Transplanting vegetables outside with -10ºC

Ok, here in Iceland growing season is very short and I am determined now to push back the season as much as possible. To plant as early as possible.

March, April and May can still bring hard freezes, around 10ºF/ -12ºC (the whole day) in March and April, and around 20ºF/ -7ºC (the whole day) in May.

However most of these three months are above freezing, and after early April, snow is much less common, and we can have some nice spring weeks (with highs around 60ºF/15ºC) despite an ocasional big freeze to around 15ºF/ -10ºC.

I have now growing trays (indoors) of broccoli, brussels sprouts, kohlrabi, beets, spring onions, lettuce, rocket, celery, broad beans and peas. Plants have now the first pair of true leaves.
My idea is to transplant them sometime within the next weeks, rather than waiting for June (when frost is almost gone and if it happens is mild). Of course I hope to have the seedlings as large as possible and setting them out when the weather is forecast to be mild for several days ahead. Still they will still face some occasional freezes to around 15ºF. Adult plants survive that, so I am gambling with transplants to survive as well.

Do you guys have experience with transplanting small plants of these vegetables and then having them survive hard freezes?

Outside I have a cold frame, which does not raise much the temperature, but helps keeping a couple of degrees more, and also shelters from the hard freezing winds. So I was thinking transplanting some spring onions, peas, broad beans and brassicas in late March, under this cover, in hopes they survive the ocasional big freezes of April and May (despite mostly spring weather).

any rocks you can smear soot on to add solar gain? sun traps. plant to avoid frost pockets. use south walls of buildings. horse or cow manure in a pile to heat things up a bit under your cold frame.

you're in a difficult climate, so it might take your whole bag of tricks.

Harden them off before you throw/plant them outside. I would also be prepared to plant 5x what I would plant in June just harvest the "weak" ones as baby spinach/etc.
I would also take a note of locations where they did well. And the best looking ones I would not eat, I would save them, let them go to seed and use those seed for next spring/fall.

Yes all sort of tricks are used.

Rocks are usually better in long sunny summer days, but colder during spring freezes.
I also plant near the wall of my house, since temperature is about 1-2°C more there. Under the cold frame is also about 2°C more, it is more exposed than near the house but soil is better there (it is just 5 meter in front of our house). I also add sometimes peat moss in top of the seedlings, since it protects further from the cold, as well as a black plastic (those add about 1-2°C more on their own). These are big helps during small frosts but are no miracle during hard freezes. Still seedlings survive better under protection than without.

Now, the weather is still very harsh. It is about 10°F and extreme strong winds. And no snow cover. I will wait for the next thaw to plant the seedlings out (by mid or late March), as I hope to have mostly 2 or 3 weeks of just around freezing kind of weather, with sleet, rain and snow. Yes that is how I harden seedlings, with sleet kind of weather! That is a much milder weather for seedlings that the current brutal freeze without any snow cover and with harsh winds. Because with around 32°F kind of weather the soil is just slightly frozen, but now it is frozen deeply and solid, and very hard. The problem is: these brutal freezes can still happen until end of May, even though spring weather is going to dominate more and more.

I will try first the spring onions, peas and broad beans and some brassicas out. I will not mind if most die. As I am curious to try them out.

(On the garden itself I still have surviving broccoli, brussels sprout and spring onions from last year, but those are adult plants already (around 30cm high). They suffer widely but they are surviving well). I also have one plant of perennial broccoli which is now going into its third year!

tel jetson wrote:any rocks you can smear soot on to add solar gain? sun traps. plant to avoid frost pockets. use south walls of buildings. horse or cow manure in a pile to heat things up a bit under your cold frame.

you're in a difficult climate, so it might take your whole bag of tricks.

I created this thread. https://permies.com/t/22575/permaculture/Ways-warming-soil-temperature-creating#184451


Basically I do not have to struggle with such low temperatures. With a cold frame, black plastic and peatmoss mulch, I have raised significantly the soil temperature.