The Perfect Soil Temperature for Seeds + Seedlings

A huge part of vegie growing success, is learning the preferred soil temperature for sowing and planting each crop. When you get this right – your crops boost away. There’s a chart below to guide you – use it alongside your soil thermometer and you’ll nail it every time!

Know your soil’s temperature – in the garden or in the seedling trays, before sowing or planting. In this way you can be sure your seedling will be happy and grow like mad. If its too cold, do something to warm it up like a heatpad or sit it in a propogating unit, and wait until its spot on.

In the interests of creating a simple chart, I’m showing the ideal temperature range, not the entire one. Most crops will germinate outside my advised range – not minding soil that’s a bit cooler or a bit hotter, but just because they will germinate, doesn’t mean they’ll do it well.

Beetroot for example, will germinate at 5°C, but it’ll likely be patchy ie not all seed will strike, nor will it be as fast as it would be at 10°C. Beans, another good example, germinate best at about 18°C – 20°C. They’ll still germinate at 15°C, but more slowly.

Fast isn’t often on my agenda, but where seed raising is concerned, it’s best to have seeds cranking along, when they linger in tray’s they risk rotting away. Fast is good also, as far as seedlings are concerned. It keeps your spirits high and the food garden humming when there is a regular supply of new seedlings to plant.

As always, indulge your own wonderings and observations, but meantime, these temps are a great beginning. You wont go wrong.

Kath’s ideal germination + transplanting temperatures

10 – 15°C artichoke, broadbeans, carrot, chard, kale, parsley, parsnip, peas, radish, spinach
10 – 20°C beetroot, brassica, celery, chive, garlic, lettuce, leek, onion
15 – 20°C beans
15 – 25°C corn, cucumber, pumpkin, zuchinni
18 – 25°C sweet peppers, tomato
20 – 30°C chillies, eggplant, kumara, melon

When germinating seed, use the mid to upper end of the range.
When transplanting seedlings, use the full range – don’t go below the minimum!

Trouble shooting

Though soil temperature plays a huge part in seed + seedling success, its not, of course, the only part.

If seeds don’t germinate well or seedlings in trays struggle (ie grow really slowly or foliage is discoloured), alongside checking the temperature, check in on your seed raising mix, watering habits (overwatering being a common cause of death), and age of seed – old seed looses its will to get up and go. Test its viability by chitting it. If you used bought compost, another likely cause is herbicide residues.

If transplanted seedlings struggle, check your soil temperature, your soil, if you used bought compost – as above check it out for herbicide residues, your watering habits and reflect on how strong and healthy your seedlings were. Seedlings should have sturdy stems, a solid (but not choked up) rootball, have similar size roots to top, and have lush green foliage – no purple tinges or yellowing please.