Q I planted oak leaf hydrangeas in my shady backyard 16 years ago, and they did great for the first 10 to 12 years, growing to 10 feet tall in some cases, and blooming well in spite of, admittedly, little care. About four years ago, some of the canes began to die back, until this last year, after pruning the dead canes out, I realized that I had very little left of what had been huge shrubs. My questions are: what happened, and should I now take them out completely or see if they recover and put out new canes?
A Once established, oak leaf hydrangeas are usually pretty carefree. Increased shade can reduce the number of blooms but should not damage the plant itself. I would investigate. Have you been piling mulch up too high around the plants? Anything changed with water — too much or too little? See how they leaf out and grow this spring before making any drastic decisions.
Q How do I prune a twisted trunk hibiscus? Can I return it to not twisted?
A As I am sure you know, tropical hibiscus plants bloom on new growth and so need to be pruned pretty heavily when you move them outdoors (or slightly before) so that they produce ample new growth and thus ample new flowers. If you are growing one of the twisted or braided standard forms of hibiscus, prune above where the twisting or braiding is to keep the twisted trunk. If you prune beneath it, they will simply grow a straight stem, as they were trained to produce the twisted or braided forms. It is a personal preference.
Q Can you tell me what this is on my rooted cuttings of fuzzy Bolivian sage and what if anything I need to do? [The reader sent a photo.] They don't seem to move and so far I haven't noticed any damage to the plants.
A You have mealybugs, which are soft-bodied scale insects. The adult is beginning to create the white, cottony protection around itself. These are sucking insects that tap sap out and give off the sticky honeydew — where black sooty mold can then grow. I can see some tiny crawlers (babies) in the photo as well, when I enlarge it. You have a few options. You can use a systemic houseplant insecticide or spray with an insecticidal soap, which could get the crawlers, and then dab the adults with a cotton swab dipped in rubbing alcohol. Come back in three to five days and repeat. I would isolate this plant from other plants until you get the mealybugs under control as they could infest other plants.
Q I listened to you for years on the radio and bought into your pleas regarding the annual massive pruning of crape myrtles that most folks subscribe to around here. My issue which is partly due to my neglect is that I now have three massive crape myrtles in front of my house. I'm looking for some advice as to what would be the best course of action now — go ahead and "murder" them, prune them or just let them go? [The reader sent a photo.]
A I love your crape myrtles, and I think they are truly specimen plants for your landscape. If you want to do anything, maybe thin out some of the top growth. They have great form, structure and impressive trunks, but they might have a bit too many twigs at the top. A pole pruner is going to be your only option since they are so tall. Thank you for not butchering them.
Q We have a large hedge of Leyland cypress. [The reader sent a photo.] They started browning out last summer. I sprayed them with an insecticide even though I could not see anything on them. I hope you can tell me something I can do to keep from losing them. Thank you for all you have done, and we hope you enjoy your retirement.
A From the picture, I don't think the problem is insects, but a disease. Leyland cypress are quite prone to branch canker, which can result in branches dying one after the other. Once the disease begins it is hard to stop or reverse the process. Here is a shortcut link to advice from the University of Arkansas Cooperative Extension Service: arkansasonline.com/309canker. To confirm the diagnosis, take a sample of a dying branch with good and bad tissue represented to your local county extension office. They can send it to the diagnostic clinic.
Retired after 38 years with the University of Arkansas Cooperative Extension Service, Janet Carson ranks among Arkansas' best known horticulture experts. Her blog is at arkansasonline.com/planitjanet. Write to her at P.O. Box 2221, Little Rock, AR 72203 or email
jcarson@arkansasonline.com
HomeStyle on 03/09/2019