Q The Yoshino cherry on my front lawn is now about 50 years old and is dear to my heart. I have lived with it for 34 years. For the past few years the tree has looked less and less vigorous. There are fewer leaves, some branches are bare, and suckers are emerging from the root zone. Also, there is some fungus growing near the base.
Should I add a thin layer of topsoil and mulch?
A The prognosis for your tree is not promising, and topsoil and mulch will only speed its demise. Like most cherries, Yoshino does not live that long. Although there are records of plants more than 100 years old, cherries more commonly live 30 to 50 years. Only a handful of the cherries at the Tidal Basin date back to the original donation of trees, and the oldest trees are slowly being replaced.
The lower branch death is not as alarming as the fungal fruiting bodies you describe. This is a clear sign that wood decay organisms have invaded the base of the tree. Even if it is otherwise healthy, the tree may not be able to support itself in the long term. Mulch and topsoil added to the soil surface will deprive the root system of some of the oxygen that it needs to survive. If a tree is in decline and you want to save it, hire an arborist to do a root excavation with an air spade to remove some of the compacted soil in the root zone and replace it with soil mixed with compost. Alternatively, use a soil auger to bore holes around the tree in a zone that extends out from the drip line to about 10 feet from the trunk. Backfill the holes with pine fines or compost. You will greatly improve oxygen and water infiltration and may stimulate the roots.
These measures are best applied to trees that are beginning to show signs of distress due to soil compaction, drought or flooding. They won't save a tree in advanced stages of decline.
It is unlikely that your Yoshino cherry tree was grafted, therefore the sprouts are probably identical to the parent tree. If it appears the tree will not survive, you may select a vigorous sprout from the root system to replace the tree, as long as the shoot is not too close to the trunk. If you do lose the tree, replant with another Japanese cherry. It is undoubtedly a landmark in your neighborhood.
How do I keep mulch from washing away in heavy rain?
If you are dealing with a slope, use a fibrous mulch that is fairly well rotted. Shredded hardwood and pine straw are good choices, as are chopped leaves. Pine bark and pine nuggets are light in weight and tend to float easily. They should not be used on slopes.
If the hill is steep, even the right kind of mulch may not be enough. You can put down a biodegradable mat before you apply the mulch, to increase friction between the soil and the mulch. Moist burlap works well, and you can peg it into the ground with small twigs. Make sure the burlap is not treated to retard decay. You can also simply push short twigs into the ground before mulching to help hold the mulch in place. Settle the mulch before the next heavy rain by wetting it thoroughly after spreading.
When is the best time to prune a rose of Sharon that hasn't been pruned for many years and is about 10 feet high. How much pruning should be done?
The best time is when it is not actively growing, so be quick. Rose of Sharon is one of those bounce-back shrubs that respond to severe pruning with vigorous growth and a renewed interest in flowering. Since it flowers on new growth, severe pruning will not compromise flowering later this summer.
Don't be tentative with a rose of Sharon. If it is an old, established plant, it is really best to cut it back to the ground. New growth will appear in late spring, and the new branches will be in bloom before summer is over. If you try to shear or shape it, you will only get a tangle of weak, spindly stems that won't produce as many flowers.
Scott Aker is a horticulturist at the U.S. National Arboretum.
