Annual Minimum Temperatures in Pennsylvania
(Click to enlarge)
Pennsylvania is in hardiness Zone 5 and 6
While it has been problem-free in our demonstration gardens
(even Bambi does not bother it), growing it indoors is more of a
challenge. The dead area on your plant could be due to a number
of factors, including overwatering, underwatering, not enough
sun or powdery mildew.
When it comes to growing rosemary indoors, the more sun, the
better. A south- or southwest-facing window is best. Be sure to
give the plants a one-quarter turn frequently to expose all
parts of the plant to as much sun as possible. This also keeps
them from growing lopsided.
Proper watering of Rosemary is important
factor is that rosemary overwinters best indoors between 50 and
60 degrees, cooler temperatures than people find comfortable in
their homes. I've had good success overwintering rosemary in a
bright attached garage where winter temperatures stay between 40
and 50 degrees.
Watering is perhaps the most critical factor in successfully
overwintering rosemary indoors. The trick is to keep the soil
evenly moist without overwatering. You want the soil to dry
slightly in between waterings, but you never want it dry out
completely. Overwatering kills rosemary with root rot, but if
you allow it to dry out completely, it will die almost
Many factors work together to determine how often you
should water any houseplant:
Potting soil texture - Light artificial mixes dry faster
than those that contain soil mixed with amendments such as
perlite, vermiculite, compost, bark, grit, sand and/or peat
moss. An ideal potting mix for rosemary would have sharp
drainage while holding some moisture.
The ratio of pot size to plant size - Small pots with
large plants require more frequent watering than larger pots.
Large pots with small plants may hold too much water and create
perfect conditions for root rot to start.
Type of pot - Plastic pots hold more moisture than clay
pots and do not need to be watered as frequently. However, clay
pots "breathe" through their sides and create a more favorable
environment for the roots of many plants, including rosemary.
Air temperature - Plants grown in cool (50- to
60-degree) temperatures use less water than those grown at
warmer temperatures (70 to 80 degrees).
Whether or not the plant is actively growing - Plants
that are putting on new growth use more water than those that
are just sitting there. New growth is more tender and succulent
and loses moisture more rapidly than older growth that has
Rather than watering on a set schedule, every Monday for
example, get into the habit of feeling the soil before you
water. If the top inch or two of soil is dry, go ahead and
water; if it is still moist, hold off until it is drier.
Evergreen foliage of Rosemary
mildew is a fungal disease characterized by a white coating on
the leaves. Since the underside of rosemary leaves and its new
growth are covered with very fine white hairs, powdery mildew
may go unnoticed until it is severe. At that point, the plant
can be defoliated pretty quickly and may not survive. Powdery
mildew seems to be more of a problem for growing indoors than
outdoors because air circulation is not adequate indoors. Space
plants to allow as much air circulation as possible, and monitor
them closely throughout the winter. You can also position a
small fan to blow on the plants for a few hours every day to
create some air circulation.
Ultra-fine horticultural oil applications easily control powdery
mildew on rosemary without using stronger fungicides. Be sure to
use ultra fine horticultural oil rather than dormant oil.
Horticultural oil is more refined and less likely to burn the
foliage. Read and follow label directions as to application rate
and intervals between applications. More is never better, and
too strong a solution or too frequent application can also burn
Weeping Fig leaf drop
Fungus Gnats - those houseplant pests
Gardenia house plants