MANAGING A MIXED COLLECTION by Brian Milligan
I'm occasionally asked the question "How do you water a mixed collection of orchids?" Thoughtfully is the simple answer! Sprinkler systems water all orchids within their reach uniformly, regardless of their needs. Unless you have several shade-houses or glasshouses that you can devote to different groups of orchids, watering by automatic sprinkler systems will not give best results (besides being illegal in this time of drought).
Hand watering is much more selective, provided that the grower recognises those orchids that need more frequent watering than others. The period between watering depends not only on the orchid genus concerned but also on the nature of the potting mix and the time of year. Cattleyas and some other orchids with thick roots like to dry out before being watered again, whereas others with fine roots, such as odontoglossums and masdevallias, prefer to be kept uniformly moist. Orchids potted in open bark mixes need to be watered twice as often as those grown in sphagnum moss. And many orchids (but certainly not all) need a comparatively dry 'resting period' during winter.
To succeed with a mixed collection you must recognise the individual requirements of of your orchids and group them accordingly. For a start, group all those orchids potted in moss separately, so that they can be watered less often than the others. Then the cattleyas should be grouped together, so that they can be allowed to dry out before they are watered again.
The cattleyas should be hung near the roof, or placed where they receive more light than most other orchids. One end of my glasshouse is covered with a second layer of shade cloth during summer, so that I can grow cattleyas and other light-loving orchids at one end, and odontoglossums and masdevallias at the other (shadier) end.
Contrary to most advice, I grow a few plants beneath the benches in my glasshouse, and find that some seedlings do well there, especially in summer. If you grow orchids beneath your benches, you will need to install a 'drip tray' immediately below the top bench to prevent water falling on the plants below. A small fan to provide air circulation beneath the bench is also recommended. Do not place flowering plants beneath the benches, because their flower stems invariably elongate and twist as they search for more light.
Watering in summer is easier to manage than it is in winter. Most orchids need frequent and regular watering in summer, the main growing season. It is difficult to over-water them, provided that the potting mix is free draining. Watering in winter is another matter, and for success you really need to know the conditions under which the various genera live in nature. Some orchids, like Laelia anceps, receive little or no rain during winter in their native Mexican mountains, although the weather is sometimes foggy. On the other hand, orchids growing on mountains in the Philippines receive rain nearly every day, summer and winter.
In summary, the best way to manage a mixed collection of orchids is to learn their individual requirements, group them accordingly, and then treat each group separately. In practice it's easier said than done, especially when it comes to hybrids between species or genera with different requirements. No doubt you will have to compromise but take heart from the fact that orchids growing in nature regularly experience droughts, floods, heat waves, cold spells and attacks by pests and diseases, yet still survive. If you get things right, you should be able to grow them better than they usually do in the wild!