UK temperature
Keeping grassy arrowhead warm in a UK home
Sagittaria graminea
More about grassy arrowhead in the UK
The UK home, in plant terms
A typical UK home creates two opposite micro-problems at the same time. Radiator-driven heating spikes the air temperature and crashes humidity in the rooms where people actually sit; the older the housing stock the more likely a single-glazed window pane is sitting at near-freezing in January with a houseplant against it. Cold unheated bedrooms, north-facing rooms and conservatories without heating run far cooler than the thermostat suggests, and the British winter gives the lowest indoor daylight in any of Growli's markets. Grassy Arrowhead tolerates a wider band, but the worst-case UK winter placement (a cold single-glazed pane plus a hot dry radiator below it) still stresses it through repeated drying and chilling.
The actual numbers
Ideally grassy arrowhead sits between 5–30°C. (That is 41–86°F in Fahrenheit.) As an aquatic marginal, it naturally occupies high-humidity waterside environments. No supplemental humidity is required outdoors. In indoor aquatic displays, ensure good air circulation to prevent fungal issues on emergent foliage. Watch for the room dropping below about 5°C overnight — common in UK unheated bedrooms in January, and the point where growth stalls and leaves chill-mark.
For the RHS hardiness side of this, see is grassy arrowhead hardy in the UK? (rating RHS H5, sourced from the RHS rating system). For the US/USDA framing of the same numbers, see the grassy arrowhead temperature guide.
Winter placement in a UK home
For grassy arrowhead through a UK winter, three placement rules clear up most problems: 1) keep it at least a hand's width back from the window pane on single-glazed or very cold double-glazed glass, especially overnight when curtains close behind the plant; 2) keep it out of the direct vertical updraft above a radiator — that column of hot dry air browns leaf tips even on tolerant species; 3) judge by the room you can actually feel, not the central thermostat — many UK rooms run several degrees below the hall reading in winter. Humidity drops to roughly 25–35% in a heated UK living room; a pebble tray, grouping with other plants, or a small humidifier puts that back to a level houseplants actually like.
Grassy Arrowhead temperature in the UK — frequently asked questions
What temperature does grassy arrowhead need in the UK?
Grassy Arrowhead prefers 5–30°C (41–86°F). The British issue is rarely the average — it is the extremes: a cold single-glazed window in January, the hot dry air directly above a radiator, or a north-facing unheated room that runs far cooler than the hall thermostat.
Will grassy arrowhead survive a cold UK winter room?
Grassy Arrowhead tolerates a wider winter band — see its RHS rating H5. Below about 5°C growth stalls; cold-wet roots, not cold air, are usually what kills it indoors.
Can grassy arrowhead go on a UK windowsill in winter?
On a single-glazed or very cold pane, no — overnight the leaves pressed against the glass can drop below the plant's comfort band, especially behind drawn curtains. A small gap (a hand's width back) or thicker thermal curtains in front of the plant fixes it, and modern double-glazing usually solves it outright.
Does UK radiator-driven heating dry grassy arrowhead out?
Yes — UK living rooms typically run at around 25–35% relative humidity in winter. That is well below what most houseplants prefer. Grassy Arrowhead tolerates this better than the calathea-and-fern family, but a pebble tray or grouping plants still helps.
What temperature range does grassy arrowhead actually like?
5–30°C is the comfortable band (41–86°F in Fahrenheit for reference). That covers normal UK living-room temperatures all year; the work is making sure cold pockets (windowsills, unheated rooms) and hot pockets (radiator updrafts) do not push it outside that band.
More grassy arrowhead care
See the full grassy arrowhead care guide, its UK watering (hard vs soft tap water), and UK hardiness.