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Seeing the pattern in a houseplant problem is the key to
I brought my potted Plumbago and my Duranta repens
shrubs in for the winter. They have been under grow lights since
September. Both were cut back by a third and have been watered on a
regular basis, but not fertilized. Both are now blooming but they
don't look so hot. The Plumbago has a dry shriveling leaf problem.
Not all, but many of the leaves are drying and browning and I can't
seem to get the watering right to battle this. The Duranta is doing
the opposite. Its leaves are yellowing, then dropping.
You're right to focus on care as a cure. Incorrect amounts of
light, water and fertilizer cause more plant problems than any
disease or insect.
The plumbago may be too cold at its roots and be receiving
insufficient light to use the water you're giving it. When roots
are too cold or in soil that has more water than air, they die and
begin to rot. Chronic root rot can cause leaves to wilt then brown
and die, while still attached to the stems. It usually affects
oldest leaves first.
Depot the plant or slide it at least part way out of its pot to
look for root rot. All root tips should be white or nearly so, and
firm like fresh carrots. If the roots are brown and mushy, they're
rotting. Trim off any rotted roots and air dry the root ball for a
few hours. Then let the plant dry down further between waterings.
If possible, increase the light. If the plant is sitting on a cold
shelf move it to a warmer surface.
The Duranta may have light problems, too, or need fertilizer.
When a plant has too little light or too few nutrients to support
its newest growth, it sacrifices its most shaded and oldest leaves.
They don't die in place but yellow gradually -- giving up their
nutrients to be reused elsewhere -- and drop off cleanly.
We're told not to fertilize houseplants in winter but that
doesn't apply when a plant is under lights and growing actively.
Apply a dilute fertilizer and watch the response.
You may think your plants are well lit but only an
extraordinarily strong grow light will penetrate the center and
lowest parts of a large plant. Intensity of light drops off rapidly
with distance, so that foliage a few inches from the bulb may
receive light ten times more intense than what falls on leaves
eight inches away. If you can't increase the light, accept some
thinning in the plant's nether region.
Read the leaves to diagnose problems.
When newest leaves yellow first, beginning at their margins and
ending with everything pale except the main veins, switch to a
fertilizer with micronutrients such as iron.
When oldest leaves yellow first, paling around their edges, then
in the middle and dropping off, the plant probably needs more light
or more nitrogen. Nitrogen is the first number of the three-digit
designation on the fertilizer label.
When oldest leaves yellow first, but wilt before they die and
remain hanging on the plant after death, apply remedies as in the
letter above for overwatering and root rot.
When tips yellow first and curl under, especially on thin-leaf
plants, increase the humidity.
Too much sun causes bleached tan, gray or silvery areas. Cut off
affected parts or whole leaves. Keep the plant out of direct
Brown tips indicate watering and fertilizer problems. This
"scorch" may extend along leaf margins, too. Inconsistent watering
can cause it, in which case newest leaves may be most affected. Too
much fertilizer -- all at once or building up gradually in the soil
-- can also cause scorch, but tends to be worst on oldest
Tan, pale yellow or white rings on leaves may be water spots.
Keep water from resting on those leaves. Never add cold water to
Brown or corky pock marks on leaves are oedema. It's common on
some plants, especially those with thick leaves, when light drops
off drastically soon after the plant is watered. Avoid watering
that plant when gray skies are predicted.
Leaves or flower buds drop off:
If it begins with the lowest leaves, give the plant more
If leaves drop while still green or buds drop unopened, shock is
a likelihood. Changes in light or temperature, or being
transplanted can bring this on. Plants near drafty windows are at
risk in winter.
Leaves that are sticky, seem dirty, are flecked white, have
brown flattened marks that pop when pressed, white fuzz or fuzzy
bumps are beset by insects. Clean the plant well, then consult a
pest control book.
Green thumbs up
to heirloom plants in a family, like K.K.'s 30-year-old
grapefruit tree, still flowerless but ripe with story. Generations
are tied together by tales of such plants grown from seed, stolen
as cuttings, lugged cross country or passed from hand to hand.
Green thumbs down
to forcing plants on a non-gardener. We may wish for offspring
to share our passion but should wait for that seed to germinate in
its own time. When tempted to saddle the unwilling with greenery,
send good wishes with cut flowers instead!
Originally published 2/1/03
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