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 bracteosa ‘Stingray’ is the most winter hardy of all brightly variegated agaves we’ve tried. Here is our plant looking quite lovely after our 11 F cold.
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.