Bulbs

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Bulbs

• Defn specialized underground structures with a
  basal plate bearing a growing point, enclosed by
  thick, fleshy scales
• Propagation methods
• offsets
• bulblet separation from flowering stems
• stem cuttings
• scaling
• basal cuttage
• leaf and bulb cuttings
• micropropagation

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Propagation of bulbs by offsets

• Used extensively for tulips and daffodils
• tulips - features
• bulbs are dug in the summer
• offsets are separated, graded for size
• stored, replanted the same fall
• offsets usu. require 2-3 growing seasons to
  achieve flowering size

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Photo showing various shapes, sizes and colors of
tulip flowers (Rix 1981)
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Fig. 15-1. Structure of tulip, a tunicate bulb,
with parts labelled.
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Developing offset
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Offset propagation of Narcissus (daffodils)

• flowering bulb continues growth from the center
  (as opposed to tulips) each year
• propagation method is similar(to tulips), by
  separation of the offset or split
• harvested bulbs are graded 1st yr (round or
  single-nose, 2nd yr (double nose), and 3rd yr
  (mother bulbs)

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Photo showing various flower colors of daffodil
(Rix 1981)
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Well-developed offsets
Double-nosed bulb
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Amaryllis (Hippeastrum)
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Bulblet separation from flowering stems

• useful for propagation of Easter lilies
• method
• underground bulblets pulled from flowering stems
• planted in late fall (Pacific Northwest)
• dug the following Sept., graded and replanted
• 2 yrs to commercial bulbs

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Fig. 15-5. The flowering stem of Easter lily.
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Main flowering bulb
Offsets attached to the stem of the flower stalk
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Stem cuttings of bulbs

• used for Easter lilies
• cuttings are made from flowering stems (after
  flowering), then stuck in moist medium
• bulblets form in leaf axils
• some lilies also form bulbils in leaf axils of
  the flowering stem

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Bulb scaling

• useful for a wide variety of lily species
• scales are separated from the bulb (individual
  scales separate readily from this nontunicate
  bulb)
• adventitious bulblets form at the base of each
  scale
• bulblets are usu. vernalized for sev. weeks, then
  planted
• scaling can also be done by tissue culture for
  multiplying virus-indexed stock

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Fig. 15-4. The structure of the Easter lily
bulb, with parts labelled.
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Basal cuttage

• useful for hyacinths
• basal plate is removed (scooped) or scored
  (to remove the growing point
• adventitious bulblets develop from the base of
  exposed bulb scales

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Photo of the hyacinth flowering shoot (Harrison
1967)
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Figure of a hyacinth bulb with bulblets forming
after bulb scoring (Clark and Toogood 1990)
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Photos showing bulb scoring and scooping (Free
1957)
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Leaf cuttings of bulb species

• useful for grape hyacinths (Muscari botryoides),
  blood lily (Haemanthus coccineus), common
  hyacinths (Hyacinthus orientalis)
• similar to leaf cuttings of other herbaceous
  plants, except a bulblet forms at the base of the
  leaf cutting

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Bulb cuttings

• useful for Narcissus, Hippeastrum (Amaryllis)
• called bulb chipping or fractional scale-stem
  cuttage
• mature bulb is cut into 8-10 vertical sections,
  then further divided by cutting between every 3rd
  or 4th concentric scale, through the basal plate
• twin scaling is a variation on this method

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Fig. 15-12. Twin-scaling of Narcissus.
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Micropropagation of bulb species

• useful for iris (bulbous), hyacinth, and
  (increasingly) Narcissus, Hippeastrum, and Lilium
  (e.g., 12 million annually in the Netherlands)
• increase is by shoot multiplication, bulblet
  induction on scales followed by bulblet division,
  or bulblet induction on flower scapes

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Photo showing micropropagation of bulbous iris
(Zimmerman et al. 1986)
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Fig. 15-10. Micropropagation of bulbous iris and
hyacinth.
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Propagation of corms

• useful for gladiolus and freesia
• corm the swollen base of a stem axis, enclosed
  by dry, scale-like leaves
• propagation methods
• separation of offset corms
• cormels (miniature corms between old and new
  corms)
• corm division (retaining a bud with each section)
• micropropagation (both glads and freesias)

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Fig. 15-13 and 15-14. Photo and diagrams of
gladiolus corms, with parts labelled.
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Photo showing gladiolus micropropagation
(Zimmerman et al. 1986)
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Recap

• Bulb propagation
• Offsets (tulip and daffodil)
• Bulblet separation from flowering stems (Easter
  lily)
• Stem cuttings (lily)
• Scaling (lily)
• Basal cuttage - scoring and scooping (hyacinth)
• Leaf and bulb cuttings - e.g., bulb chipping,
  twin scaling (narcissus, amaryllis)
• Micropropagation (iris, hyacinth, narcissus,
  amaryllis, lily)

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Recap - contin.

• Corm propagation (gladiolus, freesia)
• Separation of offset corms
• Separation of cormels
• Corm division
• Micropropagation
• And, from the text What is the advantage of
  growing tulips for bulb production in the Pacific
  Northwest (of the U.S.)? What happens if the
  bulbs are dug too early or if warm weather causes
  early maturation?