I grow lupins for many reasons aside from their being pretty cut flowers.
Because permaculture thinks in terms of “functions” rather than “elements”, plants are selected and placed in a garden depending on what functions they can fulfill.
Lupins are a nitrogen-fixing plant which means they are capable of converting the nitrogen from the air into fixed nitrogen and storing it inside little nodules on their roots. Through leaf decay and leaching from roots, this nitrogen becomes available for other plants too.
They are also capable of accumulating minerals which their deep roots can extract from the subsoil. These minerals, too, become over time available to other plants. By growing lupines next to my young apple trees, I make sure the trees are quite well fertilized without having to import nutrients from outside the garden.
Lupines are also excellent bee forage plants – I have put the vase on a table in the backyard and there’s at least one bumblebee on it at all times.
For the vase, I pick lupins when about half of the flowers on a stem are open. I love how the stems, after they are cut, twist and turn giving the bouquet such an interesting silhoutte.To prolong their not tremendously long vase life, you can prick the stems with a pin just under the blossom, then fill the stem with water and plug with a piece of cotton. But honestly, I seldom bother preferring to enjoy the flowers for several days and then picking a new bouquet.