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Division and Layering

Plant propagation is the means by which one can increase plant stock, perpetuate a species or maintain a plant in a youthful state. Division, layering, grafting and tissue culture are all methods of asexual propagation. All processes produce plants that are genetically identical to a single parent.

Although tissue culture is not commonly done at home, home gardeners have found real satisfaction using division, layering and grafting to rejuvenate and multiply favorite plants.

Propagation Methods:

Division

Division involves the splitting of a single large plant, with many crowns or growing points, into several smaller plants. Multi-stemmed, clumping, suckering plants, or those with fleshy underground storage structures (e.g. bulbs, tubers, rhizomes, corms, tuberous roots and stems), can all be propagated by division. It is one of the simplest and most basic ways to increase plant stock.

Herbaceous perennials

Most perennials should be divided every 2-3 years, when they become overcrowded and begin to show signs of reduced vigor. Cut back the stems on the plant to be divided to nearly ground level. Carefully dig up or slide the perennial from its container, gently removing most of the soil around its roots. Take care to keep the roots as intact as possible during this process. For plants consisting of mass crowns, two garden forks may be used to divide the root mass. Fleshy clumps such as Hosta sp. can be divided with the aid of a clean sharp knife, while densely formed, tight roots such as those of Phlox paniculata or Miscanthus sp may require the use of a clean, sharp spade to divide the root. Shallow rooted groundcover type perennials can often be divided by gently pulling them apart by hand. Each new division should possess some healthy roots and buds/shoots. Discard old, woody centers of lifted perennials. It is the younger, newer portions on the edge of the clump that can be replanted or potted up. During the procedure, ensure that the divisions are replanted as soon as possible so that the roots do not suffer damage from desiccation. Always make sure the transplants are positioned at the same depth as the parent plants, water the new transplants well and keep them moist during dry periods until they become established.

The general rule is to divide fall blooming plants in the spring, and spring and summer flowering plants in the fall. If the perennials are divided in the fall, it should be done early enough to ensure that new roots have adequate time to grow and develop before winter sets in. Some perennials, Dicentra spectabilis (bleeding heart) for example, should not be divided unless they show signs of decline after many healthy productive years.

Bulblets, cormlets and bulbils

Older bulbs can be dug up every 3-5 years after the foliage begins to wither. The smaller bulbs are detached from the mother bulb and replanted immediately. Tulipa (tulip) and Narcissus (daffodil) can be propagated this way.

Old corms can also be lifted when the leaves die back and allowed to cure in a dry, sheltered area for 2-3 weeks. The new corm and cormlets can then be removed from the old and stored in a dry, cool, dark location until planting time. Crocus and Gladiolus are plants that develop from corms.

Bulbils are small bulbs that are found on the above ground portions of some bulbous plants, most commonly in the leaf-axils. They can be harvested just before the foliage begins to die down. If they are damp when harvested, dry them for a couple of days on newspaper, in a warm place, and store them in a box of dry peat. They should be kept in a cool, frost-free, dry location until they are planted out. Lilium spp (summer-flowering lily varieties), Allium (ornamental onion) and culinary members of the onion family, such as Allium cepa (tree onion) and Allium sativum (garlic) are all examples of plants that produce bulbils.

It will take 2-3 years for bulblets, cormlets and bulbils to reach flowering size.

Suckering

Suckering shrubs produce new plants from underground roots and offshoots at the base. These new plants can be easily divided from the mother plant. Carefully dig around the sucker and cut the main root on either side, removing the sucker with as many small fibrous roots as possible. This new plant can be potted up, using an appropriate potting mixture. Keep the transplant watered and in a sheltered corner, allowing it to develop more roots before planting it out into the garden. Suckers can be removed at most times of the year, but the procedure is most successful in the early spring or late summer to early fall. Examples of shrubs that produce suckers occasionally or regularly include: Berberis (barberry), Cornus (dogwood), Kerria (Jew's mallow), Aralia elata (Japanese angelica tree), Symphoricarpos (snowberry) and Rhus typhina (Stag's horn sumac).

Note: Always compare the leaves, bark and growth of suckers with the young shoots of the parent shrub, making sure that the shrub has not been grafted onto another rootstalk. Shrubs, such as some varieties of Syringa (lilac), Malus (apple), Prunus (plum), Pyrus (pear), and Rosa (rose), are often grafted onto another rootstock. The suckers from grafted plants will originate from the rootstock and lack the desirable qualities of the portion of the shrub that is growing above the ground. Do not propagate these types of suckers. Removing these suckers from the rootstock will ensure that they do not 'take over' and diminish the growth of the desirable 'grafted' variety.

Offsets and Plantlets

Offsets are completely new plants that possess their own root system. They develop along side their parent, from which they can be easily detached and rooted. Many bromeliad and succulent plants can be increased by offsets. Once a bromeliad has bloomed, it will begin to die. At the same time, however, a new daughter rosette emerges from the parent's base. When the daughter rosette reaches about one-third the size of the parent, it can be cut or broken off from the main stem. Some will have a root structure. Be careful when handling a daughter rosette to avoid root damage. The new rosettes can be potted up just deeply enough so that they stand in place. Succulent offsets can be removed from the mother plant and inserted into a pot of moist potting mix. Place some grit on the surface of the mix to aid in keeping the offset in place and to prevent it from rotting at the neck.

Plantlets are small versions of the parent plant growing on its leaves, stolons, stems or inflorescences. Once they are large enough to be handled, they can be detached from the parent, taking 3cm(11/4 in) of the leaf stalk or stolon, where appropriate. Insert the plantlet stalk into the potting mix so that the plantlet sits on the surface of the growing medium. Water the pot and cover with plastic to maintain a high level of humidity. Roots should develop in about three weeks. Propagation is best carried out between mid-spring and late summer. Some plantlets may be rooted while still attached to the parent. In this case, the plantlets are layered into pots of growing medium and once they have rooted, the stems or stolons can be severed and the plantlets separated from the parent. Plants that produce plantlets include Chlorophytum (spider plant), Kalanchoe tubiflora (devil's backbone), and Tolmiea menziesii (piggy-back plant).

Layering

The process of rooting woody plant material, while the stem is still attached to the mother plant, is termed layering. There are plants that propagate themselves naturally through this process. Wounding or scraping the bark beneath the portion of stem that will be in contact with, or buried in soil can hasten the rooting process. Loosen the soil with a garden fork, in the area where layering will take place, and then firm it to remove any air pockets. Amending the soil may be necessary as it must be well-drained and rich in organic matter to promote root and shoot development in the new plant. The layering medium should be provided with a constant supply of moisture to enhance the rooting procedure. Layering is most successful when carried out during the early spring to mid-summer period and when performed on young wood formed in the previous or current season. It may take 12-18 months for the stem to root to a point where it can be severed from the parent plant.

Simple layering

This type of layering is best suited for the propagation of plants with flexible, low growing branches. Choose a low growing stem and bend it to the ground. Cover part of the branch with 10cm (4 inches) of soil and allow 15-30cm (6-12 inches) after the buried, u-shaped bend, to remain above the soil level. The exposed portion of the branch may be staked vertically and the buried stem held down with a peg or heavy rock. Roots will develop from the area of the stem that has been bent (the stem should also be wounded in this area prior to burying). Plants that are propagated using this method include Rhododendron, Forsythia, Lonicera (honeysuckle), Corylopsis (winter hazel), and Cotoneaster.

Serpentine (compound) layering

This process is an adaptation of simple layering and results in the production of several new plants from a single stem. Two or more parts of the stem will be submerged in the soil. A long, vigorous, healthy shoot should be chosen and buried at the nodes (where the leaf meets the stem), with two or three nodes between the submerged portions of the stem. Remove leaves in the area of the stem that will be covered with soil. Wound the bark on the stem, just behind the nodes that will be buried, by making an angled cut, 5cm (2 in) long. Prop the wound open with a small stone, before it is buried, to prevent it from healing over. Serpentine layering can be used to propagate many creeping and climbing plants including Clematis, Wisteria, Lonicera (honeysuckle) and Vitis (grape).

Tip layering

This process requires that the tips of long shoots are pegged down or buried in the soil to a depth of 10cm (4 in) in the area where they touch the ground. The best time for using this method is during the mid-late summer. Within a few weeks, if the soil has been kept adequately moist, new shoots will begin to appear form the buried tips. The layers may be ready to be transplanted as early as mid-autumn. Rubus spp. (blackberry, purple and black raspberry and loganberry) can be propagated in this way.

Mound layering

This method, also known as stool layering, is useful for propagating woody material that has heavy/ thick stems that are closely branched. It is also suitable for shrubs that are bushy in growth habit and produce a mass of shoots at the base. In late winter, when dormant, the shrub should be cut back to 5 cm (2 in) above the soil surface. In the spring, the remaining stem(s) will produce new shoots. When the shoots are 16cm (6 in) long, begin to mound the soil up around the young stems as they grow, making sure never to completely cover the shoots. Continue this process until there is 20cm (8 in) of stem covered with soil. Keep the mound of soil moist during dry periods. The following spring, the soil may be carefully pulled away from the base of the mother plant and the rooted stems severed below the root system. This method is suitable for ornamental shrubs that respond well to hard pruning including Amelanchier (serviceberry), Salix (willow), Ribes (currents), Spirea sp and ungrafted specimens of Syringa (lilac).

Air layering

Many plants are too rigid and upright to be propagated by bringing the stems and branches in contact with the soil. Air layering is an ideal way of replacing leggy houseplants that have become too tall, and, as a result, have outgrown their space indoors. Using a shape knife, wound the stem by making an angled cut that is 5mm (1/4in) deep and 2.5cm (1in) long. Apply rooting hormone to the incision and wedge it open with damp sphagnum moss. Wrap the adjacent stem with more moistened sphagnum moss and cover the area with plastic wrap, securing each end with tape. New roots will grow into the clump of moss. When the roots fill the plastic sleeve, the wrap can be removed and the stem severed just below the newly formed roots. The new plant can be potted up, making sure to water only sparingly until the plant becomes established. This method is suitable to propagate plants such as Ficus elastica (rubber plant), Monstera deliciosa (willowleaf) and Dieffenbachia spp. (dumb cane). Hardy outdoor shrubs, such as some Magnolia spp. and Hamamelis spp. (witch hazel) can also be propagated this way.

Grafting

Grafting involves joining together two cut surfaces, from two separate plants to enable them to unite and become one plant. Information for this method of propagation can be found in the fact sheet How to Graft.

Considerations:

• Never propagate from material that is known to be infected by or in contact with diseased plants. Always use healthy vigorous, disease- free plant stock.
• Always use sharp, sterilized tools, seceteurs and knives during propagation procedures. Pots should be clean.
• Garden soil does not make a good growing medium for plants in containers. When used in a container, soil more easily compacts. Compaction can lead to poor drainage and oxygen deprivation. It is preferable to use a good quality, sterile, purpose-made potting medium that will retain moisture while providing good drainage and aeration.
• Aftercare is important. Always provide newly propagated plants with the appropriate amount of moisture, light, and air circulation.

References:

• The Toronto Botanical Garden Weston Family Library is an excellent source for horticultural information.
• Clarke, Graham and Alan Toogood. The Complete Book Of Plant Propagation. London, England: Cassell & Company, 2001.
• www.hc.ohio-state.edu/mg/manual/prop.htm
• www.ces.ncsu.edu/depts/hort/hil/hil-8702.html

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: January 8, 2006