Light

Overall, the commonest reason that orchids fail to bloom is insufficient light. The Phalaenopsis and Paphiopedilum orchids are usually happy with the filtered light in a windowsill but many other varieties need more light. Dendrobium, Cattleya, Oncidium and other medium-to-high light orchids may need supplementary grow lights or time spent outdoors in the summer to get the kind of light levels they require to bloom.

As an orchid gets more light its leaves turn a lighter shade of green. Very light yellow-green leaves usually indicate too much light, whereas very dark forest green leaves can indicate too little light.

Roots

Good roots bring good blooms. An orchid may have deceptively beautiful leaves with a root system that is in dire trouble. Often root trouble is the result of overwatering or lack of repotting. Orchid roots need oxygen to survive and without it they smother.

Watching an orchid carefully can give clues to trouble at the root zone. When buying orchids at the store they are typically quite young. Over time each new leaf or pseudobulb should be bigger than the previous one or at least the same size.

New Growth

There are two types of growth patterns for orchids, sympodial and monopodial. The monopodial orchids, Phalaenopsis and Vanda being the two most common, grow up off a single central stem with leaves on either side. We expect to see each leaf at least as big as the leaf before it and hope to see at least one or two new leaves per year. The next bloom spike on a monopodial orchid comes from the base at the underside of a leaf, usually two or three leaves down from the newest leaf and on the opposite side as the prior bloom spike.

Sympodial orchids have multiple growths and usually grow one or more new growths per year. Often the growth pattern looks like a corkscrew with each new growth coming from the side of the one before it in a circular pattern.

Season

Each orchid type has a time of the year when it will naturally bloom. This may not be the same time of year that an orchid was blooming when it was purchased, as nurseries can force orchids to bloom off-cycle. Plant labels can be very helpful in recording bloom cycles. Most orchids grow during the summer and bloom in the fall, winter or spring.

Many orchids bloom once per year, some twice or even more. Once in bloom some flowers last weeks or months while others can last only days.

Natural Stimuli

In nature, orchids have natural stimuli that indicate to the plant that the growth season is over and it’s time to bloom. Some orchids are temperature-sensitive and some are light-sensitive. Those that are temperature-sensitive are often triggered to bloom by the natural cooling that occurs in the fall. This drop in temperature signals to the orchid that the growth period is coming to an end and it is time to get ready to set a bloom spike. Sometimes orchids grown in our homes where the temperature is fairly constant are deprived of this natural cue and will be reluctant to bloom.

Information courtesy of: www.repotme.com