Plant propagation basics - Bert Cregg, Michigan State University Extension, Departments of Horticulture and Forestry - May 26, 2006

Thanks to Russ Kidd and Brad Rowe for contributing their insights on propagation to this article.

Extension educators and specialists frequently get questions from homeowners about how to propagate their favorite tree or shrub. The answer, of course, is “it depends.” Woody plants are most commonly propagated from either seeds or stem cuttings. The relative ease of propagating woody plants ranges from ridiculously easy to nearly impossible. Plant propagation is a complex topic and complete coverage requires an entire course. In this article, I’ll cover some of the basic terms and principles of propagation from seed and from cuttings and present references for those that want details on propagating their favorite tree or shrub.

Seeds vs. cuttings

Many plants can be produced from either seed or cuttings. In some cases seed propagation is easier; in others cutting propagation is easier. If the homeowner is interested in propagating a plant for a specific ornamental characteristic (leaf color, flower display), it’s important to note that vegetative propagation from a cutting will result in a plant that is genetically identical (a clone) to the original plant. Plants produced from the seed of the same plant will be more variable and may or may not have the desired characteristics. Put in another perspective, two plants produced from vegetative cutting are genetically “identical twins.” Two plants produced from seed from the same tree are as related as step-brothers or step-sisters; they have the same mother but could have different fathers.

Seed propagation

For many plants, seed propagation is simply a reliable method of producing new plants. Seeds can be collected in the fall, either from the plant or from the ground around it. Some species may produce a high proportion of seed that are empty. Cutting a few of the seeds open can be useful to get a sense of the proportion of filled seeds. Seeds of most woody plants are dormant in the fall and will not germinate immediately if placed in the ground or in a container. Some form of stratification and/or scarification is usually required to overcome dormancy.

Stratification refers to exposing seeds to a period of chilling, usually under moisture conditions. During stratification, the embryo in the seed continues to develop and moisture allows chemical inhibitors to leach out of the seed. Most woody plants require a cool, moist stratification, which can be accomplished by placing the seeds in wet sphagnum moss in a zip-lock baggie in the refrigerator, leaving headspace in the bag for seed respiration. Seeds can also be stratified by placing them in a container outdoors over the winter. A few species also have warm, moist stratification requirements.

Scarification is used to overcome seed-coat dormancy. Some species have an impenetrable seed coat and will not germinate unless the seed coat is worn down or broken. A variety of techniques may be used to scarify seeds including nicking the seed coat with a nail clipper, abrading with a nail file, sandpaper, or rock polisher, soaking in acid, or passing the seed through bird gizzards.

For details on propagating plants from seeds consult the Woody Plant Seed Manual at:

https://www.fs.fed.us/rm/pubs_series/wo/wo_ah727.pdf

https://www.fs.usda.gov/nsl/nsl_wpsm.html

Cutting propagation

Several techniques may be used to vegetatively produce plants, but the most common are hardwood and softwood cutting. In simple terms, hardwood cutting refers to hardened stem cutting that are taken from dormant trees are shrubs. Softwood cuttings refer to cuttings that are taken from green, actively growing shoots of woody plants. Anyone that has grown houseplants probably has some experience at propagating plants from cuttings. The principles are the same with woody plants. Typically, stem cuttings are taken from the plant, and the cut end is placed in a media that is kept moist. Callus tissue forms at the cut end and eventually begins to produce roots. The likelihood that the cuttings will take, or produce roots, depends primarily on the species and the plant age. Other factors being equal, cuttings from young plants will take more easily than cuttings from older plants. Some species such as cottonwood, aspens, and willow root so easily that the most common form of propagation is to plant 6 to 10 inches of unrooted hardwood cuttings. The sticks are simply placed in the ground leaving one bud above the surface. Other species, such as pines, are often difficult to produce from cuttings and required specialized propagation equipment and techniques.

General tips on cutting propagation

• Cuttings from younger plants or younger plant parts are more juvenile and will take more easily than older plants or older plant parts.
• Cuttings from side branches can exhibit plagiotropic growth – in essence, they don’t know which end is up and lack apical dominance.
• Rooting hormones will speed rooting and reduce the likelihood that cuttings will desiccate before they establish new roots.
• Keep rooting media moist, but not saturated.
• Cover plants with a clear plastic tent or mist plants to maintain a high humidity to reduce desiccation.

For more details on cutting propagation consult: The Reference Manual of Woody Plant Propagation by Michael Dirr and Charles Heuser. Available on Amazon.com, or order through your local bookstore.