I have neglected trimming some juniper tams under our dining room window for several seasons. They are now over 6 feet tall. Can I cut them back nearly to the ground and expect them to regrow? They have no foliage under their outer surface growth.

Junipers will not tolerate heavy pruning because they do not have latent buds below the foliage area in older wood. If branches are pruned back to older wood with no foliage, the branch stub usually dies. This fact makes it important to choose a variety of juniper that has a growth habit and mature size that will suit the planting area you have selected. The growth habits of junipers vary from low-growing ground cover varieties to large conical-pyramidal forms. You might just want to replant the area with a more suitable juniper that will require much less maintenance pruning.

I have a bed that was installed with landscape fabric (to prevent weeds) and rocks for mulch. Can perennials in the bed still spread invasively?

Perennials that are invasive got that reputation because they go where they want and take no prisoners. The landscape fabric may challenge them for a time. But most invasive species do their dirty deed with rhizome type roots. The fabric will keep them warm, trapping moisture, allowing them to run until the root finds a weak point. To avoid this problem, plant perennials with a clumping habit rather than a running one. Avoid those that offer “quick coverage” or those that boast “self-seeds.” That seed will sprout in the crevices between your rocks, and the roots will work through the fabric. Remember that landscape fabric is a woven plastic material that allows air and water to pass through. Weeds need sunlight to germinate. The fabric effectively prevents that. The fabric may retard the individual growth of perennials planted through the holes cut in it, but it will not prevent invasive plants from following their natural habit.

I have crabapple, cherry, and mulberry trees. When is the best time to cut off low-hanging, big branches? Also, can I straighten an established tree?

Prune your crabapple in fall to early spring. This is the dormancy period when major limb removal causes the least bleeding. Mulberries are also mid-winter prune candidates. Even in full dormancy, older trees may still bleed profusely. Cherries, either sweet or sour varieties, should not be pruned in winter. They are susceptible to silver-leaf disease. Pruning must be delayed until bud-burst in spring. However, if a branch is dead, diseased or damaged, it should be removed as soon as you notice it. This holds true for the crabs and mulberry as well. If you are merely pruning for convenience or aesthetics, wait until the appropriate time.

As for straightening an established tree, you need to determine why it is crooked. Are there prevailing winds, which have caused the trunk to lean? Was it improperly staked as a sapling? Is it seeking sunlight from under the canopy of an overshadowing tree? You can open up the canopy of an adjacent tree if shade is the cause. You can also prune the canopy of your leaning tree so that it appears more in proportion to itself. There are methods for forcing branches to grow in another direction. I would consult a professional arborist before attempting this on your own.