Propagation is how new plants are started. This lesson explains the common methods a home gardener uses and when each is appropriate.
Assumed audience
- Reading level: general adult.
- Background: has completed the plant basics lesson and understands plant life cycles and the difference between species and cultivars.
- Goal: understand the main ways plants are started so that when researching a specific plant, the gardener can evaluate which propagation method applies.
Two categories of propagation
Plants can be started in two fundamentally different ways:
- Sexual propagation: using seeds. The new plant grows from a seed produced by a flower. It carries genetic material from both parent plants, so it may differ slightly from either one.
- Asexual (vegetative) propagation: using a piece of an existing plant. The new plant is genetically identical to the parent. Methods include cuttings, division, layering, and tubers.
Most annual vegetables are grown from seed. Many perennials, fruit trees, and herbs are propagated vegetatively to preserve the exact traits of a known cultivar.
Seeds
A seed is a dormant embryo enclosed in a protective coat, along with a small supply of stored food. Given the right conditions — moisture, warmth, and sometimes light or a period of cold — the seed germinates: the embryo breaks through the coat, sends a root downward, and pushes a shoot upward.
Direct sowing
Direct sowing means planting seeds directly into the soil where the plant will grow to maturity. It is the simplest method and works well when:
- The plant tolerates local soil and weather at planting time.
- The plant does not transplant well (e.g., root vegetables like carrots and radishes, which form a taproot that is disturbed by moving).
- The local growing season is long enough for the plant to reach maturity from an outdoor start.
Starting seeds indoors
Some plants need more time than the local frost-free season provides. A gardener starts these seeds indoors, weeks before the last frost date, in small containers with a prepared seed-starting mix (a lightweight, sterile growing medium). The seedlings grow indoors under natural or artificial light until outdoor conditions are suitable, then they are transplanted outside.
Starting indoors requires:
- Containers with drainage holes.
- Seed-starting mix (not garden soil, which is too dense and may carry disease organisms).
- Adequate light (a bright window or a grow light).
- Consistent moisture and warmth.
Transplanting
Transplanting is the act of moving a plant from one growing location to another — typically from an indoor container to an outdoor garden bed. The process is stressful for the plant because roots are disturbed, light conditions change, and temperature and wind exposure increase suddenly.
To reduce transplant shock:
- Harden off the seedlings by gradually exposing them to outdoor conditions over a week before the final move.
- Transplant on a cloudy day or in the evening to reduce heat and light stress.
- Water the plant thoroughly after transplanting.
- Disturb the root ball as little as possible.
Plants purchased as starts from a nursery or garden center are transplanted in the same way.
Cuttings
A cutting is a piece of stem, leaf, or root removed from a parent plant and placed in water or a growing medium until it develops its own roots. Once rooted, it is planted like any other plant.
Cuttings are used when:
- The gardener wants an exact genetic copy of a specific plant.
- The plant does not produce viable seeds easily.
- The gardener wants to multiply a plant they already have.
Common plants started from cuttings include rosemary, basil, mint, and many ornamental shrubs.
Division
Division is the process of splitting a mature plant’s root system into two or more separate plants. Each division includes a portion of roots and stems or buds. It works with plants that naturally form clumps or spreading root systems.
Division is used when:
- A perennial has grown large enough to divide.
- The gardener wants to spread a plant to new locations.
- A clumping plant has become overcrowded and its growth has declined.
Common plants propagated by division include chives, rhubarb, strawberries (via runners), and many ornamental perennials.
Tubers, bulbs, and rhizomes
Some plants store energy in underground structures that can be separated and replanted:
- Tubers: thickened portions of an underground stem. Each “eye” on a tuber can grow into a new plant. Example: potatoes.
- Bulbs: layered underground storage organs that produce a new plant each season. Example: garlic, onions.
- Rhizomes: horizontal underground stems that spread outward, producing new shoots along their length. Example: ginger, iris.
These structures are planted directly in the ground at the appropriate depth and spacing for the species.
Which method to use
When researching a specific plant, seed catalogs and growing guides will indicate the recommended propagation method. The choice depends on:
- The plant’s biology: some plants are only practical to start one way (potatoes from tubers, carrots from seed).
- Whether an exact cultivar must be preserved: seed may produce variation; vegetative methods produce copies.
- The local growing season: a short season may require starting seeds indoors or purchasing transplants.
- Available resources: seeds are cheapest; starts and divisions require access to existing plants or a nursery.
Understanding these methods is necessary before researching a specific plant, because the propagation method affects timing, materials, and the growing method chosen later.