• Topics: Environmental Horticulture  | Landscape Plant Propagation Workbook  | Ingram, Dewayne L 

Landscape Plant Propagation Workbook: Unit IV. Propagation by Division¹

This is one in a series of educational units presenting the basic principles of landscape plant propagation. This workbook is intended to be used in conjunction with a video-taped presentation on landscape plant propagation by division. There is more detailed information in this publication than can be covered in the video presentation and additional sources of information are listed. Study questions designed to provide a review of important points are presented.

Objectives for this Unit

At the conclusion of this unit you should be able to do the following:

1. Present the principles of propagation by division.

2. Describe techniques for dividing specialized organs such as bulbs, corms and tubers.

3. Demonstrate the techniques for division of plants with a clumping growth habit.

Introduction

Division is a method of asexual or vegetative plant propagation. It involves propagating a new plant from a vegetative part or section of a plant. As with other methods of vegetative propagation, the propagated plant will have the same characteristics as the parent plant. Division is a common means of multiplying plants in the residential landscape and the commercial landscape plant industry. The two basic types of plants propagated by division are those with a clumping growth habit and those with specialized storage organs, often termed bulbous plants.

Bulbous Plants

Bulbous plants characteristically have storage organs at or below the soil surface. These organs may be true bulbs, corms, tubers, tuberous roots, rhizomes, stolons or pseudobulbs. Storage organs evolved over the years to allow the plants to survive some extended period of environmental stress such as cold, heat or drought. Carbohydrate and nutrient reserves are stored in these organs to support regrowth of shoots, roots and flowers after the stressful period has passed. Roots and shoots, or at least root and shoot initials are contained in these organs. Bulbs, corms, tubers, rhizomes, stolons and pseudobulbs are modified stem tissue. Tuberous roots are true roots that have evolved into storage organs over many years to combat an extended period of unfavorable environmental conditions.

True Bulbs

Amaryllis , tulips, onions, daffodils and Easter lilies are examples of plants with true bulbs. Bulbs contain a short, fleshy vertical stem enclosed by thick, fleshy modified leaves, usually termed scales or bulb scales. There is a distinct basal plate, which is a compressed stem and the primary growing point for the bulb during initial phases of regrowth. The fleshy scales protect the growing point in the bulb, and further protection may be provided by an outer membrane, called a tunic. The tunic is relatively thin and dries after the bulb is harvested, creating a membranous-type covering. Onions and tulips are examples of tunicate bulbs and are better protected from drying and mechanical damage than nontunicate bulbs such as lilies.

Bulbs differ in flowering season and their tolerance of cold. Some bulbs are cold hardy and flower in the spring. Iris, tulip, daffodil and hyacinth are examples of hardy bulbs suited for fall planting. Tender bulbs suited for planting during the warm season include Amaryllis , Zephyranthes and Hymenocallis .

Bulbs produce side branches, called bulblets or offsets, from the primary bulb and the offsets and the primary bulb increase in size with age. Separation of the offsets is a fairly rapid means of propagating many bulbous plants. Commercial production of bulbs commonly involves digging the bulbs when the plants are dormant, cleaning, sorting by size, and marketing a portion of the bulbs dug from a bed. The bed is usually replanted, after storage or possible soil treatment, with bulbs of equal size that will be dug after another growth season.

Nontunicate bulbs (e.g., lily) can be readily propagated by rooting individual fleshy scales removed from a mature bulb. The bulb can also be cut into several vertical sections, each containing a part of the basal plate. Storing the sections at near 70°F for a few days to weeks to allow the cut edges to callus and a preventative fungicide treatment will reduce the threat of decay when the sections are planted. It is essential that each section contain a portion of the basal plate.

Corms

Corms (e.g., gladiolus) are propagated primarily by separation of offsets called cormels from the primary corm. Corms are modified stems which are enclosed by dry, scale-like leaves or tunic, but unlike a true bulb the solid stem has distinct nodes and internodes. Many of the axillary buds on the corm could develop into a shoot, but normally only the terminal shoot develops. Corms produce two types of roots: fibrous roots for water and nutrient absorption and enlarged roots for support and to pull the corm deeper into the soil for more uniform temperatures. Gladiolus is the most common corm produced in Florida.

The reserve carbohydrates and nutrients in the original corm are depleted for new shoot growth. A new corm, supported by photosynthates from the leaves, develops just below the original corm and could grow larger than the original corm under suitable environmental conditions. In addition, cormels develop at the base of the new corm. Cormels usually require an additional one to two years' growth before flowers are produced.

Corms are harvested after the foliage dies. They are dug and dried on a screen or slat-bottom flat to allow adequate circulation of air warmed to 90° to 92°F. After a fungicide treatment and sorting by size, curing at 95°F for a week is advised. Corms can then be stored at 40°F with a relative humidity of 70 to 80 percent.

Tubers

Two of the best known tubers are the Irish potato and caladium. There is a substantial caladium production area in central Florida. Tubers are modified, underground stems complete with nodes and axillary buds (eyes). The terminal bud is at the apical end (shoot end) of the tuber and may exhibit apical dominance over other basal buds. Shoot growth of tuberous plants is encouraged by long photoperiods, but tuber development is encouraged by reduced daylength, lower night temperatures and low mineral nutrition. This response has evolved to encourage tuber development before the onset of winter.

Tubers are harvested after shoot die-back. Propagation of tubers involves either planting the entire tuber or cutting the tuber into pieces, each containing I to 3 buds and 1 to 2 ounces of nutrient and carbohydrate reserve when possible. Cut edges should be allowed to dry overnight, or up to three days for callus formation, before planting to reduce decay and increase rooting. Dried pieces may also be treated with a preventative fungicide.

Tuberous Roots

Dahlia, gloxinia and sweet potato are examples of plants that can be propagated by division of tuberous roots. Since tuberous roots are modified, enlarged roots, they lack nodes and axillary buds. Buds are normally present only on the proximal end (shoot end). Most tuberous roots are incapable of producing adventitious shoots and must be divided so each piece contains a shoot bud. Vegetative propagation of plants with tuberous roots is often more easily propagated by stem, leaf or leaf-bud cuttings.

A few plant species with tuberous roots, such as sweet potato, can produce adventitious shoots. These are dug and laid horizontally in sand so that they do not touch and covered with 2 inches of sand. These roots should be kept near 80°F and moist until sprouts begin to emerge. As shoots develop, more sand is added (up to 4 to 5 inches) and roots develop along the stem. Once the shoots, also called slips, are well rooted they are separated and transplanted.

Rhizomes and Stolons

Rhizomes and stolons are modified, horizonal stems. Rhizomes grow in the soil, while stolons grow horizontally above the soil surface. Most plants which produce rhizomes or stolons are monocots, although some ferns and dicots produce them. Bamboo, canna and most warm-season turfgrasses produce rhizomes or stolons.

Rhizomes and stolons can be divided to yield multiple plants, or lateral branches can be removed and planted. Generally, divisions should be scheduled at the beginning or near the end of a growth season, but this differs with species. Each division must include a vegetative bud.

Pseudobulbs

Pseudobulb means false bulb and refers to modified stems used for food storage. They are commonly produced by orchids and vary greatly in appearance. With a few orchids, such as Dendrobium, the pseudobulb is elongated, jointed and reed-like and offshoots (keikis) develop at the upper nodes. Roots form at the base of these offshoots and they can be removed from the parent plant and transplanted.

Most commercially important orchids, such as Cattleya , Laelia and Miltonia , can be propagated by rhizomes or stolons containing four to five pseudobulbs. Either immediately after flowering or just as new roots start to develop is the best time to divide these pseudobulbs.

Plants with Clumping Growth Habit

Many plants characterized by multistems and/or clump growth habit (e.g., daylily, liriope) can be propagated by division. Herbaceous perennials are most commonly propagated by clump division, but several woody plants can be propagated successfully by this means. The optimum time to divide plants is during the dormant season just before the new growth. Plants that produce multiple stems and suckers are the best candidates for propagation by division. This is an excellent means of increasing a groundcover area in the landscape or commercially producing plants suited for groundcovers.

This simply involves separating the clump into pieces with adequate roots and shoots for reestablishment. A small clump with one to two shoots and adequate roots for transplanting is often called a bib. These plants may be real woody and require an ax or saw to separate them or may be soft and succulent and can be separated by hand. Divided pieces should be replanted at the same depth as they grew originally. Examples of plants that are commonly propagated by clump division include liriope, bamboo, zamia, daylilies, bromeliads and orchids.

Suckers may develop on the stems or roots of plants. These suckers can often be removed and stuck in a propagation medium under mist for root development. Sometimes adequate roots can be harvested with root suckers so that mist is not required.

Plant Propagation References

Plant Propagation Principle and Practices . 1983. Fourth Edition. By H.T. Hartmann and D.E. Kester. Prentice-Hall, Inc Englewood Cliffs, NJ.

Seeds of Woody Plants in the United States . 1974. Forest Service, U.S.D.A., Washington, D.C. Agricultural Handbook No. 450.

REVIEW QUESTIONS

What are the two basic types of plants propagated by division?

1. (null)

2. (null)

List the specialized storage organs that are modified stems in plants and serve as a means of propagation.

1. (null)

2. (null)

3. (null)

4. (null)

5. (null)

6. (null)

What is the primary natural means of protecting bulbs from drying and mechanical injury?

Bulbs can be propagated by removing the _____________________________or by cutting the ___________________________________ into pieces.

List two bulbs with a tunic and two without a tunic:

Tunic

1. (null)

2. (null)

Nontunic

1. (null)

2. (null)

Define:

• cormel

• pseudobulb

• bib

What must each piece of a tuber contain before a new plant will develop?

1. (null)

2. (null)

List two common plants that produce tubers.

1. (null)

2. (null)

What is the difference between a tuber and a tuberous root?

What is the difference between a rhizome and a stolon?

Generally, when is the best time to divide plants with a clump or multistemmed growth habit?

List four plants with a clump or multistem growth habit commonly propagated by division?

1. (null)

2. (null)

3. (null)

4. (null)

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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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