Moisture is more important - Agave americana can easily take temps below freezing as long as it is dry.

Your biggest problem will be to create an enclosure large enough for this plant, as it can get 5-6 feet tall and is highly armed. How do you plan on protecting it?

x

Thanks for the reply.

I plan to put a styrofoam box (wrapped in plastic to protect it from the elements) over the plant, with a lamp inside it set to go on when the temps gets below about 40. I'll use the kind of lamp used to keep chicks warm. I'm thinking that with our relatively short summers the plant won't grow to its usual height.

You said that it "... can easily take temps below freezing..." I assume you meant unprotected - correct? How far below freezing before it is really getting too cold for this plant?

dln949

Have you ever tried a styrofoam enclosure/ heat lamp system before? How do you know it will work? What will be the inside temperature when it is -10F outside?

An in-ground plant is better protected at low temps because the roots are not exposed as they would be in a pot. I believe A americana can survive about 15-20F...but if it is 20F constantly day and night, it may not survive. Ideally the daytime temps should be much warmer than night.

x

I have successfully overwintered a palm tree using the styrofoam-and-light method.

dln949

My Agaves toasted out below 20F,I think your plan will work fine if you can keep it dry and above freezing during the day.I also agree that repeated exposure to below about 25F will finish it off.I was going to leave mine outside here in southern Iowa with a leaf pile enclosure but decided to dig it up when it grew 10 new leaves,it has already grown 8 new leaves this season,so,I would kinda disagree with you that it won't get huge being planted outside.You basically have 6 months for it to grow outside.I would say go for it,I think it would be cool to have a huge Agave planted outside anyway and I may try something similar with mine when it's to big to bring in-they really beifit from being planted in the ground just like banana plants and my Agave is kicking my banana plants buts right now!

Also as an FYI, if you want a big plant that is probably hardier than Agave americana, you may want to look into Agave salmiana of which there are several varieties available.

x

Another thing you might try is stuffing the box with straw and on top of the soil. That will help it retain some warmth. Not all the way full, just around the pot pretty good and on the top. We used to do this at a tree nursery for the trees in ball and burlap to keep them warm over the winter. It gets pretty cold here sometimes into the single digits(F). I know trees are hardier than agave but might be worth a shot. If you did this I would be most careful of the straw being to close to the lamp. Too close and you"ll have a toasted agave.
Hope this helps
plant_junkie