Horticulture Principles and Practices

336 Chapter 10 Asexual Propagation
Tunicate Bulbs The onion is an example of a tunicate bulb (also called laminate
bulb). This type of bulb consists of concentric layers of tightly arranged scales, the outermost
layer being a dry, membranous protective layer (tunic). Other examples are daffodil,
tulip, and hyacinth.
Hyacinths and several other bulbs do not readily produce offsets. Several techniques
are used for propagating these species.
1. Scooping. The entire basal plate is cut out to remove the shoot and flower bud.
The exposed surface should be treated with a fungicide and placed in darkness at
21°C for two weeks to dry to form a wound tissue. After that, the temperature
should be increased to 30°C with a level of humidity of 85 percent The exposed
fleshy bases will produce twenty-five to thirty bulblets with this treatment. It
might take several years before the bulblets reach flowering stage.
2. Scoring. Three to four pie-type deep cuts are made to produce six to eight
sections through the basal plate. The bulb is placed in a warm dark place with
high humidity. This treatment takes several months. If done in summer, the bulb
should be ready for planting in fall. It produces about twenty bulbs that need an
additional three to four years to grow to flowering stage.
3. Coring. Like scooping, coring entails removing the basal plate, only this time, the
center portion is removed to a deeper extent, extracting the primary growing
point. The treatment is the same as for scoring. It yields a fewer number of bulbs
than scoring and scooping.
4. Sectioning. Sectioning is like scoring, only the cuts are made completely through
to produce 6–8 separate sections. The sections are treated like scoring. Bulblets
form at the basal plate of each of the sections.
5. Cuttage. Cuttage is like sectioning. The segments are further trimmed to leave one to
four scales attached to the basal plate. These materials are treated with fungicide.
New bulblets will develop after several weeks of propagating in a well-drained
medium, like vermiculite.
Scaly Bulbs Scaly, or nontunicate, bulbs lack an outer dry protective membrane. They
are more delicate and require special handling to prevent drying and damage. The scales
are not tight but loose and can be removed individually from the bulb. The lily is a nontunicate
bulb. The daughter bulb or bulblets develop at the base of the scales of the
mother bulb.
When the foliage of the plant dies back, the bulb resumes a dormant state. Bulbs
may be dug up, separated, cleaned of soil, and then stored at a cool temperature to keep
them dormant. The ability of a bulb to flower depends on its size. If it is too small, it may
have to be grown for as long as several years before it will reach flowering size. Small
bulb size may be due to premature removal of the foliage of the plant. The bulb should
be harvested after the top has turned brown by natural processes.
The scales of nontunicate bulbs may be separated by cutting at the basal plate. The
separate scales are treated with fungicide and growth hormone and propagated in a plastic
bag of moist vermiculite. The bag is placed at room temperature for about two months
and then stratified in a refrigerator to break dormancy.
Corms
Whereas the bulb consists predominantly of modified leaves, the corm is a modified stem.
Food is stored in this compact stem, which has nodes and very short internodes and is
wrapped up in dry, scaly leaves. When a corm sprouts into a new shoot, the old corm becomes
exhausted of its stored food and is destroyed as a new corm forms above it. Several small
corms, or cormels, arise at the base of the new corm (Figure 10–34). These cormels may be
separated from the mother corm at maturity (die back) and used to propagate new plants.
Plants that produce corms include crocus and gladiolus. Corms are harvested by digging up
after the foliage dies. They should be cleaned of the soil and dried at about 90–92°F before
storing at 40°F and 70–80 percent humidity until the next planting season.