Zone 8 - Growing pains and how to avoid them
Californian Don has much experience in growing
palms in a temperate climate and provides another valuable contribution.
This time, how to provide heat for those recalcitrant hardy palms.
by Don Tollefson, Venice, California, USA
Chamaerops No.27 Summer 1997
The simlpe shelter in action. The palm is a Dyctiosperma
and the photo is courtesy of Pauleen Sullivan. Though it's taken
in California, the principle remains the same wherever you are.
Most importantly, I would like to establish the ideal
outdoor planting size for palms as a large, 'substantially' root
bound five gallon (10inch/25cm diameter) pot which should be planted
during the late spring or early summer. 'Substantially' means that
the container can be knocked off the root ball with no soil falling
off the roots, with root mass equal to or exceeding soil mass. When
the container is removed from a 'ready to plant' palm, the solid
mass of entangled roots which has become compressed inside the container
seems almost like a mass of concrete rather than a root ball. Attaining
this condition requires some patience, but the pay off occurs after
the palm is planted in the ground and explodes with growth during
that first year, rather than 'sulking' (a condition of shock which
palms routinely experience whenever they are planted being less
than excessively root bound).
This is the most critical key to success, because
initially the palms can be grown to this size much more quickly
in a controlled environment than outdoors in the ground, and next,
the palms grow much more quickly after planting, so the end result
is a palm that was planted in the ground later, but ends up much
larger and healthier in the same time period. Remember, the race
is not how quickly you plant the palm in the ground, but how large
and how well established the palm is as it prepares to face its
first upcoming winter.
Growing palms to this ideal planting size quickly,
requires consistent heat and a controlled environment for many palms,
and moderate heat coupled with ample time for the remainder. In
all instances, the palms require winter protection, and in particular
should never be allowed to experience temperatures that go below
freezing. Many species can endure freezing, but nothing is accomplished
by subjecting them to it unnecessarily, and you can induce 'automatic
shut down' whereby the palm will shut down immediately at the first
sign of cold. Remember, palms have 'memory' and freezing is a drastic
cut off point for palms which they can easily 'remember' and which
they should only be required to endure after they are planted outdoors
in the ground along with whatever protective help you re willing
to provide as a grower.
Pre growing conditions
There are two methods for providing the growing
opportunity necessary for these palms to reach the ideal planting
size quickly. The conventional greenhouse and the more contemporary
HID light or the HID light used in combination with a CO2 generator
used by many indoor hydroponic growers. The greenhouse is excellent,
except that there are problems inherent with their use in Europe.
First, they require nighttime winter heat, a tremendous expense
for a palm enthusiast, simply attempting to promote and enjoy a
hobby. Greenhouses, by their construction of glass or clear plastic
(usually single layer) lose heat quickly, and the cost of nighttime
heat soon becomes excessively expensive.
The next problem is that there tend to be many
overcast autumn, winter and spring days. Cloud cover results in
interrupting the arrival of the essential infra red solar rays into
the greenhouse, and without this radiation, inadequate heat is provided
to produce the desired growth. This is inherently problematic since
without exception the secret to rapid palm growth is consistent
heat. If the greenhouse provides inconsistent heat, then the plants
will experience inconsistent growth. This is unacceptable because
it is while the palms are young that they grow most slowly and in
greatest need of consistent heat, and much of the skill in growing
palms outdoors lies in the ability to consistently provide a favorable
growing atmosphere for the palms while they are young.
Even if conditions are perfect, the palms will
not grow quickly enough for the satisfaction of most palm enthusiasts,
so the provision of the best possible growing conditions is essential
When planning to build a greenhouse, be certain
that its long side faces south, that you do not have trees and other
objects casting shadows on it, and that either it has a low ceiling
height, or that you have high shelves in it on which to place the
palms. If you have these things then you are on the right track
and you should next consider the proven benefit of reflection. If
you have too many overcast days to facilitate good growing, then
reflective devices will not help, but if you have consistent sunny
days, but experience difficulty obtaining appropriate heat levels
due to an extreme northern location, then reflection could be the
answer. Plywood painted flat white or tin foil backed polystyrene
insulation sheets both provide inexpensive reflection, reradiating
the suns rays to approximately 70 % of the sun s initial radiation.
The reflection must occur outside the greenhouse, and redirect the
suns rays into it. A good method is to attach the plywood at the
top rear portion of the greenhouse in line with the top of the rear
wall. The higher the reflective device extends above the roof the
better, but don t forget the force of the wind that can tear off
your devices and hurdle them dangerously through the air. Devices
on the west and east sides are also helpful, and correct placement
can slightly more than double the effect of the sun, so if you consistently
have 80 degree days in the winter, you can expect them to increase
to 90 degree days with reflection. And don t forget that your ultimate
test date is December 21st, because that s when the sun s rays are
most distant and your daylight is shortest, and not several weeks
later when your temperatures are at their lowest.
In most cases a double growing system is probably
best. That is, to grow the palms in a greenhouse during the sunny
months when temperatures are warm, and then move them into a protected
area such as a basement or garage when the nighttime temperatures
drop consistently into the 30sF (0-5deg.C). This eliminates the
expensive and impractical necessity of providing winter heat in
the greenhouse, but it unfortunately does forego the ability to
produce rapid year-round growth which is so essential to the psyche
of the typically impatient palm enthusiast.
Perhaps the most practical method of growing
palms in Europe would be with an HID light or with an HID light
in combination with a CO2 generator. With this system, HID (high
intensity discharge) lights produce the light necessary for photosynthesis,
replacing the need for natural sunlight. This in turn eliminates
the necessity of clear sheeting to enable the entry of natural sunlight.
Since clear sheeting allowing sunlight to enter is no longer necessary,
materials with great insulating properties can be installed to contain
heat within the growing area. For instance, a garage can be double
or triple insulated, to the extent that it maintains any heat generated
for several hours. And with the appropriate level of insulation,
a single HID light alone will suffice to provide adequate heat for
growing as well as the essential light. For conventional indoor
gardening purposes, a 1000 watt light will serve a 10 by 10 foot
area. However, palms require less light than conventional gardens,
and a 1000 watt light will probably serve a 20 by 20 foot area.
Particularly if the walls are painted flat white to reflect light
back onto the back of the palms. There are also smaller, less expensive
HID lights that work just as well, but for smaller areas.
HID light growing is a proven effective method
which has been in use since the Japanese developed hydroponic gardening
shortly after World War II. However, in order to produce photosynthesis,
palms also need water, CO2 and warmth. Water run off problems can
easily be solved with inexpensive plastic tubs and plastic gutter
systems which cost little, actually enabling the placement of a
fabulous palm growing environment within an enclosed garage. Ventilation
to provide CO2 is more of a problem. Traditionally, HID light growers
have ventilated their growing areas with conventional ventilation
systems such as mechanical draught exhaust fans which provide air
exchanges in a matter of minutes.
For growing palms, the air exchanges occur far
too quickly, removing the warm air, and if it is cold outside, replacing
the essential warm air with growth inhibiting cold air. The palms
require two things in addition to water and radiant light. They
need warmth and they need carbon dioxide and they need them in combination.
The operative word here is combination. If you provide warm air
depleted of carbon dioxide, or if you provide carbon dioxide replenished
air which is cold, you will not obtain the growth which is so critical
to maintaining your enthusiasm. If conventional ventilation is used,
install a fan which provides a slow air exchange such as a 50 or
60 cubic foot/minute bathroom fan and place it on a timer so that
you can limit and control the ventilation.
The objective is to retain as much heat as possible,
but to provide fresh air containing carbon dioxide at the same rate
at which the palms deplete it. A rule of thumb is to run the exhaust
only once or twice a day, just long enough to provide one air change
every morning and once again during the warmest period of the day
(around 3:00 p.m.), but provide the second air exchange only on
days when the temperature reaches or exceeds 90 degrees F (30 deg.C).
The ultimate growing system might be HID light
in combination with a CO2 generator. CO2 generators have yet to
be proven, but they can be purchased for two to three hundred dollars.
The smallest of these units should provide more than enough CO2
for palm cultivation. A CO2 generator enables a grower to retain
heated air within an encapsulated (insulated) environment, by replacing
only the CO2 that is extracted by the palms, without requiring the
air exchanges which trigger the excessive cost of providing nighttime
Perhaps it might seem like a burdensome financial
outlay to purchase an HID light and a CO2 generator, but compare
it to the cost of nighttime heat which can be so expensive during
the winter months. So expensive in fact, that only a few heated
greenhouses probably actually exist in the Pacific Northwest for
the purpose of growing palms. A saving can be seen after the first
season with several more seasons practically cost free. The manufacturer
s estimated life expectancy of an HID bulb is two to five years,
and only the bulb needs to be replaced when it burns out. Consider
purchasing an HID light the first year, while making do with a cheap
bathroom fan for exhaust, and then purchasing a CO2 generator the
following year. There are less expensive ways to raise palms in
cool winter areas, but they are much slower and much less gratifying.
If you are considering an HID light, here are
a few basics. Hydroponic growers of tropical plants have already
determined that the best growing format for tropicals (including
most palms, tropical or otherwise) is that the HID light be on for
12 hours and off for twelve hours, turned on once per day for maximum
growth results as well as maximum bulb life expectancy. Never splash
water on a hot bulb or it will explode with the potential of causing
serious injury, and it is strongly urged that a protective glass
cover be purchased along with the HID apparatus to prevent this
The optimum growing temperatures for tropical
palms is 93 degrees F. (33 deg.C). Above that it has been scientifically
proven that almost no palms benefit in terms of showing faster growth,
although many growers strongly claim otherwise. Heat loving palms
(Sabals, etc.) can be placed on upper shelves, while palms requiring
cooler conditions (Ceroxylons, etc.) can be placed on the floor
with other palms in between. There will be a 15 to 30 degree F.
difference between the floor and the top shelf space at any given
time and two max-min thermometers should be installed at top and
bottom locations for determining these differences and providing
the correct temperature at any given time. It is also advisable
to provide a circulating fan, and preference should be given to
installing a ceiling fan as they do the job of circulating the air
beautifully, and they are practically noise free, a welcome relief
from the obnoxious noise created by conventional circulating fans.
Post Planting Techniques
Enthusiasts are naive to believe that a 'sink
or swim' approach is best with palms at the time of planting. Consider
throwing children into the water, and allowing those unable to figure
out how to swim to drown. Ultimately, some of the smartest, strongest,
best looking and finest swimmers turn out to be children who would
have drowned. This same analogy is true for palms, not to mention
that palms are much more valuable (just kidding!). After planting
a substantially root bound five gallon palm, it is imperative to
provide some assistance. This can be in the form of a small temporary
shade house (shade cloth), or an individual cold frame (UV resistant
clear plastic). These methods meet with great resistance from growers,
but they shouldn t because they are easy to provide and they pay
off with big dividends. Shade cloth cover really prevents the shock
of direct sunlight after a palm is brought out from the greenhouse,
enabling is to establish quickly. It makes an unbelievable difference.
More importantly, there are some fine palm species
that simply cannot survive in cool climates because they require
intense summer heat which is lacking. Sabals and Braheas are examples,
but if an individual cold frame is installed they will bask in heat
which is twenty or thirty degrees F. warmer during the summer, and
not only survive, but flourish.
In the case of the individual plastic cold frame,
leave a couple of inches between the bottom of the plastic and the
ground to allow the entry of fresh air. After a couple of years,
you can let them sink or swim after which time if they can t swim,
they deserve to sink. Standard four foot wooden construction stakes
can be used to quickly provide the structure for either and for
just a little money a valuable palm is ensured the appropriate opportunity
to survive and grow beautifully far beyond the lifetime of the grower
who planted it. A grower can quickly install shade or plastic for
the palm's most important first winter, making a monumental difference
in the palm's future performance and there is really no excuse for
failing to do so. Remember, laziness is a reason, not an excuse.
In conclusion, the most important aspect of
developing a magnificent, tropical looking collection of exotic
and rare palms is to attempt to grow as many different palm species
as possible, using the quickest and best methods of growing the
palms from seedlings to a perfect planting size and utilize some
form of post planting technique. Sound simple? It really is and
as a matter of fact it s one of those rare things that s even simpler
than it sounds!
27-09-21 - 13:04GMT
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