Wednesday, July 16, 2008

Franklinia and Wisteria Questions

Two separate questions:
1. I live in Raleigh, NC and have a Franklin tree that could use some help. It's now about 3 years old, is planted in an area that includes pines and rhodos. I've seen one that has been kept in a pot and the leaves are beautiful--not like mine.
Could you advise me re: the correct soil ph as well as what the best fertilizer would be. Also, I'll be moving next year--is there a more optimal planting situation than it's present one (it's coming with me).

2. I have a beautiful Wisteria growing along the top of a large Pergola. The problem is that suckers keep breaking through the dirt in my planting bed and are not confined to the trunk area but break out all along the root system. I simply cut them off, but there are so many--is there any way to combat this or stop it altogether without killing the plant?

Let’s begin by talking about the Franklin tree, Franklinia alatamaha.

Franklin trees grow best in a moist soil with a fair amount of organic matter. They are also known to have a rather sparsely fibrous root system (according to Dirr’s Manual of Woody Landscape Pants). Given those two factors, I would think that even three years later you want to still be supplying the tree with a fair amount of supplemental irrigation. Do you have a soaker hose or drip irrigation system set up? I would think the tree’s root system should still be saturated two or three times a week for 2-3 hours each time. Hopefully you amended the soil with a fair amount of compost when you planted the tree. If not, I would top dress the area right around the base of the tree with an inch or two of fresh, rich compost. If you have mulched under the tree already then you might want to remove some of the mulch and replace it with, or at least mix in, the compost. Avoid mounding compost or mulch right up against the trunk of the tree. Spreading out a few feet in diameter, your tree pit only needs a couple inches of compost and/or a compost and mulch mix to provide enough insulation for the summer months while providing nutrients to the building root system. If I were you I would not fertilize your tree with anything else at this time, especially if you are going to move it again soon. In fact, I am rarely a fan of fertilizing trees as they will prefer to grow and produce stem and foliage tissue by their own schedule, not ours. Going back to the sparse root system Franklin trees can have, consider hiring some skilled landscapers who are really good at balling and burlapping trees for the transplanting effort. If you really want to save the tree it is going to be worth the extra investment. If the root ball gets really jarred or beaten up during the move you might be dealing with that stress for years. When it gets moved, I would recommend a product called PHC Tree Saver to be incorporated into the hole (amended with compost) once the tree is in place. Here is a link to PHC’s website, and hopefully you can find a retailer near you that carries it:

The tree can tolerate some shade but you will get the best flower and most glossy leaves if it is in a full sun application. Definitely set up supplemental irrigation in its new home for a year or two to make sure it takes to the new situation. Rely on compost and mulch to provide a steady slow release of nutrients to the root system. A few references speak to soil pH but they do not always agree with each other. A member of the camellia family, Theaceae, I would guess they would like a soil that is slightly acidic to neutral (6.0-7.0). One reference says that they can tolerate slightly alkaline soil, but I have never seen one in that kind of situation. Since wild populations of these trees have not been found in over 200 years it seems to me that there is a fair amount of guessing in this regard. The best specimens are found in slightly colder climates (Massachusetts, Pennsylvania, etc.) but obviously your tree can be grown down in the Carolinas as shown by your friend.

Then there is the wisteria:

Suckers and water sprouts are what we horticulturists call kinds of epicormic growth. The catch with pruning them back this time of year is that the plant is growing most actively and continuing to produce plant growth regulators (what people tend to call “plant hormones”) that will continue to push out new growth from dormant buds right below where you are cutting. The only trick I have learned is to prune those unwanted shoots back in the fall as the plant is beginning to go dormant. In the fall your wisteria is going to produce another plant growth regulator that will aid the plant in going dormant for the winter. By pruning at this time you will (hopefully) trick the plant to not want to produce new growth from those points. Or, if they do, the hope is that the growth is so young and vulnerable going into winter that they do not survive and eventually die-back. You will have to repeat the process for a few years as wisteria are so aggressive (invasive!?!), but hopefully you can get the situation under control.

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