What to look for

LID A clear plastic lid lets in plenty of light. Tall lids provide space for taller pots and larger plants

VENTILATORS Easy-to-open ventilators help regulate humidity within the propagator

SIZE The bigger the unit the better if you sow a lot of seeds. Smaller, slimmer windowsill propagators are better for growers with limited space

HEATING ELEMENT The temperature inside your propagator depends on the size of its element (with power measured in Watts) plus the ambient temperature

THERMOSTAT This allows you to alter the heat output of thermostatically-controlled propagators. Any numbers will indicate relative heat settings only – see point about calibration (left)