Propagation of Bulbs
Curtis E. Swift, Ph.D., Area Extension Agent (Horticulture). Colorado State University ExtensionTunicate versus non-tunicate or scaly bulbs
Bulbs consist of a growing point surrounded by layers of fleshy leaf bases. These are attached to a compact stem call the basal plate. Bulbs are classified as tunicate or non-tunicate.
Tunicate Bulbs: The onion, hyacinth, squill, amaryllis, snowdrop, tulip and daffodil are examples of tunicate or nonscaly bulbs. These have the fleshy leaf bases arranged in concentric layers around the growing point. These are called tunicate bulbs because the outer layer of leaves dry and form a protective "tunic" covering the bulb.
Non-tunicate Bulbs: The lily is an example of the non-tunicate or scaly bulb. The fleshy leaf bases composing these bulbs overlap resulting in a scaly appearance. Scaly bulbs lack the protective tunic and consequently are more easily damaged and suffer from desiccation more readily than tunicate bulbs.
Propagation of Tunicate Bulbs
An offset (small bulb - also referred to as a `split' or `spoon') develop naturally at the base of the parent bulb. When separated from the parent bulb and planted into a `nursery' area, offsets produce vegetative growth the first few years. It may be several years before the bulb is of sufficient size to produce a flower.
Hyacinth and a few other bulbs, do not readily produce offsets. In these cases scooping, scoring, coring, sectioning and cuttage is used to induce new bulb formation.
This involves removal of the entire basal plate to remove the shoot and flower bud at the center of the bulb. This exposes the fleshy leaf bases from which small bulblets will develop.
The scooped bulb should be dipped in a fungicide to protect the cut surface. Scooped bulbs are then placed in a warm (21o C - 70o F) dark location for approximately 2 weeks. This allows the bulb to dry and form wound tissue on the cut surface. As scales begin to swell during the third week, temperature should be increased to 30o C (85o F) with humidity at 85% RH. The developing bulblets can be planted when new roots form.
Scooping may produce as many as 25 to 30 bulblets per mother bulb. An additional four to five years of growth may be required before attaining sufficient size to flower.
This method is commonly used on hyacinths. Scilla and narcissus can also be scored. Three v-shaded cuts are made through the basal plate creating six pie-shaped sections. These cuts are made deep enough to destroy the main growing point and reach just below the widest point of the bulb. The bulbs can be placed in a warm, dark place at high humidity for a few months or planted upside-down (basal plate up) in clean dry sand, vermiculite or perlite. Twelve to twenty-five bulblets will normally form by fall, if the scoring is done in early summer. The mother bulb and bulblets can be planted in the garden and should sprout in spring. Bulblets produced by this method usually reach flowering size in three to four years.
Coring:This involves the removal of the center portion of the basal plate and the main growing point of the bulb. Cored bulbs can be treated as described for scoring. Cored bulbs typically produce larger but fewer bulblets, reaching flowering size in two to three years.
Sectioning involves cutting of the bulb into 5 to 10 pie-shaped section, each with a portion of the basal plate attached. Treat these sections as described for Scoring. Bulblets will form at the basal plate of each cutting.
Cut mature tunicate bulbs vertically into eight sections. Then cut the basal plate so there are one to four scale segments on each piece of basal plate. Treat with fungicide. These cutting are then planted in vermiculite with the tips of the segments above the vermiculite. New bulblets will form between the scales in a few weeks.
Propagation of Non-Tunicate (Scaly) Bulbsp>Scaly bulbs are easily propagated by offsets using the methods described for tunicate bulbs. These methods, however, are relatively slow and seldom used commercially. Scaling, however, is a common method used with non-tunicate bulbs.
The scales are broken or cut close to the basal plate. The scales are then dusted with a fungicide and growth hormone and sealed in a plastic bag containing damp vermiculite. If maintained at root temperature, bulblets will normally form in about two months. After formation occurs the scales and bulblets are cooled by placing the bag in a refrigerator. This helps overcome any dormancy. The new bulblets can then be planted.
Scales also can be planted one-half their length in a moist medium for rooting.
Problems commonly associated with the propagation of bulbs is infection by various fungi. These problems are avoided with the use of fungicides, clear media and sanitized equipment and materials. Bulb diseases include:
Fusarium bulb rot can be a carryover disease from the production field, or a result of planting in infected soil or media. A white mold growing on the tunic is an indicator of this disease. If removal of the tunic reveals soft tissue, dispose of the bulb.
Penicillium, a blue-gray mold. This is seldom a serious problem with healthy bulbs but can be problematic when the bulb is cut, scored or otherwise prepared for propagation. Bulbs should be dusted with or dipped into a suitable fungicide.
Sclerotium rolfsii (Southern Blight) creates a white, relatively coarse mycelia growing in a fanlike pattern on plant tissue.
Fungicides recommended for control of bulb diseases include:
Note: Active ingredients are in quotation marks ( - - )
Banrot - (etridiazole & thiophanate-methyl
PCNB 75W - quintozene
Placed on the Internet October 1, 1997; updated on Dec 18, 2009