Asexual reproduction in plants
Reproduction in the animal kingdom has historically been sexual. Cloning the sheep Dolly in 1997 moved us closer to the possibility of duplicating other animals or humans asexually, but the practice is not yet perfected.
In the plant kingdom, however, reproduction is possible in a variety of ways. Sexual reproduction involves male and female flower parts, pollination and seed production. All other means of plant reproduction are asexual or vegetative.
Though the process is asexual, the results can be pretty sexy. Sexy Pink heleconias, for example, are easily reproduced by root division as are other lovely members of that family. Heleconias can also reproduce by seed, though some plants have lost the ability to reproduce sexually. Centuries of cultivation of bananas have produced varieties that must be propagated asexually. Though some seeded banana varieties do exist, the varieties we prefer can only be propagated from division of their corms or by tissue culture.
Division, layering, grafting, tissue culture and cuttings are all methods for asexual plant reproduction.
Division is accomplished by separating a plant’s roots, corms or root shoots from a “mother plant” to make new plants. Layering on branches within the plant or those touching the ground involves creating an environment for roots to grow on a branch of the parent plant and removing the new plant once the roots have formed. Grafting is a process that joins plant parts from the same species to produce an improved plant. Grafted fruit trees are ones where a desirable plant is attached to a plant relative with a strong root system, resulting in good fruit and strong roots. Tissue culturing is a more complicated practice that usually requires a sterile lab to accomplish.
Of all the practices, propagation by cuttings is probably the easiest. Though some plants cannot be propagated in this way, many can, and the success rate is high when done properly.
Herbs, woody shrubs and small trees are good candidates for propagation by cuttings. Many ornamental plants, including hibiscus, croton, ti, roses and plumeria, can be grown from cuttings. Edibles and herbs including Mysore raspberry, mountain apple, mulberry, tomato, mint, oregano and rosemary also grow well from cuttings.
Success with cuttings depends on a few factors. Harvesting early in the day from healthy plants is a good start. Cuttings taken during an active growth period will often be more vibrant. Avoid choosing cuttings that are flowering or have flower buds since they can slow root production.
Quick transference from mother plant to growing media can be helpful. Prepare a growing environment for cuttings before you cut them. Plants with white sticky sap may need to dry out a bit before placing in water or growing media but most others will do best if placed in a damp or wet environment soon after cutting. A good growing media drains well but retains some moisture to keep the root zone moist but not soggy. A mix of vermiculite and perlite is ideal. Pots of growing media should be placed in a shady area to avoid the burning and drying effects of the sun.
Take cuttings that are about 4 inches long with at least two nodes. In woody plants, use soft wood sections about 1/4- to 1/2-inch diameter for best results. After cutting, remove the leaves to limit water loss and help the plant focus energy on making roots. Before placing the cutting, coat the lower stem with a rooting compound. Always label your cuttings since they may be hard to identify without leaves. Daily misting of cuttings is helpful and preferable to less frequent deep watering.
Once placed, patience is required. Don’t expect instant results. New growth, which may occur in a few weeks, is an indication roots may be forming. A gentle pull on the plant should be enough to tell if roots are beginning to grow.
Once roots have formed you can transplant to a larger pot with potting soil. At this point, you can add amendments or fertilizer and begin acclimating your plant to its new site. This process, called hardening off, helps avoid transplant shock.
When your plant appears to be actively growing and healthy, you can plant it in your garden.
Tropical gardening helpline
Brandt asks: Can you tell me if the heart of the bottle palm is edible?
Answer: The West Hawaii Master Gardener’s Association forwarded your question with their response.
According to our research, the seed of the bottle palm, Hyophorbe lagenicaulis, can be used but the heart is not known to be edible. Find an extensive list of palm varieties and their known uses at quisqualis.com/tv01ediblepalms.html.
In Hawaii, the peach palm, Bactris gasipaes, is most widely grown for its tasty heart.
Other palms with edible hearts, seeds or fruit include Dypsis pilufera, D.baronii, D. madagascariensis and the queen palm, Syagrus romanzoffianum. Several of these are locally available.
Palms provide food in many subtropical and tropical countries. Caution is advised when choosing plants to taste or eat. Don’t consume any that you don’t know to be edible or at least nontoxic. Of course, many palms have edible fruit including coconut, date, salak and jelly palms. Many of the ones that are locally available are described at palmsinkona.com/palms.asp.
Email plant questions to firstname.lastname@example.org for answers by certified master gardeners. Some questions will be chosen for inclusion in this column.
Diana Duff is a plant adviser, educator and consultant with an organic farm in Captain Cook.