Plant care
Stocktemperature & humidity
Matthiola incana
More about stock
Ideal temperature for stock
Stock is comfortable in any room a person is comfortable in, roughly 7–18°C (45–65°F). The mistakes are micro-climates: a north-facing window on a frosty night, a south-facing windowsill in a summer heatwave, the standing draught between an opened kitchen door and the radiator behind it. Read the room around the plant, not the thermostat. Below roughly 7°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Stock is comparatively hardy (USDA 7–10 (biennial types); grown as cool-season annual elsewhere, RHS H4). Within that range it tolerates a cold dormant spell outdoors; outside it, grow it in a container you can move under cover or overwinter in a cool but frost-free spot. Hardiness assumes an established plant in well-drained soil — a wet, cold root zone kills far more plants than cold air alone.
Humidity for stock
Stock sits happiest at around 40–65% relative humidity. Performs best in cool, moderate humidity. High summer humidity combined with heat accelerates plant decline. Good air circulation between plants reduces risk of grey mould (botrytis) and downy mildew on the dense flower spikes. The usual low-humidity tell is crisp brown leaf tips and edges while the soil moisture is fine — a sign the air, not the watering, is the problem. If you need to raise it, the reliable methods are grouping plants together, standing the pot on a tray of damp pebbles (the pot above the waterline, never in it), or running a small humidifier in winter when indoor heating dries the air most. Misting is the least effective — it raises humidity for minutes, not hours.
Stock temperature & humidity — frequently asked questions
What temperature is best for stock?
Stock grows best between 7–18°C (45–65°F). Keep it out of cold draughts, off freezing windowsills in winter, and away from the hot dry air directly above radiators — the extremes matter far more than the average room temperature.
How cold can stock tolerate?
Stock starts to suffer below roughly 7°C. It tolerates a cold dormant period within USDA 7–10 (biennial types); grown as cool-season annual elsewhere, but a wet cold root zone is more dangerous than cold air.
What humidity does stock need?
Stock prefers about 40–65% relative humidity. Performs best in cool, moderate humidity. High summer humidity combined with heat accelerates plant decline. Good air circulation between plants reduces risk of grey mould (botrytis) and downy mildew on the dense flower spikes.
How do I raise humidity for stock?
Group it with other plants, stand the pot on a tray of damp pebbles (kept above the waterline), or run a small humidifier in winter. Misting only helps for a few minutes, so it is the weakest option for a plant that genuinely needs more humidity.
Can stock live outside?
Stock is rated for USDA zone 7–10 (biennial types); grown as cool-season annual elsewhere and RHS hardiness H4. Within that range it can stay outdoors; outside it, grow it in a moveable container and protect the roots from a wet, cold winter.
More stock care
In the UK? Keeping stock warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full stock care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.