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Last fall I decided it was time to invest a bit more into my greenhouse and upgrade to double pane poly carbonate in order to keep some additional heat in the winter. Growing alongside the greenhouse are also my tree dahlias, hence they had to be cut down in order to do the project.
I had once read that you could propagate a tree dahlia via burying stem cuttings. As usual, I don't remember where or when I saw it, but I did remember that you needed at least 2 stem nodes. I had to cut them down, so what the heck, why not try it? The worst that could happen is I would end up with a bed of rotten Dahlia stems.
I cut them up into sections with at least 2 leaf nodes and packed a long garden bed full of them, covering with about 6" of soil. Then I pretty much forgot about them until spring. We had one really cold week, with lows down to 12F , I was sure they were toast.
On March 9th, I got brave enough to dig and check out the situation, wow, there was growth! I quickly buried them back up again, waiting for roots. I needed a place to harden off some other plants, so I constructed a simple plastic hoop structure with 1/2" pvc. I put down some slug bait and waited another month.
By April, the space became a premium, the stem sections got covered by tomatoes that would not fit in the greenhouse. They got some extra insulation however. By May, I had quite the mess, tomatoes that needed to be planted and shoots coming up that were very fragile. Several of them got broken off in the process of moving them, but they sprouted right back. Note that it is ok to trim back the cane once the shoots are coming out and starting to root.
They all got potted up or planted and now I have a little forest of Tree Dahlia plants, yay! Those that never got moved out of the smaller pots, now have tubers growing into the ground under them.
These rarely bloom here I for me, maybe in October in a good year, but I have had them over a decade with no loss to cold. I've had them in pots and in the ground, with admittedly little care and no fertilizer, they seem to make it just fine. You just need to remember slug bait in April and May.
Next year, I will add some compost and good organic fertilizer and see if I can convince them to bloom. They don't get massive flowers, many of the dinner plate ones have flowers larger than these. I do however find that they make an excellent greenhouse shading plant. They come up about the time the greenhouse needs shading and get killed back by frost about the time you want the extra light. Natural shading and the bonus of the exotic foliage is good enough for me.
Items to remember: