Fine Tuned Palm Gardening: Sunsitizing

Our most regular contributor provides more tips for exotic gardening.
Don Tollefson, Venice, California, USA
Chamaerops No.34 Spring 1999

Over the years, you gradually learn what does and doesn't work in palm gardening. As time passes, you realize that by the time you're old, you could have done it right... if you were just a little younger! The following tips are designed to keep you younger by helping you move faster than time.

"Sunsitize": What's the most common error made by palm gardeners? Failure to adequately "sunsitize" (to properly acclimate palms to increased levels of sunlight). Beware of the "double twos!." Too much sun, too quickly. It results in sunburn. Just like the white-skinned beachgoer on that first sunny day at the beach. Frequently, most or all of the palm's fronds are damaged. This leaves only the new spear. This lonely spike now has to provide all of the botanical exchanges required to sustain its fully developed root system. The palm may survive. But it will take a long time to regain its former status.

An all too frequent problem: Failure to properly sunsitize a palm results in sunburn. Sunburn happens to some of the most advanced palm gardeners' plants. Imagine the frequency with which it occurs to beginners. Sunburn results in damage to the fronds. This damage can be from minor to total. It results in diminished growth. Diminished growth results in far less ability for a palm to survive that first, outdoor winter. Why be off to a terrible start? Particularly since a successful start is one of the most important ingredients in successful palm gardening.

Plantable palms, pre-plantable palms and sunburn: Sunburn occurs most frequently when a palm is brought directly from the greenhouse and placed outdoors. This is a frequent occurrence due to the popular preference of acquiring "plantable palms." A plantable palm is one that is fully acclimated to the outdoors and sunsitized. Plantable palms are the overwhelming choice of most palm gardeners because they are capable of immediate, outdoor planting. Typically, these palms come directly from the greenhouse. As such, they are not yet plantable palms. They are "pre-plantable palms." Preplantable palms are plantable palms that have not yet been sunsitized. They are not yet capable of immediate, outdoor planting. Herein lies the recurring problem: planting a preplantable palm without first sunsitizing it.

From the greenhouse to the shade house. Failure to sunsitize palms is a major cause of sunburn damage and setback. Upon removal from a greenhouse, palms should be placed under shade cloth. This enables the double transition. To acclimate and to sunsitize. Unfortunately, palm gardeners are often uninformed and unaware that their palms are direct from a greenhouse. This occurs most frequently at palm sales and palm auctions. Palm sales and palm auctions are a major source of palms for collectors. Thus, a major source of preplantable, unsensitized palms. A recipe for sunburn. A good rule of thumb is to assume that every palm is pre-plantable. Then follow the time-proven technique of moving palms from the greenhouse into the shade house. Don't skip the shade house. It's the most overlooked, under-utilised step in palm gardening.

Shade house level: Inexpensive shade cloth can be obtained in various shade levels from any home and garden centre. The level of shade should be from 50% to 70%. A palm which is removed from 50% shadecloth seldom sunburns. But it doesn't grow as well or look as good as its contemporary under a higher level of shade cloth. A palm which is removed from 70% shadecloth occasionally will burn. But palms grow faster and look better under 70% shade cloth. It's a trade off.

Erect a simple shade house: An important technique for the beginner is to erect a simple shade house. A simple shade house can be inexpensive and quickly erected. It's merely a shaded area for sunsitizing palms. Then, after the palms are sunsitized, they can be "inched" into full sun. One of the most common tendencies with new palm gardeners is a reluctance to construct anything. And one of the most common realisations after construction is how easily it was accomplished.

Filtered light: An alternative to shade cloth is filtered light. This works well if a canopy of overhead trees exists. The palms can be positioned under the canopy with the same results as shade cloth. From there they can slowly be "inched" into the sun until they are ready for outdoor planting. Be careful not to misjudge the canopy s level of shade. Also be certain that the placement of palms is not in direct sunlight.

Timeframe: Palms can remain under shade cloth for a period of a few weeks to a few years. A rule of thumb is to allow them to remain under shade cloth for a minimum of one year. One year allows the development of a complete, new set of fronds under shade cloth. This new set of fronds is fully acclimated and sunsitized to 30% to 50% of the available, direct sunlight. An outdoor planted, shade cloth sunsitized palm, will perform far better then one arriving directly from the greenhouse. Perhaps three to five times better. That's why sophisticated shoppers of palms, first visit the shade houses of rare palm growers. This is where the plantable palms are located. The palms that don't come from under shade cloth are at best, pre-plantable. Preplantable palms must first be sunsitized. Never overlook this step. No matter where the palms come from, don't sunburn them when you introduce them into more sunlight. Sunsitize them first under shade cloth.

The individual shade house: The individual shade house is one of the most valuable tools of the beginning palm gardener. An advanced palm garden features canopy. At a minimum, side to side canopy provided by existing palms. Even if the sun blasts down from directly overhead, side to side relief provides significant protection. However, most beginning palm gardeners have no canopy. Therefore, it is impractical for them to plant palms from the middle of July to the end of August. It is too hot. The sun is too bright. For this six week period, some growers halt their planting schedule. However, this is an excellent time in which to plant. The secret is to provide an individual shade house over the top of each palm. It sounds like quite a chore, but it can be quite simple. Erect an inexpensive structure that will maintain shade cloth over each palm. A structure that can be reused from year to year.

The inexpensive, individual shade house: The key to success is quick, inexpensive construction. One of the simplest methods is to construct an individual shade house from 3/4" PVC irrigation pipe. A square top, approximately 30" x 30" is constructed from pipe and elbows. Tees are positioned close to all four corners. Legs extend from the tees, downward. These legs are positioned over stakes or canes that have been driven into the ground. Shade cloth is secured to the top with plastic ties. Voila! An individual shade house. An individual shade house costs less than £3.00. The average gardener needs approximately ten to maintain the ongoing, palm gardening process. Quick, cheap and best of all, they can be reused. The secret is to not glue them together. Attach the parts, but don't glue them. They will remain intact. Then, alter the sunny season, the legs can be disassembled and the legs and tops can be stored flat. Brilliant? Yes indeed!

Pot planting and the individual shade house: An increasingly popular palm gardening technique is the use of pot planting in conjunction with individual shade houses. It's an outstanding combination. This combination enables outdoor palm gardening advancements in species and in start up success.

Anti-transpirant: Primarily, antitranspirant is used to prevent a transplanted palm from going into shock. It is applied to the leaves of the palm's fronds prior to the palm's removal from soil. Generally, when a palm is removed from soil, the result is desiccation of the leaves. Desiccation is caused by the inability of the roots to replace the water that is transpiring from the leaves. Desiccation results in a droopy, wilted appearance.

Obviously, the fronds can be destroyed or severely damaged. This damage appears similar to that caused by sunburn. Antitranspirant inhibits the release of moisture through the leaves. This simple process prevents desiccation. It generally works to the satisfaction of the many growers who routinely use it during shipping.

Antitranspirant, sunscreen and sunsitizing: The past few growing seasons, palm enthusiasts have discovered that antitranspirants prevent sunburn. Most agree that they are remarkable for this purpose. Perhaps working better to prevent sunburn then desiccation. Anti-transpirants perform in a similar manner to palms as does sunscreen to humans. Thus, the interchange hereinafter of the word "sunscreen," for anti-transpirant. Sunscreen is first applied to the palm's fronds via a foliar spray. Then a palm can be placed in direct sunlight with a "diminished likelihood" of sunburn. Note the caveat, "diminished likelihood". Growers share divergent experiences. Most have reported that the palms performed as though they had been under shade cloth for a year or more! Quite a remarkable discovery if it proves to be true.

Immediate uses for sunscreen: There are four immediate uses for sunscreen. First, you can move a palm into the sun without first sunsitizing it under shade cloth. Second, you can protect young palms that are growing in the ground from full sun. Young palms (those that can still be reached from the ground) tolerate full sun. But, although they tolerate full sun, most grow much better under filtered light. Therefore, a good policy is to apply sunscreen to the leaves during the hot summer period. This is a fabulous technique for the young garden that lacks canopy. The third use is to apply sunscreen on palms that are coming into sun from under shade cloth. This should make this transition almost undetectable. Fourth, there is evidence that sunscreen will protect palms from hot summer and cold winter wind damage. Sunscreen could be helpful to prevent palm frond damage caused from cold, windy, wet, winters.

Effective time range: Sunscreen gradually wears off. How gradually remains the subject of debate. Manufacturers of most brands claim that their sunscreen will remain effective for an entire growing season. Certain growers have verified this to be correct. However, some growers feel that repeat applications are necessary. Some recommend as often as every two weeks. Manufacturers also claim that repeated applications are not harmful. The first application is most critical. After two or three applications, subsequent sprayings become less important. The length of time that sunscreen remains effective continues on a trial and error basis.

Inhibited growth? Sunscreen raises the question of inhibited growth due to its use. A possible trade-off? Not according the manufacturers. Manufacturers' labels assure that sunscreens, in no way, inhibit or otherwise restrict growth. Time will tell!

Sacrificial fronds: There is one final aspect of sunsitizing. When a palm is brought from one location to another, its fronds are introduced to a higher level of sunlight. For instance, from the greenhouse to the shade house. Or from the shade house to outdoors. Under even the best of circumstances, a palm's fronds cannot adapt to a significantly increased level of sunlight. Such fronds can endure, and survive, with little or no damage. But this adaptation will, day by day, cause the fronds to loose their lustre and depth of colour. The rule: A frond that was not acclimated to a higher level of sunlight during its youth, cannot, at some latter time, be totally acclimated to that higher level of sunlight. Thus, advanced growers accept the fact that the current set of a palm's fronds are "sacrificial". Sacrificial in that they will never perform to 100%. And that the palm will not perform to 100% until those sacrificial fronds are replaced. Replaced by fronds that are grown, 100% on location". And 100% acclimated to where that particular palm is located outdoors. That's why it's so important to provide all of the assistance possible to a newly planted palm.


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