Plants are pretty nifty and learning how to propagate each one makes life on Kure feel like one of Harry Potter’s Herbology lessons. In the past few months, our team has been attempting to air layer naupaka (Scaveola taccada) which should give the summer field crew rooted branches to cut off of parent bushes in two to six months. Once the branches have rooted, they will act the same age as the parent plant which means we can expect them to flower and fruit sooner than seedlings. A book on Kure suggests this process could be used on most native Hawaiian plants which made me think the process is worth sharing with our readers. The process is fairly easy, quite enjoyable and feels like an easy experiment to try at home. So this week I thought I would guide you through the process so you can experiment with air layers on bushes and trees in your backyard.
Step 1: Collect supplies. You will need: a sharp knife, plastic wrap, wet sand and waterproof ties like flagging, electrical or garden tape.
Step 2: Choose a branch. Select a stem from the previous year’s growth that is about one inch in diameter. Larger branches will grow roots but they are not always strong enough to hold up the larger plants.
Step 3: Girdle the branch. With your knife, cut a 0.25-1 inch strip of bark away from your branch. If the bark does not peel off the branch your section of the plant is not a good candidate for air layering, try a new branch and return to step 2. If the bark easily slips off the branch move on to step 4.
Step 4: Remove the cambium layer. With your knife, scrape the newly exposed area to remove the cells that form new tissues known as the cambium layer. Intact, the cambium layer will grow over the girdled area and stop new roots from developing.
Step 5: Envelope your girdle with sand. Place two handfuls of wet sand in a square of plastic wrap and tightly wrap the soil around the girdle, securing it in place by tying both ends tightly with tape. This part is tricky, requires dexterity and after a few tries everyone on Kure seems to come up with their own methods. I like to tie one end of the plastic wrap around my branch before adding the wet sand when I am working alone. Enlisting a buddy can make this step easier and keep the bundle tight enough to prevent moisture from leaving the sand as well as keeping additional moisture from entering during heavy rains.
Step 6: Monitor the air layer. If ants, birds or wind rip holes in the plastic wrap you should remoisten the sand and either reapply new plastic wrap or use tape to cover the holes so the stem and roots will not dry out.
Step 7: Transplant the air layer. When roots become visible through the plastic wrap, your air layer is ready to be transplanted. Cut off the branch below your air layer so that when you walk away you have the branch as well as the plastic wrapped roots in hand. Prune the top of the branch to make sure your plant is not top heavy. In a shaded area, remove ties and plastic wrap but keep root ball intact. When you place the branch into a pot, make sure the plant is not overly jostled in order to protect the roots.
This process is also recommended to be used on endangered plants that need to be pruned. Instead of throwing away branches, the same branches can be air layered, cut away and replanted. Currently, the naupaka bushes around camp look pretty festive with their plastic wrap/flagging tape adornments.
Reference: Lilleeng-Rosenberger, Kerin E 2005 Growing Hawai’I’s Native Plants: A Simple step-by-step approach for every species. Mutual Publishing, LLC. Honolulu, Hawaii.