Brent,
Thanks for the terrific summary of rooting cuttings. It should save folks a
lot of trial and error in getting started with cuttings.
Jerry Meislik
Whitefish Montana USA
Zone 3-4
http://www.bonsaihunk.8m.com/ Folks

You wouldn't believe how much time and thought I have put into rooting
hormones over the last fifteen years. First, do rooting hormones (IBA, NAA,
etc) work? Absolutely. Much scientific work has been done and continues to
be done on the amount, type, preparation, and strength of hormones most
effective for thousands of species. The IPPS, International Plant
Propagators Society, is devoted to it. They meet once or twice a year and
attract people from around the world. They have produced _volumes_ of
information. Dirr's wonderful propagation book, The Reference Manual of
Woody Plant Propagation is a gleaning of this information for the most
common woody plants in the nursery trade.

Can you root cuttings without hormones? Absolutely. Plants produce their
own rooting hormones that become active when a stem is removed or broken
(or sometimes submerged or placed in darkness). For some species that is
all you need. For better rooting, and higher percentage of strikes,
applying additional hormone is usually recommended. Many species will
almost never root without exogonously applied hormone. Nearly all species
root better with an appropriate hormone.

What type of hormone to use? There are two common commercial preparation
types, talc based powders and solvent based liquids. Talcs generally
contain IBA as the active ingredient, although a few also contain NAA. The
strengths range from 0.1% to 4.5%. All these strengths are available over
the counter (Mellingers.com). One of the most common is Rootone which is
0.1%. It is fine for easy to root plants, ok for moderately hard to root
plants (mostly improving quality, not quantity of strikes), and pretty much
worthless for difficult to root plants. It does contain a fungicide that
may or may not be beneficial. In my opinion, a better way to go is Hormex.
They make small 3 jar sets of two hormone ranges. The first is the low
range, Hormex 1, 3, and 8. These are 0.1, 0.3, and 0.8% IBA respectively.
The three jar set is less than $10, although I haven't check the price in
ages. The higher range is Hormex 16, 30, and 45. These are 1.6, 3, and 4.5%
respectively. The most common liquid form is Dip and Grow, which is 1% IBA
and little NAA dissolved in alcohol. The solvent also acts as a carrier,
transporting the hormone into the bark tissue. This means that in general,
a lower concentration than the talc formulation can be used. For many easy
to moderately difficult to root species, this is a clear benefit. For other
species the solvent causes necrosis and cannot be used. In general, it is
far easier to 'burn' a cutting with a solvent based hormone. The strength
of the hormone is limited due to two factors: IBA is also slightly soluble
in alcohol (and far less soluble in water), and second, the concentrated
solvent is more likely to cause necrosis. Thus for difficult to root
species, talc formulations are usually better.

The preparation and after care of treated cuttings is very important.
Liquid hormones must be diluted properly and then the cuttings must be
treated properly. The weaker the solution, the longer the cutting must stay
in the solution. Most commercial growers use 'quick dip' concentrations.
That is, they go one level higher than recommended and just dip the
cuttings for a second and pull them out. Speed is important in any
industry. This sometimes causes necrosis at the base of the cutting, which
can be limited by keeping the depth dipped to about 1/4 inch. Talc
formulations have to stay on the cutting, so the cuttings have to be wet
and small quantities of hormone are used in the dipping vessel at one time
because it soon becomes a paste from the water. Usually, cuttings are
dipped to about one inch, and tapped against the vessel to remove the
excess. The cuttings are immediately stuck in saturated media and NOT
watered for as long as possible. Subsequent watering should be minimized to
keep the hormone stuck to the cuttings. Under mist systems, this is usually
not a problem. I once lost an entire season of extremely valuable pine
cuttings because the mist system got stuck in the on position when I wasn't
around. The cuttings survived but failed to root.

If you want some really esoteric reading material try Adventitious Root
Formation in Cuttings. It covers just about every thing imaginable that
causes or effects root formation. It is not exactly lightweight reading.
Dirr's book is a walk in the park next to this baby. Things I learned from
this book: Optimum all around, in general, light requirements for cuttings-
50% natural sunlight (50% shadecloth). Mist is better than enclosure
(cloches). Hormones only work for a very brief period of time soon after
the cutting is taken, after that, additional hormone may be detrimental.
Rooting of cuttings is FAR more complex than any of you have possibly
imagined. Bottom heat does work (I knew that already). Feeding of cuttings
is still an unresolved issue. Some plants exhibit a 'flood response', that
is why willows root in water. Probably a few other things that I can't
think of right now. Bottom line, there is no silver bullet. Plant
propagation as a biz is difficult and fraught with potential disaster
waiting around every corner.

Brent in Northern California
Evergreen Gardenworks USDA Zone 8 Sunset Zone 14

http://www.EvergreenGardenworks.com

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