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 for success.

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 heat.

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 risk.

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!