Every winter I make a list of plants that have no business surviving here, and eucalyptus never used to be on it.
That changed after I dug into Eucalyptus gunnii, the cider gum, while researching hardy trees for a completely different reason. It kept coming up on English gardening forums as the toughest of the eucalyptus family, the one growers push furthest north and still expect to see green in spring. Established specimens have taken short dips to around zero degrees Fahrenheit and walked away from it. Long stretches in the teens are a different story, and that distinction matters more to me than the single low number ever does.
I have never grown a eucalyptus. I want to say that plainly before I go any further, because this whole post is me thinking out loud, not me reporting a result. But the more I read about how this tree fails in cold climates, the more it started to sound like plants I already know how to handle.
Eucalyptus gunnii doesn't go dormant the way a maple or an oak does. It keeps growing right up until the cold makes it stop, which is the same problem I deal with every year on my Phoenix sylvestris. A plant that never learns to power down gets caught mid-stride when a hard freeze finally shows up, and that is usually when the real damage happens. Sustained cold without a break does more harm than one brutal night, which is a lesson my own December 2017 windmill palm loss taught me the hard way.
The part that actually gets my attention is coppicing. English growers who push this tree past its comfort zone often cut it back hard, sometimes to a foot or two above the ground, and let it regrow from the base the following spring. That is not so different from what I already do with my bananas every fall, dig up the corm, store the important part, let the top go. If the root system on a young cider gum can survive a Wisconsin winter under a warmed root zone and a box, the top growth becomes almost optional. Lose the trunk, keep the roots, start over in spring with something that already has three or four years of root mass behind it instead of a seedling's worth.
I am not promising myself a eucalyptus this spring. But I keep circling back to the idea, because the pieces I would need are pieces I already own. A rootzone cable keeping the soil warm through the coldest stretch. An insulated box over the crown, even a small one for a coppiced stump. The patience to accept a plant that dies back to the ground every year and calls it a season.
Somebody somewhere in a zone colder than mine has probably already tried this and either proved me right or laughed at the idea. If you know who that is, I would love to hear about it.
Until next time,
— Tim
