Handbook of Vanilla Science and Technology

In general, growth is affected by humidity, nutrition, health, environmental conditions, etc. Vegetative growth during the first 2 years (3.97-5.94 m/year) is markedly less than when the plant is in the third and fourth years (7.49-7.63 m/year). After the fourth year, vegetative growth declines (5.74-6.8 m/year).

The first 2 years following establishment of the vanilla consist almost entirely of vegetative growth. By the third year, plants begin to flower and produce, when shoots have reached a minimal length of 10 m. The plants continue to produce from there on.

1.4 IRRIGATION

The main vanilla production region of Mexico - the Papantla area in northern Veracruz - characteristically suffers drought on an annual basis. The drought is most pronounced during the most critical season for vanilla, during flowering and pollination. Most growers in Mexico nonetheless cultivate vanilla in rain-fed systems.

The most frequent form of irrigation in Mexico is the use of micro-emitters to moisten the mulch layer where the vanilla roots are growing. One criterion for irrigation is to maintain at all times a moist layer of mulch without reaching saturation levels. During the dry season, watering is performed once to twice per week.

1.5 NUTRITION

The primary source of nutrition for vanilla in cultivation is organic material (humus) that results from the natural decomposition of vegetable/animal residues (mulch), composting (via micro-organisms), or vermi-culture (worm-mediated breakdown of organic material).

1.5.1 Mulch

In addition to providing nutrients, the benefits of mulch are:

• it helps maintain soil humidity;

• it serves as a porous substrate, aiding soil aeration and permitting the unrestrained development of roots;

• maintains an adequate temperature; and

• decreases the incidence of weeds.

The most common mulch for vanilla is from decaying leaf litter derived from leaf fall, pruning, and from herbaceous plants in the vainillal.

The mulch should be 10 to 20 cm deep and laid down on either side of the support where the vanilla roots will grow. To prevent the loss of mulch from runoff from heavy rains, most prevalent in vainillales managed on slopes, borders are constructed out of trunks of wood, bamboo canes, rocks, or other materials. New applications of mulch are made when roots are observed growing out of the surface of the mulch, generally 2 to 3 times/year, and mostly in the hot/dry months, when mulch is carefully managed to prevent dehydration.

1.5.2 Building compost

In addition to available natural organic material, the nutritional requirements of vanilla can also be met by developing a composting system.

Compost can be made from a diversity of primary organic materials, but it is best to use locally abundant resources. Fresh sawdust may contain substances that are toxic to plants, such as phenols, resins, terpenes, and tannins. Fresh manure or manure that has not decomposed adequately, can cause burning or root-rot and eventual mortality. When using either of these materials as fertilizer, it should be ensured that they are first well decomposed to avoid causing damage to the plant.

Compost is developed in many ways, but a simple and practical method for composting for vanilla, which gives good results, has been developed by growers in San Rafael, Veracruz. Vanilla plants are grown on orange tree supports, and are fertilized with a mixture of sheep manure and pine sawdust.

This compost is made by:

• mixing 70% pine sawdust with 30% dry sheep manure. The mixing is done on the ground with a shovel until the mixture homogenizes.

• applying water until 45 to 65% moisture is achieved. In practice, a grower decides when this percentage is arrived at by inspecting a small amount (a pinch) of the mixture in his hands. The water should not drop down onto the hands, but adhere to the mixture, and the moisture should be felt between the fingers.

• covering the mixture with plastic to protect it from the rain. High temperatures are generally not a problem, but should not exceed 65°C, which could cause the death of the microorganisms responsible for breaking down the organic material. If this temperature is exceeded, the plastic cover is removed, and the compost is re-mixed (aerated) and water is also applied.

• turning the compost over every 15 days to accelerate decomposition and to maintain good aeration, especially during the initial stages of degradation, since the microorganisms (bacteria and fungi) depend on oxygen to live.

• Compost is ready to use in generally 3 months, when the compost pile cools and has the color and smell of earth; the best indicator is when young herbs start to germinate from the compost. At this stage, the compost should have about 30% moisture.

Composts are applied 1 to 2 times each year. Immediately after they are applied, growers irrigate in order to facilitate the absorption of the nutrients.

1.6 WEED CONTROL