To own a heated propagator is to steal spring’s best hand and play it out in winter, to trick seeds deep in dormancy into thinking the weather outside is not furious and fierce because the soil inside is deliciously warm, and the air is moist.
Germination is fast if soil is a constant temperature. It’s fairly easy to achieve this in the day by starting seeds off on a windowsill or somewhere sunny indoors, but even indoors, the temperature will drop considerably at night. Steady, even germination comes when day- and night-time temperatures do not fluctuate wildly, and this is most easily achieved with a heated propagator. Basic heated propagators are pre-set to 15C-21C, which is the preferred germination temperature of many tender garden plants. More sophisticated propagators have a thermostat and a soil thermometer to check the settings. Most propagators require a background temperature of about 5C, but preferably 10C in order to maintain a compost temperature above 15C.
You can pay anything from £40 to over £400. In the middle, at £140, the Vitopod Heated Propagator is a great bit of equipment and small enough that it can be used in the house if there’s sufficient light. If light is an issue, you could up the game with a Vitopod with grow lights. At £214.49, it’s an expensive way to raise a handful of plants, but if money is no object for fine tomatoes or the fieriest chillies, it’s a bit of a dream machine.
Windowsill propagators (about £40 each) are ideal for those who have no greenhouse and cramped conditions. I have two, from crocus.co.uk, both about eight years old and still going strong. They don’t have a thermostat, but add somewhere between 5C-10C on ambient soil temperature. At night, the seedlings are kept at a snug 15C-18C and this is what matters most.
Windowsill propagators need to be on a well-lit surface but out of direct sunlight, otherwise, on a sunny day, tender seedlings will easily scorch. A watertight base means you won’t have to remove the trays to water elsewhere. Another option is a warming mat, at about £30 – try twowests.co.uk. This is plastic mat with a heating coil inside that can be rolled up for storage and will add 5C-10C.
The best propagator systems come with clear lids with ventilation. Seedlings like high humidity, but also good ventilation to prevent rotting. Look for tall, UV-resistant, shatter-proof lids. All heated propagators need electricity and there’s an environmental consequence to that.
Growing your own food, particularly organically, is a radical act: you are stepping outside the system. I haven’t done the maths, but I think a heated propagator uses less energy than an imported refrigerated tomato. However, using a 100% renewable energy supplier makes even more sense; it won’t negate the cost of making the propagator, but balances the equation a bit better.