By Dr. Leonard Perry, Extension Professor
University of Vermont
Thanks to the Internet, I'm in contact with gardeners all over the world. They have questions about growing and caring for perennials, how to deal with pests, and other horticultural issues...probably some of the same questions and concerns you have about your flower garden.
So, I thought I would share some of the most frequent asked questions. If you want to find out what else others are asking--or post a question of your own--go to the frequently asked questions section of my Website at http://www.uvm.edu/~pass/perry/faq.html. Because of the volume of questions I get, I'm not always able to answer them all, but will deal with the most popular ones on my site. It's most helpful to me if you include your geographic location and a bit about your growing environment if you submit a question.
Here's what inquiring gardeners want to know:
Q: I have a dense shade area by a corner of the house with no sun. It is hard to find something to grow here. Hostas and hydrangea do okay. I would like to plant something else but have had no luck. Could it be the soil? (Ohio)
A: It is probably the dense shade and not the soil that makes it difficult to grow plants there. Hostas are good for this, but watch for slugs. Other choices for dense shade include ferns, barrenwort (Epimedium), astilbe, ginger (Asarum), deadnettle (Lamium), lily of the valley, lilyturf (Liriope, warm climates), spurge (Pachysandra), lungwort (Pulmonaria), foamflower (Tiarella), vinca, viola, and barren strawberry (Waldsteinia). For dry shade try hostas, epimediums, deadnettle, vinca, foamflower, viola, and barren strawberry.
Q: We recently had a devastating hailstorm that destroyed all of our plants. What is the best way to care for plants that have been beaten down in such a manner? Should I cut them back? If so, how much? (North Dakota)
A: First, my condolences for your storm and plant loss. A storm a few years ago ripped my hosta leaves and put holes in them. And just recently we had another hailstorm here in Vermont that caused additional damage.
With plants such as hostas or peonies that only grow once in the season, cut off any parts that are definitely broken and will only die. The rest, even though unsightly, can be left. Just watch for signs of disease, and cut these parts off.
For most other perennials that might regrow, rebranch, or recover, cut off the broken stems that, again, will only die. If the plant tends to branch, cut back to the leaf nodes (where leaves join stems) where new branches will come out.
Some, such as the many perennial geraniums and perennial salvias, can be cut back to either new basal growth, or to within a few inches of the ground if early in the season, and new shoots should emerge. Daylilies and irises, which are normally cut back to within six to12 inches of the ground when divided, can be cut back to this height. They may not grow much this season, but the foliage will help build stronger roots for the following year.
Q: I want to know if I have to cut back my Purple Allium flowers? They are huge, and I don't want to cut off the tops if I am not supposed to. (Utah)
A: You are probably talking about the giant Allium (or globe Allium), an onion relative. For all members of this family you can cut the flowers off after bloom, and, in fact, with many you want to in order to keep them from reseeding prolifically. Just leave some foliage to continue growth. You can even keep the narrow foliage of some you've cut back (such as with chives) as they regrow from the base.
Q: "Something" ate my Solomon Seals. A rabbit? Bugs? Creepy crawlies? What can I do? (Ohio)
A: Has your Solomon Seal resprouted? If not, dig around the roots to see if they are still there, perhaps with buds, or just mushy and rotting. Many perennials with this kind of damage early in the season will eventually resprout, or if late in the season resprout next year, so be patient.
If insects are the problem, you will usually see them chewing on leaves. If the leaves have holes, and your planting is in damp shade, it could be slugs. Or the culprit could be a larger mammal, as you suggest, like a rabbit. See my leaflet on these pests and controls at http://pss.uvm.edu/ppp/pubs/OH52anml.htm
Q: My primrose leaves are very limp and falling off. Some are black. The plant doesn't look like it needs water. It has fertilizer and food. What's wrong? (Alaska)
A: If the plant has wilted leaves, yet plenty of water in the soil, it could mean that water isn't reaching the leaves due to a root disease caused by fungi, or stem disease from bacteria. If the latter, there is not much you can do except toss the plant.
If the roots are mushy or discolored or darker than the usual white roots of most plants, you probably have a root disease. Remove the diseased roots, repot or replant the plant, and keep the soil on the dry side. Hopefully, new roots will form, and the plant will recover. You can buy fungicides for root rots, but often they are specific for the disease with no one chemical covering all. Check with your local university plant diagnostic lab or your local Extension office for help in identifying the disease if the cultural treatments above don't work.
Q: My hollyhock leaves are turning brown and withering. There is enough rain, so dryness is not the problem. What can I do to save them? (Vermont)
A: It could either be a leaf disease, or other disease to stems or roots (this could include other damage) that doesn't let water get from roots to foliage. Most likely it is rust disease. You should see rusty spots on leaf undersides (yellow on top) that will eventually cause them to yellow, wither, and fall off, starting with lower ones first.
Remove the infected leaves that you see at beginning of the season. You can use chemical sprays, as well as some organic ones such as sulfur, but check with your local garden center. Control often means frequent reapplications.
My hollyhocks usually get this but still flower fine. It is a common disease, and takes a lot of effort to control. Cut back infected parts after bloom and continue to destroy any plant parts that get more rust, as it may overwinter on these.