Question
Marc,

I need some recommendations on what ground cover would be best for two in-ground planters I have.  Below are some details of the area:
I live in Northern California, Zone 9a
I am working with two 5'x 5' in-ground planters that each already contain a miniature pink rose tree.
The area doesn't get a whole lot of water.  One planter gets morning and early afternoon sun and the other is in the sun all day.  I would like to plant the same groundcover in both since they are only separated by a walkway.  
I am looking for something that blooms, but that also stays green all year and is frost resistant and low maintenance.
Any recommendations would be greatly appreciated.  I hope I provided enough info for you.
Looking forward to your response.
Thanks

Answer
I combined both evergreen flowering shrubs and groundcovers, as you have enough space to accommodate either.  Really, it is taste & preference.  My favorite is the Breath of Heaven, as it has an intoxicating aroma when crushed, so great for entryways!  It is one of the plants I抦 really disappointed that does not grow where I live.

Breath of Heaven (Coleonema pulcrum, C. alba)

Ceanothus ?(Ceanothus spp.?lower varieties like the C. Centenial, C.fenderri, Point Reyes, Anchor Bay, Carmel Creeper) ?Really a westcoast plant.  Be careful with the varieties: some get quite big/wide & will overgrow the space. The blue flowers are spectacular!

Jasmine (Jasminum floridum), Winter Jasmine (J. nudiflorum), Dwarf Jasmine (J. parkeri)

Beauty Bush (Kolkwitzia amabilis) ?will get big, but can be pruned back ?beautiful flowers.

Ice Plants (Carpobrotus, Drosanthemum, Delosperma nubigenum &  cooperi species, Lampranthus, & Cephalophyllum) ?There are LOTS of plants named 揑ce Plant?that will work for you.
Periwinkle (Vinca spp.) - Doesn抰 like full sun in hotter regions.

Hope it helps.

-Marc