What Is the Difference Between an Iris Bulb & a Lily Bulb?

Visual Characteristics

• Both iris bulbs and lily bulbs are small in size: less than 1 inch in diameter. Iris bulbs have a round, circular shape with a tapering tail end and a stubby, stemlike topknot. The bulbs are white but covered with a brown, papery husk. Once the bulb is planted, the roots will form from the long tail and the stem will sprout from the knob at the top. Lily bulbs are also white, but the husk that covers them is a much deeper shade of brown. The bulbs of the lily are more elongated and not as fat as iris bulbs, though they also have a long, tapering end and a stemlike or leaflike growth at the top.

Bulb Characteristics

• Unlike iris bulbs, lily bulbs never go dormant. You must plant lily bulbs right away or they will dry out and shrivel up. Dried bulbs are not suitable for planting and will not produce flowers. Lilies, Lillium, may also grow from seed, though they takes up to four years for flowers to blossom when the plants start in this fashion. Only bulbous iris species grow from bulbs; other irises grow from rhizomes. Iris bulbs require a period of dormancy before they may be used to produce flowers; this is why they are planted before winter. Iris histrioides "sky blue iris," Iris xiphium "Spanish iris" and Iris xiphioides "English iris" are all bulbous irises. Iris bulbs may be placed in cold storage, and as long as they are kept moist they may survive several seasons until they are planted.

Climate

• Iris bulbs require planting in the fall. The bulbs will become dormant over the winter and bloom in spring. Irises grown outdoors in USDA plant hardiness zones 8 through 10. Lilies are much hardier; you may plant them in a variety of climates in zones 2 through 8. Insulate both bulbs against winter cold with a layer of woody mulch on the soil; doing so may improve the hardiness of both plants.

Planting

• Plant iris bulbs in moist, sunny soil down to a depth of about 5 inches. Point the top of the bulb up during planting. Unlike iris bulbs, you can plant lily bulbs in the spring or fall. Plant lilies in a sunny site 2 to 6 inches deep, depending on the size of the bulb. Bury large bulbs at least 4 inches below the surface, while smaller bulbs must be closer to the surface of the soil. Lilies will grow only in well-drained soil, but irises require constant moisture during the growing season. So you can't really plant them together without a lot of effort all season.