The areas where vanilla cultivation has been practiced in the recent past are less desirable because they are likely to contain remnant populations of Fusarium oxysporum.
Land Preparation
The most prevalent form of vanilla cultivation in Mexico is the vainillal: a secondary forest regrowth the managed to cultivate vanilla. The first step in its preparation is to thin the forest to increase luminosity and space, leaving only those trees or shrubs that would serve as supports. Where deforestation has occurred, weedy herbs are cut and left to compost on-site in lieu of being burned. On level ground, where the soil may become waterlogged, drainages are dug to eliminate excess water. On steep terrains, terracing is done to control erosion, mitigate runoff of organic material, and to conserve soil humidity.
Support Trees
The primary function of the support tree is to provide an appropriate framework and microenvironment for the growth and management of the clambering vanilla plant. In addition to providing physical aid, the support trees give shade and, in deciduous or semideciduous species, apportion organic material. The choice of the support tree should be the species that is most adapted to the area, and feature the following characteristics: (1) maintain a canopy throughout the year, (2) be easy to propagate and able to reestablish readily, (3) respond positively to periodic pruning for form/shade management, (4) lack spines and leaves near its base, (5) be strong enough to support the weight of the vanilla plant, and strong winds, (6) possess bark that does not shed,(7) be fairly resistant to pests/diseases, and (8) have a deep root system that does not compete in the shallow soil layers for nutrients and water with the vanilla plants.
In the low-intensity vainillales of Mexico, where other crops and species of economic importance are managed, the species chosen for supports are the shrubs and trees that grow in that area. Fruit trees are also chosen: orange (Citrus sinensis), grape-fruit (Citrus grandis), and mandarin (Citrus reticulata). In intensively managed monoculture of vanilla (Figure 6.1), support trees must first be planted. The following are the most commonly planted vanilla support trees in the world:
Erythrina sp. (Mexico, Costa Rica, India, and Indonesia)
Gliricidia sepium (syn. G. maculata ) (Madagascar, Tonga, India, Indonesia, Reunion Island, and French Polynesia)
Leucaena leucocephala (Tonga and Indonesia)Casuarina equisetifolia (Madagascar, Tonga, Reunion Island, and India) Jatropha curcas (Madagascar, Uganda, Tonga, Reunion Island, and French Polynesia)
Plumeria alba (India)
FIGURE 6.1 Intensive cultivation of vanilla on living supports (Erythrina sp.).
In the most recently established system of vanilla cultivation, artificial or “dead” supports are used (Figure 6.2). In this case, the function of the support is purely physical, while the shade is provided by 50% shading cloth (green, red, or black), which is stretched above all the plants at ca. 3–5 m high, on the four sides of the planted area. These systems are referred to as “shade houses.” In size, they are usually on the order of 25 m × 40 m (1000 m²), and some are up to 1 ha (Hernández Hernández 2007a).
FIGURE 6.2 Vanilla intensively cultivated on concrete support under shade houses.
Establishing Living Support Trees
Supports such as Erythrina sp. and Gliricidia sp. are propagated mainly through stem cuttings, although some species such as L. leucocephala are propagated by seed.
In Mexico, transplanting and establishing the supports can be done at any time of the year, but is most successful when done at the onset of the rainy season. Cuttings are normally 1.5–2 m long and at least 5 cm in diameter. Cuttings are planted at about 30–40 cm depth, and six months to one year in advance of establishing the vanilla cuttings.
The most common planting distances between supports are: 1.2 × 1.50 m, 1.5 × 2.5 m, 2.0 × 2.5 m, 1.8 × 2.5 m, and 2.0 × 3.0 m, or a density of approximately 1600–5000 supports/ha (Childers et al., 1948; Dequaire, 1980; Tiollier, 1980; Sasikumar et al., 1992; Soto, 2003; Anandaraj et al., 2005; Ranadive, 2005). Smaller planting areas are problematic due to insufficient air circulation, which lead to diseases (Childers et al., 1948; Soto, 2003; Ranadive, 2005). For each support, 1–2 vanilla cuttings are planted.
Planting distance between fruit tree supports varies with the species. For orange, the planting distances are normally 4 × 4 m, 5 × 5 m, 6 × 6 m, and 7 × 7 m (roughly equivalent to 204–625 supports/ha). For each orange tree, 3–6 vanilla cuttings are planted, producing an estimated 1224–1875 vanilla plants/ha.
In polycrop systems that include vanilla, usually associated with coffee, banana, and coconut palm cultivation, it is common to use Erythrina sp. or Gliricidia sp. as vanilla supports, planting them at distances of 1.5 × 2 m. These are smaller densities than are encountered in monocrop systems, but have the advantage of allowing for at least two products to be exploited.
When used, the native tree species are planted at variable distances, depending on the standing distribution of those that are selected, and can be 500–1500 supports/ ha. In shade houses, supports are spaced 1–1.5 m between each tutor and 2–2.5 m apart between each row. In 1 ha, 4000–5000 supports are set up, with 1–2 vanilla plants/support. Vanilla generally thrives in shade house cultivation. However, at the reproductively mature adult stage, their management becomes difficult and tedious, air circulation is reduced, and the spread of pathogens can be very rapid and devastating (Ranadive, 2005).
Propagation
Vanilla is propagated almost entirely by stem cutting. The cuttings are procured from another grower or from a government agricultural entity. Cuttings are made from highly productive and vigorous individuals, which are selected and marked before the harvest. The cutting itself should not be a flowering shoot and should have at least three nodes with viable axillary buds for producing new shoots from which the plant grows. Cuttings should be free of damage or of symptoms of pests/diseases so as to avoid future proliferation of the disease.
Cuttings are normally 6–8 nodes (80–120 cm long, 1 cm in diameter) in length. Longer or thicker cuttings form new vegetative and reproductive shoots more rapidly (Ranadive, 2005), but are more difficult to deal with during planting and are also more expensive. Cuttings that are less than 60 cm long are best managed as nursery plants before they are transplanted permanently (Anandaraj et al., 2005; Ranadive, 2005).
In Vitro Plants
Another option for sourcing and reproducing commercial vanilla stock is in vitro propagation. In vitro propagules are accustomed in having their nourishment provided, and so before they are transplanted directly into a cultivated area, they must first be placed in climate-controlled greenhouses, where they can adapt in providing their own food via photosynthesis. These propagules are transplanted as soon as they reach a height of about 30 cm.