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Sabal minor isn't quite tough enough to emerge from a Trenton, NJ area (mid zone 6b) winter looking at all fresh. I've had one in my foundation planting in Ewing, NJ for nearly 8 years. The fronds start to burn somewhere between 0 and +5 (probably closer to the latter). When temperatures do not drop significantly below that of the onset of freeze damage, it is difficult to separate the effects of freezing from those of other factors such as wind and ice. Even after the mild El Nino winters that occurred in this region in the early and mid 1990's, years when the coldest 1 or 2 mornings were approximately +3 or +4 and little or no ground frost, Sabal minor looked tattered and ragged. During the last 3 winters, I've had it under a plastic tent along with the adjacent Trachy. wagnerianus, and both look great in the spring. This fall, S. minor ripened its first crop of seed.
Several years ago, a friend went to Cape Hatteras fishing, and I asked him to look for seed in Buxton Woods. He returned with quite a bit. As an experiment, I planted 2 of the stronger second year seedlings along the road at the base of the Milford Bluffs, along the Delaware River, about 35 miles north of trenton. The site is above the river. The cliffs face almost due south and receive the maximum available sun. It was the best natural microclimate I could find. This will be their 5th winter. Three winters ago, temperatures in Trenton reached -8. At the Bluffs, it must have been below -10. In the spring, the S minors were brown to the ground but recovered. They seem very resistant to heart and stem rot. In a normal winter, all the foliage, except perhaps the extending spear, is killed back or at least badly damaged. The condition of the spear depends on the length of its extention and the protection it receives from snow an fallen leaves. Snow and leaves may protect mature foliage from cold, but sustained cold and wetness takes a toll of its own. In the mildest winters, mature fronds survive but look very ragged by spring.
In the early part of my experiment, winters were mild, and the palms produced about 2 to 2.5 fronds per season - similar to the growth rate of my home specimen. Two of the last three winters have been harsh, and growth has slowed to only about 1 to 1.5 fronds per season. The reason for the slowing seems to be cold not moisture. At the Milford Bluffs, the soil is very well drained and dryer in summer than S minor prefers. The home specimen gets far less sun but much more water and is in a soil that holds water better than the soil at the Milford site. Typically, the home example begins growth in April when the soil temperature at 6" reached about 53 degrees. Growth accelerates ,and from late May until early Sept., the new spears extend at approximately 2" per week (25.4"/100 days). Growth then slows and ceases by mid-Oct. However, this past summer was the wettest in a very long time and the Milford Bluff palms still grew at the slower rate.
In the Fairchild Tropical Garden Bulletin, Oct., 1973, Popenoe relayed a report that a Sabal minor at the Henry Foundation (about 30 airline miles SW of Trenton), after a number of years of growth, went into decline and died for undetermined reasons. It may be that during a period when winters are on average milder, S. minor can just barely hold its own, but when the less favorable side of normal occurs, decline is triggered by slow starvation. In colder conditions, increased winter foliage loss and the delay of spring growth may tip the palm's nutritional balance to the negative, slowing the foliage generation rate. It seems likely that reduced foliage generation is a self accelerating process. I suspect that, in the central New Jersey climate, the eventual onset of decline in unprotected specimens of Sabal minor is inevitable and that unaided recovery would require unrealistically favorable circumstances. At this writing, the palms are still there and it will take a few more seasons to know their true course.
At this point, the evidence suggests that in central NJ Sabal minor is not killed outright by cold. Sabal minor, unprotected, will almost certainly fall victim to the secondary effects of winters that tend to be a little too cold for a little to long.
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Revised December 6, 1996