University of Vermont Extension
Department of Plant and Soil Science
Winter News
Article
OVERWINTERING TENDER
PERENNIALS INDOORS
Dr. Leonard Perry, Extension Professor
University of Vermont
While perennials are hardy in their
native climates, if they aren't in yours but die with cold in fall,
they can be
considered tender. Many of what we
consider annuals in our climate are in reality perennials in their
native
habitats, such as annual geraniums (Pelargonium), salvia, snapdragon,
begonia, and impatiens. Whether annuals,
summer bulbs, woody plants such as hibiscus, or exotic plants such as
angel's
trumpet, knowing which of the four main climates they prefer will help
them to
live (or to remain dormant in the case of summer bulbs such as canna
and
dahlia) successfully indoors all winter.
Sunny and warm conditions can be
provided by windows facing east, south, or west in warm living areas.
Temperatures should remain between 60 and 70
degrees F. A heated greenhouse or
solarium also can provide such conditions.
The cooler the temperature, the drier you should keep the soil. These
plants require as much light as
possible. If plants become spindly with
thin leaves, consider adding supplemental light or moving plants to a
southern
exposure if possible and not there already.
Sunny and warm mimics the winter conditions for many tropical
plants. Plants keep their leaves, and
growth slows but remains active.
Some common "annuals" that
prefer sunny and warm conditions include coleus, begonia, impatiens,
lantana,
thunbergia, and Egyptian stars (Pentas).
Hibiscus prefers these conditions too. Flowering maple (Abutilon), fuchsia, begonia,
and succulents often survive fine near windows with east or west
exposures. Succulents include such
plants as aloe, jade plant and its relatives (Crassula), and kalanchoe.
Sunny and cool conditions can be
provided in an unheated sunporch or guest room, minimally heated entry
halls,
or a cool greenhouse. Temperatures
should remain between 45 and 55 degrees F ideally, or at least above
freezing. These cool temperatures help prevent insect
problems as an added benefit. The goal
with sunny and cool is to keep plants from growing, or growing very
slowly,
most the winter. They are provided a
rest period, and so are low maintenance.
Most tender perennials prefer sunny
and cool winters indoors. Mediterranean
plants such as pomegranate and rosemary, citrus such as lemons and
miniature
oranges, and silvery plants such as lavender prefer sunny and cool
winters. Some South African natives such as
lily-of-the-Nile (Agapanthus) and annual geranium are in this group, as
are the Australian hebes. Tropical
"annuals" in this group include cigar flowers (Cuphea), summer
snapdragon (Angelonia), and sages (Salvia). Many subtropical and
tropical woody plants
prefer sunny and cool winters, such as oleander, gardenia, osmanthus,
and
angel's trumpet (Brugmansia).
Some such as fuchsia and hibiscus do well under these conditions as
well
as with sunny and warm, just with less growth.
Dark and damp conditions are useful
for a handful of plants, especially tubers (swollen roots) of
sweet-potato
vine, dahlia, and canna. Store tubers in
a plastic bin or bag in a barely moist, not wet, material such as
sawdust or
peat moss. Fountain grasses (Pennisetum)
in pots can be cut back to 6 to 12 inches, and stored here as well.
Some even have luck in dark and damp winters
with pots of salvias and geraniums that normally need more light.
Provide these conditions in an
unheated cellar, garage, or crawl space.
Lacking those, a cool closet may work.
Temperatures for
cool and damp mean between 35 and 50 degrees F.
Dark and dry conditions are needed
for a handful of tender perennials, gladiolus corms being the most
common. Some salvia in this wide-ranging genus can be
stored here, unless they have formed tubers that should be stored
damp. Similar to dark and damp, cool temperatures
should range between 35 and 50 degrees F.
Plants dropping their leaves may be
a sign of too cool, too much water (rotting roots), adjusting from high
light
outdoors to lower light indoors (in which case you should see new
leaves soon),
or simply may be normal. Some woody
plants such as angel's trumpet, butterfly bush, fig, and lantana
normally lose
their leaves in winter. They can be
shaped, left in their pots without repotting (so not to stimulate new
growth),
and kept barely moist but not wet until growth resumes with the longer
days of
spring.
Much more on the correct conditions
for many individual plants, as well as tips on such topics as problems
and propagation,
can be found in the excellent reference from Storey Publishing by Alice
and
Brian McGowan, Bulbs in the Basement Geraniums on the Windowsill.
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