Maeve asks: When is the recommended period of time to prune the vertical water sprouts out of my ornamental plum tree? Each year they grow several feet.
Plum trees are recognized for their tendency to produce prolific water sprouts and, if not removed, they literally take over the tree, producing shade so the limbs and foliage become starved for sunlight. Not only do they create a shade problem, they prevent the wind from flowing through the tree canopy, and even more importantly, they rob the rest of the tree of energy that is needed for the tree to thrive and keep its attractive form.
Now to answer your question: Most gardeners will prune out the tall sprouts, sometimes 5 feet or more in length, when the tree is dormant since it is much easier to visualize one's pruning cuts when the leaves have fallen.
I prefer to keep ahead of the on-going problem and prune out the newly forming water sprouts midsummer, and as needed, again during dormancy. Summer pruning doesn't seem to invigorate the sprout growth as much as the traditional dormant pruning. Whenever you choose to remove the vigorous vertical sprouts, remember, pruning in any form always stimulates new growth near cuts.
When removing the sprouts, use caution not to cut too deeply into the main limb as that can leave an open wound that will not heal as readily.
Mike asks: What is wrong with my boxwood? The hedge has been in this location for several years and then all of a sudden one of them will start to turn brown-yellow and dieback begins.
There are two immediate cultural problems that can cause dieback: Poor draining soil that is waterlogged or very dry soil. Perhaps you have failed to check on the soil moisture, thinking that during the winter it isn't necessary to waste water.
Our cold weather can also add to the problem. If you see some new growth down in the center of the shrubs, prune the dead sections out above the new growth and add some mulch at their base, keeping the mulch away from the main stem. Surface mulch will aid in breaking up the soil compaction.