It being a dogwood it won't appreciate exposure of the bark (and probably the root zone as well) to hot sun. It will also be hard to cut it back much with an attractive result. Try to find side branches you can prune back to that leave enough room for the work, yet make it look like the tree avoided growing out on the drive on its own. If there are forks with one branch growing over the drive and the other parallel to it, cut at the fork so only the parallel branch remains.

TRY, if you can, to prevent/limit any digging around the roots. I hope the widening is all on the other side of the driveway, because if it will be on the dogwood side as well, then I can see your tree declining and dying in a couple of years. It might be worth going back to your neighbor and seeing where the work will be done - obviously close to the tree or the trimming wouldn't need to be done.

I think I would be proactive, and, if the work will affect the tree roots as well as the branches, ask if the neighbor will pay for a replacement tree. He may quibble, but, it's worth asking. Just because the damage is not immediately visible doesn't mean there isn't a direct connection - he may not understand that now, but maybe you can explain it. An exact replacement probably isn't possible - BIG trees are expensive - but a smaller one should be doable.

Do as you wish about your neighbor. There's nothing that can be done, however exept to get to pruning.

I'd recommend a uniform rounded look with common sense dictating how much you need to cut from your neighbors side and doing the same to your side of the arc.

Hit it with some fungicide sprays consistently from now up till next year this time. For a dogwood I'd use liquid copper which is organic and keeps things from being effected and you might consider, in fact you should, treating with an insectide for a year as well.

Water deeply once a week and from now through spring use as a top dressing application as directed of granulated phosphorus and next spring fertilize it only till the beginning of August with an all around fertilizer switching back to phosphorus after August.

It can't hurt!

Dax

Dax, I have to ask, but what will adding phosphate do? Remember, most soils except those heavily worked like agricultural fields seldom lack phosphate. That's one of the big reasons why VA and some other states passed laws limiting the amount of phosphate in fertilizers. Excess fertilizers usually end up in run-off, effecting bodies of water.

Also, on top of the fungicide treatments (It would help to know what you are treating for) I would probably spray the trunk/branches, especially near where they have been cut, with an insecticide containing permethrin or bifenthrin. Dogwood borer (aka Pecan Tree Borer) loves openings where wood is exposed.

Mature dogwoods generally are not enhanced by much pruning, certainly not by being barbered into round shapes.

Pesticides should never be applied without a pest problem having been identified and the correct chemical for that particular problem having been selected.

Phosphorus is detrimental when applied to excess. If phosphorus is already adequate, additional applications will produce an excess. A soil test should always precede phosphorus applications.

It can hurt.

The result of phosphate overfertilizing is leaf chlorosis. Phosphorus is known to compete with iron and
manganese uptake by roots, and deficiencies of these two metal micronutrients causes interveinal
yellowing. It's my belief that many of the chlorotic shrubs we see in urban landscapes are suffering
indirect iron (or manganese) deficiency from overapplication of phosphorus. Moreover, it has been
experimentally demonstrated that high levels of phosphorus are detrimental to mycorrhizal health and
lower the rate of mycorrhizal infection of root systems. This mutually beneficial relationship between the
fungus and the plant roots allows the plant to more effectively explore the soil environment and extract
needed nutrients. In the absence of mycorrhizae, the plant must expend more energy growing additional
roots and root hairs to accomplish the same task.
In addition to harming beneficial soil organisms, excess phosphate will eventually find its way into
waterways. Unlike urban landscapes, aquatic plants are most often limited by phosphate and the addition
of phosphate will induce algal blooms (eutrophication). Such blooms are always followed by increased
bacterial activity, resulting in lowered oxygen levels and the eventual death of fish and other animals. As
green industry professionals, it is incumbent upon us to recognize that excessive use of phosphorus in
landscapes is a resource-wasteful, ecosystem-damaging practice

Here is a link that might be useful: The Myth of Phosphate Fertilizer

Unfortunately all of the digging will be done next to the tree. The previous owners of my house planted the tree fairly close to the property line. My neighbors have held off widening the driveway for a couple of years, but with son#2 now driving they have 4 cars and a driveway that will only fit 3. As much as I hate it, I understand their need.

I will make sure that I water deeply every week and will try to keep the pruning to as little as I can get away with. The tree isn't so tall, but it is very wide and unlike any dogwood I've seen before as it is a weeping tree. The branches are very long and and bend down, which is why I have to keep it out of their driveway.

I'd worry more about root and soil damage than anything else.

Probably, the best you can do is to watch soil moisture. This will not mitigate the potential damage from pruning a tree that resents being pruned, but it will at least keep it as vigorous as it can be.

+oM