Place the seeds in slightly damp peat or soil, place in the fridge for 30-45 days (stratification). then bring out into the warmth. Catalpa grows fast! It is a virtual weed in my garden.
On another note, we have Catalpa sp(?) growing here in the north country in z4a(almost z3b) above the 45th parallel. These seem to be very hardy and I wonder if this is unusual.
I would have no idea! Below is a link to the USDA Database. It shows Catalpa Speciosa growing in MN. Whether or not it's indigenous there, the site didn't say. Sorry I couldn't be more helpful.
If the USDA website has a map like the one referred to, at the bottom left corner is "native status". If you click on it the map changes color and by the shading you can tell if it is native to your area. In this case Catalpa is native to the Canadian border. Probably native along the border area but not shown on map.
