One reason could be the plant is not ready to flower, e.g., cymbidiums usually do not flower unless there are at least three to four green bulbs.
Also if a flower spike has been left on the plant for too long last year or the plant had been badly disturbed when repotted late in the season.
Most orchids like some form of lighting, some more than others. Cymbidiums seem to enjoy full sun up to December and then some shade is required. Rock Orchids such as Dendrobium speciosum/Sarcochilus are happy with full sun throughout the year, but need protection from the direct light on hot summer days. Masdevallia and Paphiopedilum (slipper) orchids prefer shaded areas. Most orchids need to be moved to a couple of locations during the year. Research where your orchids have originated from and replicate the growing conditions. For example, tropical orchids need heat and bright light; forest floor type terrestrials usually like cooler environments and some like more shade. Both can be grown with ease if given their preferred conditions.
Most orchids choose to live and develop flower spikes in areas where there is good air movement. In confined spaces, such as glass/plastic housing, a fan is recommended. Stale air will lead to poor conditions and will become breeding homes for some pest and diseases.
If potting mix has broken down and offers little support for the orchid and the plant wobbles in the pot, use a stick for stability for all orchids, especially when first repotted.
Orchids need the right potting mix which allows for drainage. Standard potting mix retains way too much moisture.
Watering has a lot to do with the well-being of orchids. If the plant dries out too much for too long a time, it will not flower. Yet the plant might flower as a last effort to propagate before dying. On the other hand, too much watering will have the same effect with the root rotting off and the plant’s well-being will suffer.
Regular fertilising throughout the year is essential for regular, strong bloom. Species orchids require a little less fertilising because of their tree/rock/ground type background and have adjusted themselves to the supply of fertilisers given to them from birds and animals. Hybrids are a different proposition because of their sometimes complex mixture of parents and therefore need more fertilising to improve the flowers and growth. Remember to use half strength of the manufacturer’s recommendations along with some Seasol or PowerFeed.
When cutting up a plant, be aware to use clean cutting instruments – wash in a sterilising substance and use a sterilising product on the newly-cut plant, such as Steriprune. It is important when cutting up orchids that all dead leaves and plant parts are disposed of in the garbage and not in the garden as diseases and viruses can easily spread.
Pest control, such as red spider, scale, snails can be treated by many products on the market. Note the following:
Snail and slugs can usually be controlled by the regularly sprinkling around snail pellets.
Caterpillars: Usually those brought to the orchids by the white moth, can becontrolled by Carbaryl.
Dendrobium Beetle: (long and reddish/brown in colour) can be controlled by Carbaryl.
Aphids: Can be controlled by Carbaryl.
Spider mite: (usually red spider) can be controlled by Eco-Oil.
Mealy bug: Can be controlled by white oil.
Scale: (which is detected by secretion of honeydew or the formation of sooty mould and yellow spots on leaves and dropping leaves) Control by white oil.
Why not go along to an orchid society meeting? There are usually free to visitors and there are many benefits in joining a local orchid society: you can mix with other growers who share your interest; you receive helpful orchid newsletters; and you can participate in shows and outings.