Hi Splendid,
I don't grow
Scotch Broom (Cytisus scoparius) but doing a little research I found information regarding pruning that says they should only be pruned in late spring, immediately after flowering; cut back the flowered shoots to a side shoot that hasn't produced flowers yet and never cut more than 1/4 of the foliage in any one year. Experts say once the tree has gotten large, if no previous pruning has ever taken place, it's too late to repair the scraggly look. Mature branches apparently do not retain a lot of green buds and if you severely prune the old branches you may kill the plant.
Hopefully members who grow this beauty will be along soon with advice and suggestions.
