Perennial vegetables for Northern Europe

I came across this video about a grower in Sweden:



Hanna Jönsson grows perennial vegetables in a plant nursery in southern Sweden. She has participated in a study of perennial vegetable growing in Scandanavia. This report is the result of interviewing twelve growers in Denmark, Sweden, Finland and Norway who share their experiences of perennial vegetables in diverse conditions.  Note: hardiness zones are not the same as US zones. Author: Eva Johansson. The growers sometimes sell the produce for people to eat or cook and sometimes as seeds or plants, but share their experiences of growing and marketing the plants.

Here are some links to the growers (websites generally not in English of course!):
https://www.permakulturhaven.dk/
https://www.inspiratoriet.org/
https://ronnsaker.se/verksamheter/skogstradgardens-vaxter/
https://gammelgaard.se/
https://atligatradgarden.se/
http://www.groblads.se/
https://www.facebook.com/fridenstradgard/
https://www.ranbogarden.se/
http://www.ntnu.edu/museum/the-onion-garden
https://vaeresvenner.no/
http://www.siementarha.fi/ (apparently growing rice in Finland!!!)
https://www.xn--sytvmetspuutarha-xnbbe56a.fi/
http://www.taimitaivas.com/

I like the sound of the garden that Stephen Barstow has been involved in designing: Væres Venner Felleshagen based on his book and other plants. It would be on my list of gardens round the world to visit!

There are a few plants mentioned that I'm interested in knowing more about:
Giant fleeceflower (Koenigia alpina) Hanna talks about being a really good groundcover,
Perennial wall-rocket (Diplotaxis tenuifolia) was mentioned as becoming a bit invasive, but popular as a salad plant.
They seem to have better success with seakale than I have had...I wonder whether it would like my mini hugel beds?
A few seem to get on well with Korean Celery (Dystaenia takesimana) which is a plant I have already on my wish list (actually I think I may have bought some this year...)

Some other titbits:

Violet is a good ground cover together with various onions.

Hosta and spring beauty complement each other well - spring beauty is early and hosta covers well in the summer when spring beauty has finished flowering.

The lanolin in raw fleece was found to deter deer by one grower.

We .... investing a lot in covering herbs that have a competitive advantage and quickly create large popluations such as lungwort (Pulmonaria officinalis), mint, Lady's mantle (Alchemilla vulgaris) and sweet cicely

They dug a 15-20 cm deep ditch, newspaper along edges and as a lining, then filled with straw to keep out quackgrass, this works well.

Stephen Barstow's new favourite perennial vegetables (discovered since '80 plants'): Ligularia fischeri (gomchwi), Rudbeckia laciniata, Allium stipitatum

If anyone else has resources to share for Northern lattitudes that would be great!

Have you seen this other documentary from the same channel?
A nut tree farm example in Skåne, Sweden. The farmers here also work in an art collective, very cool: https://gylleboverket.se/

Thank you for posting that Birgit! It was interesting to see their forest tree planting technique - basically planting a little island of support plants at the same time.
Disappointingly I haven't found sweet chestnuts to thrive here, I just don't have warm enough summers, and the soil is too acidic as well.