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Tender Perennials Indoors: Problems/Solutions
By Dr. Leonard Perry, Extension Professor, University of Vermont

Temperature, and its balance with light, are the two most important conditions
for successful overwintering of tender perennials indoors, in addition to
proper watering.  

Your plants will show symptoms if these conditions aren't to their liking, but
these may be confused with other causes, and once they show these it may be
too late!  

While perennials are hardy in their native climates, in colder regions they may
grow as an annual, and so are called "tender perennials."  These include such
plants as coleus, cannas, geraniums, and sages or salvia.
Even if plants didn't get inside during fall, but they were left in a protected
location, many will withstand some cold and some will even withstand some
frost.  If they were subjected to such conditions, try cutting back when bringing
into the warmth.  If they are still living, you should see signs of buds or new
growth in a week or two.  
Plants Losing Leaves?

If a tender plant you are overwintering inside is losing its leaves, perhaps it is
too cold, or cool for too long a period.  With high energy prices, and many
turning down thermostats especially at night, such conditions are more
common.  Wilted, pale leaves in spite of adequate watering is another sign the
plant is too cold.  

If a plant such as coleus has lost its leaves, it may be too late to revive it.  Try
moving such plants into a very warm area (above 55 degrees F at night and in
the 70s during the day), and don't water if the soil is at all damp.

Other plants such as lemon verbena and hibiscus normally lose their leaves, or
"defoliate", as part of the normal cycle.  Others that were outdoors in sun
during summer, when brought indoors to much lower light in fall, may lose
their leaves in the process of making new leaves better adapted in their cell
structure to the lower light indoors.
Over or Under Watering Problems

Over and under watering may also cause plants to lose their leaves.  Check the
soil with your finger, an inexpensive soil moisture meter you can get at
complete garden stores, or look at the surface.  

If leaves are falling and the soil feels wet, or is dark, and the pot is heavy, it
may be too wet.  If it feels dry, is light in color, and the pot is light, it may be
too dry.  If either of these, correct gradually, don't immediately go to the other

Check plants in saucers to make sure when watering that the water doesn't
remain in the saucer for more than a half hour.  If room, place plants on a tray
of pebbles you can moisten when you water.  This is great for house plants too,
allowing the water to drain from pots, and keeping humidity higher around
the plants.  In general, and if in doubt, keep tender plants indoors on the dry
Make Sure Moisture is Right for Summer Bulbs

Moisture also is critical for storing of some summer bulbs.  Dahlias and cannas
should be kept moist, while gladiolus should be stored dry.  Too much of the
other for these may cause them to rot or die overwinter.  Temperatures below
freezing may kill them as well, as I've learned in years past when they were
placed too near a cold wall with minimal heat.
Don't Make it Too Hot for Plants

On the other hand, if plants are in too warm conditions such as next to heater
vents or a wood stove, they may have elongated and thin leaves with spindly
stems.  This is a sign they are getting too much warmth and not enough light.
So the solution is to move to a cooler location with similar light, or increase the
light.  The latter can be done by supplemental lighting from lamps.    
Portable clamp-on light fixtures can be used, either to supplement natural
daylight or to add light during the night.  Aim for 16 to 18 hours of light per
day, with lamps a foot or so away from the plants.  This is enough space to
allow the heat from incandescent bulbs to not burn the leaves, yet to provide
sufficient light.  If using energy-saving bulbs that emit much less heat, lamps
can be placed closer.  Inexpensive timers from garden and hardware stores are
used to control such supplemental lighting.  
Keep Indoor Plants Away from Drafts

Keep tender perennial plants, as well as house plants (many of which can be
considered tender perennials), away from drafts.  These could be from doors or
windows.  If a sunny day in winter and you open the window for a short time
for some fresh air, make sure to remember and shut it.  Even a brief exposure
to cold once the temperature drops is enough to injure many tender plants, and
is more common than you might expect.
Just as with house plants, check tender perennials indoors regularly (at least
weekly, or when watering), for pests.  Many of these are small, so you may
need a magnifier such as for coins, or reading glasses.  Especially check under
leaves, the growing tips, and the leaf axils where leaves join the stems.  If you
find pests, deal with them then before they spread to other plants and get out
of control.  You may find that some plants are just too much trouble, being a
favorite of pests.  I've found this the case with lantana and whiteflies, for
Much more on the correct conditions for particular plants, troubleshooting problems then
dealing with them, can be found in the excellent reference from Storey Publishing by
Alice and Brian McGowan, Bulbs in the Basement Geraniums on the Windowsill.