Answer: I'd start by giving the tree a deep soaking around its entire canopy, allowing water to penetrate past its root system, thus flushing away residues from the pool water. For mature trees, most roots are in the top 3 feet of soil, so water should penetrate slightly past 3 feet. If it was a small size when you planted it, say a 5 or 15 gallon pot, you might get away with watering 2 feet deep. A soil probe (any pointed piece of metal rod) will help you determine how far water has soaked. It moves easily through wet soil but stops when it hits hard dry soil. Since the tree is starting to resprout, I wouldn't prune off any "dead" branches until you are absolutely certain they won't come back. It won't hurt to leave them on another month. You don't want to inadvertently cut off live tissue, and surprisingly "dead looking" plant material can come back. Spread organic mulch, such as compost, dead leaves or chipped matter, around the tree. It will moderate soil temperatures, maintain soil moisture, and as it decomposes, provide some nutrients. Or, use an organic fertilizer with a low NPK ratio. Chemical fertilizers typically are faster-acting, with higher NPK ratios, but since your tree is suffering a bit, I wouldn't recommend a burst of feeding that basically "forces" it to grow, which is stressful. Allow it to regain some of its vigor.
To make a proper pruning cut, do not cut the branch off flush with the trunk. Cut just beyond the branch collar, a slightly raised area where the branch and trunk meet. At this point, the tree's own meristematic tissue will seal the pruning wound. It's the tree's natural healing system.
For a large heavy branch, the proper way to prune is to make three separate cuts. The first two are to eliminate the weight of the branch and prevent it from tearing bark down the trunk of the tree, which is unsightly and also allows disease/pests an entry. 1. Start with an undercut (cutting from th underside of the branch upwards) about 8-10 inches from the trunk, but cut only about half way through the branch. This prevents splitting and stripping of bark down into the trunk. 2. About 2-4 inches further past the undercut, cut the branch off (from the top to bottom). 3. Now that the weight of the heavy branch is off, make a clean, smooth cut just past the branch collar.
Don't apply any sealants to pruning cuts. Research shows that sealants will not prevent decay and actually interfere with the tree's healing ability. If we prune properly, the tree can take care of itself. I hope this info is helpful. Good luck with your willow.
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