GrowingHQ

Kale: lower leaves turning yellow

2 causes GrowingHQ holds specifically for kale, what separates them, and what is safe to do before you are sure.

What you are looking at

The oldest leaves — those nearest the base — losing their green while the growing tip stays healthy. Extremely common on tomatoes and peppers, and one of the least specific signs in growing: at least four unrelated things produce it, and one of them is the plant behaving perfectly normally.

It may be nothing

One of the causes below is a normal process rather than a problem. Read that one first: treating a healthy plant does more harm than leaving an unhealthy one a day longer.

Described view

A kale plant in the ground with nitrogen deficiency: the oldest lower leaves faded to a uniform pale yellow-green including the veins, the newest leaves at the top still properly dark, and the whole plant noticeably smaller and thinner-stemmed than a well-fed one beside it

What it is likely to be on kale

  1. Nitrogen deficiency

    Candidate 1common on this plant
    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Brassicas — cultivation
    • Agriculture and Horticulture Development Board — AHDB: Brassica nutrition

    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uniform yellowing that starts on the OLDEST leaves and works upward, because nitrogen is mobile within the plant and is withdrawn from old growth to feed new.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 moves within the plant, so a short supply is taken out of the oldest leaves and put into the newest
    • · the whole leaf pales together, veins included, rather than marbling
    • · the entire plant is a paler green than it should be, not just the yellow leaves
    • · a bed crop on a long season is where this appears

    Argues against it

    • · a green vein network held against yellow tissue is magnesium rather than nitrogen, and feeding nitrogen will not touch it — this rules it out entirely.
    • · nitrogen shortage cannot show on new leaves while old ones stay green, because the plant robs the old to supply the new — this rules it out entirely.

    Check this next

    Stand back and judge the colour of the whole plant against a neighbouring one before looking at any single leaf. A brassica short of nitrogen is uniformly light green all over with the oldest outer leaves fading to yellow first, and it is SMALLER than it should be for the date — a full-sized plant with a couple of yellow bottom leaves is doing something else.

    What to do now

    Top-dress with a balanced general fertiliser or well-rotted manure and water it in, and expect the response in the new growth rather than in the leaves already yellow — those do not come back. Brassicas are on the ground for most of a year and a bed that fed them well in May is usually empty by August.

    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Feeding vegetables

    Checked 2026-08-13

  2. Normal leaf ageing

    May be normalvery common on this plant
    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Kale — 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

    • · kale is picked from the bottom up over months, so the lowest remaining leaves are always the oldest ones on the plant
    • · it is confined to the bottom of a stem whose crown is growing strongly
    • · nothing was done to it, which fits a plant simply getting older from the base up

    Argues against it

    • · a plant that is pale all over including the crown has run short of something, where ageing only ever reaches the bottom leaves — this rules it out entirely.

    Check this next

    Look at the crown rather than the base. Kale is a cut-and-come-again plant harvested upward all winter, and a tall bare stem with a few yellow leaves at the bottom and a dense blue-green rosette on top is exactly what a well-cropped plant looks like in February — the crown being tight and dark is the evidence that nothing is wrong below it.

    What to do now

    Snap the yellowing leaves off cleanly at the stem and compost them, which tidies the plant and removes the damp cover that whitefly and slugs shelter in. Keep picking from the bottom and leave at least the top six or eight leaves on the plant so it can keep feeding itself through the winter.

    source

    Sourced guidancemoderate confidence

    • Royal Horticultural Society: Kale — harvesting

    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.

Work through it for your kale

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 kale — 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 Kale profile lists the problems it is prone to.