Tweaking thinking

After a few more emails and questions, the thought occurred to me that presenting these ideas may make this a bit more logical to readers, so here goes!


Why should wrapping cuttings and maintaining them in the lower temperatures work better?


First, remember the instructions on packaged bare roots about mounding? The idea is keeping the plant cool, dark and damp stimulates the formation of roots instead of top growth. Absence of light and heat combined with dampness is what roots grow in. Adding heat and light stimulate leaf, cane and flower bud growth.


Wrapping the cuttings in damp paper simulates damp earth, as does the darkness. Keeping them cooler prevents formation of the chemicals which trigger top growth, favoring the formation of callus and roots instead. The cuttings already contain the programming to form callus which further develops into roots. Providing them the appropriate conditions to favor that kind of development speeds the process along. Holding them in higher or warmer temperatures stimulates both growth and callus, often the former at the disadvantage of the latter.


The whole reason for the rose to grow is to create flowers. The whole reason for the creation of flowers is to attract pollinators to create seed and perpetuate the species before the plant dies. Pollinators and the plants evolved together. The more successful roses broke into growth and flower as the appropriate pollinators arrived. Both were stimulated into the appropriate state of development simultaneously. Providing different conditions than those outside "trick" the rose into doing what is wanted from it, much like the Romans passing steam under potted roses to force them into flower out of season. Also, much like forcing Paper White Narcissus into flower earlier than usual for the holidays.


If your temperatures are already higher than the suggested sixty to almost seventy degree temperature range which I've found beneficial, why not wrap them, and presuming you have enough room, put them in your vegetable crisper? Prevent them from freezing, of course, but the cooler temperatures in the fridge should also stimulate callusing, though probably at a slower rate. Rose roots continue growing in near freezing soil. Not as quickly as they do in warmer soil, but they do still grow. You might find the need to hold them for three weeks at the lower temps than is optimal at the upper end of the suggested range. Only experimentation will determine that.


I've been repeatedly asked about my potting soil. I have some humidity and more than a little heat. Though no where near as extreme as many other places, it does get HOT here now. The evaporation rates are quite high, yet the evenings remain cooler and even with the heat, it is still humid enough to rot plants sealed under plastic or inside a terrarium. For these reasons, I use moisture control potting soil. If your humidity is greater so evaporation is slower, that man remain too wet for the conditions, rotting the cuttings. Many years ago when propagating for The Huntington Library as a volunteer, using their mist propagator, we used half coarse builders sand and half perlite. It remained damp after the water drained through it, but it also had a lot of air space in the mix so the cuttings didn't rot.


I've known people who tried to replicate the mist propagator and failed because of using organic based soil mix. Continuous wetness causes organics to sour. Dampness works, constant watering, doesn't. The wetter and more humid it is, the more open and fast draining you need your soil mix to be. Same holds for cool temps. Hotter and drier makes for greater evaporation, hence greater water holding capabilities.


It's dramatic the difference humidity makes. My old climate had none (usually) and required keeping everything covered in plastic or they'd die nearly immediately. Here, covering anything in plastic results in it molding nearly immediately. I've never been able to just stick any kind of cutting in a pot in the shade and have it root, but I've done it with hibiscus over winter. I'm going to mess with Mutabilis this winter attempting the same thing. I figured I'd have to put callused rose cuttings under plastic once planted out, but they're forming roots with half day full sun in foam cups. That wouldn't have happened in Santa Clarita. But, then, I never had the fungal issues there I have here, so the humidity is far different. I can FEEL it here, I couldn't there 99% of the time.

The best way is to get a handle on your humidity and how it varies with the year (presuming it does). Surf and absorb all the various methods you find explained and develop one combining the best of all of them, tweaked to your heat and humidity, then begin experimenting with it to see how it has to evolve to work where you are with what you are trying to propagate. 

Once you figure out your humidity and evaporation rate, you can determine what kind of soil is best for you to use. You can also decide whether or not you need to cover the cuttings once callused. I'm finding planting them deeply in the soil to maintain cooler, damper, darker conditions, is working quite well without rotting or drying out before rooting. Think of the cutting in terms of a bare root plant as they really do require the same conditions until they form the root system necessary to support the leafed out plant.

Progress and assorted thoughts on wrapping

After some discussions on Garden Web and a few private emails, I thought it might be of interest to share some further thoughts about wrapping and show progress of the China rose cuttings which were planted just ten days ago (June 11).

It's guaranteed this will require tweaking to be as successful as it can be in other areas, as does anything else related to gardening. I'd originally felt thicker cuttings were going to be more successful. That doesn't explain the 18 foam cups of China roses (really thin, twiggy cuttings, some a quarter the gauge of an eyebrow pencil)  pushing roots out the bottoms of their soil balls. It also doesn't explain the thin cutting of Escapade developing nicely into a maturing plant in a pot.

I do tend to try to make thinner cuttings longer than thicker ones and that appears to have helped. The China cuttings are all five to seven inches long. For any new shoots sprouting from them, I just cut them off leaving the side buds alone so there isn't a lot of softer growth. The "joints" and increased growth buds appear to help, like the traditional "heel" always suggested to take with cuttings with.

These images show cuttings in 16 oz. foam cups followed by each one's roots at the bottom of the soil ball. Clicking on the images enlarges them for more detail.

Chinas can be difficult to select wood to cut for propagation. There are so many "joints" with new growth pushing out everywhere. I selected wood I could cut the five to seven inches of growth. Any buds which had pushed leaves or new canes, I simply trimmed off, leaving a few growth buds on the cutting so new growth was possible from that sprout once rooted. Some of the trimmed, newer growth actually callused and formed roots. Buds which had begun to push and form new foliage were also trimmed so there was no leaf tissue to rot in the damp paper.

Genetics definitely play a role as some just don't have the genetic ability to form callus well nor to form roots which will support the plant efficiently. Shadow Dancer has been a difficult one to encourage to callus and root. Gauge of wood doesn't seem to matter, nor does cutting length. What has rooted most easily are the actually flower clusters where you traditionally don't expect to find growth buds.

The level of stored nutrients available in the cutting will probably also help determine success. Any pathogens already on the cutting when wrapped should also play a part. I'm not sure how wide the successful range of moisture there is with the paper, but too wet WILL cause failure as they suffocate, drown, rot. I haven't experienced what I might consider too dry yet.

It appears temperatures higher than the sixties degrees F range to hold the wraps are too high and inhibit callus formation.

As I've collected the cuttings, I have dropped them into a bucket of water to hold them until I was ready for processing and wrapping. Perhaps if they are too dry when wrapped, that might play a role in failure? I collected, cut, stripped foliage, bundled and tied together with twist tie with label strung on the tie, then dropped the bundle into the water where they waited for collection to finish. Then, I'd shake off the water, dunk them into the Dip'n'Grow and wrap. The wrap would then go into a plastic bag, sometimes several together, and into the work room.

I haven't tried any really soft cuttings yet. My impression is they would benefit from mist propagation to prevent them from collapsing or rotting where harder wood, perhaps better described as hard wood cuttings, seem more appropriate for the method.

Traditionally, you'd use a flowering stem from a recently shattered flower for propagation. I have used that with the wraps and they have worked. I've also used wood older, more mature than that and that has worked. I haven't used anything newer or softer than that with it. They have just 'felt' too immature.

If it's difficult to squeeze out enough water from the paper, try an old rolling pin you wouldn't mind getting printing ink on. That might  provide a make-shift wringer for your paper. You should be able to squeeze out even more water than possible by hand, and it should be a lot easier on your (MY) hands!