Giant cold hardy cycads?

[Stan]

Cycas rumphii and Cycas circinalis both pass as "hardy" for California and grow trunks many feet tall eventually. In a greenhouse they can flush 3-4 times a year. So,for speed they are fastest to trunk. Ultimate hardiness is around the mid 20's is my guess and not for long...

[Meangreen94z]

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

5 days straight below freezing, two nights in a row of those temperatures (February 15th and 16th). Austin is 8b, I thought you were 8a? The Zamia and Ceratazamia are mostly subterranean. So you bury the caudex when you plant them. Dioon and Encephalartos I would halfway bury and then during the winter mound mulch over the caudex to protect it. This will insulate them and keep their minimum temperatures closer to just freezing level.

From my understanding the cycads in Zilker were given 0 protection. Obviously in the case of trunking sized cycads mulching will do little with the growth point exposed. It will help protect the roots and any offsets forming though.

[plantguy]

Do you think you could do with trunking specimens what they do with tree ferns? Stuff the caudex with straw and wrap some of the leaves around it?

[Paul S]

A friend of mine in the UK (Newport in south Wales, for detail) grows many cycads outside and has particualrly impressive specimens of Macrozamia communis and Ceratozamia robusta. If the weather threatens to go below -5C (23F?) he ties up the leaves and puts a sleeping bag, bought secondhand from a charity shop, over the top. Then a plastic sack. He's been growing it like that for many years. Wales is cool and wet but they seem to grow just fine like that.

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[Meangreen94z]

Any kind of insulator will benefit them to a degree. Some people wrap cycads and palms in incandescent Christmas lights for the duration of winter. If inclement weather is predicted they wrap them again in something that won’t easily ignite(canvas, tarp, etc.), to trap that heat. If it’s weather that will burn the fronds anyway, you can cut them off and just wrap the trunk to make it easier.

[TropicalplantloverOH]

Does anyone have any climate data/history on Pine Knoll Shores, NC? I know it’s a zone 8b. But I thought sometime in history they’d have some cold under 10F. They have a Cycas revoluta planted outside in a pot at the aquarium. They definitely won’t be able to move it in in the winter because of how heavy that concrete pot is!