Bulbs

Bulbs are underground structures from which some flowering plants grow. The bulb contains the entire plant in miniature. There are two kinds of bulbs: trinicate, or onion-like, and scaly. Within each type, bulbs are sized from DNI (the largest) to DNIII (the smallest): larger bulbs are generally considered the most productive.

I recommend: Learn the basic terms referring to bulbs from the University of Arkansas Division of Agriculture. Compare bulb sizes with a guide from EasyToGrowBulbs.com.

Corms, rhizomes and tuberous roots

Though not true bulbs, other flowering plants grow from similar structures and are often included in the general category of bulbs. Corms, including crocus and gladiolus, are rounder and shorter than bulbs. Rhizomes, including iris and lily-of-the-valley, are fleshy underground stems that send out runners. Peonies and daylilies are examples of flowering plants that grow from tuberous roots, potato-like structures with many "eyes" or growing points.

I recommend: Distinguish true bulbs from corms, rhizomes, tubers and other bulb-like structures with this guide from the University of Illinois Extension.

Hardiness

The term hardiness refers to a bulb's ability to remain in the ground through cold winters. Hardy bulbs require freezing temperatures to promote growth; they are planted in fall for spring flowering. Tender bulbs, planted in spring for summer or fall bloom, cannot weather cold temperatures. They are treated as annuals or overwintered.

I recommend: The Helpful Gardener offers more on determining bulb hardiness, including a climate zone chart and info on which bulbs to plant when.

Overwintering

Many tender flower bulbs can be overwintered, or lifted from the soil after flowering and stored in a cool, dry place through the winter to be planted again in spring.

I recommend: Review overwintering techniques and terminology at Flower Gardening Made Easy.

Bulb planters

Bulbs can be planted in formal rows or in clusters known as bouquet plantings. They can be allowed to naturalize, or grow randomly, on lawns or in wooded areas. Several special tools have been designed to assist in digging holes for bulbs, especially in hard or clay soil. The dibble is a funnel shaped tool that digs out a cone-shaped segment of ground. Short or long-handled bulb planters utilize sharp, curved blades. The long garden auger, which can be attached to a standard electric drill, makes digging precise holes for bulbs an easy task.

I recommend: Popular bulb planting tools are described and pictured at MarthaStewart.com. Find a description of the garden auger at GardenAuger.com.

Bulb fertilization

Special bulb fertilizers have been developed that apply nutrients in a slow-release form. Organic gardeners use combinations of bone meal (sterilized, ground animal bone), blood meal (dried, powdered blood) and greensand (powdered rock that's high in potassium) as fertilizers.

I recommend: This University of Minnesota Extension article defines and discusses various types of flower bulb fertilizers.