Houseplants FAQ

Parlor Maple Woes. 5/4/2004

"I have a parlor maple that frequently has leaves turning yellow and then dropping.  Is this too much sun or a watering problem.  Thanks.......L. M."

Yellowing and dropping of leaves could be little more than normal attrition. I said, "could." On the other hand, any more than a very few over the space of weeks could indicate some sort of physiological or environmental stress. I suggest you look carefully at:

• Nutrition. Is the plant fed on a regular basis? Have fertilizer salts built up around the lip of the container or around drainage holes? I'd recommend weekly feeding with any commercial liquid fertilizer that has a slightly higher middle number to encourage flowering, and that also provides micro-nutrients ("trace" elements). I'd also encourage to give the plant a thorough fresh-water "flush" once a month to dilute any accumulated salts (that usually manifests as yellowish-brownish scale-like deposits on the container's lip, soil line, and drainage holes).
• Root ball. How many years has the plant been in that container. Most houseplants (those held captive in the oftentimes hostile environment of a container) benefit -- and appreciate -- repotting into fresh soil and a clean container every year...certainly no less frequently than every other year.
• Watering. Over-watering (that includes allowing the container to remain in a water-filled tray or saucer constantly) is a frequent cause of stress. Water when the soil surface dries out, then (and then only) water sufficiently that excess freely flows through drainage holes.
• Lighting. Parlor maples are low- to medium-light plants. They can handle brief periods of direct sun, but prefer to remain far enough away from south or southwest facing windows so the period of any direct sunlight is minimized.  Too little light, on the other hand will cause the plant to "stretch" and become weakened...usually leaning in the direction of the most predominant source of light.
• Insects. Aphids and scale insects, or soil-dwelling aphid-like mealybugs, can all cause symptoms of physiological stress...including leaf-drop. Look for aphids on the undersides of upper leaves and along tender new top growth. Any natural insecticide like Safer's Soap or Pyrethrin will destroy aphids. (Pyrethrin is little more than processed Painted Daisies.) You might want to do the spraying out side or on the porch because the odor is a bit like rancid soap. Not offensive, but not something you want your guests to smell in the living room. Scale appears as very small (1/16th to 1/8th inch across) upside-down-saucer-like critters that hug stems (usually not leaves) in the upper half-to-third of the plant. An indication of scales would be blackish, sticky deposits on the surfaces of leaves below where the scales are. Scale is more difficult because they have a highly-effective protective shell made of chitin that must be penetrated before any insecticide can have any effect. Plain drug store rubbing alcohol straight out of the bottle dissolves that external shell...allowing the Safer's or Pyrethrin to do its job. After the spray has dried from the leaves, give the entire plant a good, fresh-water (room temperature) shower. Soil insects are a simpler matter. Repot, removing as much of the original soil as practical without damaging the root system, then flushing with a half-recommended-strength Safer's or Pyrethrin.

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