Friday, November 9, 2007

Greenhouse - Bulb Forcing 1

This is the first in a series on bulb forcing for greenhouse growers

Basic Principles

Given that geophyte (bulbing flower) storage organs evolved in response to adverse climatic conditions, it is logical that the most important variable to consider in geophyte production is temperature; thus, for many bulb plants, it is necessary to mimic the natural temperature sequences of the environment to which a geophyte is naturally adapted in order for the plant to flower properly. Spring-flowering bulbs develop flower primordia inside the bulb during the summer, are planted outside in the fall, overwinter under low temperatures and then flower in the warmth of spring. For forcing, it is necessary to give these geophytes a warm-cool-warm temperature sequence.


Five phases comprise horticultural production of geophytes (bulb flowers):

1. bulb (storage organ) production
2. bulb (storage organ) programming
3. greenhouse flower forcing
4. marketing
5. the consumer (after care)

The bulb production phase involves the production of bulbs for subsequent forcing or use in the garden. These two bulb markets are referred to as the forcing market and the dry-sale market. Forcing bulbs are sold to greenhouse forcers for production of cut flowers, flowering potted plants, and growing potted plants. These bulbs go through programming and forcing regimes to accelerate or delay flowering. Dry-sale bulbs are sold after the production phase for use in outdoor gardens and landscaping; thus, these bulbs skip the programming and forcing phases.

The bulb programming phase involves all temperature treatments given to bulbs from the time they are harvested until they are placed in the greenhouse. Again, the basis of this phase is the need to provide the proper temperature sequence to ensure proper flowering. The most common method for providing these artificial growing conditions involves a temperature-controlled rooting room; however, not all geophytes require a rooting room for programming. Those that do not are forced entirely in the greenhouse.

The greenhouse forcing stage begins when bulbs are moved from the rooting room into the greenhouse or, in the case of non-rooting room bulbs, when bulbs enter the greenhouse upon arrival from the bulb producer. It ends when the cut flowers, flowering potted plants or growing potted plants are sent to market.

For successful marketing, it is essential that consumers of bulb flowers and plants receive the products at the proper developmental stage to allow for maximum enjoyment. In order to optimize this process, the cooperation of all stages of the flower bulb industry is essential. If producers, wholesalers, and retailers work together, they can increase customer satisfaction and profits for all.

Finally, it is important to consider the consumer stage because interior conditions and the level of care given by the consumer have a major impact on quality.

Extracted from "Geophyte Horticulture" from the Cornell University Flower Bulb Research Program. For more information on research on bulb crops go to

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