Sticky residue on houseplants is almost always honeydew, a sugary substance excreted by sap-sucking insects including mealybugs, scale insects, aphids, and whitefly. If your plant has sticky leaves, check it carefully for these pests, particularly on the undersides of leaves and in stem junctions where sap-suckers congregate. The honeydew itself is harmless to the plant, but it is a reliable indicator of an active pest infestation that needs treating, and if left on the leaf surface it can develop a black sooty mould that blocks light absorption.
Identifying the Pest From the Sticky Residue
Different pests produce honeydew in slightly different distributions, and they leave other distinctive signs alongside it. Mealybugs produce sticky honeydew alongside white cottony deposits visible in leaf axils and stem junctions. Scale insects produce honeydew and leave small brown or tan shell-like bumps on stems and the undersides of leaves. Aphids cluster on new growth and produce copious honeydew quickly; they are most common on soft new growth, particularly in spring and summer. Whitefly produce honeydew and, when disturbed, flutter up from the underside of leaves as a cloud of tiny white insects.
Check the undersides of all leaves and all stem junctions. A magnifying glass is helpful for identifying smaller pests like scale crawlers. See our comprehensive guide to pests and how to manage them here.
What to Do About Sticky Residue
First, treat the underlying pest infestation. Sticky residue without treating the pests will recur as long as the insects are feeding. Treatment depends on the pest, and you can read more information in our detailed guide.
Once the infestation is controlled, clean the sticky honeydew from the leaves with a damp cloth. Left in place, honeydew encourages the growth of sooty mould, a black fungal coating that blocks light. Wipe each affected leaf with a cloth dampened with water or a very dilute soap solution, taking care not to press too hard on delicate foliage. New growth produced after the infestation is cleared will be clean.
Can the Sticky Substance Come from the Plant Itself?
Yes, in some cases. Some plants produce natural sticky exudates from glands on their stems or leaves that are not related to pests. Carnivorous plants (sundews, some Drosera) produce sticky mucilage on their leaves as a trapping mechanism. Some Ficus species can exude small amounts of latex from stem wounds. However, if the stickiness appears on a plant that was previously clean and is not a carnivorous species, pest inspection should be the first step.