I say bury the whole thing! Once the leaves die (probably sometimes after a very cold spell in mid winter, or maybe a heavy snow) then you should cover the whole thing in a very dry mulch covering the entire trunk. Put a tarp over the mulch to keep things dry and check up to make sure no moisture is getting in. You can uncover all the mulch after the last frost probably by mid april.

I had one (as a bonsai plant) that I got cheap. It was in glued stone (now I would never get a plant like that), but anyway it was pretty small and I left it outside. It stayed green for a very long time. It eventually rotted, but not until very cool weather came. I cant really remember specifics, but I thought it was cool for a cycad with no soil in a small pot to survive so long into the winter like that. It was probably exposed to some low 20s.

As long as it doesnt go below 20 it will do great, but when it gets lower than 20 it will start getting a little stressed and if its been in a greenhouse for its entire life it might not handle frost well. I would try to accumulate it to some cold this winter, but keep it in a sheltered spot away from forst and remember a potted plant will be affected from cold much quicker than a plant planted in the ground.

Good luck.

They handle mid/upper teens here with no problems, although that is not sustained all night long, it's usually just for a few hours in the early morning. The last time it got into the single digits I was in diapers ;)

I don't know, maybe some of those net type Christmas lights made for shrubs? I'm not sure how much heat they actually produce though.

I have seen sagos planted in the ground here in VB...some turn brown during the winter..but always come back during the summer...

Good Luck!!

Laura in VB

I'd plant the trunk an extra 6 inches deep and try covering the rest of it with dry mulch and plastic garbage can for Dec, Jan, Feb and uncover mid March depending on local forcast.

I am all for zone pushing but I'd hate to see you lose those after all the care you have given them. 15 gallons is a very good size. You must have had them for many years. Can you keep it as an indoor houseplant? If they were mine I dont think I would risk losing them.

I'm in Clemson, SC which is in the foothills, extreme southwestern SC. I've had mine in the ground for years. Usually they stay green until January when it gets cold enough to kill back the foliage. When it turns brown I trim it off. They throw new leaves as soon as they think it's warm enough, usually about May. There's a motel I drive pass every day that has some big ones growing in the ground that have been there at least 25 years. I also have a couple of other cycads that have been in the ground a long time as well and behave in a simliar fashion:

Cycas taitungensis
Cycas panzhihuaensis
Dioon edule

I'm currently experimenting with these newcomers:

Encephalartos lebomboensis
Encephalartos lehmannii
Encephalartos trispinosus
Encephalartos altensteinii

If you do decide to put them in the ground just be sure that they have good drainage. Maybe mound some leaves up around the caudex but don't bury it any deeper in the ground than it's already growing.