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I was turned on to the Empress by an answer that Jan Steinman gave to a question here on the forums. You can check it out here if your interested: How to grow a tree on steroids?

I was showing my sister a picture of the tree and she fell in love with it. She wants one; however, there is a problem, the tree is meant to grow in zones 5-8 and her house is zone 3/4 depending on the year. She lives @ around 6,500 ft in the Livingston mountain range here in Montana.

I was hoping to get some insight. In general, I realize its a stretch (to say the least) to think that I might get one growing up there but I have seen, Elm, beach, willow, cherry .. ext growing in similar conditions so there might be hope. Let me know what you guys think and what steps you think I would need to take in order to make it happen if, in theory, you think it might be possible.

Environment variables (soil):

  • Depth class: Very deep (more than 60 inches)
  • Drainage class: Well drained
  • Permeability: Moderately slow
  • Landform: House sits on top of an alluvial fan
  • Parent material: Alluvium, colluvium, or alpine till (high volume of moderately large rocks 6x6 in on average I would say)
  • Slope range: around 20%
  • Elevation range: 6,400 to 6,500 feet
  • Annual precipitation: 20 to 30 inches
  • Temperature: 60-70 F (summer) -10-30 F (winter)

Please keep in mind that the house is newely built and the land has not been managed (rather wild). I will have the ability to move large volumes of dirt (tractor) and there are plans for installing a pond. In general, it is rather windy and the natural tree is the conifer.

  • I hate to tell you this, but this tree is hardy only down to max -15 and -10 deg C. I know the answer you link to says minus 20 - not sure what that means, but surely it can't mean -20F, which is -28.8 C - if its meant to be minus 20 C, that information is incorrect too. Listed H5 with the Royal Horticultural Society rhs.org.uk/Plants/21410/i-Paulownia-tomentosa-i/Details – Bamboo Dec 21 '18 at 0:27
  • @Bamboo Oh no I was under the assumption -10 F was it's lower limit. However, I was thinking I would insulate it for the first 4-5 years of growth. In the hopes that it would be able to handle lower temperatures around the 6'th year or so without directly insulating it. Another thing that might help. I was thinking what if I built the dirt up around it. Like a 3-4 foot wall about 3 feet back 180 degrees around the tree for the first few years... maybe? – Rob Dec 21 '18 at 16:15
  • Well that probably won't do much, to be honest, though you could try, as long as soil is not heaped up around the trunk. The trouble is, it won't only be vulnerable at the root, but also through the woody parts (which may split or crack), even in maturity,if it gets that far. The only way you'll find out is to try - it either works, or it doesn't. Sad fact is, there are lots of plants I'd love to grow here in the UK, but can't... though this tree isn't one of them. – Bamboo Dec 21 '18 at 16:52
  • @Bamboo I might give it a shot just for the heck of it. I was thinking I would try about 8 different plants in 8 different regions on the property. Each would have a similar but slightly different setup. I am going to try and Bonzai this tree for myself so I will prob have 16 saplings growing by this march so she can have half. – Rob Dec 21 '18 at 17:23
  • @Bamboo seems to be under the impression that "H5," a hardiness rating for the British Isles, is somehow relevant to Montana. Plants For A Future (pfaf.org) says it's good to USDA zone 6, which is — TA DA! — -20°C. I thing the things you mention might coax it into working in your location. – Jan Steinman Dec 27 '18 at 9:54
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One thing you didn't note in your otherwise excellent "Environment Variables" section is exposure direction, which could be crucial, since your winters in Livingston will tend to be clear and sunny.

If you have good southern exposure on a 20% slope, you might be able to coax this tree into growing there. The good news is this tree normally grows so fast that you won't waste much time finding out!

So, choose a south-facing protected position. Put dark rocks, like the local basalt you have there, on the north side of it. Your idea of insulation is good, too. I would not bother with synthetics, rather, a straw mulch will work well. (You should be able to get plenty of straw in Livingston!) The straw decomposes and eventually fertilizes, unlike synthetic insulation.

This tree coppices readily after establishing, and if it gets freeze damage, those bits (typically the branch ends) will die and the tree will branch out around it.

If you're on a 20% slope facing north, then I have to think it's just not going to work. But with the bright winter sun of eastern-Rockies Montana, there's a good chance it can make it on a south slope. You can span two USDA zones depending on exposure direction!

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