Bulbs for Sonoma County

Because a majority of the world's bulbs are native to the Cape of South Africa and the Mediterranean Basin, most thrive in the same Mediterranean climate we enjoy in Sonoma County. Even tulips (Tulipa) that originated not in Holland but in the temperate Middle East and Central Asia do very well in our gardens. 

What Is a Bulb?

The botanical term "bulb" refers here to all true bulbs as well as to rhizomes, corms, tubers, and tuberous roots.

• Inside the true bulb is the entire embryonic plant.
  • When cut in half vertically, the outline of the mature plant is visible: the outer protective papery "tunic", the stem, the layers of scales that become the leaves, and the flower bud.
  • The larger the bulb, the larger the mature plant will be. When selecting bulbs from a bin, opt for the largest and firmest with the tunic still intact.
  • The most numerous of all are the true bulbs for gardens are Narcissus, Tulipa, Amaryllis, Lilium, and Hyacinthus. Some irises are bulbs.
• Bulb-like structures differ in several ways.
  • Bearded Iris is likely the most familiar rhizome. It forms a modified stem underground growing horizontally with buds that produce upright growth.
  • Dahlia is perhaps the most common tuberous root plant. These underground structures are swollen roots with growth buds at their top where stems erupt.
  • Cyclamen, Caladium, Anemone, and Watsonia are tubers. True tubers are also underground stems with growth buds on the surface that produce above-ground stems, similar to a potato.
• Brodiaea, Gladiolus, and Crocosmia grow from corms, also a type of stem, usually flattened with buds on the bottom that develop roots and a bud or buds on top that lengthen into a stem. New corms form on top after a year’s growth and the old ones shrivel

Planting Times

Fall is the perfect time for putting spring-blooming bulbs and other bulb-like structures in the ground. If the soil is too dry to allow digging, it’s better to wait until after rains begin. Local nurseries, hardware stores, home improvement centers, and bulb catalogs all offer a wide variety of bulbs for sale.

• Spring-blooming bulbs planted in early fall are ready and waiting for rains to begin and for some winter chill to arrive before their internal calendar prompts new growth.
  • The first growth is not obvious as small roots emerge under the base of the bulb in soil still retaining summer warmth.
  • Generally, late winter- and early spring-blooming bulbs are available for sale and ready to plant in fall.
• Summer-blooming bulbs that do not tolerate winter cold or heavy, wet soil must be dug up in late fall before rains and cold temperatures occur.
  • They may be over-wintered in a warm environment and replanted in spring.
  • Summer- and fall-blooming bulbs are for sale in the spring.
• Fall-blooming bulbs may be planted from early spring to summer while they are dormant and before growth begins.
• Most package directions and gardening books specify both the planting time and the season of bloom, whether early, middle, or late.

Planting and Growing Conditions

The majority of bulbs all prefer similar conditions: somewhat rich soil, adequate fertility, full sun, and good drainage. Seasonal winter rains naturally provide irrigation, although summer bloomers may require supplemental water.

• True bulbs are usually planted to a depth twice their height, while corms, rhizomes, and tubers most often prefer to be planted just below the soil surface or partially on top. Always consult package directions for planting depth.
  • One exception to deep bulb planting is Amaryllis belladonna (locally known as naked lady), which does better with the tip exposed. If planted too deep, abundant foliage dominates with fewer blooms.
  • Iris rhizomes are another exception. Even when discarded haphazardly and left on top of the soil, gardeners find that roots go down, that plants grow and bloom wherever they land.
  • One technique for container culture is layered planting, relying on bulbs that require different soil depths. The deeper bulbs push their stems up around the more shallowly planted ones.
• An important consideration when selecting bulbs is their susceptibility to pest damage.
  • Generally, deer and rabbits don't seem interested in them.
  • Gophers are known to avoid daffodil (Narcissus) bulbs but are attracted to tulips (Tulipa). Protecting bulbs in underground cages provides a barrier from gophers as does planting in pots.

Bulb Choices

Besides the popular bulbs mentioned above, some other easy choices include Allium (with a slight onion fragrance), Muscari (grape hyacinth), Crocosmia, Liatris spicata, Crocus vernus (for spring), Crocus sativa (for fall), Freesia, Sparaxis tricolor, Ranunculus asiaticus, and Watsonia.

• Most of these are readily available and are spring- and summer-blooming.
• A popular native rhizome is our own Iris douglasiana—Douglas or coast iris, so named because it thrives in coastal meadows and woods.
  • These iris also do well in inland heat but may require additional water.
  • Lavender and violet are the common colors, though there are white and yellow varieties as well.
• Brodiaea, which some taxonomists lump together with Triteleia and Dichelostemma, is a native corm quite abundant in grassy, sunny meadows of Northern California.
  • Blue, lavender, and lilac are typical, though there are also white, yellow, and crimson species.
  • Generally, their active growth is during fall and winter rains, appearing when summer annuals and most perennials have faded.
  • These all need to be protected from deer and rabbits which love the tender leaves, and from gophers, field mice, and raccoons that relish the corms.
• Other less common bulbs that grow well here are Ixia (African corn lily), Ipheion uniflora (blue spring star flower that naturalizes quickly), Tigridia pavonia (Mexican shell flower), Scilla peruviana, Chasmanthe aethiopica, Babiana (baboon flower (similar to Freesia but taller), Fritallaria imperalis (aptly named skunk lily), Leucojum vernum (spring snowflake), and Schizostylis coccinea (crimson flag, a late summer and fall bloomer that naturalizes readily).

September 2023