Greenhouse salt: white frost under the film, the bed gets saltier
The film is an umbrella, not a pickaxe. Salt has nowhere to go.
- Open-field salt comes from groundwater or the parent material; greenhouse salt is usually fertiliser that piled up.
- Dry soil is dry; salt injury wilts more after watering and shows white crust.
- Don’t throw compound on the frost; don’t keep the film on all year.
- Drip concentration: Thin and often. Start at the labelled lower rate. The thicker it is, the more it burns
- Name what you see before you feed.
- If leaves, roots and the surface disagree, stop.
- A greenhouse is a bowl; salt cannot leave.
- Heavy base dressing and strong drip make the bowl saltier.
What you see in the field
White frost under film, a ring at the dripper, more wilt after watering.Squat on the whitest, worst strip and scrape the crust. Compare with a neighbour that is still green. White crust plus scorched margins count; wilt without a crust may just be drought. Note whether the ditch actually runs.
Tap to enlarge. The caption says what to photograph. Missing field photos are marked as to-be-added.
Why it looks like this
The field looks like this because the root cannot take water or nutrients the usual way. Fix the soil condition first — drainage, salt, acidity, compaction or a salt of fertiliser — then a thin feed. Rates live in the range on this page; confirm with a local station and the label.
Easy to mix up
Looks like “Open-field salty-alkali land”
Open-field salt comes from groundwater or the parent material; greenhouse salt is usually fertiliser that piled up.
Looks like “Shortage of water”
Dry soil is dry; salt injury wilts more after watering and shows white crust.
Do this / don’t do that
- 1Compare the worst plants with a neighbour ridge. Photograph whole plant, close-up and soil surface before you add fertiliser.
- 2Match roots, leaves and the soil surface to this guide. If they do not line up, do not copy a bag count.
- 3Use the rate range on this page only as a range. Confirm with a local station and the product label.
Don’t do this first
- Don’t throw compound on the frost; don’t keep the film on all year.
Rate range
Drip concentration
Thin and often. Start at the labelled lower rate
The thicker it is, the more it burns.
Washing salt
In summer, lift the film, or a big watering plus a drain
At least once a year.
These are ranges. Confirm with your local extension station and the product label.
Read these three first
Then nitrogen, phosphorus, potassium and the micronutrients.
When you see White frost under film, test. Take soil from the bad patch and from a greener neighbour, separately.
Lesson video
2026-03-07 · Li Zeyu · For learning. Serious damage: local agronomist or a soil test.
For learning only. Fertiliser and pesticide decisions need a local agronomist and a soil test.
Not sure? Photograph the field to identify the problem