Here is a more detailed response I found on the internet and paraphrsed. "With a power drill bored a hole through the tree at the site of the split. Then use large brass bolts that won't rust, and being an alloy of copper it may have some antifungal properties. Put a large bolt through the hole and secured it. Then use a wrench to tighten nuts on the end. Eventually the tree will grow over those metal rods, incorporating them into itâÂÂs structure, and being all the more stronger for it, with no adverse damage, because they go through the cambium layer, not around it. Now use both a can of tree pruning sealer and a can of natural shellac wood sealer. Shellac is an all natural waxy resin made by insects and used in everything from wood products, to food, to pills. You probably eat a little bit every day, it is harmless, but it seals wood good. Insects and diseases love open wounds and so it was important to seal the tree with something. That taken care of, the last thing you need to worry about was water. Just like with concrete, water can get in a crack, freeze, and then widen and make the crack worse. Even with the shellac the force of water expanding as it freezes was a potential hazard. Put silicone caulk over the crack (but not the bottom) preventing any water from seeping in, but if any does, still allowing it to seep out. Silicone is a neutral and inert substance and the tree will probably grow around it fine, or, after healing has progressed, I can take it out."

Linking to the original thread, just to save anyone having to look for it: http://forums2.gardenweb.com/forums/load/namegal/msg0920290511810.html?4

Sara, I can't say I specifically know what is going on with your trees. To be honest it does not surprise me that a seed grown tree would take more than 8 years. However the Perkin's Pink should be a clone from an older tree, and therefore I would expect it to flower early. The only clue I can offer you is that there is a local business with Yellowwood planted in landscape islands. These trees are about 2" in caliper (at chest height), and those do indeed flower. So assuming those are seed grown, if your trees are that size then I would expect them to flower. I know trees in full sun, and understory shade. In both instances flowering does not seem to be an issue. The only other thing I can think of is perhaps summer climate. I remember you are in Northern California, but don't remember if you are near the coast. My summers are warm to hot days, and warm humid nights. Average in late July to early August would be 90F (but can be significantly hotter) days, 68-70 overnight lows. It's a shot in the dark, but maybe the warm temps could have something to do with stimulating flowering. If it were me in your circumstance, since the trees are doing well otherwise, I would probable wait it out UNLESS I just couldn't stand to look at them anymore. We have a "Princeton Sentry" Ginkgo that I have whined about many times. It grows out (slowly), but not up, suckers like crazy, and has produced yellow fall color one time in 7 years. It is time for that Ginkgo to go, and you may very well have the same opinion of your Yellowwood's. Arktrees

Craig, sorry I'm not certain of how the Cape Chestnut will perform in your micro-climate. Below I've typed out the description from the book "Ornamental Trees For Mediterranean Climates: The Trees of San Diego." (Don't worry, I type fast.) Calodendrum capense (kal-oh-DEN-drum kuh-PENCE) Cape Chestnut Rutaceae Southern and Eastern Africa Magnificent is the word for a mature Cape Chestnut in bloom, and it is certainly a tree that once planted will entertain generations to come. Unrelated to the true chestnuts, this African tree is famous in Kenya for a large specimen that forms part of the structure of the Tree Tops Hotel. In Southern California, the Cape Chestnut is a slow-growing evergreen or briefly deciduous tree to 25-40' tall and wide whose dense, gradually spreading crown deserves the space it needs to show off its handsome dark green floiage and showy flowers. Flowering usually occurs in late spring or early summer, when the whole tree is covered with candelabra-like basketball-sized flower clusters composed of many individual 3" rosy-lilac blooms. Although this tree seldom blooms when young, a mature specimen will often rebloom in the fall. Seed pods are produced on mature trees and when ripe split open to reveal shiny black seeds. The Cape Chestnut is somewhat frost-tender when young, but mature trees will withstand temperatures as low as 15�F. It prefers a deep soil in full sun, and will usually lose most of its leaves for a brief time following cold winter temperatures. Quail Botanical Gardens is indicated as a place where this specimen can be viewed.