Q. How can I maintain a smaller rounded habit of perennials such
as Sedum 'Autumn Joy' and Coreopsis 'Moonbeam'? They are 4-5
years old. A. 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 slightly delayed bloom
(which provides a longer bloom season for you and pollinators).
This cutting back generally won’t work with thin stems, as on the
Moonbeam. Make sure this one has full sun, and not too much
fertilizer nor rich soil, any of which can cause tall and floppy
Q. What do you suggest for a grass to plant along the driveway
like a hedge? A. 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, with reddish leaves.
Another group for a great upright effect of similar height is the
Feather Reed Grass (Calamagrostis), Karl Foerster being a
popular and good cultivar. These are being used just for this
purpose all over the University of Vermont campus. 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.
Q. What are the most common problems that I should be aware of
with soils? A. If a soil has a problem in our area, it is often
too low pH (too acidic). This can be corrected by adding lime,
according to a 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 that you can use 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.
Q. I have hostas with twisted, stunted, and puckered leaves. Is
this normal, or a disease? A. It depends. Some varieties show
twisted leaves normally, but there is a virus that could be the
cause on others, called Hosta Virus X or HVX. Some varieties such
as Eternal Father, Lunacy, and Leopard Frog actually have their
traits due to less virulent viruses. This HVX virus, though,
causes such deformed traits, 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
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
these symptoms, 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)
Q. Should I cut back perennials in the fall, or wait until
spring? A. Ideally you should wait until spring, so the plants
can recycle their leaves and nutrients back into the soil, provide
winter cover for wildlife, and seeds in fall for birds. Leaves of
some protect the plant crowns over winter. But, with this not
being an ideal world, many gardeners (including me) cut them back
in late fall as there is so much else that really needs attention
in spring. If foliage is diseased, make sure to discard it rather
than adding to the compost.
An alternative, hybrid approach would be to leave some perennials
that are attractive and favored by birds, cutting back the rest.
Coneflowers (Echinacea), Black-eyed Susan (Rudbeckia),
ornamental grasses, ferns, coralbells, and sedum are perennials
that you might leave and then cut back in early spring. Bearded
iris, catmint (Nepeta), bee balm, daylilies, perennial
sunflowers (Helianthus), hollyhock, peonies, tall garden
phlox, perennial salvia, speedwell, false indigo (Baptisia),
and yarrow are among those perennials to cut back in late fall.
They either become unattractive late in the season or flop to the
ground with the first snows.
Return to Perry's Perennial Pages: Green Mountain Gardener Articles-- your reliable source of gardening information for over 50 years.