Nitrogen deficiency
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uniform yellowing that starts on the OLDEST leaves and works upward, because nitrogen is mobile within the plant and is withdrawn from old growth to feed new.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.
Described view
Two tomato leaves photographed flat side by side against a neutral ground: one showing magnesium deficiency, yellow between the veins with the vein tissue itself staying distinctly green in a herringbone pattern, and one showing nitrogen deficiency, faded uniformly pale from the whole leaf including the veins
What brings it on
Light sandy soil where nitrogen leaches over winter, a container that has not been fed for several months, heavy rain on an unprotected bed, or a plant in old exhausted compost. Also common where woody material has been dug in, which locks up nitrogen while it breaks down.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Nitrogen deficiency
Checked 2026-08-13
Preventing it
Ordered by how much difference each measure actually makes, not by how often it is repeated.
- Feed container plants through the growing season and top-dress beds with compost or a balanced fertiliser in spring. Nitrogen is the nutrient most readily lost from soil and the one most often short.
source
Sourced guidancehigh confidence
- Agriculture and Horticulture Development Board — AHDB: Nitrogen management
Checked 2026-08-13
Dealing with it once it is there
- Apply a balanced liquid feed and expect a visible response within one to two weeks in the growing season. A plant that does not green up after feeding did not have a nitrogen problem, which makes this a useful diagnostic as well as a treatment.
source
Sourced guidancehigh confidence
- Royal Horticultural Society: Feeding plants
Checked 2026-08-13
Signs that lead here
Each of these lists the other things that produce the same sign, and how to tell them apart.
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.