Rhododendron: lower leaves turning yellow

What it is likely to be on rhododendron

1. Lime-induced chlorosis

   Candidate 1very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Lime-induced chlorosis

   Checked 2026-08-13

   Yellowing between the veins of the YOUNGEST leaves while the veins stay green. The soil usually contains plenty of iron; what is wrong is that the pH is too high for the plant to take it up. Adding iron to the soil without correcting the pH changes nothing.

   Points towards it

   • · iron cannot be moved around the plant, so the yellowing appears between the veins of the YOUNGEST leaves while the veins stay green
   • · on an acid-loving plant this is the tell: iron shortage strikes new growth first, where nitrogen shortage strikes old growth first
   • · it follows the soil, and is far commoner in the ground than in ericaceous compost

   Argues against it

   • · yellowing confined to the oldest leaves points to nitrogen or to normal ageing. Iron is immobile, so a shortage cannot show on old leaves while new ones stay green — this rules it out entirely.

   Check this next

   Look at which leaves are yellow and test the soil pH. Youngest leaves yellow with green veins, on a plant that wants pH 4.5–5.5, is lime-induced chlorosis — and it will keep happening on alkaline soil however much you feed it.

   What to do now

   Test the pH before doing anything else. If it is above about 6, the long-term answer is to grow it in a container of ericaceous compost rather than to keep treating the ground — feeding does not fix a plant that cannot take up what is already there.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Lime-induced chlorosis

   Checked 2026-08-13

2. Root rot

   Candidate 2common on this plant

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Rhododendron — problems
   • Plant Finder — Missouri Botanical Garden: Rhododendron root rot

   Checked 2026-08-13

   The consequence of prolonged waterlogging rather than an independent event: water moulds that are present in most soil and compost become active when roots are deprived of air, and colonise tissue that is already dying. The treatment is therefore the watering, not the fungus.

   Points towards it

   • · a rhododendron's roots occupy the top spit of soil, which is the layer that stays saturated on clay
   • · a failing root plate starves the entire shrub at once rather than a branch or a flush
   • · it follows the drainage of the planting site

   Argues against it

   • · the ground is dry, so the roots are not drowning — a dry rhododendron is a thirsty one, and the two want opposite treatment — this rules it out entirely.
   • · a clear green vein network on yellow tissue points at iron availability rather than at dead roots

   Check this next

   Scrape the bark at the base of a stem with a thumbnail and dig a hand's depth into the soil beside it. Live rhododendron tissue under the bark is green and the roots are fine, pale and springy; brown under the bark, or roots that are dark and break rather than bend, means the root plate has gone — and no amount of ericaceous feed reaches a plant that cannot drink.

   What to do now

   Stop watering entirely and check whether the plant is sitting in a hollow that collects run-off. On heavy ground the durable fix is to lift the shrub and replant it high, on a low mound of composted bark and leafmould proud of the surrounding soil, rather than to improve the hole it is already in.

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Rhododendron — planting

   Checked 2026-08-13

Narrow it down

This page lists everything at once, which is the right shape for reading and the wrong shape for deciding. The interactive tool asks one question at a time, starting with whichever would separate these causes fastest, and stops as soon as further answers would not help.

Opens with the plant and the symptom already set. Nothing you answer is stored or sent anywhere — the answers live in the address bar and nowhere else.

What this does not cover

These are the causes GrowingHQ holds rules for on rhododendron — not every cause there is. Where several problems look alike, the honest answer is often that they cannot be told apart by eye, and a page that named one would be guessing. If none of the above fits, the general lower leaves turning yellow page lists causes across all plants, and the Rhododendron profile lists the problems it is prone to.