AUTUMN PERENNIAL GARDEN QUESTIONS
Dr. Leonard Perry, Extension Professor
University of Vermont
Throughout the year I get gardening questions on my Perry’s Perennial Pages website. Here are a few gardening questions you too may have for this season.
How can I maintain a smaller rounded habit of Sedum 'Autumn Joy' and
Coreopsis 'Moonbeam'? They are 4-5 years old. Often plants
too tall or floppy are a sign of too little light. Both of these
plants in particular grow best in full sun. Even then with
age some plants, such as the Autumn Joy, may flop. Plants that bloom late in the season such as Autumn Joy, Asters, or even tall garden phlox may be cut back by one third to one half in early summer. This will result in shorter growth with more branching, and generally only slightly delayed bloom, if at all. This cutting back generally wont work with thin stems as on the Moonbeam. Make sure this one has full sun, and not too much fertilizer, or rich soil which can cause tall and floppy stems.
What do you suggest for a grass to plant along the driveway like a hedge?
If you want a tall grass (four to five feet), then consider one of the
Switch grass (Panicum) cultivars. Heavy Metal is bluish with
reddish seed heads. There are several other
good blue cultivars, but Prairie Sky tends to flop. Shenandoah is shorter, and more red.
Another group for a great upright effect of similar height is the Feather Reed Grass (Calamagrostis), Karl Foerster being a popular and good cultivar. If in a warmer climate or microclimate (USDA zone 5 and warmer) you might consider Fountain Grass (Pennisetum), about three feet high. There are many good cultivars of Eulalia (Miscanthus), from four to eight feet, which with short and cooler seasons in the north do not tend to seed nor become seed invasive.
What are the most common problems I should be aware of with soils? If a soil has a problem in our area, it is often too low pH or too acid soil. This can be corrected by adding lime, according to the soil test. A soil pH that is between 6 and 7, 7 being neutral, is often best. A soil pH that is too low or too high makes nutrients unavailable to the plant. Soil test sampling bags are available from state agriculture testing labs, often at state universities, or from garden centers. If purchasing inexpensive soil testing kits you can do at home, make sure they are new, as old chemicals in such kits can give wrong results. Fall is a good time to add lime, if needed, as ground or dolomitic limestone is slow acting. Add it now and your soil will be ready for spring planting.
I have hostas with twisted, stunted, and puckered leaves. Is this normal, or a disease? It depends, some varieties show this normally, but there is a relatively newly discovered virus that could be the cause, called Hosta Virus X or HVX (a Potexvirus). Some varieties over the years such as Eternal Father, Lunacy, and Leopard Frog actually have their traits due to less virulent viruses. This virus, though, causes traits as you note, and is highly contagious through contact of infected sap from one plant with another. This is commonly spread by hands or tools such as through pruning, so make sure to wash in between with antiseptic soap. As with other viruses, there are no cures, so infected plants should be discarded. Also like many viruses, plants may carry this one yet not show symptoms, which makes diagnosis sometimes very difficult.
The cultivar Breakdance has been reported 100 percent infected, while commonly infected cultivars include Gold Standard, Striptease, and Sum and Substance. Before buying these, or in fact any hostas, get familiar with what they should look like, and don't buy them if they look otherwise. It is easiest to see symptoms on gold and gold-centered plants, which in addition to those you note, may include random green mottling, and mottling along the veins. Since this virus must be transmitted in sap and living plants, you can safely plant where an infected plant was removed as long as there are no living roots from the old plant. Considered resistant are the cultivars Blue Angel, Color Glory, and Frances Williams. Considered immune are Bressingham Blue, Frosted Jade, Love Pat, Great Expectations, Sagae, and (sieboldiana) Elegans.
More questions and answers can be found under the FAQs on my Perry’s
Perennial Pages (www.uvm.edu/~pass/perry/faq.html).
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