Late Fall!
When Leaves Drop from Houseplants, Aim to Fix Low
Light, Improper Watering and Drafts
Dear Janet,
I have two ficus trees. One has a leaf drop problem. It
spent summer on a covered porch which faces east. It looked
fabulous! It was moved to a westerly door wall window corner --
it's probably getting more light now than during summer but it's
lost nearly half its leaves. My other ficus summered on a shaded
open deck facing west. This tree has not dropped a single leaf
since being brought indoors to a well-lighted sun porch with a west
exposure.
I know the ficus is notoriously finicky but I don't
understand the difference between these two trees'
reactions.
C.D.
Dear C.D.,
The simple answer is that conditions are worse for the one tree.
Sometimes it's tough to discern such a disparity, but I think
there's less mystery here than you think.
Low light, improper watering and severe temperature swings are
common causes of leaf drop. Look at each, for each plant.
I doubt your troubled tree is receiving a tenth the light it had
in summer. Even on a cloudy winter day outdoor light levels reach
200 to 5,000 foot candles -- foot candles measure light intensity.
Inside at our brightest work bench we operate with 40 foot
candles.
Our perception of light is so different than plants' that we may
never recognize the deep shadow next to a window. A tree at the
window's corner is greatly disadvantaged compared to one at the
center -- it may receive only 20% as much light.
Leaves shed for lack of light usually yellow first, then drop
from lower, older and interior branches. Plants that need full sun
or bright filtered light like "Ficus benjamina" suffer most, living
off stored energy and shedding leaves they can't support until they
once again receive the optimal 5,000 to 10,000 foot candles.
Next comes overwatering, which can exacerbate low-light leaf
drop. Give one plant 80% less light but water both the same and the
first can't draw the water up to its foliage -- a movement that's
directly dependent on sunlight. Unused water sits around the roots,
killing and rotting them so the plant has even less ability to take
up water when it's next in the light.
Different potting mixes or variation in pots can also cause
otherwise identical plants to need separate watering schedules.
Depot a plant and look at its roots to see if rot is at
work.
Water only when the soil surface becomes dry. Add enough to wet
the entire root ball -- you'll see water exit the drain hole when
this has happened. Pour off excess from the overflow saucer after
20 minutes.
Draftiness might be causing or contributing to the problem. A
draft can create a 20-degree temperature change, enough to put a
plant in danger. Have you experienced the misery of being the only
one in a party shivering, because you're in line with the cold
breeze or fan? Perhaps your one tree has that sad lot but no voice
to tell you. If the leaves aren't yellowing before they fall, it's
likely. Move the plant or baffle the draft with a screen.
Still puzzled? Then rely on the tenacity of plants. I have two
crotons that summer outdoors. They come in and immediately begin
defoliating. Although they're both centered in south windows, low
light is their problem. I should aim a grow light at each one.
Instead, I water carefully, keep the leaves clean to beat back
mites and other pests that could make things worse, and accept that
the plants will drop 90% of their lovely foliage before spring. I
rush them back out to their covered north porch in May where they
revive and look spectacular all summer and fall.
Dear Janet,
I had my hibiscus outside this past summer. It didn't
bloom. I brought it inside and began feeding it. I was so happy --
it formed buds on every stem. It opened a few flowers and then the
buds started to fall off. What could be wrong?
A.G.,
Dear A.G.
Decreasing light intensity and shorter days may be the trouble
but drafts or low humidity are often to blame when flower buds
drop.
Plants need at least 40% humidity to be healthy, but in winter
we subject them to desert-like 5% humidity. Change this by running
a cool vapor humidifier. As side benefits your wood furniture will
be less likely to crack, and you'll suffer less from chapped lips
and dry, virus-susceptible nasal membranes.
Green thumbs up
to fingernails, now making their seasonal reappearance on
gardeners' hands. How much more we appreciate what a nail-tipped
digit can do, since we operate without them for months every
year!
Green thumbs down
to heavy-handed packing of poinsettias. Please, when you wrap my
poinsettia for its trip home, remember how brittle its branches
are. I hate to unwrap it and find half the plant I bought.
Originally published 12/7/02