fire can suddenly burst into flower because long-dormant seeds in the soil are finally getting the warmth and light they need.

For how flowers attract pollinators, see pollination and flowering plants. For the biggest plants, see trees.