Nitrogen Deficiency
This problem spreads through handling, insects or soil rather than the weather, so there is no live forecast risk — focus on prevention below.
When it strikes
Fix the cause, not the leaf
No spray will help here. The trigger is soil, water supply, nutrition or temperature, so change the growing condition and judge the result on new growth, not on damaged leaves.
Not contagious
Nothing spreads from plant to plant here. Neighbouring plants showing the same signs are reacting to the same soil, water or weather, so fix the cause rather than isolating plants.
Safe to compost
No pathogen carries over on this material, so it can go on an ordinary heap with the rest of the garden waste.
When and where to look
This problem has no weather threshold. Check it on every routine walk round the bed, especially after handling plants and after bringing new stock in.
The signs that lead here
About
Nitrogen deficiency is one of the most common nutrient problems, since nitrogen is mobile and leaches readily from soil, leaving plants pale and slow-growing, especially in wet springs and sandy soils.
Symptoms
Uniform pale green to yellow colour starting on the oldest lower leaves and moving up, spindly slow growth, and small pale new leaves; older leaves may drop early.
Organic Treatment
Feed with blood meal, fish emulsion, composted manure or a balanced organic fertiliser, and mulch with compost. Plant legume cover crops to fix nitrogen.
Chemical Treatment
A quick-release nitrogen fertiliser (such as ammonium sulfate or a balanced soluble feed) corrects acute deficiency within days.
Prevention
Build soil organic matter, use cover crops and compost, avoid leaching by not over-watering, and feed hungry crops through the season.