The author draws on the activities of the Native Plant Study Group, which studies the horticultural merit of California plants and is now anticipating publication of a handbook on California monocots. Cultural and descriptive information was provided by Wayne Roderick, Nevin Smith, and Roger Raiche. Further information is available in Mann, Louis K. and Margery, “Decorative Onions,” Journal of the California Horticultural Society, 21(4): December 1960.
Mark McDonough of Bellevue, Washington, who has written extensively on alliums, says: “I am drawn to the wildflower attitude assumed by most alliums I see, admiring their quiet existence and restrained flamboyance. At the same time I can be amused and amazed by the more lavish oddities that nature has conjured up, adding spice to an otherwise understated genus.” Thus the stage is set for investigating the delights of alliums as ornamental plants for the garden.
In California there is a wide assortment of wild onions of the genus Allium with forty species and many subspecies and varieties. Onions are known the world over for their culinary value as they include the commercial onion, garlic, chives, shallot, and leek. In California the genus is highly developed, and by their numbers alliums often provide great drifts of color on dry slopes, ridges, and open fields. Plants having white flowers do occur, but this genus is noted for vivid shades of pink, rose, rose-purple, and wine. Flowers may be in tight or open umbels on smooth stems where they spill out of the enclosing papery sheath as they unfold. Leaves are mostly grass-like, sometimes thin and lax, but in others thick and curved like a sickle. Some have flat leaves while in a few species the leaves are hollow and sedge-like. As a rule the leaves die back at flowering time or soon thereafter. In size our native onions range from the two- to three-foot tall Allium validum of swamps and meadows to the almost stemless A. hoffmanii of serpentine inclines. Alliums grow from a small, solid bulb of tightly packed fleshy scales covered with a thin tunic.
Only recently have gardeners come to appreciate the ornamental value of our wild onions. Experience with them in botanic gardens reveals that many are adaptable to garden cultivation, and that others with desirable traits that are not so adaptable are still worth every effort to discover how they may be brought into cultivation. The majority of those described are a foot or less in height and are suitable for rock gardens, border edgings, raised borders, and pots, situations in which their diminutive charms can be fully appreciated. Wherever they are used, alliums should be planted in close groups for maximum effect.
Close inspection of these onions reveals traits characteristic of certain of the species. In Allium falcifolium, coast flatstem onion, and A. platycaule, pink star onion, the flower heads are open with recurved petals that form a star design. These two also have decorative, flattened broad leaves. In the pink star onion flowers of brilliant rose-purple occur along with less desirable white or intermediate colors, so careful selection is necessary when it is grown from seed.
Allium amplectens is an easy garden plant with globose heads of white, and occasionally pink, flowers. Seedlings of it present a variety of leaf forms also, from very fine to coarse. Although not as colorful as most, the papery inflorescence is interesting against a dark background. This narrow-leaved allium is considered by Leslie Haskin to be the most beautiful of the Pacific Coast onions. He reminds us that the flowers continue to open in water, and says that “the whole head retains its freshness for weeks, and opens out in marked perfection.” A. amplectens is native to dry slopes and fields of foothills north to British Columbia.
Allium peninsulare is another species deserving close inspection. The vibrant red-purple flowers have two kinds of petal segments: the outer ones are ovate-lanceolate with pointed tips and the inner ones are spreading and narrower, giving a two-dimensional flower. This species is native to dry open or wooded foothills over much of California.
Allium crispum is similar, and was once considered to be a variety of A. peninsulare. The flowers are rose-purple and spreading, with the inner segments crisp or undulate and margined in white for a striking effect. Both of these species have been grown in pots, although A. crispum is somewhat more difficult under cultivation. Both have the endearing quality of holding their color late in the season, making them valuable for dried arrangements. Several other species hold their color into early autumn, including A. amplectens, A. hickmanii, A. serratum, and A. dichlamydeum.
Allium dichlamydeum, coast onion, has congested heads of pink to cerise flowers, forming amazingly brilliant patches and sometimes decorating sheer rock faces with a blaze of color. This onion is native to outer Coast Ranges, Mendocino to Monterey counties. Fortunately, it is adaptable to cultivation given full sun and gravelly soil, and will even tolerate occasional summer water. It is also an easy plant for pot culture.
Two wild onions of rocky soils are practically stemless, and on slopes where they are native they always appear about to roll downhill. Allium hoffmanii has spherical heads of silvery pink flowers, and a single leaf that exceeds the scape in height and juts backward as if to break the headlong flight of the roly-poly flower head. A summer-flowering species, it is native to serpentine soils of Trinity, Shasta, and Humboldt counties.
Allium cratericola is similar with spherical heads of pale to dark purple, and is said to be equally attractive in bud stage when bits of color can be seen. This species blooms from March to May, depending on the weather and exposure. Both of these would be excellent in a rock garden, but are not totally adaptable and are usually grown in pots. Full sun and sharply drained soil are their known requirements.
There are several other small alliums that follow the same pattern as those already described, but whose adaptability is in question. Allium praecox has flowers of rose-purple or lighter purple with dark mid-veins for a sparkling effect. It is native to slopes and canyons of southern California and the Channel Islands. A. serratum, pom-pon onion, has tight heads of tubular flowers in dark rose-pink. It is native to grassy slopes and meadows on serpentine in foothill regions of central California. A. fimbriatum is mostly a desert species, but also occurs in foothills; it has seven named varieties. Experience with these is limited, but all are considered worth the effort because of their fine color and other distinctive qualities.
In contrast to these small onions that grow in gravelly or rocky soils are several native to fields and meadows, some of which are quite adaptable to garden cultivation. Primary among these is Allium unifolium, a species that is becoming increasingly popular among gardeners. It inhabits moist fields of foothills from Del Norte to Monterey counties. Large, open heads of clear, pink flowers make it a pleasing addition to mixed flower borders, as well as a companion to other native plants. These might include blue-eyed grass, Sisyrinchium bellum, the lovely violet-blue of Brodiaea laxa, the delicate blue and white flowers of Iris longipetala with a border planting perhaps, of five-spot, Nemophila maculata. The pink meadow onion remains in good color for several weeks and even when dry retains a delicate tint. A. unifolium takes eagerly to cultivation, increasing by seed as well as bulb, and should not be planted where space is restricted. It will tolerate some high shade and dryness, but does best in sun with regular amounts of water all during the year.
Allium validum, swamp onion, is a coarse plant of meadows and swamps, with flowers of rose, lavender, or white. All who visit the Sierra and Coast Range mountains are familiar with this onion as it pushes up among the busy masses of plant life typical of meadows. Although not considered one of the best for cultivation, its bulb has an excellent onion flavor.
Allium hyalinum, glassy onion, is another adaptable species that thrives with or without water. The large, open umbels are composed of many flat flowers, white to pink-tinged, with an almost translucent quality. This species also increases rapidly so ample room must be allowed. Suggested companions include blue-eyed grass and the lovely powder blue of Gilia capitata. Glassy onion is native to grassy or rocky places where there is some moisture in the Sierra foothills from El Dorado to Kern counties.
Most of our native onions grow readily from seed, although there is some variation in germination time from three weeks to two or three months. For both pot culture and seed beds use a soilless mix, as this is rich in humus and drains well. Some growers add pumice or fine gravel to the mix for alliums that grow in screes — those rocky places where nature has provided constant moisture along with sharp drainage. Use deep flats, pots, or an outdoor bed for the seed and allow the seedlings to remain in the containers for two or three years. Three to four years is required from seed to flowering. Plant groups of bulbs close together for maximum effect in borders or in the rock garden. Due to their sparse foliage, the wild onions are inconspicuous as they go dormant. The adventurous gardener who grows alliums from seed can expect variations in flower color and leaf size and shape.
Aside from the suggestions already made, there are other natives that go well with the rich colors of the alliums. Several of the annual monkey-flowers have glowing shades of deep rose, rose-purple, and crimson, and these would greatly enhance a colony of onions with flowers in similar colors. Unfortunately, only a few of these diminutive plants are known, and garden experience with them is limited. Some of the alliums might be set off nicely by loose carpets of monardella, such as Monardella purpurea or the common foothill M. villosa. Both have fuzzy heads of lavender flowers on moderately spreading plants that tolerate considerable dryness.
Future trials with native alliums now considered difficult to grow may well reveal more successful cultural methods. In a few cases it has been decided that some species might thrive with summer water even though they grow naturally under dry conditions. We must be diligent in sharing our experiences — both successes and failures — as both will tell us how to proceed in the future. Experience in growing some of our worthy alliums is limited, but the way is open for adventurous gardeners to make their own discoveries.