Normal autumn leaf fall
A deciduous tree, shrub or cane turning yellow through autumn before dropping its leaves. The plant is withdrawing nitrogen and magnesium out of the foliage and storing them in wood for next spring, which is precisely why the leaves go yellow — the green is being taken back. Diagnosing it as a deficiency inverts what is happening, and the feed that follows arrives at the one time of year the plant has no use for it.
What brings it on
Shortening days and falling night temperatures, on any deciduous woody plant. It runs to a timetable rather than a cause: the whole canopy goes together over two to four weeks, the tree is otherwise sound, and nothing was done to it beforehand. A single branch yellowing in August is something else entirely.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Trees and shrubs — seasonal change
Checked 2026-08-13
Usually seen: September, October, November
Dealing with it once it is there
- Nothing, other than not feeding. Autumn is the wrong time for nitrogen on a woody plant — it pushes soft growth that will not harden before frost — and the leaves are worth raking up and composting rather than treating.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Feeding trees and shrubs
Checked 2026-08-13
- Where a fruit tree carries a leaf disease, autumn is the moment to collect and remove the fallen leaves rather than compost them, because that is where next year's spores overwinter. That is a sanitation job on top of a normal process, not a treatment for the yellowing itself.
source
Horticultural consensusmoderate confidence
- Royal Horticultural Society: Apple scab — control
Checked 2026-08-13
What it affects
On sprays and treatments
GrowingHQ does not tell anyone what to apply, at what rate, or how often. Pesticide approvals differ by country, change without notice, and the product label is legally binding — it is also the document you are holding. What is described here is cultural and physical control, which is what a home grower can act on without a label in front of them.
Plant-specific guides
Where this is one of several causes that look alike on a particular plant, GrowingHQ publishes the differential rather than the general answer.