Advice on minimum temperatures tolerated by seedlings in a cold greenhouse

[Adrian]

Due to this year’s long winter here in Scandinavia, we are still experiencing nightime temperatures this week (April 16th) as low as -3. I have germinated vegetable seeds indoors (onion family, brassicas, lettuce) over the last four weeks, and all growing well, but don’t have time to ferry them back and forth to the green house each day.

Which crops at seedling stage can tolerate a bit of frost if they go straight out to the cold greenhouse? Or is it just better to wait until all chance of frosts have passed? Do such crops need a few days of acclimatisation first?

Is there any good online resource or literature on seedling cold tolerance, as mostly what I have found is subjected at either seedling germination temperatures or tolerances of crops already growing outdoors.

Best Regards,
Adrian

[charles]

Adrian it’s a good question.
I would plant them out with fleece over but supported by hoops, since frost damage under fleece occurs mostly where leaves touch it.
Check out also thermacrop.
I guess you have some sun by day at least, your days are long now and plants will benefit from being in the ground to grow by day, even if they just are in survival mode by night.

[Adrian]

Thanks Charles. Unfortunately, the ground is still frozen. Then there will be a period of having to let it drain and dry a little before mulching with a well-rotted compost before considering planting.

We have been having some remarkable sunny days, yet as mentioned with cold nights, hence wanting to get seedlings out of the house and into the greenhouse to get the light they need (still using grow lights in the house). Previous years have been kind and I would normally have everything in the greenhouse by now, but all dates are at least 3-4 weeks late here.

Do you think brassica, onion and leek seedlings would survive a few minus degrees if covered in fleece for the night in the greenhouse? I have been considering the option of buying one of these small plastic greenhouse/tents and putting that in the greenhouse to provide some added warmth and protection against night frosts.

[charles]

Ah I see.
I would apply compost in autumn if possible to speed progress in spring.
Yes those plants will be fine in a greenhouse that freezes, though I would not have sown leeks yet in your situation. Everything recommended for February sowing on my timeline resists some freezing.

[Adrian]

Charles I agree compost should have been applied in autumn, but it’s the first year of going completely no-dig this year and I’m waiting for a delivery of compost from the municipality’s green recycling department anytime now.

Growing times over here in Finland are a little different to the UK (a steep gardening, learning curve coming to live here 15 years ago from England) with a much shorter growing season. No vegetables can be left in the ground over winter as temperatures can dip to -25 by Christmas! Despite being an amenity horticulturist all my life, more at home growing hardy nursery stock, designing and constructing gardens, I only seriously started growing vegetables a few years ago. Like everything in gardening though, once you get bitten by the bug, there is no turning back!

Thanks so much for taking the time to reply and much respect to you for this great work you are doing. I hope one day when I come back to settle in the UK to come pay you and your garden a visit.

All the very best,
Adrian

[charles]

Cheers Adrian, and wow, Finland, have a great summer!

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