I'm wondering if Mahonia - the taller ones - possibly with the smaller ones at foot would be of use.

I have the same question: What tall shrubs or screening plants to plant under a Giant Sequoia? We live on the Central Coast of California, in a "frost-free" zone, wind-protected area above and back from the ocean about 1/4 mile. No salt spray. Water is available. Plants should reach at 8 feet or more fairly quickly. Thanks!

I know that some of the taller Coprosmas grow under/around Sequoia - and rambling roses. Bamboo - the non-suckering varieties. Some of the flowering plums and cherries also make headway against that root mat and the sprouts.

For understorey - Crocosmia, Hedera, some of the hardy dry place ferns, Arthropodium, and the Aloes. Some of the aroids.

I'm not saying they're 'ideal' - I just happen to know they will grow there.

Thanks! Will look into the Coprosma. Will NOT plant any Hedera - I'm pulling it out of there! Ivy grows very well under the redwood, but it climbs everything. It was even heading up the coast redwood - would have hidden the beautiful bark!

You might consider some California natives and exotics such as Toyon/Heteromeles arbutifolia, (deer will browse this if they are really hungry), Strawberry Tree/Arbutus unedo, Pacific Wax Myrtle/Myrica californica, Italian Buckthorne/Rhamnus alaternus, Portuguese Laurel/Prunus lusitanicus. All of these are pretty tough with root competition, and will get to be the size you indicate.

You might also consider some controllable running bamboos, such as Metake/Pseudosasa japonica, which will only spread within irrigated areas, typically, and not into dry areas beyond. If you are USDA zone 9 conditions, the Mexican Weeping Bamboo can be stunning, but it gets closer to 15 feet tall, and needs room to weep.