Plant care
Annual Phlox 'Sugar Stars'temperature & humidity
Phlox drummondii 'Sugar Stars'
More about annual phlox 'sugar stars'
Ideal temperature for annual phlox 'sugar stars'
Temperature kills fewer annual phlox 'sugar stars' plants than you'd think. What kills them is the micro-climate within a normal-temperature room — a leaf pressed against single-glazed winter glass, the hot dry updraft directly above a radiator, the cold blast from an AC vent. The thermostat reading at 10-27°C (50-80°F) is fine; the spot you put the plant in matters more. Below roughly 10°C growth pauses; cold beyond that pushes it into dormancy rather than killing it outright.
Cold tolerance & winter care
Annual Phlox 'Sugar Stars' is comparatively hardy (USDA 2-11 (grown as a warm-season annual), RHS H3). 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 annual phlox 'sugar stars'
Annual Phlox 'Sugar Stars' sits happiest at around 40-60% relative humidity. An outdoor annual unconcerned by ambient humidity, but humid, stagnant air dramatically increases powdery mildew, so prioritise spacing and airflow. 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.
Annual Phlox 'Sugar Stars' temperature & humidity — frequently asked questions
What temperature is best for annual phlox 'sugar stars'?
Annual Phlox 'Sugar Stars' grows best between 10-27°C (50-80°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 annual phlox 'sugar stars' tolerate?
Annual Phlox 'Sugar Stars' starts to suffer below roughly 10°C. It tolerates a cold dormant period within USDA 2-11 (grown as a warm-season annual), but a wet cold root zone is more dangerous than cold air.
What humidity does annual phlox 'sugar stars' need?
Annual Phlox 'Sugar Stars' prefers about 40-60% relative humidity. An outdoor annual unconcerned by ambient humidity, but humid, stagnant air dramatically increases powdery mildew, so prioritise spacing and airflow.
How do I raise humidity for annual phlox 'sugar stars'?
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 annual phlox 'sugar stars' live outside?
Annual Phlox 'Sugar Stars' is rated for USDA zone 2-11 (grown as a warm-season annual) and RHS hardiness H3. 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 annual phlox 'sugar stars' care
In the UK? Keeping annual phlox 'sugar stars' warm in a UK home covers the radiator, single-glazing and heating-season humidity angle. Temperature and humidity are one piece. See the full annual phlox 'sugar stars' care guide, its cold-hardiness guide, and watering schedule — humidity and watering problems are easy to confuse.