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Straits Times

Plant Parenting: How to grow orchids

Sign up now: Get ST's newsletters delivered to your inbox Depending on their growth habits, which can be upright or pendulous, these plants can be cultivated differently. SINGAPORE – Orchids, such as Singapore's national flower Vanda Miss Joaquim, are popular garden plants that are admired for their colourful and flamboyant blossoms. They are also epiphytic plants that grow on another living plant for support. The most common epiphytes here grow on trees in streets, parks and gardens. They are not parasites, as they do not depend on the host plant for nutrition. There are two types of epiphytes, the first being holo-epiphytes. These grow entirely off the ground and include not only orchids, but also air plants from the genus Tillandsia. Holo-epiphytes' roots need to dry out between rainfall. They are not accustomed to constant moisture and should never be planted in soil. Hemi-epiphytes, the second type, grow in the ground at one stage or another of their life cycles. Many aroids, which are popular houseplants, are hemi-epiphytes. They often grow along the soil of the forest floor until they find a tree. There, they produce aerial roots that attach to the tree's bark, and subsequently grow upwards towards light. Many of the orchids sold in local nurseries are epiphytic species and hybrids. Common ones come from the genera Dendrobium, Cattleya, Oncidium, Phalaenopsis and Vanda. Depending on their growth habits, which can be upright or pendulous, these plants can be cultivated differently. Orchid growing in containers A sympodial orchid has a horizontal growing stem at the base. Pseudobulbs (false stems) emerge from this stem and store water for the plant during harsh weather. PHOTO: NATIONAL PARKS BOARD Orchids with vertical stems are called monopodial orchids. Those with a horizontal growth habit, with upright pseudostems growing at intervals, are called sympodial orchids. In local gardens, epiphytic orchids are mostly grown in containers using charcoal chips or chunks. Charcoal is an affordable, durable and lightweight growing medium suited for tropical climates. A monopodial orchid has a single stem that grows upwards. Such orchids do not have pseudobulbs. PHOTO: NATIONAL PARKS BOARD In the past, broken bricks were used as a growing medium, as their weight prevented pots from toppling over. Pine bark chips are often used in temperate climates where the material is plentiful, but can be expensive here as they need to be imported. When using charcoal chips, their size needs to be customised according to the root system. Smaller chips are better for smaller plants with fine roots to anchor themselves for stability. But there must also be air pockets within the growing medium for drainage, so the roots can dry out quickly between each watering. A properly aerated root zone is crucial for epiphytic orchids. Charcoal is a common growing medium for orchids in Singapore. PHOTO: NATIONAL PARKS BOARD When growing orchids in charcoal in harsh environments, such as windy high-rise homes and exposed outdoor gardens, more frequent watering is required. Some gardeners add coconut husk chips to retain water in the root zone. Imported orchids often arrive on a buyer's doorstep in a pot of densely packed sphagnum moss. This material retains moisture very well. In humid Singapore, however, the moss can quickly become waterlogged from wet weather. This can cause root rot and disease, killing the plant. As such, it is essential to remove sphagnum moss from an orchid's root zone and repot it in charcoal chips. In the past, orchids were grown in heavy terracotta pots with holes in the sides to aerate the root zone and improve drainage. Now , gardeners can grow these flowers in lightweight plastic pots in a similar design. Hanging containers, such as wooden baskets or those with a mesh-like plastic coated material, will also serve this purpose. Plastic pots without holes, designed for conventional terrestrial plants, may not aerate the root zone well enough. Mounting orchids Some orchids are mounted on a flat surface, such as on a slab of fern bark or wood. The root systems of orchids grown this way are spread flat on the material, and plants are held in place by tying them to the material. This method of cultivation allows the roots to dry out due to the porous structure of fern bark, which is made up of a network of numerous thick fibres with air pockets in between. Plants grown on tree bark also have their roots exposed directly to the air. Epiphytic orchids can be mounted on a slab of fern bark, but these will dry out faster and need to be watered more often. PHOTO: NATIONAL PARKS BOARD Growing epiphytic orchids this way is an effective and practical way to display those with a pendulous growth habit, characterised via their long, hanging stems. One such orchid is the native Pigeon Orchid (Dendrobium crumenatum), which can be found on trees here. Mounting orchids also circumvents the issue of water accumulating within the crown of some orchid types, such as Moth Orchids (Phalaenopsis). Fertilising orchids The porous nature of potted media and mounting of epiphytic orchids make conventional fertilisation quite challenging. Orchid growers usually provide the necessary nutrients for their plants via water-soluble fertiliser. Fertilisers specially formulated for orchids are also available in salt form, which need to be dissolved in water. This means plants can be fed and watered simultaneously. Nutrients are taken up by plants via their roots and leaves, in a process known as foliar feeding. Slow-release fertiliser pellets can be kept near, but not in direct contact with, an orchid's roots. PHOTO: NATIONAL PARKS BOARD Slow-release coated fertiliser pellets can also be used. First, put these pellets in a small bag fashioned from a piece of cloth or plastic netting. Next, tie the bag up and hang it near the orchid's roots. To prevent fertiliser burn, ensure they do not come into contact with the roots. Whenever the plant is watered, the pellets will release a small amount of nutrients.