Tomato: lower leaves turning yellow

What it is likely to be on tomato

1. Normal leaf ageing

   May be normalvery common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Tomato — cultivation

   Checked 2026-08-13

   Not a problem, and included as a candidate because it is one of the commonest explanations for a single yellow leaf on an otherwise healthy plant. Every plant sheds its oldest leaves; a differential that cannot return 'nothing is wrong' will always find something to blame.

   Points towards it

   • · only the oldest leaves are affected, working steadily up from the base as the plant matures
   • · the progression is even rather than patchy

   Argues against it

   • · the newest growth is affected, and ageing works from the bottom up. Yellowing at the top is never senescence — this rules it out entirely.
   • · yellowing between green veins is a deficiency signature rather than an ageing one

   Check this next

   Look at where the yellowing stops. Ageing is confined to the lowest leaves and moves up one leaf at a time as the plant grows; a deficiency affects a band of leaves at once and usually leaves the veins green.

   What to do now

   Remove the yellowed lower leaves and carry on. On a cordon tomato this is routine maintenance rather than a problem — it improves airflow around the base, which reduces disease risk.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Tomato — cultivation

   Checked 2026-08-13

2. Magnesium deficiency

   Candidate 2very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Magnesium deficiency

   Checked 2026-08-13

   Yellowing between the veins of the OLDER, lower leaves while the veins themselves stay green. Magnesium is mobile within the plant, so it is withdrawn from old growth to supply new — which is exactly why the pattern starts at the bottom.

   Points towards it

   • · yellowing between veins that stay green is the magnesium signature, and tomatoes in containers show it more than almost any other crop
   • · magnesium is mobile, so the plant strips it from the oldest leaves first
   • · high-potassium tomato feeds compete with magnesium uptake, so heavy feeding can bring it on

   Argues against it

   • · an even yellowing with no vein pattern points to nitrogen or to ageing rather than to magnesium

   Check this next

   Hold a yellowing leaf up to the light. Magnesium leaves a clear green network of veins against yellow tissue; nitrogen shortage and ageing both yellow the whole leaf evenly, veins included.

   What to do now

   Very common in tomatoes grown in containers and growbags, and rarely serious. Keep feeding and watering even; a plant carrying a heavy crop will show some of this whatever you do, and the fruit is unaffected.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Magnesium deficiency

   Checked 2026-08-13

3. Nitrogen deficiency

   Candidate 3common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Nitrogen deficiency

   Checked 2026-08-13

   The classic pattern is uniform yellowing that starts on the OLDEST leaves and works upward, because nitrogen is mobile within the plant and is withdrawn from old growth to feed new. That directionality is what separates it from most other causes of yellowing, and it is observable without any equipment.

   Points towards it

   • · nitrogen shortage yellows the whole leaf evenly, veins included
   • · nitrogen is mobile and moved to the newest growth first

   Argues against it

   • · the veins are staying green, and a clear green vein network against yellow tissue is the magnesium signature rather than the nitrogen one
   • · nitrogen is mobile: the plant moves it out of old leaves to supply new ones, so a shortage never shows on the newest growth first — this rules it out entirely.
   • · the plant has been fed recently, which makes a nitrogen shortage less likely

   Check this next

   Check whether the veins stay green. Uniform yellowing including the veins, with the whole plant a paler green and growth slowing, is nitrogen; a green vein network is magnesium.

   What to do now

   Feed with a balanced fertiliser at the rate on its label. On a fruiting tomato be cautious about pushing nitrogen hard — it produces leaf at the expense of fruit.

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Nitrogen deficiency

   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 tomato — 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 Tomato profile lists the problems it is prone to.