Teaching Organic Farming & Gardening

Propagation/Greenhouse Management

Unit 1.3 | Part 1 – 103
Lecture 1: Seed Biology, Germination, & Development

C. Typical Life Cycle of Seedlings Grown in the Greenhouse: Timeline for Days to Seedling Maturity

1. The duration of seedling life cycle and growth rate depend on a number of factors

a) Photoperiod and the hours of light available to support growth. For most species longer
days translate into more rapid seedling growth, shorter days mean slower growth.

b) Temperatures within, above, or below the desirable range to stimulate or constrain
growth

c) Sufficient, consistent moisture to fuel growth. Too much or too little can inhibit normal
development.

d) Air circulation and gas exchange both above ground and in the root zone. Both are
critical to healthy seedling development and timely development, while too little
circulation or exchange invariably slows growth.

e) Nutrient availability, although note that excess nutrients may make for lush, weak
growth, vulnerable to pest, diseases, moisture, and temperature stress. Limited nutrient
supply will likely mean slow growth and poor performance. Appropriate nutrient supply
will fuel steady, uninterrupted growth and reduce vulnerabilities.

f) Container type and cell size, with seedlings maturing as smaller transplants more rapidly
in smaller cells and more slowly as larger transplants in larger cells (see more at Lecture
4, Soil Media, Fertility, and Container Formats)

Internal metabolic processes in motionEmergence of root radicle

Expansion of root radicle and

emergence of root hairsEpigeous germination beginningEpigeous germination continues, cotyledons

begin to unfold, and root system expands

Emergence of true leaves and shoot tip

fully visible; and branched root system

expands rapidly

Illustration by José Miguel Mayo