My question is about Cytisus. People with allergies complain about the Scotch broom that grows wild. Are the other tame varieties like C. x praecox going to be a pollen allergy problem also? I want to plant it as an informal hedge and my customers are worried. I want to tell them there is no comparison in the plants. Am I right?
To answer your second question first, Scotch broom (Cytisus scoparius) is an invasive European species that has given all brooms a bad name. Spanish broom (Spartium junceum) is also invasive, and is considered a Class A noxious weed in Washington State. There are garden-worthy brooms such as C. x praecox. A staff member here grew one in her previous garden for many years (and loved it). Some species of Genista, such as Genista stenopetala, are reportedly not invasive.
According to the book Allergy-Free Gardening by Thomas Leo Ogren (Ten Speed Press, 2000), Cytisus ranks 5 on the allergy index scale of 1 to 10, but allergy to this plant is uncommon, except in areas where there is a lot of it growing. Spartium junceum rates a 7, while Genista rates a 4, about the same as a begonia or a primrose.