|Golden catalpa peaking through Geranium palmatum|
The blue wall is about 6 feet tall and the planting bed in front of it is about 6 feet wide, so it is not a huge space. Also, I do not want too large a tree in that spot because I do not want it to cast too much shade and I do not want it to impede various sight lines in the garden. That is why I do not let this catalpa grow to be a large tree which it would do if I did not cut it back every year. For a few years I did let it become much larger than it is now, but it was getting too big and I did not like the effect it created, so about 3 years ago I decided to cut it all the way to the ground and if that killed it I was willing to take that chance. It did not, however, kill it, and from the stump which was pretty much level with the ground, grew one stalk which was at least 6 feet tall by the end of the season. So the next year, I again cut that stalk all the way off, and it grew another one and did basically the same thing. So this year I left a few feet on the stalk and allowed some branching on the stalk. What you see in the picture is this year's growth from that structure. As you can see, this treatment does not seem to hurt the catalpa and it creates these very nice large golden leaves. This catalpa is just now reaching over 6 feet in height and I am sure it will be taller than that before the summer is over.
I first read about pollarding golden catalpas in the writings of Christoper Lloyd, one of my favorite gardening authors. If you want to grow one of these catalpas as a full grown tree, I would recommend them for that purpose. I once saw one grown that way in a park in Vancouver, BC, and I thought it was spectacular. However, they look best in my opinion if they are grown as specimen trees, and not bunched with a lot of other trees and that means that they require a lot of space. If I had to do it over, I might plant a golden catalpa where my Magnolia macrophylla is now, since it would fulfill the same purpose--i.e., create a broadleaved focal point tree in contrast to the much finer leaved trees around it.
I am not sure I would plant this catalpa in front of the blue wall if I were starting over for two reasons. First, a plant like this develops an extensive root system and that makes the soil around it very dry and root filled and hence difficult to plant. Second, this tree does not leaf out until very late in the season, so the space is bare for a long time. If I were starting from scratch I probably would plant some cannas in this location, like Canna 'Pretoria', and perhaps some other plants to take up the slack before the canna got going.
Since these catalpas do not get going until fairly late in the season, they can be cut back fairly late in the spring. I would do this chore whenever you can get around to it and not worry too much if you are doing it a the right time of the year. I have found these trees to be very forgiving of whatever treatment you may give them.