Choosing a perfect propagator

They’re a gardener’s best friend... so use our handy guide to pick the right one for you and all your gardening needs

It’s often said that Easter marks the start of the new gardening year, but with a propagator we can cheat the seasons and get sowing as early as January, even if snow lies deep outside.

These ingenious but simple devices are among the most useful weapons in a gardener’s armoury. By warming up the compost, locking in moisture and raising humidity, propagators create a unique microclimate that provides optimum conditions for seeds to germinate and cuttings to strike. Garden centre shelves may be groaning under the weight of fancy propagators for sale, but you don’t need to spend a fortune – and you can even make your own. Whether you’re raising bedding from seed, starting off young veg plants or dabbling at growing exotics, see our handy guide to choosing a propagator that’s perfect for your needs.

1 BUDGET PROPAGATOR

The cheapest propagators at the shops usually comprise a half seed tray with a lightweight clear plastic lid. They can be bought for a couple of pounds. The lids don’t offer much height for seeds and cuttings, but they’re effective, especially for raising bedding or veg plants from seed. The downside is that you don’t get any vents, and lids are easily squashed or broken. Flimsy propagator lids can go cloudy and brittle if left exposed to hot summer sun in greenhouses, so store them in a shed when not in use.

2 FREEZER BAG PROPAGATOR

If you watched TV gardener Geoff Hamilton on the box in the 1980s and early ‘90s, the chances are you were inspired by his penchant for ‘knocking things together for a few bob’. The home-made propagator is a classic example, and you may already have the necessary bits and pieces at home. Take a plant pot, fill it with compost and sow. Place a plant stick (or a few sticks, depending on the size) in the compost, then pull a clear freezer bag over the top. Secure the bag to the rim of the pot with an elastic band. The downside to having no vents is you’ll need to regularly remove the bag to see how seeds are getting on.

3 WINDOWSILL PROPAGATOR

If you don’t have a greenhouse, a windowsill propagator is the answer to your prayers. And if you do have a greenhouse, chances are you’ll run out of growing space anyway. Look for a narrow propagator with a rigid seed tray base with no drainage holes (you don’t want water leaking out and damaging the paintwork on your sills). It should have a strong plastic lid with two adjustable ventilators – one at each end. Measure the depth of your windowsill before heading to the garden centre: you don’t want to buy one that’s too wide to fit! Propagators on windowsills can quickly turn into an oven if sunlight hits the lids, while temperatures can dip too low at night if the curtains are closed. Consider placing propagators on sills that benefit from bright, filtered light and not direct sunlight.

4 UNHEATED RIGID PROPAGATOR

Go for the biggest that you can afford – ideally choose one that can accommodate at least two full-size seed trays. Those with bigger, higher canopies will maintain a more constant level of warmth and humidity, while a sturdy tray will allow you to cram more in. An adjustable vent is a must, but look for those with two vents, as they create better airflow to keep seedlings healthy. If looked after, these propagators should last for decades.

5 PROFESSIONAL ROFESSIONAL PROPAGATION UNIT

If you plan to germinate large quantities of seeds or take numerous cuttings, building a customised propagation unit incorporating a soil-warming cable can open up a world of opportunities. Build a timber base, sit it on your work bench and fill with 2.5-5cm (1-2in) of horticultural sand. Spread the soil-warming cable evenly, then bury the cable under a further 2.5cm (1in) of sand. Sit seed trays on top where they’ll benefit from gentle bottom heat – you’ll need to cover them with propagator lids, or place a clear plastic cover over the entire unit. Heat mats, pictured, offer similar benefits with less fuss, and choosing one with a thermostat increases control. Both options require a power supply.

6 ELECTRIC PROPAGATOR

Perhaps you need to germinate seeds in a chilly room of your home, have an unheated greenhouse or plan to dabble at trickier seeds that need heat? If so, an electric propagator is a must. Models that only allow heat to be switched on or off offer limited control. Instead, it’s worth going for a thermostatically- controlled propagator that allows you to set the precise temperature. The thermostat will maintain a constant level of heat – far more cost effective than heating an entire room or greenhouse. Vents in the lid are essential to strike the right balance between heat and ventilation.