Fig 1: Rooting of a basil cutting in water, photo by Jim Farr

Plant propagation is a rewarding practice that allows home gardeners to multiply their favorite plants, save money, and share beloved species with friends and family. Whether you're looking to expand your garden without breaking the bank or preserve a cherished heirloom plant, understanding the basics of plant propagation can open a world of horticultural possibilities. This is the first in a series of articles on propagation. The next article in the series will address grafting methods of plant propagation.

Understanding Plant Propagation

Plant propagation is the process of creating new plants from a variety of sources: seeds, cuttings, bulbs and other plant parts. It falls into two main categories:

•    Sexual Propagation: Involves the use of seeds, resulting from the fertilization of the ovule in flowers. This method produces offspring that are genetically different from the parent plants.

Fig 2: Parts of a flower showing ovule, Image source: USDA Handbook 495.; https://ucanr.edu/sites/btfnp/generaltopics/AnatomyPollination/Pollination1/

Illustration of an insect pollinated peach flower with multiple reduced anthers (dark blue), large pollen grains (orange), smaller stigma (dark purple), long exerted style (light purple), showy petals (pink), and nectaries (yellow).

•     Asexual Propagation (Vegetative Propagation): Involves reproducing plants from stems, roots, leaves, or other vegetative parts, resulting in offspring genetically identical to the parent plant.

Benefits of Plant Propagation

There are a number of benefits with learning the techniques for plant propagation. These benefits include:

•     Saving money: Propagating plants at home reduces the need to purchase new plants. Depending on the rarity of the plant species, this can be a substantial cost benefit.
•     Preservation: Helps in preserving and multiplying one's favorite plants to add to your garden or to provide to others as gifts for their own gardens.
•     Customization: Allows gardeners to select the strongest and most desirable plants from their propagation. Propagating multiple “copies” of a plant allows one to choose the strongest and the most vigorous of the plants to have the best chance of success of growing them in your garden.

Seed Propagation (Sexual Propagation)

University of California Video Demonstrating Seed Propagation: Seed Starting 101

Growing plants from seeds is one of the most common methods of propagation, ideal for annuals, vegetables, and some perennials.

Advantages

• Genetic Diversity: Seeds produce plants with some genetic variations, which can lead to new traits. New, or more valuable and commercially important plants can be produced this way. For example the popular Better Boy Tomato Hybrid was created by crossing two different tomato varieties
• Large Quantities: It's easy to produce many plants at once. Depending on the plant variety, even a small 1 gram packet of seeds can contain hundreds of seeds. This is more than enough for a home vegetable garden with enough left over to donate to neighbors or a local seed exchange.
• Longevity: Seeds can often be stored for future use. Properly stored (typically in cool, dry places), seeds can be fertile for a few years. While seed packets have “expiration dates” for legal reasons, they are still useful and fertile for years after that date depending on the type of seed. Germination rates of older seeds can be checked with the seed germination test: Assessing Seed Viability - The Backyard Gardener - ANR Blogs

Steps for Successful Seed Propagation

1. Seed Selection: Choose high-quality seeds from reputable sources or collect them from healthy plants in your garden. It can be useful to let one's favorite plants “go to seed”, collect the seeds and save them for replanting the following year. In this way one packet of seeds initially can, in principle, be propagated for decades.
2. Seed Preparation: Some seeds, particularly seeds with hard coats, might require scarification (scratching the surface). Examples of seeds that respond well to scarification include morning glories, lupine, sweet peas and nasturtiums. Alternatively some seeds may require stratification (cold treatment) to germinate. Some examples of seeds that are helped by stratification include black-eyed susans, purple coneflowers and many milkweeds. If the seeds have been purchased, carefully review  the planting instructions. If you have collected the seeds, do a little research to find if any pre-planting procedures are required. A good source such as:  The California Garden Web. Another source is the Sunset Western Garden Book.
3. Sowing: Plant seeds in a sterile, well-draining seed-starting mix. Sow at the recommended depth on the seed packet. If the seed packet does not indicate planting depth, a general rule is to plant seeds twice their width.
4. Environment: Maintain consistent moisture and provide adequate, indirect light, for example on a window sill. A warm environment typically encourages germination. While some may use heating mats to provide the heat to the seed trays, often just the temperature indoors (65-70F) near a window is more than sufficient. Be careful not to let seeds dry out before germination. Some seed coats harden if dried and may not germinate at all.
5. Transplanting: Once seedlings develop true leaves, they can be transplanted into larger containers or directly into the garden. The first leaves are not true leaves but cotyledons which provide food for the sprout to initially grow. True leaves are the second set of leaves and are different in shape and size from the cotyledons (seed leaves).  Typically, plants can be planted into larger trays or outside after 2 or 3 true leaves have emerged.

Fig 3: Cilantro showing 2 cotyledons (smooth edges) and 2 true leaves (jagged edges), photo by Paula Pashby, https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=46056

Asexual Propagation Methods

Asexual propagation produces clones of the parent plant, ensuring the new plants retain all the desirable characteristics. Some plants can be easily propagated from cuttings and in fact that may be the preferred method of propagating. Many herbs such as basil are examples of this. A cutting from a basil plant, placed on a windowsill in a cup of water, will produce roots in days or weeks at the most.

1. Propagation by Cuttings (Asexual Propagation)

University of California Video Demonstrating Propagation from Cuttings: Cloning Garden Plants

Stem Cuttings – when propagating from stem cuttings, it is recommended to choose stems that are in a certain stage of wood. Below are examples of three stages of wood:

Types of stem wood:

•  Softwood Cuttings: Also known as “herbaceous” wood, taken from new, soft growth in spring or early summer.
•  Semi-Hardwood Cuttings: Sometimes referred to as “green wood”, taken from partially matured wood in mid to late summer before the wood is fully mature and hardened. These are less flexible than soft wood but do not snap to produce sharp edges like hardwood cuttings. They produce smooth edges when snapped.
•  Hardwood Cuttings: Taken from dormant, mature stems in late fall or winter. Hardwood is the hardest form of wood and usually brown in color vs. the green of semi-hardwood.

For examples of softwood , semi-softwood and hardwood see page 16 of University of California Presentation: Asexual Plant Propagation

Procedure:

1. Selection: Choose healthy, disease-free stems. Soft yellow or black stems or mushy black areas are signs of unhealthy stems.
2. Cutting: Make a clean cut just below a node (where leaves attach). The best type of knife are razor blade knives that have been rubbed with alcohol to sanitize them. See Propagation from Cuttings for examples of where to make cuts.
3. Preparation: Remove lower leaves and dip the cut end in rooting hormone to encourage root development. Rooting hormones can be purchased online or from any nursery. Typically, they are in powder or liquid form. Powder is preferred since it will stick to the cut area better.
4. Planting: Insert the cutting into a pot filled with moist, well-draining medium like perlite or sand mixed with peat moss. Make a small hole first with a pencil or small stick to put the stem in. Pushing the stem directly into the soil will remove some of the rooting hormone on the tip. For the best results soil should be sterilized in an oven. To sterilize soil, heat the soil in an oven at 180 F for 30 min or get the temperature up to 212 F where sterilization is immediate.
5. Aftercare: Keep the medium moist and place the pot in a warm area with indirect light. It is a good idea to cover the pot loosely with plastic wrap or some other covering to keep moisture in and prevent the soil from drying out.

Fig 4: Examples of potted cuttings from a fern and purple sage, photo by Jim Farr

Leaf Cuttings

See University of California youtube video: Mastering Stem and Leaf Propagation starting at 37 min.

•     Suitable for plants like African violets and succulents.
•     Procedure: 
  • Cut a healthy leaf with a short piece of stem. Examples of what this looks like are in the above video.
  • Insert the stem into the growing medium. This is similar to above for stem cuttings.
  • Maintain high humidity until roots develop. Again, plastic wrap or some other covering that will let light through is useful to keep the soil moist and prevent it from drying out.

Root Cuttings

See: Propagation from Root Cuttings

• Used for plants like phlox and horseradish.
• Procedure:
• Dig up a healthy plant and cut 2–3-inch sections of thick roots. As above, cutting tools should be sanitized and sharp.
• Place horizontally in the growing medium and cover lightly. Soil should be sanitized (see above) ahead of time to give the best chance of success.

2. Layering

See University of California youtube video: Mastering Stem and Leaf Propagation starting at 60 min

Layering involves rooting a part of the parent plant while it is still attached. Essentially, the branch of the rooted plant is bent down and covered with soil. Roots form from the branch covered in soil. Examples of some plants that can be propagated this way include climbing roses, rhododendrons and azaleas.

Simple Layering

    Procedure:

1. Bend a low-growing, flexible stem to the ground. If you are bending rose branches, be sure to wear heavy gloves to prevent skin punctures.
2. Scrape the stem slightly to encourage rooting.
3. Bury a portion of the stem in soil, leaving the tip exposed.
4. Secure with a U-shaped pin if necessary. U shaped pins that are used to hold down irrigation lines (sometimes referred to as garden staples) are very useful here.
5. After roots develop, sever the new plant from the parent. Once the rooted stem has roots that are at least several inches long, the stem can be cut and potted like above for propagation from cut stems.

Air Layering

Simple and Air Layering

•     Suitable for houseplants and woody shrubs. Examples of plants suitable to this method of propagation include: camelias, acers, daphnes, jasmine and viburnum.

•     Procedure:

1. Select a healthy stem and make an upward 1-inch cut. See picture for example.
2. Insert a toothpick to keep the cut open.
3. Apply rooting hormone to the wound. Follow the instructions for use of the rooting hormone above.
4. Wrap moist sphagnum moss around the cut area and cover with plastic wrap. See Simple and Air Layering
5. Once roots are visible, cut below the rooted area and plant. Plant per the instructions above for rooting cut stems.

3.  Division

See University of California youtube video: Mastering Stem and Leaf Propagation starting at 55 min.

Division is ideal for perennials and grasses that form clumps and also bulbs. Many types of bulbs over time will form large clusters of bulbs. Eventually some of the bulbs will stop sprouting when the clusters get too large. It is best to break up these large clusters and then plant the separate bulbs.

•     Procedure:

1. Dig up the entire plant or bulb cluster
2. Gently separate the plant into sections, ensuring each has roots and shoots. Some bulb clusters may be difficult to separate and a garden knife is sometimes helpful. Be careful and always wear thick gloves.
3. Replant the divisions promptly at the same depth they were growing before.

Fig. 5: Bearded Iris before and after division, photo by Patsy Babbitt

4.  Grafting

Grafting is the propagation method that involves taking cuttings (called scions) and attaching them to a root stock or existing stem. This is often considered a more advanced technique and will be addressed in the second article in this series.

Conclusion

Propagating plants at home is a fulfilling endeavor that enhances your gardening experience, saves you money and provides an opportunity to grow unusual varieties not readily available in nurseries. By mastering these propagation techniques, you not only expand your garden but also contribute to plant conservation and biodiversity.  So, roll up your sleeves, gather your tools, and start multiplying your garden's beauty one plant at a time.

References:

General Propagation Methods including cuttings, layering and division

https://ucanr.edu/sites/ucmgnapa/files/81929.pdf

Propagation from Cuttings:

https://marinmg.ucanr.edu/CARE/PROPAGATING/Cuttings/

Layering Techniques:

https://marinmg.ucanr.edu/CARE/PROPAGATING/Layering/

Asexual Plant Propagation:

https://ucanr.edu/sites/EDC_Master_Gardeners/files/175642.pdf

Plant Propagation Books:

1. American Horticultural Plant Society - Plant Propagation by Alan R. Toogood
2. The Plant Propagator's Bible: A Step by Step Guide to Propagating Every Plant in Your Garden by Miranda Smith

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