What is the sticky stuff falling from my jacaranda onto my windows?
Honeydew, which is aphid excretion rather than tree sap or nectar. Aphids feed on the jacaranda and excrete a sugar solution that rains down continuously through a bloom running from late April to mid June. Fresh, it comes off with plain water and almost nothing else. Left on hot glass in full sun it cooks into the surface, and then black sooty mold grows on the sugar, at which point you have a biological problem on the pane rather than a film. The practical answer is timing rather than chemistry: hose the worst panes during the bloom, and book the actual cleaning for early July once the drop has finished.
When it happens: Late April through mid June, with sooty mold appearing on hardened film from late May onward.
Can it be fixed?
Usually removable
Almost always, and it rarely damages the glass. Fresh honeydew rinses with plain water. Hardened honeydew needs warm water with real dwell time and gentle agitation, and it will come off; the sugar is water-soluble even when it has set. Sooty mold that has established on top of it needs a mild cleaning solution rather than water alone, because you are removing an organism rather than a residue. The genuine risk is not permanence, it is scratching: dried honeydew traps grit, and dry-wiping it drags that grit across the pane. Flood it, wait, then work it.
Jacaranda mimosifolia is an enormously common street tree across Los Angeles, and it blooms from late April into mid June. That bloom supports very large aphid populations feeding on the flowers.
Aphids consume far more plant sugar than they can process. The excess is excreted as honeydew, a sticky carbohydrate solution, and with a large enough colony it falls more or less continuously for the length of the bloom.
On a cool surface honeydew stays water-soluble and rinses off easily. On glass in direct Southern California sun the water fraction flashes off within minutes and the sugars concentrate and harden onto the surface.
Hardened sugar is a food source. Sooty mold, a group of dark fungi that live on honeydew rather than on the plant, colonises it within days to weeks. That is the black film people mistake for pollution, and it needs to be killed rather than simply wiped.
Nothing beyond a normal window cleaning in most cases, and that is worth saying plainly because it is sometimes sold as a specialist service. Where sooty mold has established across a large elevation it adds a solution step and some dwell time, which is a modest addition rather than a separate job. The genuinely useful cost saving is scheduling: a clean in mid-May on a jacaranda block is money spent on a result that lasts about a week.
This is one of the more DIY-friendly window problems there is. A hose and plain water, used on fresh honeydew before it bakes, does most of the work. For hardened film, warm water with a drop of dish soap and several minutes of dwell before agitating will lift it. Do not dry-wipe it, do not scrape it, and do not reach for a solvent; hardened sugar does not need one and solvents on a warm pane risk streaking and can damage some frame finishes. If black mold has established, a dilute cleaning solution rather than water is the difference between removing it and smearing it.
Removing it once is half the job. This is the half that determines whether you pay for it again next year.
This problem is not evenly distributed. These are the markets where local conditions make it common, and why.
Jacaranda-lined streets through the Flats, with hot south-facing glass that bakes honeydew in within days.
Hancock Park, Windsor Square, Mid-City and much of the Eastside carry heavy street jacaranda cover.
Older districts with mature jacaranda alongside a genuine deciduous canopy, so honeydew and leaf litter arrive together.
Carlson Park and the older residential grid, where the bloom and the corridor film overlap on the same elevations.
Mature street planting through the historic districts, with original wood sash that must not be scrubbed hard.
No. Trees do not drip sap from their flowers. It is honeydew, the excretion of aphids feeding on the tree, and it is essentially a sugar solution. That matters practically, because sugar is water-soluble and sap is not: plain water handles honeydew, whereas actual tree sap would need a solvent.
Sooty mold. It is a group of dark fungi that live on honeydew rather than on the plant or the glass, so it appears wherever honeydew has been sitting long enough. It is harmless to the window but it needs a mild cleaning solution rather than plain water, because you are removing an organism rather than a residue.
Wait, if the tree is still in bloom. A clean in mid-May on a jacaranda block gets undone within about a week, because the drop continues into mid June. Early July is the appointment that holds. Hosing the worst panes with plain water in the meantime is worth more than an extra service call and costs nothing.
Almost never. The real risk is not the honeydew, it is what people do to it: dried honeydew traps grit, and dry-wiping or scraping drags that grit across the pane and leaves fine permanent scratching. Flood it, give it a few minutes, then work it gently and the glass will be fine.
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