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HERBACEOUS ORNAMENTALS -PERENNIALS, ANNUALS AND BULBS |
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KEY CONCEPTS
I. General Discussion of Perennials, Annuals and Bulbs
II. General Cultural Requirements of Perennials, Annuals and Bulbs
III. Perennials
IV. Annuals
V. Bulbs
BULBS
Bulbs provide a lot of color in a small space, with minimal effort from the gardener. Bulbs can lengthen the time a flower bed displays color. Bulbs bloom before winter is over and are some of the last flowers to display in fall. The foliage of most bulbs is spiky, creating textural interest.
During the growing season bulbs produce foliage and store up a reserve of food for the next year's flowering. Bulbs must store up energy during the growing season for continued vigorous growth and flowering.
A true bulb consists of a modified underground stem surrounded by modified leaves which contain stored food for the plant. There are two types of bulbs: tunicate and scaly. Daffodils and tulips are examples of tunicate bulbs, and lilies (not daylilies) are scaly types. The following diagram shows a cross section of both types of bulbs:
True bulbs have scales held together by stem tissue called a basal plate. Hardy true bulbs usually bloom in spring. They go into a state of rest in summer. After a period of low temperature, they begin growing again in fall and early winter. Tulips, daffodils, and lilies are common examples of true bulbs.
A corm is a compressed stem. It is round, solid and somewhat flat. It contains stored food with a bud on the top. Like true bulbs, it has a basal plate. Crocus and gladiolus are examples of corms. Glads have fibrous and CONTRACTILE root systems, while all other bulb plants have only fibrous systems. During the growing season the glad corm that produces the current season's flower shrivels as stored food is used up. The contractile root system pulls down on the new corm as it forms on top of the old flowering corm. This special system keeps glad corms at the same soil depth.
Tubers are swollen underground stems flattened at one end. Although tubers vary in size and appearance, all are thick, solid bulbous organs. All tubers have "eyes" or buds on the surface from which new growth begins. Tubers do not have scales or basal plates. They have rough, leathery skin. Examples of tubers are begonias and dahlias.
Rhizomes are thick, swollen, underground stems with no basal plate or scales. They usually grow horizontally, just below or at the soil surface. They often spread easily. Iris and lily-of-the-valley are examples of rhizomaceous plants.
Excellent drainage is critical for almost all bulbs. Bulbs will rot if the soil remains wet, especially during the dormant period. Avoid low areas or sites where water does not drain quickly. Raised beds or soil amendments should be considered for sites with poor drainage.
Choose a site in full sun with protection from hottest midday sun for most bulbs. Afternoon protection is especially important for summer-blooming bulbs. Give flowers with red pigmentation afternoon protection to keep the color of their blooms from fading.
Spring-flowering bulbs will grow well under or near large deciduous trees. This is because trees are not leafed out when bulbs are blooming. Bulbs planted in full sun will bloom earlier than those in partial shade. Planting in full sun may result in earlier blooming and frost damage to the flowers. Slightly increasing the planting depth will negate this tendency toward blooming too early.
Bulbs are adaptable to rock gardens and woodland plantings. Random, nonformal placement of bulbs is called naturalizing. Spring-flowering bulbs can be planted in lawns for a naturalized look. However, the need to mow conflicts with the requirement to keep the bulbs' foliage intact. Some gardeners plant massed areas of spring-flowering bulbs, then dig and move them after flowering. This allows beds to be replanted with other plants.
There are many bulbs, corms, rhizomes and tubers from which to choose. Most gardeners plant crocus, daffodils, tulips, iris and gladioli. Try other lesser known bulbs, such as scilla, puschkinia, ranunculus, muscari, tigridia, winter aconite, allium, anemone, chionodoxa, among many others. Most of these selections will reward the gardener by multiplying from year to year.
There are bulb plants that will bloom every season. The spring bulbs have further subdivisions of bloom time. They are described as "early," "mid-season" and "late" spring bloomers. This information is provided by commercial growers so you can plan a succession of blooms.
Purchase from reputable nurseries and mail-order companies that guarantee their stock and provide named varieties. These companies do not collect from dwindling populations of wild plants. Reputable nurseries propagate their bulbs rather than gathering them from the wild. Gathering from the wild has threatened many native species, such as snowdrops and jack-in-the-pulpits, with extinction. Nursery-propagated bulbs are fairly uniform in shape and size, whereas gathered bulbs vary in size and may be misshapen.
When purchasing bulbs at a garden store, choose those that are heavy and feel solid. Choose the largest bulbs available. They will have the most stored energy for flowers and foliage. Avoid bulbs that are nicked or soft. The skin on bulbs should be smooth and free of any injury. The basal plate must be intact. Handle all bulbs with care even while dormant.
When purchasing bulbs, buy early because most bulbs grow better if not kept out of the ground too long. True lily bulbs should not be left dry or uncovered. They will become limp and grow poorly.
Bulbs make the biggest impact when they are planted in groups. Their splash of color is lost when they are spaced out in single rows. However, large, showy specimens may be planted singly. Plant bulbs in the garden with annuals, perennials and shrubs. Bulbs can be planted singly with a bulb planter or in groups where a large planting hole has been dug. Bulbs can be used in containers for a splash of color
Work soil well to prepare new beds for spring-flowering bulbs. The quality of soil under the bulbs is especially important. Loose soil below the bulbs is important for root development. If the soil is heavy clay, mix in 1/4 to 1/3 organic matter (compost, aged bark, peat) by total volume. Add fertilizer based on a soil test or at a general recommendation rate of 3 pounds of 5-10-10 per 100 square feet.
The inexperienced gardener may become confused about when to plant specific bulb-type plants. Not all bulb-type plants are winter hardy. Those that are not must be planted in spring after the frost-free date. They then are dug in the fall and stored during winter for replanting the following spring. Common members of this group include gladioli, dahlias, cannas, caladiums and tuberous begonias.
Plant hardy, spring-flowering bulbs from late August until the soil freezes. Daffodils should be planted in September or early October because a longer period is necessary for root development, before soil freezes and all growth stops. Fall-blooming bulbs are planted in August.
Planting depth and distance apart varies with bulb size. As a general rule, the top of the bulb should be planted at a depth equal to 3 times the bulb's diameter. Less harm is done by planting too deeply than is done by planting too shallowly.
Water thoroughly after planting. This helps to remove any air pockets that may remain around bulbs after planting. Also, moisture is important to begin root growth.
Plant gladiolus corms at a depth of 4 to 5 inches and 6 inches apart. Although this may seem unusually deep, glads need to be anchored deeply to support the flower stalk. Fertilize lightly as the flower spike develops. Stagger planting over 2 months, beginning as early as May, to produce continuous blooms.
Plant tuberous plants outside in May after danger of frost is past. Dahlias, tuberous begonias, cannas and caladiums are four tuberous-type, nonhardy plants commonly grown in Ohio. They each have special requirements to initiate sprouting early in the growing season. They all must be dug in fall and stored under specific conditions over winter.
Lily bulbs have some special requirements for planting depth. There are two groups of lilies: those that form basal roots, and those that have both basal roots and additional adventitious roots on the stem.
Follow planting depth recommendations given on packaging. Lilies that have both stem and basal roots usually are planted at least 5 inches deep. Those lilies with only basal roots should usually be planted at a depth equal to 2-1/2 times the diameter of the bulb.
Store nonhardy, bulb-type plants in a cool, well-ventilated place during winter. After the first frost, dig dahlias carefully with a fork and lift. Allow tubers to dry, then store. Dig and lift gladiolus in late fall and store. Caladiums begin to fade as the growing season ends. Gradually reduce watering and allow to go dormant. Begonias are dug and stored after frost has killed above-ground foliage.
These are popular plants with many gardeners, despite the extra care they must be given. For detailed information see the following references: tuberous begonias - Reference Herbac.7, canna - Reference Herbac.8, and dahlias - Reference Herbac.9.
Water all bulbs during times of growth and especially during foliage and bloom development. Irrigate summer-flowering bulbs during dry weather. Keep water off foliage and blooms.
Fertilize tulips as foliage appears and make another application after flowering. Fertilize all other spring-flowering bulbs after flowering. Apply 2 pounds of 5-10-10 or 6-12-12 per 100 square feet. Daffodils and tulips should be fertilized again in early to mid-August.
It is especially important to mulch after planting if bulbs are planted very late in fall. Mulch insulates the soil, keeping it warmer longer so root growth can occur. If MARGINALLY HARDY bulbs are heavily mulched to survive winter, pull back the mulch toward the end of winter. This prevents premature growth as the sun warms the soil.
Remove the flower stalk as the blossoms begin to fade. For good bulb growth and rebloom the following year, do not disturb foliage until it begins to yellow. Cut off all faded foliage. Braiding the foliage is not recommended.
Some bulb plants must be dug and divided periodically to retain plant vigor. Some lilies can increase so rapidly that division is necessary. Thin, crowded stems and noticeably fewer and/or smaller blooms signal the need to divide. Divide and transplant during the dormant period.
Many of the minor bulbs, such as snowdrops, multiply readily without loss of quality. They are used in the landscape to fill in as ground cover and in naturalized areas.
In the case of tulips, bulblets form at the expense of the parent bulb. This causes flower size to decrease and eventually, the bulb ceases to flower. For perennial use, choose species or botanical-type tulips. They multiply without decreasing in quality. Hybrid tulips often perform as annuals and are dug and thrown out at the end of season.
Tuberous and rhizomatous plants should be divided as shown in the following illustration.
Each division must include a piece of the stem or crown with an eye. The fact sheet on growing dahlias explains how to propagate dahlias by division and seed.
Lily bulb scales can be detached and used for propagation, as is seen in the following illustration.
Bulb-type plants propagate by making new, smaller versions of themselves: BULBLETS, CORMELS and BULBILS. They also produce seeds. Smaller offshoot bulbs or cormels can be detached from the main bulbs. These smaller bulbs will flower in 1 to 3 years. Aerial bulblets (bulbils) form where the leaf meets the stem on various lilies. These will produce flowers 2 to 3 years after planting.
Although there are other methods of propagation, they are not commonly used by the home gardener. Growing bulbous plants from seed is impractical for most gardeners.
Tulips, hyacinths, daffodils and crocuses can be forced. This means that with special treatment, bulbs can be made to bloom out of season. To enjoy spring blooms in your home during the dead of winter, check Fact Sheet 1225, Reference Herbac.10.
Squirrels, chipmunks and mice dig and eat tulip, crocus, Chionodoxa and lily bulbs. They will not eat or bother daffodils and hyacinths and fritillarias.
Aphids, spider mites, leaf hoppers, stalk borers, thrips, viruses, fungal diseases and slugs will attack bulb-type plants. The iris borer is a particularly troublesome insect pest in Ohio. Fungal diseases that attack roots and bulbs can be discouraged by planting where drainage is excellent. Fact Sheets provide information on lily, dahlia, tulip and iris problems.