Every year when we have a significantly cold winter, we are reminded of the wonder of the Southeastern native needle palm, Rhapidophyllum hystrix. This native of Northern Florida and nearby areas in the adjacent states of South Carolina, Georgia, and Alabama, is the most winter hardy palm in existence.
Established needle palm clumps have been documented to have survived -15 F to -20F. I still remember checking on the old specimen at the JC Raulston Arboretum in Raleigh after we dropped below 0F for two consecutive nights in January 1985 (-3 on Jan 20, and -9 on Jan 21). I was amazed I was to find the plant undamaged by the cold. Below is one of our many specimens in the garden after our 11 F freeze a few weeks ago.
Needle palm is generally considered to be a non-trunking palm, although with great age, it will develop a short trunk, that will eventually become decumbent. I’m fascinated why this and other native palms are never promoted by the native plant enthusiasts.
I had to chuckle as folks on several Facebook plant groups were wringing their hands in worry prior to the recent cold snap, while we were secretly hoping for even colder temperatures than forecast.
JLBG registered three consecutive nights in the teens recently; 11F, 19F, and 19F. While this was certainly not abnormal for our area, folks with very short memories thought the horticultural world was coming to an end. In reality, we recorded similar temperatures in the winter of 2017/2018, albeit a week later that year.
When we first started the gardens at JLBG, we were squarely on the Zone 7b side of the Zone 7a line. We are now on the Zone 7b side of the Zone 8a line. In order words, we have shifted about 1/4 of a hardiness zone. Since 2018, JLBG has registered three consecutive Zone 9a winters, so it’s not surprising the new gardeners or those with short memories start assuming that all kind of plants are reliably winter hardy, which is not the case.
We long for cold temperatures because we want and need good winter hardiness data, and while mild winters may be enjoyable to us Homo sapiens, we don’t learn anything about plant hardiness from those winters. So, here are a few things we learned this year.
Agave weberi ‘Stone Cold Austin’ is Patrick McMillan’s collection of Agave weberi from Austin, Texas. We’ve tried Agave weberi a couple of times prior, and could never get it through one of our milder winters. Patrick’s original plant at Clemson got large enough to flower there, so we’re hoping for the same. The older foliage is showing damage from 11F, and will most likely be lost, but the bud seems fine so far.
We’ve never had any luck with any of the dwarf Agave lechuguilla mutants we’ve tried in the garden, but this new one, shared by plantsman Hans Hansen, that we call Agave ‘Tater Tot’, had no problem with 11F. These are often sold as Agave x pumila, which actually doesn’t exist. Everyone assumed that A. x pumila was a hybrid, but when one in Europe recently mutated back to the original form, it turned out to be nothing more that a super dwarf form of Agave lechugullla.
Mangave ‘Racing Stripes’ is a plant we had high hopes for in terms of winter hardiness, but we had not had a cold enough winter to get good data. Our only reservation was that it contains genes from the tropical Agave gypsophila. Thankfully, our plant came through the 11F freeze in reasonably good shape. The wrinkled nature of the older leaves are indications of cold damage that will show up in a few more days, but the core seems intact and should re-grow.
We fully expected Bambusa multiplex ‘Green Giant’ to be defoliated after 11F and the stalks killed to the ground, but our fully exposed clump still looks like it’s mid-summer…at least from the north side.
On the south side, the same clump has fried foliage. There are typically two causes for such damage. One is wind desication when the winds are blowing from a single direction and the ground is frozen, making it impossible for the plant to replenish water lost through the foliage. During the time that our ground was frozen, our winds were coming from the West, so that wouldn’t account for damage only on the south side of the plant.
In this case, the more likely scenario is that this is due to sun scorch when the soils was frozen, since the damage is on the south side. If the canes are indeed undamaged, as it appears, new leaves should reflush in spring.
We didn’t hold out much hope for the Mexican palm, Brahea decumbens, but it sailed through 11F unscathed.
Since we know that genetics matters, we will often plant more than one clone of a marginal plant like a new palm. Below are two seedlings of the small-seeded European Fan Palm, Chamaerops humilis var. microcarpa. The first shows significant foliage burn, while the second plant, growing nearby shows no damage after 11F.
The hardiest of all Sabal palmetto forms are those from NC’s Bald Head Island. Our plant from there came through the cold unscathed. We expect many local businesses and even homeowners who purchase large trunked forms directly from Florida growers will probably be in for a disappointing spring.
All of our hardy cycads have assumed the straw-color we see every year when the temperatures drop below 18 degrees F. The plants are fine, but we recommend waiting to remove the dead fronds, since doing so now, can cause the new foliage to emerge in the middle of winter, which is never a good idea. April 1 is our target date to remove the fried foliage.
One of the real surprises was the fried foliage of Viburnum ‘Moonlit Lace’, where it was growing in full sun. The same plant growing in shade looks untouched. The stems are fine and the plant should re-sprout fine, but gardeners who grow this in full sun may be disappointed.
This is the coldest temperatures we’ve seen since planting Patrick’s hardy selection, Opuntia microdasys ‘Dripping Springs’. Our clump looks great after the cold. It’s hard to imagine that this clone is so much more winter hardy than any of the other forms of this species that we’ve tried previously and killed at much warmer temperatures. Although we don’t offer this for sales, I’ll remind you of our great prickly pear cactus giveaway at our Summer Open Nursery and Garden in July.
The Mexican Sedum praeltum looks a bit sad, but actually seems to be fine with sound buds up and down the stem. This little-known perennial forms a plant that looks almost exactly like the tender Jade plant, Crassula ovata.
Lastly, our patches of Living Stones, Lithops aucampiae, sailed through 11 degrees F. I wonder if we can ever get all the disinformation on the Internet regarding their tolerance to cold corrected.
One of our favorite palms for the garden is the US native Sabal minor var. louisiana. While it can’t outgrow the Himalayan Trachycarpus fortunei (windmill palm) for speed of developing a trunk, Louisiana palmetto is the most winter hardy of all trunking palms. One of the mysteries is that in the wild, the same population can have both above ground as well as subterranean trunks.
Our garden specimen in the photo below was planted from a 1 qt. pot in 2005. Eventually, Sabal minor var. louisiana will develop an above ground trunk, which on our specimen below is just beginning.
The background on Sabal minor var. louisiana is a botanical mystery. Some taxonomists consider it a valid species, while others consider it variety of the subterranean trunked Sabal minor. Others consider it to be an old hybrid of Sabal minor and either Sabal mexicana or Sabal palmetto. A similar hybrid, Sabal x brazoriensis from near Dallas, had its DNA analyzed several years ago, and was found to be an old hybrid of Sabal minor and a now extinct population of Sabal palmetto.
Sabal sp. ‘Tamaulipas’ from Northern Mexico is another mystery palm in need of some family history work. Thankfully, palm researcher and grad student, Ayress Grinage at Cornell has begun to look at these mystery sabal palms to figure out how they came to be. We, and others have sent material, and now await the results of the paternity test.
Considered the hardiest of the genus Brahea, this rare endemic palm hails from the alkaline Sierra Madre Oriental Mountains in northeastern Mexico, where it’s endangered thanks to the abundance of hungry goats.
Brahea decumbens is ridiculously slow growing. Eventually, the immature green leaves turn a beautiful silvery grey and adorn the 6′ tall x 10′ wide specimen that, with age, develops creeping (decumbent) trunks…much like a blue-leaf Serenoa repens.
We’ve failed three times, loosing each in the winter. Zac mentioned that these need an extremely abusive and neglected environment to survive, so we planted our fourth attempt in our gravel crevice garden where it receives no irrigation. After 3.5 years, it’s actually thriving and looking particularly nice this fall.
If you’ve lived in the deep south…the land of palmetto palm trees, you know that they typically don’t flower until they have at least 5 feet of trunk. Of course, flowering can be sped up by a combination of precocious genes and good growing conditions. Those who have studied Sabal palmetto in the wild have noted that the earliest populations to flower are those from the most northern, naturally-occurring population on North Carolina’s Bald Head Island.
Well, sure enough, our oldest specimen of Sabal palmetto ‘Bald Head’, planted in 1999 finally decided to produce flower this summer, and will hopefully seed. We’ve only had enough plants of this cold hardy form to offer through Plant Delights three times in 36 years. Fingers crossed, we’ll be able to make it available more regularly now. Hardiness Zone 7b and warmer.
Here’s a garden shot at JLBG, using a good bit of gold foliage in addition to flowers. Left to right: Viburnum dentatum ‘Golden Arrow’, Sinningia ‘Amethyst Tears’, Baptisia ‘White Gold’, Canna ‘Tama Tulipa’, Lysimachia nummularia ‘Aurea’ (groundcover), Hibiscus ‘Holy Grail’ (purple), Spirea thunbergii ‘Ogon’, Trachycarpus fortunei (palms).
We love our Mediterranean blue fan palms…one of the coolest palms we can grow outdoors. We’re right on the edge of winter hardiness for Chamaerops humilis var. argentea, so the key is to grow it to a larger size before planting in the ground. We’ve lost a few that we planted too small, and when that planting coincided with a cold winter.
This is a photo taken this January of our oldest clump, now 17 years old. This is a very slow growing palm, so a good bit of patience is required when getting it established. When we do experience single digits F winter temperatures, all of the foliage is burned back, but it re-sprouts from the base in spring. Mediterranean blue fan palm hails from high elevations in the Atlas Mountains of Morocco, where it eventually makes a 15′ tall specimen. In our cold winter climate, we doubt it will ever top 4′ in height. It should be winter hardy from Zone 7b and warmer.
Due to having three consecutive mild winters, with no temperatures below 20 degrees F, we’ve actually been able to get a trunk on our Washingtonia filifera palm. Typically not hardy in our climate, our plant was grown from seed collected from a wild population in Arizona that had experienced 10 degrees F. We’ll see what this winter has in store.
We love plant mysteries, and Sabal ‘Blackburniana’ fits the bill nicely. This pass-along seed strain has been considered by some to be an old hybrid of Sabal minor, while others consider it to be synonymous with Sabal palmetto, yet others consider it to be Sabal domingensis. Whatever it is, our plant is looking quite good in the garden. After growing it, unscathed, since 2008, we finally decided to propagate some for the upcoming Plant Delights catalog. If you know any more historical background about this curiosity, please share.
No, we’re not talking about your favorite football or basketball team, but the amazing blue Mediterranean fan palm. Here’s our oldest (16 year) specimen in our alpine rock garden this week. Chamaerops humilis is a Southern Europe native that’s marginally hardy in our region, but the blue form, know as var. cerifera (or var. argentea). is much more tolerant of our cold winters. If our winter temperatures drop into the single digits F, the foliage dies back to the ground, but quickly rebounds in spring.