I spoke to a group last week that included some truly passionate propagators. As part of the program, I opened the floor for questions and there were some doozies. I know I learned a thing or three from the dialogue and believe you will, too.
Q. My mother-in-law has a huge corn plant with several tall stems each about 2 inches in diameter but only a few leaves at the top. We have tried several times to make an air layer. What tips can you give us?
A. You may have better luck by taking a deep breath and saying, “Off with his head!” When canes get as big around as these and have few leaves, you can see that the canes are compromised and may not air layer well. These canes sometimes root faster in a pot of damp sand mixed with some potting mix. Make the cut several inches below the lowest leaf and roll its base in Hormex #1 or dip it into Hormex Liquid Concentrate for 1 minute before sticking into the pot. Make another cut, this time much closer to the base. Prepare a flat of damp sand, cut the bare cane into 3 inch pieces, and slice a narrow strip off one long side of each. Roll the cut side in Hormex #1 or soak in HLC for 1 minute and then sink each cane sideways into the sand, cut side down, until they are almost covered. Chances are very good that the mother plant will sprout, the cutting will root, and at least some of the bare canes will grow, too. From one sad cane, you can clone a crowd.
Q. I put forsythia and pussywillow stems in warm water to force the flowers and sometimes they root. When I potted some up, they died. What did I do wrong?
A. It’s not easy to get viable roots by sticking woody stems into water. But when you do, the roots are usually thin and just do not have what it takes to support a new plant once you put them into soil. Since you have better-than-average success at rooting those prized flowering stems, take one more step. Instead of potting them up as ready to grow, slip the rooted stems into a pot of damp sand mixed with finely ground bark and water them well with HLC. The stems that we force for flowering are often quite long and it would be a good idea to cut at least half their length off after potting. With your good propagating skills, they will probably root, too.
Q. Are you supposed to check on hardwood cuttings while they are in storage during the winter? Some rotted on me once and I could have made more if I had known. I have heard that it is hard to do this process where the ground does not freeze. Is that true?
A. We are challenged by mild winters, but not enough to abandon hardwood cuttings. Although it is not usually necessary to unpot or dig up hardwood cuttings, you either need to do that or change how you store the bundles. I suggest you abandon the trench if you use one and use pots of damp sand to bury the bundles of clones. Pick a pot big enough to surround the bundle with an inch of sand on all sides and put the pot in a cold spot like under the house or in the spare refrigerator – move the beer and you will have a perfect 40 degree chilling storage.
Q. Is it a good idea to slice off some of the bark when you root azalea cuttings in the spring after you prune? How do you root spireas? I tried some of both last year and had okay results with the azaleas, but nothing from the spireas.
A. Yes, it is wise to wound the semi hardwood cutting of azaleas to propagate them. Take a six inch cutting so you can slice the thinnest bit of bark from the lowest inch of the cutting right before you stick it and still have about 3 inches of wood under the soil. Exposing the cambium layer and then rolling it in the appropriate strength Hormex (#3 for azaleas) increases rooting percentage and may speed the process. As to spirea, its thin stems root best for me a bit earlier in the season while they are soft or later, as hardwood cuttings. Here’s what I do with the soft wood: Take a group of cuttings that are 6-8 inches long from the new growth and fill a shallow flat with a well-drained rooting media. Roll the cuttings in Hormex #3 and slide them sort of sideways into the flat. Slip the entire flat into a big plastic bag to increase the humidity around them, water enough to keep the conditions just damp, and ventilate as needed.