Garden Q&A: Dead trees in wooded areas should be left alone

I have 10-plus acres of woods that have never been thinned and resemble a jungle. I would like to cut up the downed trees and invasive plants — such as multifloral rose — shred them with a chipper, and compost them. Would I run the risk of transferring unwanted plant species to my garden and beds in the compost?

A healthy woods has a top, middle and understory, which can make it look sort of like a jungle — but in a good way. Plants constantly die and new native plants normally replace them, provided deer do not eat them all. Deer feeding is a huge detriment to woods. It's important not to remove anything that is native or supplies wildlife needs. That includes dead trees, standing or downed. An incredible number of bird and animal species depend on dead trees for shelter or food. (The insects that move into dead wood don't harm living wood, so no need to worry about that.) You can leave the downed trees, which saves you a ton of work.

If you hot compost the chipped invasive plants, it may not decompose their seeds. So, yes, you run the risk of spreading non-native invasive plants if you use the compost elsewhere in your landscape. However, if you can chip the invasives (which deer don't eat) in place, you can use the chips to cover the bare soil and compost them there. Invasive species will take advantage of any bare soil. If you have invasives full of seeds — say, bittersweet vines with berries — you may think using their compost will cause those seeds to be "planted." However, chances are there is already an undecomposed buildup, or seed bank, of invasive seeds in your soil. A thick chip mulch can prevent those seeds from germinating.

My new Knock Out roses were devoured by Japanese beetles last summer but survived. Now I see dark rough spots on the stems. Is this beetle damage or something else?

That would not be beetle damage. Knock Out roses are highly resistant to the most notorious of rose diseases, black spot, but are susceptible to several canker diseases. The most likely one is called common canker; the treatment is simply to prune out the affected areas.

Double trunks

Shade and evergreens trees usually have one dominant main stem or trunk, known as the leader. In a double-trunked tree, the crotch, where two trunks diverge, can become a point of future problems. A U-shaped crotch allows bark to expand as it grows. But a V-shaped crotch pinches bark in the narrow space between the growing trunks. This included or embedded bark can't grow normally. It also pushes outward on the trunks. This creates a weak juncture that is susceptible to failure in storms. Bradford pear trees are a perfect example of this type of narrow-crotched breakage. A double trunk is best remedied when the tree is small. Choose the strongest, most vertical trunk. Prune off the competing trunk at a downward angle so water does not collect on the cut area. If the best trunk is not very vertical, support and lash it upright for a season.

—Ellen Nibali