Growing Supplies

Starting seeds or rooting cuttings on a cold windowsill is a gamble. A heating mat takes most of the guesswork out of it. Our growing supplies start with two mats that sit under your tray or pots and warm the root zone from below: a compact 15 x 28 cm mat and a wider 35 x 20 cm one.

Why bottom heat works

A seed doesn't care how warm the room feels to you. It responds to the temperature of the damp medium it's sitting in, and that is usually several degrees cooler than the air, especially at night or next to a window. A mat puts gentle, even warmth exactly where the seed is. Germination becomes quicker and, more importantly, more uniform, so a whole tray comes up within days of each other instead of in dribs and drabs.

Getting the temperature right

Most seeds sprout best when the medium stays at a steady 18 to 24 °C. Heat lovers such as chillies and tomatoes like the top of that range or a little above; lettuce and many herbs prefer the bottom. Whatever you grow, steadiness matters more than the exact number, and that is what a mat gives you through cold nights, which is when unheated trays stall.

Three habits make the difference:

• Push a thermometer into the medium, not the air above it. Too much heat cooks seeds as surely as cold stalls them.
• Check moisture more often than usual. Warm trays dry out faster, and a lid or humidity dome over the tray slows that down.
• Take the tray off the mat as soon as the seedlings are up. Left on bottom heat, young plants shoot up too fast and turn thin and weak.

Which size to choose

Pick the mat by the footprint of what stands on it. The 15 x 28 cm mat suits a small propagator or a row of pots on a shelf. The 35 x 20 cm mat takes a wider tray. A mat that is much larger than the tray wastes its heat at the edges, and one that is smaller leaves the outer cells cold, so match them as closely as you can. Put the mat on a surface that doesn't draw the warmth away: a wooden shelf or a sheet of cork or foam works better than bare stone or metal.

Using a mat safely

Keep the mat flat, never folded or rolled while it's switched on, and keep the plug and cable out of standing water. Wipe up spills from watering rather than letting the mat sit in a puddle.

A note on what you grow

Heating mats are sold for seed starting and propagation in general, from kitchen herbs to chillies. If you plan to use one for cannabis seeds, check the law where you live first: germinating them is illegal in many countries, even where owning the seeds is not.

Everything in this category ships in plain, discreet packaging from Express Highs, together with the rest of your order.