Basil: lower leaves turning yellow

What it is likely to be on basil

1. Overwatering

   Candidate 1very common on this plant

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Basil — problems

   Checked 2026-08-13

   Not a matter of volume but of frequency: roots need air as well as water, and compost that never dries suffocates them. It kills more houseplants than every pest and disease combined, and its cruellest feature is that the early signs — yellowing, wilting, dropping leaves — look exactly like drought, so the instinct is to water more.

   Points towards it

   • · waterlogged compost starves the roots of air before it does anything else
   • · the oldest leaves yellow first as the plant sheds what it cannot support

   Argues against it

   • · dry compost rules out overwatering as the cause — this rules it out entirely.

   Check this next

   Lift the pot. A basil that has been overwatered is heavy, and the yellow leaves come away with a soft wet stalk rather than a dry one — the pot weight is the fastest single check on this plant.

   What to do now

   Let the compost dry until the pot is noticeably light before watering again, and empty any saucer it has been standing in. A supermarket pot holds several plants in far too little compost, so splitting the clump into two or three pots also fixes the underlying cause.

   ·source

   Sourced guidancehigh confidence

   • Royal Horticultural Society: Basil — care

   Checked 2026-08-13

2. Nitrogen deficiency

   Candidate 2common on this plant

   ·source

   Sourced guidancemoderate confidence

   • University of Minnesota Extension — University of Minnesota: Growing basil

   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uniform yellowing that starts on the OLDEST leaves and works upward, because nitrogen is mobile within the plant and is withdrawn from old growth to feed new.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 pales the whole leaf evenly rather than in patches
   • · the plant moves nitrogen out of its oldest leaves to feed the newest
   • · correctly watered compost points away from the watering explanations

   Argues against it

   • · a recently fed plant is unlikely to be short of nitrogen

   Check this next

   Compare the oldest leaves with the newest. Nitrogen shortage produces an even pale green fading upward from the bottom while the growing tips stay dark; overwatering yellows leaves individually and unevenly wherever they happen to be.

   What to do now

   Feed with a balanced liquid feed at the strength on the label, and repot if it has been in the same small pot for more than a couple of months. Basil in a supermarket pot has usually exhausted its compost rather than caught anything.

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Basil — feeding

   Checked 2026-08-13

3. Normal leaf ageing

   May be normalcommon on this plant

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Basil — growing

   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 lowest pair of leaves is involved
   • · a plant shedding old leaves loses them one or two at a time, not in a wave
   • · nothing has been done to the plant, and it is still growing at the top

   Argues against it

   • · ageing takes the bottom leaves only; a whole plant yellowing is something else — this rules it out entirely.

   Check this next

   Look at the top of the plant, not the bottom. If the growing tips are dark green and putting out new pairs of leaves, losing the lowest pair is a basil doing what basil does — especially on a plant you have been picking from.

   What to do now

   Pick the yellow leaves off and carry on. If you want fewer of them, pinch the growing tips out regularly: a bushier plant carries its leaves higher and shades its own base less, which is what triggers the shedding in the first place.

   ·source

   Sourced guidancemoderate confidence

   • Royal Horticultural Society: Basil — pinching out

   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 basil — 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 Basil profile lists the problems it is prone to.