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Tropical Gardening Helpline: A refresher course on plant propagation

Updated: 
June 25, 2017 - 12:05am

Deb asks: I want to expand my garden from plants I already have, I need a refresher course on plant propagation. Can you give a brief summary of the techniques?

Tropical Gardener answer: A good way to create a new garden is to start from seed. Free seeds are available at the Community Seed Library in the Kailua-Kona Public Library. The CSL is set up as an exchange hoping that those who take seeds will grow out their plants, save the seeds and bring them back to the library. Those who take seeds can also leave a financial donation for CSL to buy seeds or donate new or opened seed packets to the exchange.

Best seeding results will come from planting in six- or four-pack seeding containers using one of the sterile seeding mixes on the market. Placing seeds in wet mix is best, but then let it dry out for a few days before watering. Keep the trays out of the rain so you can control the moisture level. Spraying with chamomile tea can prevent damping off, a common disease that kills seedlings. Keep the mixture moist, not wet, and you can add fertilizer and move it to a larger pot when it’s true leaves start to grow. Once the plant is sturdy it is ready to go into the garden.

If you want to propagate asexually (seeding being sexual propagation), you can either take cuttings, do air layering or graft a desirable branch onto existing root stock.

Taking cuttings is easy but doesn’t work universally. The best way to find out if it will work is to take a semi-hardwood cutting from a plant, remove most of the leaves, dip the cut end in rooting compound and place the cutting in a moist mix of 50/50 vermiculite and perlite. Daily misting will encourage the cutting to put out roots. Once rooted and putting out new leaves, you can move the plant to soil, add some fertilizer and either put it in a larger pot or in the garden.

Layering is another way to propagate vegetatively. As with cuttings, the new plant will be genetically identical to the mother plant. Basically, layering is a technique to get a stem to develop roots and produce a new plant. Simple layering can be done in the ground by bending a flexible stem that is growing low to or on the ground and burying it at the bend. You’ll want to stake at least 6 inches of the stem to get it to grow vertically. If bending doesn’t break the stem a bit, wounding it can help provide a spot for roots to develop. It may take almost a year for the plant to be safely separated from the mother plant.

Air layering takes place above ground. Chose a fairly young woody stem at least a 1/4 inch in diameter that will make an attractive plant when separated from its mother. Choose an area just below a node and remove any leaves or twigs within 4 inches of this point. Using a very sharp knife, cut two parallel circles around the stem about an inch apart and through the bark and cambium layer. Remove the bark between the two cuts leaving the inner tissue exposed. Scrape the ring removing all the cambium tissue and apply some rooting hormone to the cut area. Wrap the wound with moist sphagnum moss. Wrap the moss in saran wrap then tin foil to retain moisture and protect the new roots from the sun. In a few months the package should feel hard and full of roots. You can then remove the wrapping, cut the new plant below the roots and plant it in a pot or in your garden.

Grafting is a way of growing a desired plant on the rootstock of a hearty but less desirable member of the same species. Successful grafting takes practice. Basically, you want to make a clean cut in the rootstock plant and match its cambium layer with the cambium of the scion (cutting) from the new plant being grafted onto it. A variety of videos with different techniques can be found on the internet. You need the rootstock and the scion as well as an exacto knife and some tape to seal the combined plants until they grow together. Once you have seen it done a few times, practice with scrap wood until you have your method down. Then you can try it on a live plant and it should work.

“Creating and Expanding Your Garden” is a free class covering all of these propagation techniques that is being offered at the Kailua-Kona Public Library from 10 to 11 a.m. on Saturday, June 24. For more information, visit www.librarieshawaii.org/branch/kailua-kona-public-library.

Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.

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