According to Potty and Krishnakumar (2003), vanilla can be successfully cultivated in areas nearer to the equator, where warm and humid climate prevails throughout the year and up to an altitude of 1100 m asl.
Vanilla prefers land with gentle slope and light porous soil with adequate drainage. Soil with high humus content is preferred, although the plants can thrive well in sandy loam to even lateritic soils. The humus-rich soils of Western Ghats and the northeastern states of India are highly suited for its cultivation. Vanilla is grown successfully as an intercrop in coconut and arecanut gardens (Sasikumar et al., 1993).
Propagation
Vanilla is amenable to both sexual and asexual methods of propagation. The stem cuttings are capable of striking roots at nodes when they come in contact with soil or any other rooting media. Vegetative propagation through stem cutting is, by and large, the accepted method because it is easy and quick to establish. However, vanilla being a monopodial orchid, collection of sizeable quantities of stem cuttings from the main plantations could lead to the arrest of vegetative growth of mother plants (Ayyappan, 1990) and will be at the expense of subsequent years’ crop. Hence, production of planting materials in nurseries is resorted to under commercial farming. In areas where viral disease is rampant, virus-free certified micropropagated materials are recommended for reviving the plantations.
The primary source of cuttings for the nurseries may be collected from disease-free, healthy, and vigorous mother plants from yielding plantations. The length of the vine used for planting varies from place to place, but has profound influence on further growth and time taken to attain maturity. In situations where there is scarcity of mother vines, cuttings of three to four nodes are used. It is recommended to use such cuttings in the nurseries to raise longer vines rather than directly planting in fields because shorter stem cuttings take longer time for establishment and yielding.
Trench Multiplication
A simple and rapid multiplication procedure for planting material production was described (Kuruvilla et al., 2003). The site for the rapid multiplication nursery should be ideally located with respect to accessibility, availability of water source, gentle slope, and deep and fertile soil of loamy nature having optimum natural shade. Wherever the optimum shade is not available, it is necessary to provide adequate shade using agro-shade nets permitting 50% light intensity. Trenches of 60 cm wide and 60 cm deep are opened at convenient length, leaving 40 cm in between. The trenches are filled with topsoil, well-decomposed farmyard manure (FYM), and sand in the ratio 3:1:1. Standards of 2–2.5 m length for trailing of vines are planted at a distance of 1 m along the trenches at least two months before planting vanilla. Fast-growing trees possessing low branching habit, small leaves, and rough bark are preferred. Plumeria alba, Erythrina lithosperma, and Glyricidia maculata, and others are the common live standards used in India. One-meter vanilla vine cuttings with at least 10 nodes are to be used for planting in the rapid multiplication nursery. Three or four basal leaves of the vines are cut retaining one-third of leaf blades and dipped in 1% Bordeaux mixture for 15 min and then kept in shade for about one week for partially losing the moisture.
The basal portion of the vine is laid on the soil surface near the standards and covered with a thin layer of soil in such a way that the cut end of the vine is bent upward above the soil surface to avoid contact with soil. The rest of the vine is then tied on to the standards so that the nodes are pressed to the standard. The plant base should be mulched with partially decomposed wood debris or leaf litter. The vines are allowed to grow on the supports to a height of 1.5–2.0 m and later coiled loosely around the branches of the supports. The plants are to be irrigated at frequent intervals, as per need. Vanilla responds well to fertilizers. Application of 50 g N, 25 g P2O5, and 80 g K2O per vine in six split doses in a year at bimonthly intervals enhances the growth of vines. Alternatively, foliar application of fertilizer could be given at bimonthly intervals. A well-maintained plant would produce about 5–7 m of growth per year, and therefore the size of the nursery can be planned taking into account the annual requirement of the planting materials. On an average 1 ha of nursery would be sufficient to produce about 40,000 m of planting material annually.
Polybag Nursery
An alternative method to generate planting material when there is shortage of standard vine cuttings of 1 m is to raise the shorter cuttings with two or three nodes in polythene bags and growing it to 8–10 nodded rooted cuttings of standard size. Field establishment of polybag plants is invariably better. Nurseries should be located close to the main field for early to transportation. Black polythene bags of 20 × 20 cm size and 100–150 gauge thickness are normally used for planting stem cuttings. In order to facilitate proper drainage, five to six holes are given at the lower half of each bag. The bags are filled with potting mixture prepared with jungle topsoil, decomposed FYM, and sand in the ratio of 3:1:1. Siddagangaiah et al. (1996) observed that vermicompost and decomposed coir pith are better rooting media for vanilla.
Cuttings with three nodes are planted in polybags and tied to bamboo splits/stakes inserted in the bags for support. The length of the cuttings used has been found to have profound influence on subsequent growth. When two node cuttings were used, vine growth was only 32.6 cm in six months, against 51.8 cm with three node cuttings (Krishnakumar, 1995). The exposed soil in the polybag should be given a layer of mulch, preferably decomposed leaves to protect the soil, to retain soil moisture, and to serve as a source of plant nutrients. Partial shade should be provided either by using agro-shade nets or coir nets.
ICRI, Spices Board of India has standardized a more convenient and economical method of raising polybag nurseries. Vanilla cuttings planted in polybags are allowed to trail in coir yarn as illustrated (Figure 20.1). The fully grown nursery vines along with the coir yarn would be tied to the standard during field planting ensuring least disturbances to the poly bagged seedlings. The moisture holding capacity and rough surface of the coir yarn favored better vine growth (ICRI, 2006).
FIGURE 20.1 Nursery production of vanilla on coir yarns (ICRI method).
The plants are maintained with regular watering. Foliar application of 1% diam-monium phosphate (DAP) can be given to growing vines two months after planting, which can be repeated at monthly intervals. Alternatively, vermiwash can be used for enhancing the growth of vines. Spraying vermiwash once in two weeks increased the length of vine to 66 cm in six months compared to 42 cm obtained in the control (ICRI, 1999). The cuttings so raised in the polybags will be ready for field planting in 6–7 months, by which time they should have reached about 50–70 cm of vine length.
Supports for Vines