The recommended soil
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A two years old seedling of Thelymitra macrophylla in a 90 mm pot. |
Terrestrial orchids need lots of air space on their roots, as all other orchids do. Therefore, the soil has to be well drained, uncompacted and crumbly. As orchid roots also need a permanent water supply during the growing period, the soil must have a good water-holding capacity, too. The soil has to contain a certain amount of organic matter. Dead plant and wood residuals slowly break down and supply orchids and mycorrhizal fungi with nutrients. An appropriate pH affects the availabilty of many nutrients and strongly influences the activity of mycorrhizal fungi. Numerous trials have shown that a combination of perlite as mineral and wood fibre as organic residue gives an excellent growing response and by far the best substrate for most terrestrial orchids. Mix 60% to 70% fine to medium grade Perlite (0 to 6 mm) and 30% to 40% wood fibre (Toresa is recommended). This mixture will show a pH between 5 and 6, which is optimal for terrestrial orchids prefering acidic soils. For orchids, naturally growing on limestones, add a small amount (not more than 2%) of coarse lime containing material. Note: Even for those orchids, too much lime is more detrimental than to less. If you water with calcareous water you don´t have to add lime at all. The recommended pH for orchids prefering limestone is between 6 and 7. If you don´t have access to commercialy impregnated wood fibres (as Toresa) use old decayed choped wood chips. Heat the wood in boiling water or in the microwave to give some fermentation. Fresh wood is not suitable as it fixes important plant nutrients. Add about 10% of a proven commercial potting mix for flowering plants. Fertilize in pot culture as recommended in the orchid pages. If you grow your orchids in garden beds, fertilization is less important. Potted orchids have to be repotted every 2 to 3 years. For planted orchids, just add occasionally a small amount of wood fiber into the garden bed. The best time for repotting is during dormancy or just when the plants start to grow at the beginning of the new growing season.
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