Far from being an expert on the subject and having killed my share of orchids, mainly due to the impossible weather conditions I have provided them by moving from region to region within Australia, I'll share my 2 bits worth.
This is the stuff that a lot of the old experienced growers
won't tell you....the sort of info that takes years to weasil out of people.....the info that you can learn fairly quickly by doing visits to orchid nurseries and other club members orchid houses who have a climate similar to yours and by looking in this forum. Take note of the equipment they use to regulate the temps, ask them what the minimum temp is that they run that part of the house at, check the light and humidity and which species is placed where. Also what they use as growing media. Regarding watering and fertilising, well, you are just going to have to suck it and see, this can only be learnt by over-watering, starving, rotting and generally painfully killing
a few of the most expensive orchids in your collection. After all, why should you be any different to any one else! You can however get a pretty good idea of a plants requirements by searching for info on habitat for the particular species on the net, or reading (yes, that was r e a d i n g) up on them. Some plants like a break from watering in winter, some like to dry out before being watered again. Whatever the plant, you're not going to get it right every time, we are but humans (well, some of us anyway!).
From observations and experience taken over the last decade I have formulated the 'Big Four' commandments of orchid culture, listing them in
my order of importance:
A) Temperature Gradient. The system that I use is the tried and trusted classification of plant temperature gradients. These are:
1. Cool Growing. Meaning plants that can handle a cool winter depending on the species. For example there are plants that I'll grow down to 0*C, some will even go down to -2*C, (but I don't like to trust my luck) that are classed as cool growers like some Cymbidiums and some Aussie Dendrobiums. Then there are plants that just don't like zero on a continued basis like native Sarcochilus and some of the Oncidinae alliance that I place as cool growers also, so for all the cool growers I currently grow them at 3*C under polyethylene film, then for summer I'll try to keep them at below the low 30's and take some of the film off the house.
2. Intermediate Growing. Meaning plants that
can't take temperatures much below say 10-12*C, like a lot of Oncidiums, Aussie Dendrobiums that are hybridised with warm growing types and some Aussie dendrobium species and even some Sarcochilus species and their hybrids. For summer I try to keep these below 35*C.
3. Warm Growing. Sometimes referred to as 'hot'. Plants that
can't handle much below 18*C. Summer not much above 40*C. I am still experimenting with this group as I only want to go up to 'Intermediate' in my hot-house due to the cost of heating. (Ambient temps from a winter low of -5*C to a summer high of about 32*C here, a 6 month winter due to sun's low angle of incidence and a three month summer, you can figure the other seasons for yourselves.).
Some orchid nurseries will give these temp gradients of the stock in their catalogues with the letter C, I,or W after the name of each entry. For a sample go to this link:
http://www.speciesorchids.com/plist_a.html
OK, so we have the temperature thingy out of the road, the first of the 'Big Four'.
B) Light. Or alternately, lack thereof. Both sections of my orchid house have a dark section that I keep the shy ones in, things like Sarcochilus and Bulbophylums, then at the other end of the light spectrum, the bright light lovers such as Den bigibbum. A lot of the time you can tell the plant is recieving too much light from the pale colour of the leaves, of course not to mistake this colour for a plant that is going to kark it. Again, read up on the particular species and it's native habitat.
C) Humidity. This depends to a great degree on your climatic location. Those that live by the sea need to induce less humidity, but those that live inland apart from tropical climes need some form of a humidity 'sink' that is to say, maybe a wet floor, a tray with pebbles and water that you sit your windowsill orchid on, an overhead misting system for the dryer areas. You'll get the hang of it....just notice the humidity difference when you visit someone else's orchid house, if the thing is running 'on song' then you
will notice when you step thru the door.
D) Media. This is a hard one, as there are so many different types and combinations for all occasions. Take note of what the nurseries / other growers are / have grown the species in. Again, check species habitat. If the thing grows out in full sun, on trees, you can bet it'll curl up its tootsies at the sight of a pot of sphagnum, conversely, if it grows in the mosses beside a waterfall, it'll fall in love with the pot 'o' sphag, so don't go sticking it onto a dry old mount. Personally, I use three ingredients, pine bark, coco chunks (about half inch) and graded river quartz in varing ratios depending on the species and its stage of growth (seedling, adult etc'). Also like cork bark for mounting. I don't use sphagnum moss as I tend to over-water it and turn it to goop if I over fertilise. I am also starting to veer away from using too much coco chunk in the mix, as it grows great moss on top which starts to exclude airflow from the pot.
There are a myriad more 'Little' commandments to growing good orchids, but hey, I have to go to bed sometime.
Hope some of this rant helps someone. I sure could have used this info when I was starting the insecurity and uncertainty of being a newbie to orchids.
Good growing!