Value Village ／ Everyday know-how
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Japanese balconies grow things — herbs, tomatoes, and every summer a wall of bitter gourd or morning glory trained up a net over the window. The "green curtain" is a government-promoted cooling measure, not a hobby, and the balcony rules that govern it are strict.
| Item | Detail |
|---|---|
| Plants | Gōya (bitter gourd), morning glory (asagao), cucumber, passionfruit, loofah (hechima) — fast annual climbers |
| Set-up | Net (10 cm mesh) fixed from the balcony rail or planter to a hook above the window; planters 30–40 L with 2–3 plants per metre; sow May, cover the window by July |
| Effect | Municipal measurements: window surface 5–10°C cooler, indoor 1–3°C cooler, with the cooling of transpiration added to shade |
| Water | Daily, morning; a 30 L planter dries in a day in August |
| End | Cut down in October; seeds saved; the net stored |
| Promotion | The Ministry of the Environment's "Green Curtain" campaign and many cities (Itabashi, Yokohama, Kyoto) distribute gōya seeds and run contests |
[Verify] Temperature effects with municipal green-curtain reports (e.g. Itabashi Ward); load figures with the Building Standards Act; bylaws with your building's management rules.
They are a cooling device: exterior shade stops solar gain before the glass (see the summer heat article), and the leaves cool the air by evaporation. The aubergine and cucumber harvest is a bonus.
Almost universally prohibited: a falling planter is the condominium's nightmare. Planters sit on the floor; nets fix to hooks on the building side or to free-standing frames.
Fast annuals with big leaves: gōya is the standard because it grows 3 m in two months, resists pests and heat, and is edible. Ivy and perennial climbers damage walls and are banned.
In August a balcony planter dries in a day; the vine wilts by noon. Morning watering, saucers or self-watering planters, and mulch.
Illegal dumping. Soil is not collected as rubbish in most cities; refresh it with compost and reuse, or use a garden centre's take-back service.
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https://ondankataisaku.env.go.jp/coolchoice/
https://www.city.itabashi.tokyo.jp/
https://www.mlit.go.jp/jutakukentiku/house/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
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