December 2022 post-freeze damage assessment

I don’t like winter. It’s dark and it’s cold. OK, I’ll admit, it’s all relative, because what I consider “cold” may seem laughable to others. But it matters to me, because I routinely buy plants that are technically not hardy for my zone (USDA hardiness zone 9b).

This December has been colder than usual, both in terms of nighttime lows and daytime highs. Above all, we had two nights, December 18 and 19, when the lows dropped to 27°F—a temperature I don’t recall seeing in 5+ years. For reasons I don’t have a scientific explanation for, many of the tender succulents I grow are perfectly fine at 28°F, but start showing leaf damage below that. This is exacerbated by surface and soil moisture, something we’ve had plenty in the second half December.

Winter has just begun so any damage assessment is premature, but here’s a quick snapshot of what was damaged (and what wasn’t) in the wake of the cold spell a couple of weeks ago.

Damaged

↷ Most of my mangaves are fine, but a few show leaf damage. And it isn’t the more tender varieties like ‘Lavender Lady’, but sports of ‘Jaguar’, a hybrid involving Manfreda guttata, a high-altitude manfreda species from Central Mexico. As such, it should have decent cold tolerance...

Mangave ‘Pineapple Punch’...

...with fairly significant cosmetic damage

Mangave ‘Arctic Frost’ with some frost spots

↷ Several agaves show similar leaf damage, especially hybrids involving Agave pablocarrilloi (the species formerly known as Agave gysophila). In itself, that’s not surprising, considering how Agave pablocarrilloi begins to develop frost spots at around 32°F.

Agave pablocarrilloi × isthmensis (front) with some leaf damage. Agave chazaroi (back), itself a fairly tender species, is fine.

Leaf damage on Agave pablocarrilloi × isthmensis

Agave ‘Chisum’ (A. pablocarrilloi × colorata) with fairly significant spotting. This hurts, because it’s one of my favorite agaves in the garden. This is its second winter in the ground; there was no damage last year.

↷ Agave titanota, and the closely related Agave oteroi, often develop black spots at or just below freezing. However, the Agave titanota selection in the next photo has several damaged leaves:

Agave titanota ‘Blue Sphere’

Surprisingly, two Agave titanota ‘Lion’s Mane’ right next to ‘Blue Sphere’ have no damage.

Agave titanota ‘Blue Sphere’ (left) has cold damage, Agave titanota ‘Lion’s Man’ (right) does not. Go figure!

Agave ‘TBG’, an Agave titanota hybrid with ‘Blue Glow’, shows similar leaf damage as ‘Blue Sphere’ above:

Agave ‘TBG’ (A. titanota × ‘Blue Glow’)

Leaf amputations may be in order for ‘Blue Sphere’ and ‘TBG’ to prevent the rot from spreading to the core.

↷ Agave gypsicola (not to be confused with Agave gypsophila) is a newly described species (2019) with pliable blue-gray leaves. San Marcos Growers rates it as being hardy to 20-25°F, but in my experience, it’s less cold-tolerant than that. I lost my first gypsicola a few years ago to rot when it was barely below freezing. My second specimen (below) is OK, but it has quite a bit of cosmetic damage near the leaf tips. When I visited Greg Starr in Tucson a few weeks ago, he told me that he’s seen damage on his gypsicola in temperatures near freezing. Agave gypsicola is a beautiful species, but definitely more suited for places with warmer winters.

Agave gypsicola

↷ On the aloe front, there are no outright disasters, just some spotting, like on this Aloe beetsilensis × striata:

Aloe beetsilensis × striata

↷ Dyckia ‘Tarzana’ has been happy in our backyard for 2+ years ago. No damage ever, until this year. I have no idea why. One degree may make a difference: between 28°F, the coldest we’ve had in the last few years, and 27°F this December.

Dyckia ‘Tarzana’

↷ The hardest hit group has been the kalanchoes. No surprise there since this is a fairly tender genus overall. In my experience, they’re OK at 30°F, but anything below that becomes iffy. 27°F was not to their liking!

Kalanchoe luciae ‘Fantastic’ with pretty ugly leaf damage

Kalanchoe beharensis with fairly significant leaf damage. It’ll grow out of it, but it’ll be ugly for a while. The plant is so big now that I can’t really cover it anymore.

Kalanchoe ‘Oak Leaf’ (K. beharensis × millotii) with significant leaf damage

The entire top of Kalanchoe orgyalis is soft and has flopped over. I’ve had a very hard time with this species anyway, so maybe it’s time to give up.

↷ Some miscellaneous plants with damage:

Dragon tree (Dracaena draco); just some leaf damage

Lotus hirsutus (left) perfectly fine, Plectranthus neochilus ‘Mike’s Fuzzy Wuzzy’ (right) partially melted

Asparagus plumosus with a fair amount of browning. It’s a fast grower and will be fresh and green again come spring.

Not damaged

Some plants that I thought would struggle didn’t. This goes to show that you cannot blindly trust labels; there simply is no substitute for trying a given plant in your own garden to see how it handles your unique conditions.

↷ Curio ficoides ‘Mount Everest’ (aka ‘Skyscraper’, as the Sunset Western Garden Collection calls it) proved to be impervious to two nights at 27°F. I expected at least some damage, but there is none. This is great news, considering how useful a plant this is.

↷ Usually, I bring my variegated Euphorbia millii inside for the winter, but this time I forgot. Fortunately, I don’t see any damage, not even to the leaves.

↷ I have several aloes I thought would be iffy as far as cold tolerance goes, but they turned out to be positive surprises:

Aloe schoelleri from Eritrea is hardier than I thought

The same goes for Karin Zimmerman’s fantasy aloe hybrids

Aloe laeta is a beautiful species from Madagascar. Last year, I accidentally left a small A. laeta outside, and it rotted completely. This year, I got an A. laeta hybrid from Brian Kemble (I don’t know what the other parent is), and not only did it not get damaged, it’s pushing a flower stalk!

Aloe bulbillifera is a fairly tender species from Madagascar that forms bulbils (live plantlets) on its inflorescence. My A. bulbillifera hybrid from Jeff Moore/Arid Adaptations in Tucson doesn’t make bulbils, but it’s been a stellar performer in one of the hottest (and coldest) spots in the garden. As a bonus, it flowers repeatedly throughout the year.

↷ Aechmea fasciata is a popular houseplant because of its silvery leaves and extremely long-lasting (and showy) inflorescences. People thought I was crazy for leaving mine outside all year, yet here we are, winter #2 with no damage. Admittedly, it’s right up against the house, but even so, this is a very nice surprise.

I’ll have more damage reports throughout the winter. If the forecast for the next 14 days is even remotely accurate, we’ll have a lot of rain. As much as we need it to fill our reservoirs, too much rain too quickly can cause its own kinds of problems, as in r o t.

© Gerhard Bock, 2022. All rights reserved. To receive all new posts by email, please subscribe here.