It lightens up shady places, makes green shine even darker and stands out as softening persistent glow in the stark summer light, whether against bare dirt or fresh mulch.
The first I would like to recommend is Flannel Bush or Fremontia Fremontodendron californicum, a California native. It has by far the most flamboyant and thrilling display of yellow-orangey star-shaped flowers that covers the deep green maple-like foliage almost entirely for 4 to 6 weeks in spring, beginning in spring. Even when the blossoms begin to fade, they hang on in dark golden, rusty tones for several more weeks. (Some people find them unsightly, especially the rust-colored seed capsules – I like their look.) Give this fast growing evergreen shrub room – it can grow to 20 ft typically reaching 12 or 15 ft with an irregular shape. (It profits of some pruning to remain dense – but wear a long-sleeved shirt; the fuzzy hair on the leaves can irritate your skin.) There are several cultivars of this shrub grown here that are regarded as some of the most spectacular native plants in California. In my garden in Ramona it is planted in almost pure DG and doing well. I guard against watering it in the hot months – it could die prematurely from fungal root or crown rot if watered in summer. Give it a place with good drainage in sun or partial shade (and tie it up while it’s young – the roots are shallow and in a strong wind it could topple over from which it won’t recover). One of my gorgeous shrubs succumbed suddenly last summer – perhaps it was planted too close to my septic/leach system… but the remaining 3 are doing well, now in their 5th or so year, without any supplemental water even in the hottest months.
By the time the Flannel Bush steps back into the round of other plants, my rambling rose ‘Mermaid’ is in full bloom. Beware to give this shrub room, too: it is a vigorous shrub whose long canes with serious thorns need training unless you can give it all the room it needs (I assume it would make a large mounding shrub; according to my book the canes can reach up to 30 ft!); mine is trained into a single-trunk small tree whose branches are supported by an arbor. The flowers that appear in clusters are very charming: large 3 or so inches, single, light-yellow with a darker center, deep buttery-yellow stamen and a lovely orange scent. What I also like about it is that the petals fall neatly without hanging on faded, and most of the dried dark remaining bottom receptacles can be knocked off cleanly. It blooms until the summer heat reaches the upper nineties in July and picks up again when the nights get cooler in September, to go almost non-stop until the beginning of January. It doesn’t require much water, even in this hot zone 20/21. It likes my light soil well and is very healthy and disease resistant.
A surprisingly persistent perennial is Coreopsis grandiflora (one of the common names is Tickseed – I wonder why?). To 1-2 ft high in my light soil, it spreads to 1-2 ft wide. Although the faded flowers and seed heads remain on the plant making it somewhat unsightly in summer (this is a note for lazy gardeners like myself), several considerations stop me every year from pulling it out: the plant is remarkably tolerant of drought, neglect and heat and reseeds itself freely (whether this is a trait worth recommending is a personal choice). But mostly its warm yellow flowers are so bright and cheerful throughout the long warm months that now and then I ‘bite the bullet’ and prune it back, pretty hard, and within no time the plant is again noticeable from afar because it’s covered with lovely bright flowers.
Last but by no means least is Calylophus hartwegii Trailing Buttercups. This western native sports one of the most enduring, bright yellow, four-petaled flowers against narrow leaves and after giving it the hardiness test in my lean soil and intense summer heat, I will set it out all over my garden as ‘tie-together’ plant: low to about 8-10”, spreading to about 24”, in protected spots it has not stopped blooming since I planted it last year. Once this plant is established it can tolerate a great deal of drought but can tolerate regular water if drainage is excellent.