The Perfect Soil Temperature for Seeds + Seedlings ⋆ Edible Backyard

What a difference when we sow seeds, and transplant seedlings, into soil that’s at the perfect temp for each crop – seedlings boost away with strong growth!

Use your trusty soil thermometer along with my chart below that shows the ideal temperature range. Most crops will germinate outside this range – not minding soil 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 likely with a patchy strike rate and not as fast as they would at 10°C.
• Beans, germinate best at 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 keep seeds cranking along to avoid rotting before they germinate, which is typical of legumes, also to prevent fungal disease on the foliage of young seedlings. Faster growth of seedlings turns up trumps as well – they are sweeter, beetroot, salads and radish are perfect examples of this.

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 grow slowly, or foliage is discoloured, check:

If transplanted seedlings struggle, check:

Reflect, also, on how strong and healthy your seedlings were when you planted them out. They should have sturdy stems, a solid (but not choked up) rootball, have similar size roots to top, and lush green foliage – no purple tinges or yellowing please.