How to look after your orchids

How do I water an orchid? How do I help my orchid bloom? What should I do about thrips? Kew Tropical Nursery supervisor Bala Kompalli has the answers.

By Ellie Wilson and Bala Kompalli

We love orchids here at Kew - in fact, we host an orchid festival every year. Whether you're a budding orchid owner or your orchid collection is in full bloom, you'll know these beautiful plants have unique needs and challenges.

A South Asian woman in a Kew uniform standing in a plant nursery filled with orchids — Bala Kompalli © RBG Kew

Bala Kompalli has worked with the orchids in our Tropical Nursery for 20 years, so we asked her to answer your most pressing orchid questions, sourced from Kew's Instagram followers.

Contents

Horticulturist wearing blue gloves and watering seedlings with a watering can — Bala Kompalli © RBG Kew

Q: How much should I water an orchid?

A: Only when the pot feels light and the compost is dry. The orchid pot can be placed in a bowl of clean water, such as rainwater or Reverse Osmosis water, at room temperature and once it is soaked well, it should be removed from the water and placed back in its tray. Leave until it's dry again.

Generally, watering once a week should be fine. During wintertime, when orchids are not actively growing, water less.

Q: How do I help my orchids bloom?

A: From October to March, if the orchid is given a fertiliser specifically for blooming, or tomato fertiliser at a weaker strength, this should help in reflowering. During the active growing period of the orchid, every other watering can be a feed.

Another factor which helps a typical orchid to flower is lowering the temperature: for example, if an orchid is growing in a constantly warm environment around 24C and then dropped to 14C, that 10 degree variance can trigger flowering.

Some types of orchids, such as Pleione and Thunia, have complete dormant periods during the winter months and should be kept completely dry. Others, like Phalaenopsis and Oncidium orchids, remain green during their dormant months. Reducing watering and feeding during the winter months when the orchids are resting should help them rebloom once the light levels get better.

It’s normal for orchid flowers to die off after a while, and your orchid will still be healthy. Prune the flower stalk when the orchid has finished flowering to encourage the orchid to flower again. Cut the stalk 2 nodes above the base with clean and sterile secateurs. You don't need to prune orchids otherwise.

Asian woman in a Kew uniform working at a gardening bench, patting down soil around an orchid with white flowers — Bala Kompalli repotting orchids in the Tropical Nursery © RBG Kew

Q: How do I repot my orchid?

A: Gently remove the plant from its pot by pressing around the sides of the pot, and remove the old bark or compost. Cut and remove any old roots or stems which are brown and place the plant in a bowl of clean water to rinse the roots.

Select a new, clean pot which suits the root ball of the plant and add some coarse materials at the bottom of the pot for better drainage. Now gently place all the roots into the pot and fill the pot with any good grade orchid compost, while gently tapping around the pot.

Use a couple of clean wooden stakes to hold the plant firmly inside the pot. This is very important in order to let the orchid establish well. Water the pot thoroughly and place in a bright location, but not under direct sunlight.

Q: Do orchids need special pots or soil?

A: Orchids don't need a special pot: any pot of the right size is enough.

Orchids do need special soil. The best soil for an orchid is usually a good grade bark-based compost. Do not add any soil to it. Mixing bark with other open substrates like perlite or pumice will give better drainage, but it's not essential.

Q: Do orchids need special feed?

A: Any feed with an NPK ratio (nitrogen to phosphorus to potassium) of 21:7:21 should be used in diluted form from March to September to help the orchid grow.

Use any feed which is high in phosphorus and potassium (for example, an NPK ratio of 10:30:20) later in the year, or simply use tomato feed once every 2 weeks, to help your orchid flower.

Horticulturist spraying an orchid's leaves with a spray bottle — Bala Kompalli spraying orchids © RBG Kew

Q: How can I get rid of thrips?

A: Isolate the plant and spray with insecticidal soap water, and cut and discard the flower buds before they open. Placing blue coloured sticky traps opposite the flower spike can attract and kill the adult flies.

Woman in Kew uniform standing in a plant nursery, reaching up to an orchid in a hanging basket — Bala Kompalli in tropical nursery © RBG Kew

Q: What’s the best light, humidity and temperature for orchids?

A: Indirect sunlight for at least a good 5 to 6 hours should help orchids grow better. Place the orchid in a bright location. Artificial grow lights, too, can be helpful during the dark winter months.

Tropical orchids such as Phalaenopsis and Oncidium enjoy warm and humid conditions, around 18C to 26C. Placing the orchid in a bathroom windowsill or near the kitchen sink area will give the orchid enough humidity. If it is in a dry area, such as a centrally heated room, the orchid can be placed in a water tray filled with pebbles or live sphagnum moss, which will help it to get enough moisture.

Some orchids, such as Cymbidiums, are cooler-growing (happiest at 10C to 22C) but they still enjoy humidity during growing seasons.

Orchid with yellowing leaves — "Herzfäule" by blumenbiene is licensed under CC BY 2.0.

Q: Why are my orchid’s leaves yellowing?

A: Maybe the orchid is kept in conditions that are too cold, or in direct sunlight. Sometimes, plants may also show nutrient deficiency by "chlorosis", or yellowing leaves.

In the above picture, the orchid's crown or growing point is dead. This may be due to over-watering, which eventually kills the plant.

Yellowing can also be a sign of ageing on older leaves before they drop. There's no need to worry if that happens only on the old leaves and the rest of the plant looks healthy.

Q: Why are my orchid's roots growing, but not the leaves or flowers?

A: When the orchid is active during the early months of the year and taking advantage of sunlight and heat, it can produce many new roots - especially if the plant is in a transparent pot. Giving the orchid a balanced fertiliser will help the leaves and flowers to grow as well.

Q: What should I do to stop root rot?

A: Reduce watering, remove the infected part of the root and apply cinnamon powder or wax to stop the rot. Secateurs used to cut the infected root should be sanitised thoroughly to avoid spreading it to other plants.

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Q: Are there any orchid books you would recommend reading?

A: Growing Windowsill Orchids by Philip Seaton and Growing Orchids at Home by Manos Kanellos and Peter White.

Q: What companion plants are best for orchids?

A: You can try any houseplants coming from similar climatic areas, such as ferns, air plants (Tillandsia species) and begonias (Begoniaceae family).