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WHY WON’T IT FLOWER? by Brian Milligan

Many of us have orchids that we’ve seldom, if ever, flowered. I have lots and therefore consider myself eminently qualified to write about this topic! There are many reasons why an orchid won’t flower but most can be summarised under the single heading – poor culture.

The question most often asked by visitors to our orchid shows in winter and spring is “why won’t my cymbidium flower?” If you then ask “Are its leaves nice and green”, the most common reply is “Yes, they’re a nice deep green”. That reply provides the clue that the orchid is being grown in too much shade. It often transpires that it’s growing in the dense shade of a tree or under a veranda with a heavily tinted fibreglass roof. To flower well, cymbidiums need full sun throughout the entire day during the winter months and no more than 50% shade for the remainder of the year. When grown under these conditions, their leaves will be yellowish green rather than deep green.

Of course, there’s more to flowering cymbidiums than providing them with good light. They also need regular (frequent) watering and fertilising, so that they produce large pseudo-bulbs. As a general rule, the larger the bulbs, the more flower spikes they will produce. Low night temperatures during summer encourage the development of flower spikes – some growers cool their cymbidiums during hot summer weather by watering at night.

However, lack of light or irregular watering and fertilising doesn’t explain why an orchid will flower reliably each year, while its neighbour seldom does, even though it receives the same treatment. It’s a fact of life that some cymbidium hybrids flower more regularly than others, no matter how well they are grown. Some seedlings never develop large pseudo-bulbs due to a genetic problem and there’s no point in persisting with these plants when you could be growing a more productive plant in its place.

Some Australian native dendrobium hybrids flower at a much earlier age than others. Those bred to produce pink flowers tend to grow faster and flower much sooner than those bred for yellow flowers. In general, hybrids of Dendrobium speciosum seem to take longer to flower than almost all others, especially if its pod or pollen parent also has D. speciosum in its ancestry. After ten years, I’m still waiting for some D. (speciosum x Sunsprite) seedlings to flower! The secret to flowering Australian dendrobiums well is to provide the plants with good light, to hang them where they receive good air movement and to apply a potassium-rich liquid fertiliser regularly.

The above discussion relates to orchids grown in a ‘cosy’ shade-house. There are additional reasons why those grown in the glasshouse won’t flower, depending on the conditions under which they grow in nature. For example, you can’t expect most vandas to flower for you if the temperature in your glasshouse consistently falls below 15˚C and you cover it with shade cloth throughout the year (Vanda coerulea is an exception, being tolerant to quite low temperatures in winter, although it still needs high light). Cattleyas don’t need such a high minimum temperature but they do need more light than many other orchids if you hope to flower them well.

Paphiopedilums, masdevallias and other pleurothallids need much less light than cattleyas and vandas, so don’t expect to be able to grow and flower all of them together under the same conditions. My advice is to find out which genera grow best under your conditions and then to concentrate on those.

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