Giant cold hardy cycads?

[plantguy]

Are there any giant cold hardy cycles out there? By cold hardy I mean zone 8a, and by giant I mean easily taller than most, if not all, cycas revoluta.

[Paul S]

Beyond Cycas revoluta I imagine Cycas panzhihuaensis is about it. There are a handful of others that take a decent bit of cold but I am not sure about a polar z8a winter.

[plantguy]

Are there any giant cycas species that could be crossed with those species then?

[Paul S]

I don't know, I have reached the end of what I know here. Maybe someone who knows things can pitch in, but I think cycad hybridising is something of a dark art.

[Meangreen94z]

Here is a great list. Cycas taitungensis grows larger than revoluta with similar speed and look. Encephalartos paucidentatus is massive. I suspect there are others within the Encephalartos genus that will survive as well.
https://blog.jlbg.org/winter-hardy-cycads/

[Meangreen94z]

Here are the Cycas taitungensis at John Fairey garden. They have survived 6°F

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[Meangreen94z]

Macrozamia moorei, johnsonii, and communis are all large and have come back from low teens. That list includes communis coming back from 4°F

moorei

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johnsonii

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communis

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communis

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[Meangreen94z]

Encephalartos paucidentatus is massive. Encephalartos altensteinii is comparable in mature size to Cycas revoluta but both are much slower growing than revoluta.

Encephalartos paucidentatus

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Encephalartos altensteinii

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I’ve heard good things about Encephalartos hildebrandtii and kisambo taking atleast mid teens with their caudex mulched.

[Meangreen94z]

Dioon angustifolium is the hardiest Dioon I’m aware of. It came back from 4-5° in the Austin area.

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[Paul S]

Wow. That list has turned a lot of what I thought I understood on its head. Thanks Daniel!

[Meangreen94z]

Wow. That list has turned a lot of what I thought I understood on its head. Thanks Daniel!

I have a local friend I’ll try to contact and get additional feedback. He ran out of time and left half his collection in the ground during February 2021.

[Meangreen94z]

Here is his list of cycads that were left unprotected at his rental house in Dallas. They saw 2-3°F at that location: Large- multi headed dioon edules, c. panzhihuaensis, panzhihuaensis x Taitenguensis, cerratozamia hildae & c. latifolia. A cycas revoluta w/ 4.5’ of trunk was killed back to the ground, but the in-ground pups & trunks survived. He has more at his other house south of Austin that saw 6-7°F.

[plantguy]

I like all of those plants! Which would be easiest and cheapest to find and buy?

[Meangreen94z]

I like all of those plants! Which would be easiest and cheapest to find and buy?

The most ideal if only one is the Cycas taitungensis

[plantguy]

What is the growth rate on Dioon edule? I've found quite a few of those for sale.

[Meangreen94z]

What is the growth rate on Dioon edule? I've found quite a few of those for sale.

They are a lot slower. Certain forms are hardier than others, I’ve heard the Palma Sola variant is hardiest, along with Queretaro blue. Angustifolium used to be a variant of edule before being split off. All of the Dioon angustifolium in Zilker Garden in Austin and the specimen in front of Barton Springs Nursery survived single digits and 5 days straight below freezing in 2021. Size will also matter. Seedlings will be vulnerable but the more above ground trunk, the more exposed the growth point will be. A caudex of several inches wide but not yet trunking is most ideal for extreme weather. A lot of people bury the caudex in mulch during the winter.

[plantguy]

Is there any hardiness info on dioon spinulosum?

[Meangreen94z]

Is there any hardiness info on dioon spinulosum?

It’s the least hardy Dioon. Don’t even bother. Zone 9B and up

[plantguy]

Well then, it seems we need to cross it with D. angustifolium!

[Meangreen94z]

Zilker Botanical Garden saw 7-9°F

Ceratozamia kuesteriana sign

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Ceratozamia kuesteriana

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Ceratozamia kuesteriana

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Ceratozamia kuesteriana

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Cycas taitungensis sign

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Cycas taitungensis

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Cycas taitungensis

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Ceratozamia mexicana sign

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Ceratozamia mexicana- possibly tenuis

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[Meangreen94z]

Cycas panzihihuaensis sign

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Cycas panzihihuaensis

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Cycas panzihihuaensis

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Cycas panzihihuaensis

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Zamia integrifolia sign

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Zamia integrifolia

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Zamia integrifolia

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Macrozamia moorei

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Macrozamia moorei

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[Meangreen94z]

Dioon edule

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Dioon edule

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Dioon edule

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Dioon edule

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Dioon edule

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[Paul S]

What a fabulous collection of cycads! And don't they look superb en masse like that!

[gave_agave]

All cycads are pretty slow growing. Many species have 1 flush a year, or less. C. taitungensis is one of the faster growing ones, and even the seedlings in my greenhouse in the UK have 2-4 flushes a year, however, the 2 I have in my house didn't have any flush this year. I think the reason they crossed C. taitungensis with C. panzhihuanensis is to get a relatively cold-tolerant, fast-growing cycad. There was a bit of a hype with C. panzhihuanensis and it being very cold-hardy, but it seems (at least in the UK), that many didn't survive UK winters and weren't that cold-hardy after all, at least not when they were small. I do have a few C. tait x C. panz seedlings, which were single-leaved seedlings last year, and they have had one flush of one leaf this year.
If you want a big plant, buy a big one, don't buy a small one and wait for it to grow big.

[plantguy]

how long were they exposed to these temps? I'm guessing a day of that cold is very different than months of it.