I have a narrow (15" wide and 8 foot long) bed immediately alongside the front of a new conservatory, edged by paver path.

I want to put lavender in it. The soil level is fairly low so I can add to it: I don't think the bed's ever been used by the prev. owner.

The soil seems OK- it isn't builder's rubble! But it seems a bit on the heavy side as is a lot in the rest of the garden.

Do I dig out a foot, mix it with- what?- and return it?

Sand?
Grit?
Compost?

I have been given 12 small lavendar plants so though I understand the 'plant something else' concept, I want to exhaust the lavender possibilities first!