We have a really old and huge plum tree. It has many burls on it, and we are wondering if it is possible to cut some of them off? We don't want to kill the tree in the process.
Although I'm not completely sure, the most common reason for what you're seeing is a disease called crown gall in your tree.
Is there any way that you could email me a picture? Seeing it would help confirm my suspicion. If, in fact, it is crown gall, cutting the burls off won't get rid of them. They'll just grow back.
Crown gall is caused by a bacteria and has an extremely wide host range. In fact, there are researchers who think all plants are susceptible.
It lives in the soil and can persist for years and years without a host plant. The vast majority of galls occur underground on the roots. In fact, people who have surface roots in their lawn from trees growing there and complain about their "bucking bronco" lawn mower going over them are usually going over galls growing on the roots.
Crown gall needs a wound where it can enter a plant, and there's almost always something available to them. Even tiny microscopic cracks in stems — cracks caused by the wind moving the branches around — provide an opportunity for infection.
Galls are less common on the branches of plants, but certainly not unheard of. They're usually caused by water splashing up from the ground or an existing gall.
Crown gall is a funny disease. In many cases, probably a big majority, it doesn't affect a plant's growth dramatically. The tumor-like growth causes a lot of undifferentiated tissue, but the plant usually copes by creating vascular connections to circumvent any interruption. However, it can occasionally cause the decline and death of a branch or even an entire plant.
Controlling crown gall is difficult. My usual recommendation is to just let it go as long as the portion of the tree it affects continues to grow. If the gall is on a branch, that branch can be removed to eliminate the gall. This is a rather drastic step and only used if it's a scattered one or two galls or if they're on small branches that won't be terribly missed when removed.
There is a commercial product out there called Galltrol. It's a biological control agent made up of a related bacterial that's antagonistic against crown gall bacteria. I'm pretty sure it's only available in commercial quantities. I'm not aware of a homeowner product available.
Any suggestions for a clay tolerant, shade tolerant — the area gets about one hour of late afternoon sun — shrub or perennial that gets between 3–6 feet tall and wide? It also needs to be drought tolerant.
I don't have anything to offer you that would perfectly fulfill all of your desires. There are several broadleaved evergreens that might work.
Boxwood doesn't get that tall — it is only 3–4-feet tall and fairly slow growing. It is moderately drought tolerant once established, but do best with regular garden watering.
Another choice would be an evergreen variety of euonymus such as Manhattan, Emerald n' Gold or Emerald Gaiety. Manhattan would get to 6 feet high or even taller and the other two would be much shorter, about 3 feet.
There are several deciduous shrubs that would work with that much shade, too. Chokeberry is a lovely smaller shrub that would get 3–5 feet tall or you could consider a viburnum variety such as Mohican or Compact European.
Shrubby Dogwoods also will tolerate a lot of shade and will get 5–8-feet tall. The problem with pretty much all of these is that none of them is very drought tolerant. I don't know how much you can water them, but they'll need a good soaking every five to 10 days on the average.