Humidity in my growing areas used to be something I didn’t think about much — and took for granted. In this article, I would like to share my humidity-enhancing solutions for a small collection. If you have a larger collection and fully equipped greenhouse, then you probably don’t need this article: turn on a hydrofogger or automatic misting system and the humidity problems go away.
I don’t have the option to install extensive plumbing in my growing areas since we currently rent our house and property, so I’ve worked out several ways to sustain my outdoor and indoor orchids in optimal environments. I’ve read and tried many recommendations, and have identified several that measurably work. As a former scientist, I’m fond of data — I have two weather stations outdoors, and eight temperature/humidity sensors in different locations indoors. I want to create real humidity — not just the idea of it.
From then to now: a lot less natural humidity
In the San Francisco Bay area, winters are the rainy season, so there’s plenty of natural moisture even if the heat is on indoors. Outside, it has been fine if I didn’t water the cymbidiums and dendrobiums at all in December, our coldest month; the largely dormant plants don’t dehydrate in the cool, damp air and roots stay dry — perfect. During the summer, we would get regular fog and a breeze from the Bay, plenty of natural air conditioning. I’ve lived in this area since 2003, in five different houses, and this is the first one that even has central AC. It just wasn’t needed — summer highs rarely got above the 80s before the fog came in and nights are in the 50s.
The key phrase in the above paragraph: “used to.” Weather has been a lot different in California over the past five years, and 2017 reached new extremes. Over the past three years, we’ve seen daytime highs over 100 for several days in a row, on numerous occasions in the season. With these higher temperatures has come extraordinarily low humidity for this area: over 100F and about 25% relative humidity. Summer heat here is NOT muggy.
In October 2017, with the fire weather that created the historic firestorm in Sonoma and Napa counties, it was in the low 60s for a daytime high — with a relative humidity of 15-20%. Even in December, while the fires were raging near Santa Barbara hundreds of miles to the south, we had the effects of the high pressure system and unprecedented winter daytime humidity of 25-35%.
Handling the heat and humidity outside
My humidity solutions for the outdoor orchids are tied to temperature; most of the time, problematically low humidity corresponds with unusual heat. With the exception of Dockrillias, most of our outdoor orchids are in pots or baskets, so they can tolerate lower humidity, with supportive misting, much better than mounted orchids. Additionally, many of our outdoor orchids (dendrobiums , cymbidiums) are from Australia, and tolerate high heat and low humidity conditions quite well. Over the summer, each heat wave stimulated a new flush of canes from many of the Aussie Dens.
Simply, high humidity orchids aren’t suitable for outdoor growing at our location, and I’ll cover them in Part II on providing humidity for indoor growing.
However, there are other orchids that benefit from summer outdoor life (cooler nights in particular), but aren’t fond of record-setting heat waves.
Therefore, my first suggestion is simple: identify the less heat tolerant orchids, and move them elsewhere (inside) for heat waves. When the daytime temperatures go over 90F in the shadehouse, I bring the cooler-loving dendrobiums (Den victoria-reginae, Den papillio, Den unicum, etc.) into the house for a few days; the wind and heat sucks the moisture out of baskets rapidly and, early in the summer, I observed the outside roots on a few plants became crispy despite misting 2-3 times per day. They aren’t growing during the extreme conditions anyways, so I believe it is better to not stress the plants, and move them to a cooler location for a short period, even if light is not as optimal.
For all of the orchids, to enhance hydration, I water in the EVENING during the hotter summer periods so that the roots can absorb and retain water during the cooler night hours, rather than have it evaporate quickly with daytime heat. This way, the roots stay optimally moist much longer, and only have a shorter period during the day when they dry out. Additionally, I heavily mist the plants in the morning so they start with lots humidity and full hydration before the most unnaturally hot period. (In the cooler months, I do the opposite — water in the morning so they are drier for the colder nights).
Evaporative cooling is extremely effective. Even if you don’t have a special “wet wall”, you can create a similar effect with a hose and your time! During peak heat, I soaked the walls and ground of the shadehouse 2-3 times per day. The cold ground water cools the shadehouse by 5-10F for at least an hour or so after hosing. On the hottest days, when it reached over 110F here, the shadehouses stayed under 95F. And obviously, the evaporating water raised the humidity considerably — from 25% to about 40-45%. Those are much friendlier conditions! Given that I know several people whose greenhouses were over 120F, I considered those temperatures and humidity levels to be quite an achievement for orchid well-being.
Obviously, a hose doesn’t work too well on hardwood floors, so I’ve tested and created very effective indoor humidity solutions, for orchids that truly need high humidity — the highland New Guinea dendrobiums. Click here for Part II on “indoor humidity: the practical cloud forest”.