All commercial growers and many large-scale hobby growers use automatic sprinklers to water their orchids and many smaller growers therefore believe that they should do the same as soon as they can afford the cost. But there are pros and cons to both systems, which you should consider before you install an automated watering system.
The obvious advantage of a fully automated sprinkler system is that you can program the computer and theoretically take off for a round-Australia holiday. Unfortunately, it’s not quite as simple as that. The optimal frequency of watering is highly dependent on the weather, even when the plants are grown under cover. They become dry very rapidly under warm, windy conditions and may need watering two or three times as frequently under such conditions as they will if the weather is cold and windless. Maybe this isn’t so important during the summer months but orchids greatly resent being continually wet during cold, wintry weather, so an automated system with a simple timer is not ideal, especially in winter.
Another disadvantage of sprinkler systems is the difficulty of ensuring even water distribution over all the plants. It’s possible to achieve this by judicious placement of the sprinklers but much water is still lost on paths and beyond the boundaries of the growing area. Even then, complete coverage may not be achieved if a strong wind blows from a particular direction.
Hand watering, for preference using a water-breaker spray head (e.g. a Dramm head), permits each plant to be watered individually and for the water to be directed both over and beneath the leaves, thus ensuring that the compost is thoroughly wet and both the upper and lower surfaces of the leaves are wet (thus, minimising the likelihood of infestation by spider mite, commonly referred to as red spider, which prefer the drier conditions beneath the leaves). Sprinkler systems are seldom effective with large-leafed orchids like lycastes or anguloas, because their leaves very effectively shed most of the water beyond the confines of the pot. Hand-watering is also advantageous at flowering time, because it permits the orchid to be watered without wetting the flowers. Many cymbidium flowers develop unsightly fungal spots if their flowers remain wet for any length of time and so it is best not to water them overhead, especially on still days when the water may take hours to evaporate.
From the above arguments you can see that I strongly favour hand watering. Yes, it takes quite a time to do but at the same time you can also note those orchid spikes that need staking and detect any insect pests or diseases – just remember to take action when you have finished watering. I have an automated sprinkler system, but use it solely beneath the benches in my glasshouse and masdevallia shade house to maintain a continual high level of humidity.
So why do professional growers use automated sprinkler systems? Solely because it would be hopelessly uneconomic to water all their orchids by hand. Large nurseries take most of the night to water, section by section; they usually water at night, especially in summer, because less water is lost by evaporation then and the mains water pressure is higher at that time.
The big advantage of an automated sprinkler system for the hobbyist comes into play if he or she takes frequent or extended holidays. Fortunately I have several good orchid-growing friends who water my orchids when I go on holidays, a strategy that works well if you are able to reciprocate when they are away. If you ask someone to water your orchids when you go away, try to persuade an orchid grower to do the job. Others with little experience of orchids tend to over-water or else do it each weekend regardless of the weather.