Geophyte Horticulture

Basic Principles

Given that geophyte 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 geophytes, 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.

Phases

Five phases comprise horticultural production of geophytes:
1. bulb (storage organ) production,
2. bulb (storage organ) programming,
3. greenhouse flower forcing,
4. marketing, and
5. the consumer.

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.

Rooting Rooms

As mentioned above, the most common method for providing the necessary cold-week requirement during bulb programming of spring-flowering bulbs is a temperature-controlled rooting room. In addition to providing dormancy breaking for flowering, the temperature in the rooting room is manipulated to promote rooting and to inhibit stem elongation. The alternative to a rooting room is an outdoor rooting bed, but the lack of environmental control with this method makes it undesirable.

Commonly a rooting room consists of a walk-in cooler with a thermostat for temperature control. In addition to proper temperature, it is important to maintain good ventilation within the rooting room to prevent disease and a buildup of ethylene gas, which causes flower abortion and other problems. At least one room air change per day is needed for bulbs, but more is required if the space is utilized for storing flowers or other plants. Lighting is unnecessary except for those working in the room. Bulbs need to be kept moist, often in crates filled with soil or media. A high relative humidity (between 80% and 90%) is desirable to reduce evaporation from the media. Since the humidity also promotes disease, it is important to maintain proper sanitation.

The timing of rooting room temperature sequences varies, but in general three temperatures are used. When first placed in the rooting room, bulbs are held at a constant temperature of 48 degrees F (9 degrees C). This is relatively warm and allows for proper rooting, but it is cold enough to begin "dormancy" breaking. After roots begin to protrude from the pot, the temperature is reduced to 41 F (5 C). This promotes dormancy breaking, reduces growth and slows elongation of the stem. Finally, the temperature is decreased to 32-35 F (0-2 C) to greatly slow stem elongation until bulbs are removed for forcing.

There are two basic temperature sequences, A and B, used for standard forcing of rooting room bulbs. Both sequences involve use of the same three temperatures listed above. Sequence A is for early forcing, and Sequence B is for late forcing. The two sequences are delineated below:

Sequence A
48 F(9 C) to November 5-10 (or until the roots protrude from the pot)
41 F(5 C) to January 1-5 (or, when the stem is 1 - 2" tall)
32-35 F(0-2 C) to Finish

Sequence B
48 F(9 C) to December 1-5 (or until the roots protrude from the pot)
41 F(5 C) to January 1-5 (or, when the stem is 1 -2" tall)
32-35 F(0-2 C) to Finish

Most rooting rooms are designed with two compartments that have separate thermostats to allow for simultaneous programming of early and late crops using these two sequences.

Rooting rooms are relatively cheap to operate. Crates are stacked on top of one another; thus, lots of plant material is held within a small space. In addition, the rapid turnover time of rooting room crops and the fact that these flowers are grown pot-to-pot in the greenhouse makes for efficient use of square footage and high profit potential.

Growing Media

Using the proper planting media is an essential aspect of bulb production. The purpose is to provide the bulb with an anchor and a source of moisture. The most commonly used media consist of mixtures of sand, peat, perlite, vermiculite, bark, and other amendments.

There are several factors to consider with respect to media. First, it should be analyzed for pH and soluble salt levels. Soluble salts should be low (less than 1.0 mmho/cm with a 2:1 soil test), and the pH should be between 6.0 and 7.0. The media needs to be well-drained but have the capacity to retain the moisture required for growth. Finally, the media should be pasteurized to ensure that it is pathogen-free.