As we start a new year, how about learning a new skill? Air-layering is a propagation technique I like to do with my woody houseplants that will produce fairly large plants quickly.
The technique I will discuss today is best used on woody dicots (broadleaf plants, like a rubber tree or a schefflera). In a future post I will cover air-layering a woody monocot (grass-like plant, such as a dracaena or dieffenbachia).
Plants have two types of vascular tissues, phloem and xylem, just like arteries and veins in people. While arteries and veins carry blood to and from the heart, xylem translocates the water-mineral solution from the roots to the rest of the plant, and phloem translocates photosynthates from the leaves to where they are needed, including the roots.
The actively-growing roots produce hormones that encourage stem and leaf production (cytokinins) and the actively-growing tissue at the ends of the stems produces hormones that encourage root production (auxins). With air-layering we interrupt the flow of the auxins at the point where we want the roots to grow. As those damaged tissues heal the auxins from the tip of the stems encourage the cells to form roots.
- Sharp knife
- Dry cloth
- 5” x 10” plastic sheet (a 1-gallon storage bag, cut into the right size works well)
- 1 cup moistened sphagnum peat moss
- Some sort of tape (electrical works very well)
- 6” x 12” aluminum foil
- Some plants may benefit from a rooting hormone, but I’ve never used them
On broadleaf, woody plants the active phloem and xylem form concentric rings between the bark and the wood. The xylem is the wood-side ring and the phloem is the bark-side ring. In between is a thin layer of actively-dividing cells (meristematic tissue), creating more xylem and phloem as the stem gets larger around. Old xylem and phloem become the wood and bark of the stem.
- Select the site where you want the roots to grow, removing any leaves or stems about 5 inches above and below the air layer site.
- Score and remove about one inch of bark all around the stem, so the phloem tissue is girdled, but don’t cut into the wood as we still need the xylem tissue to translocate the water solution from the roots to the upper part of the stem.
- Rub the exposed stem with a dry cloth to remove moist meristematic cells.
- Using the plastic and tape, form a tube around the stem.
- Close the bottom end of the tube tightly around the stem below the work zone (tape does not need to stick to the stem, just the plastic).
- Stuff the moistened sphagnum peat moss into the tube so it is situated around the work zone.
- Close the top end of the tube with tape.
- Wrap the ball with aluminum foil to block out light.
Remove the aluminum foil to check the root ball for moisture and replenish if needed (shouldn’t need it). After about six weeks you should see newly formed roots growing in the peat moss.
At this point you can carefully remove the plastic and peat moss. Cut the stem below the root ball and plant in an appropriate pot. Give the plant a week or so out of high light so the roots can get established.
Have fun with your houseplants.