Answer: Katsura trees should be pruned in late winter or early spring, just as new growth begins. Branches that weep all the way to the ground can be attractive, but they can also make it next to impossible to grow grass beneath it. And, even if the grass does grow, getting the mower underneath the branches can be a royal pain, often leading to broken tree limbs. What's more, if the leaves remain in contact with the grass, especially if the grass is wet with dew, the leaves may be more susceptible to fungal diseases. I suggest removing those branches, or at least shortening them. If you look carefully at your katsura, you'll see where the graft was made (look for a swelling at the top of the trunk, where the branches are attached). You want to preserve the graft and most of the branches, but you can safely reduce the length of the branches, expecting that where you cut, you'll get one or two new branches, which will make the canopy of the tree much thicker. I'd avoid pruning all the branches evenly - you'll end up with an umbrella like top. Instead, alternate the length of each of the weeping branches.
Best wishes with your landscape!
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