Categories of cuttings.
For the home owner the above can be as simple as keeping the cuttings under the bonsai bench (But off the ground) that is watered once or twice a day where they will receive no direct sunlight. The next step up is to build a propagation case and provide it with automatic mist. The first case I built was eighteen inches wide by about six feet long and two feet high and covered with clear fiberglas. It held three or four flats. It had three mist nozzles overhead (available from mellingers for about a buck apiece). I am a great tinkerer which gets me in trouble but I have a lot of fun designing and building stuff. I built my own mist system and put heating cables in a bed of sand in the bottom. I built my own 'leaf type' mist switch that opens a circuit when wet, it is counterbalanced and drops when wet opening the contact on a microswitch, and rises when dry closing the circuit and kicking in a solenoid allowing the water to flow to the misters. Commercial units are available for about $150. Mine never did work right and I was always frying cuttings. I now use timed mist, as do most professional growers. You can now get these from Charlies Greenhouse supplies, they are about $75. They are timed periodic mist, so you can vary the period between mist and the duration of the mist. For our climate I find seven seconds of mist every fifiteen minutes sufficient to keep the leaf surfaces constantly wet. Mine is in series with a 24 time clock that is programmed to turn it off during the night. It can still be too wet on cloudy days so I also have it in series with a themostat that does not allow it to come on unless the temperature is about 72 degrees F. In a propagating case leaving the doors cracked open will allow sufficient air for ventilation.
Bottom heat acts a stimulant for the production of roots as well as for faster root growth. In general bottom heat should be ten degrees hotter than the ambient air temperature, although any amount of bottom heat is useful. I have mine set on a themostat that turns it off during the day when it is over 75 in the propagating room to save propane. The temperature should not be allowed to fall below sixty five and optimal seems to be about 75 ot 80 for most species. Some species are more sensitive to heat than others. Most of the tropicals I have grown in the past, liked it hot. Maples also root much faster when hot. It is thought that a few cultivars of Juniperus actually prefer cooler temperatures once they callus, but the jury is still out on that one. I have had Fuchsia root in five days on high heat, pomegranate in seven to ten. I even had some Japanese Maples begin to root in ten days last year.
The easiest and cheapest way for the homeowner to get into bottom heat is by purchasing a heating mat and controller, you can get a small system for about one hundred bucks. They use a lot of electricity, even a small one, be prepared for your bill to jump. Larger systems are hot water fed. A regular hot water heater can be used with a small circulation pump hooked to thermostat. Commercial units are called Biotherm and manufactured by a small company here in California. I designed and built my own with drip tubing parts. It has worked fine for eight years.
By far, most semi hardwoods require hormone in the range of 0.3% to 1.6% IBA, or Hormex 3 to 16. There are some that require no hormone such as willow, Salix, although I shallow dip my Salix species now and start them flats instead of water. They begin rooting in less than a week and are ready to transplant in two to three weeks. The root systems are denser and more fibrous with hormone treatment. Some cultivars of Japanese Maple, Acer palmatum, require high levels of IBA, I am now using shallow dips in Hormex 30 (3% IBA) for some of them. Many species will not root immediately, although most root over four to ten weeks. Some species will take a year or more to root after initially callusing in a few weeks. These I take off the heat at the end of the season and keep shady and cool until they do root. Hawthorns and many Chamaecyparis fall into this category.
Many semi hardwoods respond favorably to wounding. The bottom of the cutting is sliced thinly through the cambium for about an inch, taking out a sliver of bark without removing much wood. This is best done with the edge of sharp shears or a sharp knife to make a clean cut. This provides a surface for callus and hopefully root development. It helps Malus, Acer, and roses. It is also interesting to watch where roots develop on various species. If you wound, the roots will often form in a line along the callus tissue. Many cuttings form in a ring around the bottom of the cut (Chaenomeles), others form at the lenticels (openings in the stem similar to stomata on leaves), and yet others form at the leaf scars (roses). For some it is necessary to have a node at the bottom of the cut, other not (Clematis, Acer).
Well, you can see that I like to do cuttings, actually this is the specialty of our nursery, and we are doing some things that very few people people in the world are doing such as Hawthorns and Birches. Probably more than you ever wanted to know, but a nice diversion for me on a hot sunday morning when I am supposed to out there doing......CUTTINGS!
Evergreen Gardenworks is a mail order nursery. To receive their catalog just send your name and snail address to PO Box 1357 Ukiah CA 95482 or request it via email bonsai@pacific.net.
P.S. Clean! To avoid fungal infections, a very serious problem with cuttings keep everything as clean as possible. Think of it as handling meat in the kitchen. You must always remember where those hands have been. Use a ten percent bleach solution (nine parts water, one bleach) to clean everything including the flats, shears, your hands and the cuttings. After the cuttings are made soak them in the bleach solution for fifteen to twenty minutes, rinse all of the bleach off thoroughly (it will oxidize the IBA) and dip in hormone and stick.