Propagation is the means by which plants are reproduced. In some cases, plants are propagated by seed; others are propagated by dividing roots or rhizomes. Bulbs are usually split apart as the bulblets become large enough to support themselves with food reserves. In the case of lilies, the scales are removed from the bulb to propagate new plants. Some plants can also be propagated by using leaf, stem or root cuttings or by layering. Propagating by cuttings, division and layering will produce plants that are identical to the parent plant and is a good choice when trying to duplicate a cultivar or hybrid. Seed, on the other hand, does not guarantee a plant with the same characteristics as the parent.
When determining if division is a good method of propagation, it is important to consider the crown and root system of a plant. Plants that can be divided are those with root systems that spread from a central crown and have a clumping habit. Plants that have tap roots - a central root such as Baptisia or Asclepias tuberosa - are not usually candidates for division, but are better propagated by stem, leaf or root cuttings, or by seed.
Division is usually done when a plant has grown to considerable size and needs better spacing. It may also be necessary to promote optimal plant health. If the roots at the center of the plant have begun to die, they should be removed to make way for the new roots and to eliminate the potential of root diseases. Perennials, wildflowers, ferns, bulbs, ground covers, herbs and some landscape grasses are examples of herbaceous plants that are propagated by division. How often a plant is divided depends on the species of plant, its size, the climate, and the gardener's objective. Plants such as coral bells (Heuchera sanguinea) and fernleaf bleeding heart (Dicentra eximia) may be divided every one to three years to improve plant health and increase stock, respectively. Perennials such as gooseneck loosestrife (Lysimachia clethroides) and gay feather (Liatris species) may be divided every 3-5 years to improve plant health. Bearded iris (Iris) should be divided every 3-5 years to promote blooming. There are some plants that should rarely (if ever) be divided because they do not transplant well and should not be disturbed. Examples are gas plant (Dictamnus albus), false indigo (Baptisia australis) and baby's breath (Gypsophila species).
Timing is also important when dividing plants. Depending on the species, plants may be divided in early spring, late summer, early fall or, in some case, anytime during the growing season. When dividing plants in the spring, it is advisable to divide plants when they have just begun to grow, giving them a full season of growth in which to establish a new root system and form new buds at the crown. The plant will also be able to recover from any damage from the division process. Some spring-flowering plants such as hellebore (Helleborus) should be divided after they have finished blooming. Other plants should be divided in late summer or early fall. For example, peonies (Paeonia species) and asiatic lilies (Lilium hybrids). Some plants like daylilies (Hemerocallis), can be divided any time during the growing season. For a list of plants and when they should be divided, visit Dividing Perennials by Susan Barrott, University of Minnesota Yard and Garden Brief.
Landscape grasses should be divided in the spring as fall division often is not successful, especially in warm season grasses. In addition to creating new plants, landscape grasses benefit from division through the removal of the older, dead roots at the center of the plant.
A rhizome is defined as an underground stem that bears nodes, buds, or scale-like leaves. Iris (Iris hybrids and species) are probably one of the best-known rhizomatous herbaceous plants. Bearded iris should be divided in late summer when they are somewhat dormant. For more information about dividing iris, see Iris: Dividing Iris from the University of Wisconsin Extension Service.
Some ferns, such the ostrich fern (Matteuccia struthiopteris), have an erect crown that can be divided, but also have rhizomes from which the fronds emerge and new plants can be propagated. On a fern, roots form from the rhizomes or sometimes directly from the stipe. Dividing a fern entails taking a cutting with a node with a frond from the rhizome and re-planting the cutting with node and frond upward. Detailed instructions about dividing ferns can be found at the University of Georgia Extension website, Growing Ferns.
Starting Plants from Seed
A seed is one of Nature's best engineering feats. Each seed contains all of the necessary ingredients to grow a single new plant that will produce more seed and carry on the plant species. In nature, seeds germinate when the conditions are right. However, it is easy to start plants from seed if one understands about seed germination.
Moisture is important to seed germination. Some seeds are protected by a tough seed coat. Some must be soaked in water to soften the seed coat prior to germinating. Other seeds must have their seed coat nicked or pierced (scarified) in order to allow moisture to reach the seed, causing it to expand and break through the seed coat; two examples are in the legume family - sweet peas (Lathyrus species) require soaking, and lupine (Lupinus species) require scarification.
Some seeds require periods of exposure to moist, cold temperatures and then warmth in order to germinate. This is called stratification. The goal of stratification is to mimic the temperature changes that occur from winter to spring. Seeds are placed in damp conditions of 34 - 41° Fahrenheit, then moved to a warm location. The exposure to cold temperatures required by hardy bulbs is an example of stratification.
Many plants are easy to grow from seed including most annuals, vegetables and herbs. Most require little more than moisture and a sunny location. They can be started from seed sown indoors in pots or sown directly into the garden bed after the soil has warmed. The depth requirement of specific seeds should be noted when planting. Some herb seeds, such as basil (Ocimum basilicum), are very small and can be sown with very little soil covering them. Other seeds such as nasturtium (Tropaeolum majus) should be planted about 1/4" deep. Plants such as dill (Anethum graveolens) and fennel (Foeniculum vulgare) should be planted directly in the garden and not transplanted. For details about sowing annual seeds and transplanting the seedlings, visit Planting Annual Seeds and Transplants in the Landscape here on the SULIS website. Another good website, Starting Seeds Indoors is located on the Ornamental Plants database from Michigan State University and the Michigan Nursery and Landscape Association.
Perennials can also be propagated by seed. Perennials drop their seed where it lies dormant until spring or it may germinate, producing a few leaves prior to frost. It should be noted that cultivars must be propagated vegetatively as some perennials propagated by seed may not have the same characteristics as the parent plant. For tips about planting a wildflower garden, visit Seeding a Backyard Wildflower Garden from The Greene Mountain Gardener. Prairie wildflower sources can be found by visiting Prairie Wildflower Seed / Plant Sources by Purdue University.
Collecting & Saving Seed
Collecting and saving seed to plant in the future can be a rewarding way to preserve some varieties of plants. This is especially the case with annual plants such as flowers, herbs and vegetables. Heirloom varieties have been preserved through the centuries thanks to diligent gardeners who harvested seed and replanted seed from heirloom plants. Seed can be collected from landscape grasses and other annual, biennial and perennial plants in the late summer / early fall. When starting perennial plants from seed, it will take several years for the plants to reach maturity.
Some skill and understanding of the plant lifecycle in relation to environment - phenology - is important to successful harvesting and preserving seed. The SULIS website features a good webpage on Collecting Wildflower and Prairie Seed. Some of the basics noted in this article apply to collecting other kinds of seed as well.
Self-sowing plants produce a large number of seeds each year that are easily scattered by wind, rain, animals etc. to form new plants. Many of these plants are annuals or biennials. By self-seeding, they sometimes appear to be perennial because they "come back" each year, when in reality, these are entirely new plants.
Self-Sowing Plants for U.S.D.A. Cold Hardiness Zones 3 & 4
|Scientific name||Common name|
|Cleome spp.||Spider flower|
|Convolvulus tricolor, C. major||Dwarf morning glory|
|Eschscholzia spp.||California poppy|
|Ipomoea tricolor||Morning glory|
|Hesperis matronalis||Sweet rocket|
|Lobularia spp.||Sweet alyssum|
|Lunaria spp.||Money plant|
|Matthiola tricuspidata||Wild stock|
|M. bicornis||Night-scented stock|
|Malcolmia maritima||Virginia stock|
|Mirabilis jalapa||Four o-clock's|
|Portulaca grandiflora||Moss rose, portulaca|
|Tanacetum parthenium, T. ptarmiciflorum||Feverfew|
|Viola x wittrockiana, V. cornuta, V. tricolor||Pansy, violet, Johnny-jump-up|
Propagation by Vegetative Cuttings
Many plants can be propagated vegetatively by taking leaf, stem, or root cuttings. A major advantage to vegetatively propagating plants over propagation by seed is the major ability to produce plants identical to the parent plant. Dividing a plant accomplishes the same. In all cases, use only disease-free and pest-free parent plants as these conditions are likely to be transferred to the new plant.
Propagation by leaf cuttings is a technique best reserved for plants belonging to the families Begoniaceae (begonia) and Gesneriaceae (geranium). Most of these are grown as annuals or houseplants. The cell tissues of the leaves of these plants are able to differentiate to form buds and roots, a requirement with leaf cuttings which lack both shoot and root meristems. For details on propagating by leaf cuttings, leaf bud or single node cuttings, see The Complete Book of Plant Propagation by Arbury, Bird, Honour, Innes and Salmon.
Propagating by stem cuttings is a technique applicable to both herbaceous and woody plants. Some herbs can also be propagated by stem cuttings as can rhizomatous plants. Cuttings should be firm, but not too woody. They should be 3-6 inches long, can be taken from late spring to summer, and should be cut just below a node. Cuttings can be placed in a starter mix and should root within two to four weeks. Root hormone can be used to speed rooting for some species. Transplant rooted cuttings in pots or directly into the garden after threat of frost has passed and the new plants have been properly hardened off.
Some plants can also be propagated by root cuttings. Herbs such as horseradish can easily be reproduced taking a root cutting, burying it in starter mix and keeping is slightly moist. Root cuttings should be taken when the plant is dormant and should be taken from a healthy section of the root. Cuttings should be 2-4 inches along and inserted into the moist medium with their top almost level to the soil surface. The roots should be covered with soil or sand. Top growth will appear first, new roots second. The new plant can be potted when the cutting is well-rooted. (Asbury et al., pgs. 163-164).
Layering is usually a method used for propagating woody shrubs; however, some herbaceous perennials respond well to layering as a propagation method. According to The Complete Book of Plant Propagation, pg. 33, layering can be used for propagating pinks and border carnations (Dianthus). Leaves are removed from low-growing, healthy stems. A nick is made in the stem to promote root formation, and the stripped area of stem, still attached to the parent plant, is buried in the soil. The stem is secured in place with a u-shaped wire. The leafy part of the stem may be held upright above the soil with a stake. When the stem has produced roots, it can be cut from the parent and transplanted.
Propagation by Spores
Ferns have an asexual and a sexual stage of reproduction. In addition to propagation by division, ferns develop from spores that are born in the spore case - the sporangium - located on the fronds of the fern. The individual spore germinates and forms a flat, leaf-like form called the prothallus, the gametophyte and sexual stage of fern reproduction. Sexual organs develop on the underside of the prothallium and fertilization occurs. Depending on the fern species, the first fronds will appear in two to six months. A fern as we know it is called the sporophyte generation, the spore producing generation. The sporophyte reproduces asexually by growth of the rhizome. It can be difficult to propagate ferns from spores in the landscape, so most ferns are propagated by division of rhizomes. There are many good resources for more information about propagating ferns:
For a detailed drawing of the fern lifecycle, visit Pterophyta, a webpage written by Michael Knee of Ohio State University for a course in general plant biology. This site also features great photographs of the various stages of fern production including the prothallus, sori, and the spores being released.
Transplanting Seedlings, Cuttings and Divided Plants
Once a new plant has been propagated either by seed, division, layering or vegetative cutting, it should be transplanted into a site with the proper conditions for growth. Many plants can experience shock when moved from one site to another. An example is when annual seedlings are moved to the outdoor garden or landscape. Lessening the shock to the seedlings is done through a technique called ‘hardening off'.
Seedlings propagated indoors prior to being transplanted into the summer garden have often not been exposed to such conditions as direct sunlight, cool evenings, wind, low humidity, etc. Hardening a plant is a gradual method of exposing plants to varying temperatures (especially cooler temperatures), and increasing the amount of direct sunlight. If done properly, the process of hardening causes the plant tissue to become firm and thicken in such a way that the plant is able to withstand and flourish under the changing growing conditions often seen in the Midwest. For more information, visit the Colorado State University webpage, Hardening Transplants.
American Fern Society, online information about ferns and fern allies. Revised November 12, 2001. http://amerfernsoc.org
Arbury, Jim / Bird, Richard / Honour, Mike / Innes, Clive / Salmon, Mike; The Complete Book of Plant Propagation. Reed International Books Limited, Taunton Press, Newtown, CT. 1997.
Arizona Cooperative Extension, "Plant Propagation", Master Gardener manual. http://ag.arizona.edu/pubs/garden/mg/propagation/
Clemson University Cooperative Extension Service, "Dividing Perennials", Home and Garden Information Center, HGIC-1150, Karen Russ and Bob Polomski. February 1999. http://hgic.clemson.edu/factsheets/HGIC1150.htm
Colorado State University Extension, "Hardening Transplants", Curtis Swift, February 3, 1997. http://www.ext.colostate.edu/ptlk/1802.html
Flora locale, "Seed Collection and Plant Propagation", Margaret Cole.
Michigan State University Extension, "Growing Native Ferns", 03900005 . January 1, 1996.
Michigan State University Extension and Michigan Nursery and Landscape Association, "Starting Seeds Indoors", 00001573, Ornamental Plants Plus database, November 12, 1999. http://msue.anr.msu.edu/news/selecting_and_starting_seeds_indoors
Montana State University, "Harvesting and Saving Seeds", Montguide, volume 13, number 2, Bob Gough. February 2002. http://store.msuextension.org/publications/YardandGarden/MT199905AG.pdf
North Carolina State University, "Ferns", Erv Evans, Hort On The Internet, August 2001.
Ohio State University Extension, "Plant Propagation", Master Gardener manual, Jack Kerrigan and Margaret Nagel.
Ohio State University, "Pterophyta", Michael Knee. http://hvp.osu.edu/resources/hcs300/svp2.htm
Oregon State University Extension, "Flower Cuttings: Grow New Geraniums, Perennial Vines, and Fuchsias from Cuttings", Carol Savonen. July 9, 1999.
Pacific Northwest Extension Publications, "Propagating Herbaceous Plants from Cuttings", PNW151, W.E. Guse and F.E. Larsen. Reprinted January 2001. http://4h.wsu.edu/em2778cd/pdf/pnw0151.pdf
Purdue University Consumer Horticulture, "Some Prairie Wildflower Seed / Plant Sources", Ricky Kemery and Dr. Michael N. Dana. April 16, 2002. http://www.hort.purdue.edu/ext/sources_IN_wildflowers.html
University of Georgia Cooperative Extension, "Growing Ferns", Paul A. Thomas and Mel P. Garber.
University of Minnesota Extension , "Dividing Perennials", H140P, Yard and Garden Brief, Susan H. Barrott, August 1999. http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/h140perennialdivide.html
University of Missouri-Columbia, "Growing Herbs at Home", agriculture publication G06470, David H. Trinklein and Ray R. Rothenberger, Department of Horticulture. Reprinted August 15, 2000 http://muextension.missouri.edu/xplor/agguides/hort/g06470.htm
University of Missouri-Columbia, "Home Propagation of Garden and Landscape Plants", agriculture publication G06970, Mary Ann Gowdy and Christopher J. Starbuck, Department of Horticulture. Reprinted May 15, 2000 http://muextension.missouri.edu/xplor/agguides/hort/g06970.htm
University of Rhode Island, "Iris Culture", Greenshare, Leslie Diebec, Ohio State University Extension. 2000.
University of Vermont Extension, "Seeding a Backyard Wildflower Garden", The Green Mountain Gardener, Dr. Leonard Perry. http://pss.uvm.edu/ppp/articles/wildflow.html
University of Wisconsin Extension, "Perennials: Dividing in the Fall", Infosource #446, Sharon L. Morrisey. Revised 1996.
University of Wisconsin Extension, "Iris: Dividing Iris", Info Source, #449, Sharon L. Morrisey, 1996. http://wimastergardener.org/?q=DividingIris
University of Virginia Cooperative Extension, Virginia Tech and Virginia State Universities, "Plant Propagation from Seed", 426-001, Diane Relf and Elizabeth Ball, June 2001. http://pubs.ext.vt.edu/426/426-001/426-001.html
University of Virginia Cooperative Extension, Virginia Tech and Virginia State Universities, "Sowing Perennial Seeds", Diane Relf. April 1997. Originally published by Robert E. Lyons, Professor of Horticulture, in The Virginia Gardener Newsletter, Volume 7, Number 8.
Wylie House Museum, University of Indiana, "Some Tips On Saving Seeds". October 15, 2001. http://www.indiana.edu/~libwylie/garden_tips.html