One of questions we are most frequently asked concerning palms is, "How fast do they grow?" Reference books may give relative terms, such as "slow" or "moderately fast," but actual growth rates are seldom reported. Spurred by questions from fellow palm enthusiasts, we present the following growth rate data gathered from seed-grown palms in Fairchild Tropical Garden, Miami, Florida, USA.

The palms included in our sample were chosen at random, according to accessibility and availability of records. We measured the height of singlestemmed palms from the ground (or the top of the root mass) to the bottom of the sheathing leaf base (where the lowest live leaf attaches to the stem). In other words, neither the crownshaft nor crown was included in height measurements; only the trunk was measured. For certain palms in which the bottom of the leaf base was obscured by dead leaf base fibers (certain Coccothrinax, for example), we visually estimated the position of the base of the lowest live leaf and measured from there. We used a measuring rod graduated in centimeters (Hastings Tools & Equipment, Hastings, Michigan) that telescoped to 750 cm, supplemented with a measuring tape, as needed.  Age was determined from the year in which the seeds were received by Fairchild Tropical Garden. Stem height was divided by the age of the palm to give the growth rate, expressed in cm/yr and rounded to the nearest centimeter.

In interpreting the growth rates given here (Tab. 1), certain caveats apply. First, these rates are lifetime average growth rates. They do not take into account the variation in growth rate over the life of a palm, which may grow quickly as a juvenile but slowly as a reproductive adult. These rates do not take into account the pre-germination period, which may be many months in certain Cocoeae, nor do they account for the establishment phase, during which a seedling palm may form no above-ground stem. Second, these rates are taken from individual palms growing in Miami whose growth rates may not be typical. Palms grown elsewhere may have significantly different growth rates (slower or faster).

Our results (Tab. 1) indicate, not surprisingly, that considerable variation exists in average growth rates. In instances where we measured several individuals from the same seed lot (individuals sharing the same accession numbers but with different letter suffixes – Calyptronoma rivalis and Ravenea rivularis, for example), growth rates may vary two-fold or more. The four fastest-growing palms in our sample are Livistona ro b i n s o n i a n a, Carpentaria acuminata, Bentinckia nicobarica and a young P t y c h o s p e rma salomonense. The slowest palms in our sample are two Bahamian accessions of Pseudophoenix sargentii ssp. saonae var. saonae and an individual of Ravenea hildebrandtii. The difference in rates between the slowest and fastest palms is greater than twenty-fold.

Growth rates are governed by the interplay of genetic factors and external factors, such as availability of light, water, nutrients, etc.; however, we are unable to determine which of these factors is the most important in explaining the tremendous variation in our data. Nevertheless, we hope these data will give growers of palms some idea of the growth rates that can be expected for these species and that the data will be useful in making informed planting decisions.

Acknowledgments

We thank Dena Garvue for the use of the measuring rod, and we thank Chuck Hubbuch for reviewing the manuscript and offering useful suggestions.

Table 1. Average growth rates of palms growing in Fairchild Tropical Garden. The growth rate can be converted into inches per year by dividing the figure by 2.54.