Water the soil, not the leaves
Water the soil, not the leaves. A film of water on a leaf is what most fungal spores need in order to germinate.
Well established A person has checked it against its sources. If you skip this, it still grows, just less well. The planner suggests it.
How it works
A spore landing on a leaf needs liquid water on that surface to germinate and enter it. Water delivered to the soil never puts a film there; water thrown over the plant does, and the longer it lasts the more of the spores already present can use it.
What to do about it
Put the water at the base with a soaker hose, a drip line, or a wand held low, so the foliage stays dry. If overhead is all you have, water when the leaves will dry quickly, so they are not wet into the night.
How much it matters: Not quantified by any source read. The mechanism is stated categorically (spores require the water film), but no source read gives an infection rate, a wetness-hours threshold, or a difference in disease incidence between watering methods. Deliberately left unquantified.
The evidence
Evidence: checked against 3 sources in the research-based literature.
The 3 sources
This layer of water is exactly what most plant diseases-causing fungi require for their spores to germinate and infect.
Soaker hoses, drip irrigation, or watering at the base of the plant all help keep the foliage dry.
If possible, avoid watering at the foliage of the plant which can lead to disease.
Where this rule stops
This rule is about where the water goes. It does not set a time of day. Of the sources read, one names early morning and another suggests mid-afternoon when overhead watering is unavoidable; both are reasoning about how fast the leaves dry. So the rule says what they agree on and leaves the hour alone. It also says nothing about how MUCH or how OFTEN to water. That is a weather question, and the planner will not answer it: it has no weather feed, so it will not invent a watering schedule.
Read next
How this rule has changed
Every change is dated, newest first. The full record, with each reason, is in the data download.
- Wording made clearer
- Added to the rules
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Cite this page
Milpa Gardens. “Water the soil, not the leaves. A film of water on a leaf is what most fungal spores need in order to germinate.” Evidence grade: Well established. https://milpa.garden/rules/water-soil-not-leaves-film-water-leaf/
A garden planner built on graded evidence. Every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.
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How we grade evidence
- Well established
- The rule names its mechanism and is settled, by sources a person has read and checked or by plain arithmetic and geometry.
- Promising
- The mechanism is named and the literature backs it. A few questions are still open.
- A good hunch
- Plausible by its mechanism, but field studies are thin, so treat it as a lean.
- Contested
- The evidence points both ways, or no study has tested it, so the planner does not enforce it.
- Refuted
- The claim did not survive its sources. It is kept so the folklore can be answered.