I would like to know how to propagate the black gum tree. Is it true that it has a big tap root, so that is why you do not see it a lot in cultivation? What about stem cuttings? Is it hard to root? Would it take a very long time to get a medium-size tree from a stem cutting? Does this species need to be grafted?
The black gum tree (Nyssa sylvatica) is one of our most beautiful trees native to the eastern U.S. Somewhat pyramidal in youth with densely set branches, it grows about a foot a year, reaching about 15 feet in 15 years. It is an excellent specimen tree, acceptable for residential streets, but not in dense urban areas where pollution is high. Despite its outstanding, dark lustrous green summer foliage and its broad range of fall color from yellow to scarlet, it is often passed over.
You are correct that it has a big taproot. However, that probably isn’t the deterrent to more frequent urban cultivation. Balled-and-burlapped nursery stock for early spring planting can be readily obtained. More likely its need for swamp-like conditions, a soil high in organic matter with a pH of about 6.5, and a naturalized setting are what keep it from the current suburban developments. And although its stiff horizontal limbs and irregular bark may endear it to some, its overall irregular shape does not adhere to the script for a manicured yard.
Michael Dirr, author of Manual of Woody Landscape Plants, has raised numerous seedlings from seed. Black gums are generally not rooted from cuttings or grafts. Each half-inch oblong blue-black drupe contains a single seed. The fruit ripens in late September through early October. Since seeds are obtained in the fall, you will need to overwinter them. Dirr recommends using container culture and transplant the second spring while still a very small sapling. The potting mix should be moist, sterilized potting soil, enriched with organic matter. You need to mimic the conditions of a mucky swamp, which means watering the pot very well once the seeds are planted. Place the mucky pot in a large freezer bag and store in a location where the temperature will be near freezing over winter. Germination occurs in spring. Put the potted seedlings outside during the first growing season. Dappled sun is best to prevent scorching of the new leaves. Keep the pots well watered and fertilized. Overwinter in the pots, continuing to maintain the muck-like conditions the black gum loves. Plant out the seedlings in the second spring. To estimate the length of time to a medium-sized tree, you should apply the one foot per year rate.