🍅 Tomato How hard it is to control: ★★☆☆☆ 2/5

Calcium deficiency on tomato

A physiological disorder whose best-known symptom is blossom end rot. Calcium cannot move around inside the plant — it travels only with the water stream — so the shortage hits the fastest-growing, least-transpiring tissue: fruit tips and the youngest leaves. Usually there is enough calcium in the soil; the plant simply cannot get it to where it is needed.

Symptom photos

Calcium deficiency — Green fruits — dark, sunken patch at the tip — Green fruits — dark, sunken patch at the tip Photo: Siltloam, licence Public domain

Symptoms

A dark, watery, sunken patch at the bottom of the fruit (blossom end rot)
The youngest leaves at the top of the plant dying back and deforming
Edges of young leaves drying, curling and hooking over
The growing point dying back in a severe shortage
Chlorosis and necrosis on young leaves while older ones stay green
Flowers and young fruitlets dropping

What it does to the crop

Part of the crop lost — fruit with blossom end rot is inedible
Growth at the tip held back and the plant deformed
Damaged fruit left open to secondary fungal infection

What encourages it

Irregular watering — alternately drying out and flooding
High temperature and low humidity in the tunnel
Too much ammonium nitrogen, potassium or magnesium, blocking calcium uptake
Salty growing medium making water uptake harder
Acid soil (pH below 5.5) and sandy soil low in calcium
Root damage during transplanting or weeding

Prevention

Water regularly and evenly — this matters more than the calcium feed itself
Mulch to keep soil moisture steady
Keep soil pH at 6.0-6.8, liming if needed
Foliar feed with calcium chloride or calcium nitrate at the first signs
Avoid overfeeding with nitrogen, potassium and magnesium
Ventilate the tunnel on hot days to bring the temperature down

⚠️ Before you reach for a spray

This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.

Keep the disease atlas with you in the garden

In the app you can identify a disease from photos, work out the spray dose for your own bed and log the treatment in your task calendar. Free, no sign-up, works offline.

Open the atlas in the app →

📅 When to Sow Tomato? →