December 2, 2005

Bulbs 101: what to grow, when and how to grow it

By Shari Kaplan
Staff writer

It’s too late in autumn to start certain flowering plants from seed, but it’s not too late to plant a variety of bulbs for a cheerful spring bloom.

Freesias, which grow from corms, are popular for their fruity-sweet fragrance and brilliant array of colors. Photograph by Shari Kaplan

As my favorite horticulturist advises: “If you can buy it in nurseries now, you can plant it now!” Some bulbs may bloom a bit later in spring if planted later than usual now, but in successive years they’ll revert to their usual schedules.

What’s more, much of the Santa Clara Valley lies in USDA Hardiness Zone 9, which www.bulb.com, a good online resource, says is suitable for planting through early December.

Bulbs
First, let’s clear up a few misconceptions. Some people use “bulb” to describe any bulbous, firm, protective structure that contains all the sustenance and genetic information to produce a complete plant.

However, only certain plants grow from true bulbs. These include amaryllis, daffodil, grape hyacinth, hyacinth, tulip and certain types of beardless iris.

Bulbs are short underground stems with swollen fleshy leaves (scales) surrounding an embryonic plant. They have a definite top and bottom; the latter is the “basal plate.” Around the outer scales is a papery covering, or “tunic.” Peel a supermarket onion and you’ll see all of these parts.

When it comes to bulbs that naturalize, daffodils and jonquils (Narcissus genus) are a good choice. They aren’t fussy about soil as long as it’s well-drained, they don’t need summer irrigation and are quite cold-hardy. They’re also available in many color combinations and petal styles.

Grape hyacinths (Muscari genus) are good naturalizers too, and are often planted with yellow daffs because the hyacinths’ typical shades of blue and purple make a great color contrast. White varieties are also available.

Two of my favorite bulbs—snowflakes and snowdrops—come only in white, although their tips may be lightly dotted with green. Despite a dainty appearance, certain species are such hardy early bloomers that in colder climes, they bloom and thrive in snow!

In mild-winter climates, snowflakes generally perform better than snowdrops, with the summer snowflake (Leucojum aestivum) the best bet. Ignore the misleading name; it does not bloom in summer.

Corms
Corms are swollen underground stems covered with dead leaf bases. Like bulbs, they have basal plates. Unlike bulbs, which divide by “bulblets” that form on the basal plate and appear alongside the bulb, corms reproduce by forming new corms (“cormels”) on top of old ones. Brodiaea, crocus, freesia and gladiolus are examples of plants grown from corms.

Snowflakes look delicate, but actually bloom during winter and early spring and can tolerate snow. They are closely related to snowdrops.

Although gladiolus is one of the few summer-bloomers, nurseries sometimes sell the corms early. That’s because glads have a precise “time clock” and don’t bloom until they know summer is around the bend. The festive colors and fruity-sweet scent of freesias make them perennially popular sellers. They also naturalize rapidly.

Rhizomes and tubers
Rhizomes are thickened food storage organs with a horizontal pattern of growth and spread. Buds that form along the rhizomes will grow into the plant’s different attributes, such as foliage, roots and flower stalks. As long as a rhizome has some growth buds, it can be cut into sections for starting new plants.

Callas (“calla lilies”), cannas, society garlic, trillium and numerous types of iris grow from rhizomes. Cannas technically grow from tuberous rhizomes, not true rhizomes, but most folks don’t know the difference, and that’s fine.

It’s important, however, to recognize two additional storage structures: tuberous roots and tubers. Common plants grown from the former include dahlia and four o’clock; those from the latter include cyclamen, glory lily, gloxinia and tuberous begonia. Morning glories may have tubers or tuberous roots—it depends whom you ask!

Care tips
In general, bulbs, corms and their kin grow best in rich, well-drained soil with regular irrigation during their periods of growth and bloom. Many prefer full sun exposure during bloom as well. Some prefer soil amendments; others don’t care.

Their cold and heat tolerance varies, but many can remain in-ground all year here in the Santa Clara Valley. The greatest variable is planting depth, which ranges from an inch to a foot. The rule of (green) thumb is to dig a hole three times as deep as the bulb’s widest diameter.