I LOVE this plant, John, and have tried it a number of times, but alas it does not like us , or myself, or the place. I saw huge specimens in UK last June, blooming as if there is no tomorrow, in what I would define as hight moisture cool temperate areas (not far from Alasdair's)
, so I doubt it will ever accept our completely different conditions. Actually, it is not a mediterranean plant, but rather, a mountain dweller for temperate gardens. One reads Morocco and immediately thinks of the Imperial cities, the terracota hues, the yards and the desert oasis, but really this broom comes from the high Atlas mountains where it grows in oak and cedar forests at heights of 1500 - 2000 m, and it does want cool climate. Not for nothing it is hardy is Scotland and North US!
So our very light soil verging to dusty, that does not retain humidity, the level of insulation (pizza-oven style), and very very hot summer days are not really the thing.