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Propagation
of Woody Plants by Cuttings
By Brent Walson (From
the Evergreen Gardenworks web page. http://www.evergreengardenworks.com/cuttings.htm)
Introduction
Most cuttings are
pretty easy with the proper environmental conditions.
Cuttings need: 1) a clean well drained rooting medium, 2) a
rooting hormone provided either naturally or by applying
one, 3) a constant supply of moisture to make up for the
lack of roots, 4) sufficient light to allow the manufacture
of food (softwood and semi hardwood), 5) bottom heat in some
cases, although almost all do better with it.
Rooting Medium
The medium must be sterile for good rooting
percentages over a wide range of species. Some species
appear to be immune to ever thing fungal in the soil and
others are very prone to infection . Most roots also need
air to form, as well as to minimize infection. You must
balance the need for drainage against the need for a
constant supply of moisture. Without automatic mist the
medium must hold more water. A good place to start is 50%
peat and 50% perlite. With automatic mist or in an
environment of cool moist air such as a coastal area, it is
better to move closer to all perlite.
Perlite is now nearly
universally used instead of sand or volcanic aggregate
because it is lighter, sterile, and inexpensive. I use about
eight parts perlite to one part peat and one part
vermiculite. The peat and vermiculite make the perlite
easier to handle, reduce the fluffiness and aid in punching
the holes for the cuttings. I also harden off and grow out
the cuttings in the propagating flats so the peat and
vermiculite give me a small amount of nutrient holding
capacity, perlite has none.
I use 18 inch square
propagating flats with mesh bottoms that give excellent
drainage but still hold the medium inside. The mesh is about
half inch squares. Ground covers are frequently grown in
these flats. I use a dibble board that I made to punch the
holes for the cuttings, 182 per flat. All of this is old
fashioned these days with the advent of Oasis type cells,
but for me it is cheap and easy and allows me to keep the
rooted cuttings in the flat longer.
Rooting Hormones
There are two types of rooting hormones on the
market, talcs and solutions. Talcs such as Hormex contain
the hormone indolebutyric acid, or simply, IBA at various
concentrations, that's what the numbers mean, Hormex #1 is
0.1% IBA. Rootone is 0.1% IBA and also contains another
hormone. Rootone also contains a fungicide, Thiram. Rootone
is fine for easy cuttings but will be worthless for cuttings
needing a high level of IBA. The liquid hormone solutions
such as Dip and Grow and Wood's are a solution of IBA and
NAA in alcohol. The alcohol acts as a carrier so lower
concentrations can be used. Both are only 1% IBA at full
strength. Some cuttings are sensitive to alcohol and can
burn. I have found the solutions not effective for cuttings
requiring how levels of hormone.
How do you know what levels
for each species? There is one book that is far superior to
all the others for this type of encyclopedic information,
Propagation of Woody Plants, by Dirr and Heuser, available
from Timber Press, they have a Web site. It costs about $40.
It is my propagating Bible, although I know most of it by
heart now. It is a compendium of studies from around the
world including the information complied by the
International Plant Propagators Society, IPPS. If you have
only one propagating book it should be this one. Beginners
will find it only slightly overwhelming at first.
Moisture
Without a root system cuttings rely on absorbing
moisture through the stem and leaves. This works just fine
if the medium is constantly wet and the humidity is high and
it is cool, seventy to eighty degrees during daylight hours.
This is the toughest aspect to achieve at home. You must
reduce the rate of transpiration to protect the cuttings
from wilt. You can do this by keeping them cool, keeping the
leaf surfaces wet, and by reducing the leaf surface area.
You can remove some leaves to reduce surface area so that
only two or three small leaves remain, or you can, as I
prefer, remove the bottom leaves then cut the remaining
leaves in half. After a while you get a feel for how much
leaf area each species can support given your individual
conditions.
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 fiberglass. It held three or four flats.
It had three Floramist 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 was counterbalanced and dropped down
when wet opening the contact on a microswitch, and rising
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 sophisticated
periodic timers from Charlies Greenhouse supplies, they are
about $75. They allow timed periodic mist, so you can vary
the period between mist and the duration of the mist. For
our climate I find five seconds of mist every twenty 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 thermostat that does not
allow it to come on unless the temperature is above 72
degrees F. In a propagating case leaving the doors cracked
open will allow sufficient air for ventilation.
Sufficient Light
It is thought that roots are stimulated in cuttings
by high light levels, although I have not seen the studies
to support it. But cuttings do root as a response to food
moving down the stem in the phloem (remember your botany
test, phloem and xylem) and stopping at the bottom cut.
Finding no roots to store the food, it backs up at this
point and changes take place in the presence of hormones to
convert stem tissue to undifferentiated tissue (callus) to
finally root tissue.
This process works better
of course if there is sufficient food to make this happen,
thus the need for retaining leaves on softwood and semi
hardwood cuttings. Food is also stored in the stem tissue
itself, and this is sufficient for leafless hardwood
cuttings, although the process is much slower. High light
levels obviously play a role here by keeping up
photosynthesis. You must balance out the need for light
against the buildup of heat. For simple systems all shade
works just fine. A VERY light foliar feeding also seems to
aid in this process, although nitrogen encourages algae to
grow in the medium and will soon create a wonderful swamp if
you overdo it.
Bottom Heat
Automatic mist and bottom heat revolutionized the
nursery industry around the time of the second world war.
Before that most production was by hardwood cuttings, which
was slow and effective for a limited number of species.
These days there are very few plants that cannot be
propagated from cuttings and those that can't can usually be
done by tissue culture.
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 thermostat
that turns it off during the day when it is over 75F in the
propagating room to save propane. The temperature should not
be allowed to fall below sixty five and optimal seems to be
about 75F to 80F 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.
Cuttings fall into
three categories, 1)softwood, 2) semi hardwood, and 3)
hardwood.
Softwood Cuttings
These cuttings are taken from new growth at the
succulent stage. When a turgid plant tip snaps when bent at
ninety degrees it is ripe for softwood cuttings. Most
perennial cuttings are done this way, very few woody plants.
In general low levels of IBA improve rooting but are not
necessary. I find that Hormex #3 on the very bottom of
Fuchsia cuttings, not more than 1/8 inch stimulates
incredibly dense roots starting in about one week. This
would ordinarily be too strong for this type of cuttings and
there is some necrosis where the cutting was actually
dipped, but roots are amazing.
Semi hardwood
Cuttings
Most woody plant cuttings these days are from semi
hardwoods. These cuttings are taken from wood that grew this
year but is now firm and hard, with hardened leaves. It is
well lignified at the base but still may have a soft tip
that may or may not be removed. It is better to go by the
feel of the wood instead of the calendar. The peak season is
June and July. There are also infinitely varying degrees of
hardness and each species and sometimes cultivar will
respond differently. This is a matter of experience and
volumes have been written about it. Some species such as
birch and Picea have very narrow windows of opportunity.
Others, such as most crabapples can be taken all summer
long.
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).
Hardwood Cuttings
Hardwood cuttings can be taken at any time of the
year, but are usually taken late in the season or winter and
stored in sand, sawdust, etc. They are cuttings from wood
that has gone through an entire season of growth. The can be
treated just like softwood cuttings in summer for some
species, but most are done at the end of the season and
either stored and planted in the spring after they callus or
simply planted in open ground in the winter. With the advent
of mist and bottom heat their popularity has diminished
except for some commercial crops such as grapes.
And Finally
Be 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), then dip them in
hormone and stick.
About the Author
Brent Walson
runs a nursery near Clearlake, CA and is very giving with
his knowledge. He also carries some very fine bonsai and
pre-bonsai stock available by mail order. His nursery is
not open to the public.
We recommend visiting his web site
and also visiting the IBC (Internet Bonsai Club) to expand
your information base.
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