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I think you will find my greenhouse to be VERY different from what most of you think of and use as a greenhouse. I live in southern Arizona, where the trick is NOT to keep it warm, but to keep it cool. I’m sure a lot of you Florida and some other southern states (and some other countries too) growers face the same situation. There is a good-sized, and very active Orchid society here in southern Arizona, and it seems that everyone does things differently, mostly with success. There are some other members that have greenhouses similar to mine (I got the idea from one of them).

Don’t know if many of you are interested in THIS much detail about greenhouse construction, systems, conditions, etc., but here goes. It’s really TOOOOO much information, but if some of you are interested, feel free to question, criticize, etc.

I’m also very interested in what others do, especially those facing some of the same climate conditions.

Structure

Size is 6 ½ ft x 21 ft. Ceiling ht ranges from 9 ½ ft to 8 ft. Attached to my house (along a long side). Walls are concrete block, no windows (slower indoor/outdoor temperature exchange). Roof is sloped about 15 degrees, with skylights (triple-pane, tinted glazing - 40% screen) covering about 80% of the roof area (the other 20% is heavily insulated). The main “exposure” is to the northwest. The floor is just dirt covered with “lava rock” for drainage, and a path down the middle made of recycled rubber (hard) “grid” squares, for better footing. For benches, I used metal wire shelving, on three levels (1st just a couple inches above ground, 2nd about 20 inches above, 3rd about 24 inches above that), along both long sides with the grid path between them. I also have a grid system (from a store display supplier) against the upper walls for hanging plants, as well as rods (rebar and conduit) suspended along the ceiling for hanging.

Systems

I use a heat pump for heating and cooling. It is an Amana PTAC unit (I believe it is about 15,000 BTU), a small “through the wall” unit like those you find in motel rooms. Mine is mounted at about 7 ft off the floor in a “short” side, opposite the door. I had first tried a similar G.E. Zoneline unit, and it was TERRIBLE (and so was G.E.’s service!). I’ve had this one in for 4 years now with only 1 problem (and immediate, unquestioning warranty service resolved it within two days, at no cost to me). It is wired for a “remote” thermostat which is at the opposite end of the greenhouse. The thermostat is programmable for time of day settings, and high/low (cool/heat) ranges. It will also switch automatically from cool to heat, which is important in the winter here, since you often want to cool during the day and heat at night. This set-up has handled outside temperature ranges from 15f up to 110+f. It is surprisingly efficient, adding about $40-45 per month to my summer electric bill, and maybe $15-20 in winter (that seems pretty good to me).

I have an R.O. system which feeds a 30 gal pressure tank. This supplies the watering and fertilizing set-up. I have 5 watering zones with different programs, plus 1 zone for misting. These are controlled by two standard lawn irrigation timers, and these have been extremely reliable. I cover each zone with overhead spray from standard irrigation tubing and sprayers. There is a wide variety to choose from. In addition to the irrigation, there are connections to the tank/R.O. for two fertilizer injectors, a water wand (use it sometimes to “flush” plants), and a spigot for drawing water for any general purpose. Everything is supplied with the R.O., except the misters, which just use “house water”. For fertilizing, I use a hand-held wand, supplied by a Dosatron injector, driven by the pressure tank.

There is a “control panel” for all of this in a corner near the door, a “dry area” that never gets water on it directly.

For air circulation I have several waterproof fans (from Grower’s Supply). They are up high (above the air conditioner/heater discharge) at one end of the house, and down low (in the two lower bench levels) at the other. This produces VERY good air movement on all bench levels, and keeps the climate more uniform throughout the greenhouse (has been a problem with my long, narrow greenhouse, but this fan set-up has cured it).

I have two dataloggers (extech) high and low at opposite ends of the house, so I can “keep an eye” on conditions. They are “offline”, so I periodically download the data into the computer to see what has been happening. These have been very helpful as I have worked to get the environment “tuned up” to the right (? For now at least ?) growing conditions.

Environment

I keep temperatures between 85f (day) and 65f (night) in the summer, and 80f (day) and 55f (night) in the winter. I don’t have any set schedule for that changeover, just whenever it seems right. My thermostat (Honeywell TH8000 – it’s just a regular “home heating/cooling” one)) can “step-program” so that I can set an intermediate range, for morning and evening, so as to not have too sharp a change from daytime to nighttime (and vice versa) temperatures. The thermostat settings I use will FORCE down the night temperatures during the summer, so I get a good daily differential. In summer I also use 40% screen shade cloth in addition to the skylight shading to help out.

Light levels (at mid-day, summer) are: 4-5,000 plus (often plus) fc at 8 ft above floor, 2,5-3,000 fc at 6 ft above floor, 1-1,500 fc at 2nd bench level and 500-1,000 fc at lowest bench level. In the winter, when I don’t have the shade cloth cover, but these are slightly lower regardless, maybe 500 fc at all levels. Of course they are considerably lower on cloudy days. I try to arrange plants according to their light needs, and when I can’t make something “fit”, I will usually go with lower, rather than higher light levels. This is probably what most needs “tuning up” in my environment.

I keep humidity between 90% (just after watering or misting) and 60% (seldom gets quite that low). I have had bad luck with humidistats, so I just keep an eye on my logged data and adjust my mister timing and duration. I mist 1,2 or 3 times a day, for just a minute or two, depending on season/outside high temperatures. The timer is set for mid-day times, between noon and 3:00pm. This, plus the weekday watering keeps the humidity up to good levels.

I water comparatively little, just 1 minute (winter) to 2 minutes (summer) for each zone, each on a different day of the week. The zones on the lower benches get a bit more, since they get run-off from zones above as well as their own watering. I try to be careful of plant placement, avoiding “rain shadows”, being aware of run-off and drip locations, etc. It is surprising how much variation you can get in water conditions. A few of the plants like a “touch-up” with a little extra water, which I can do by hand. I also have a small section of one of the upper zones set up as a “dry zone” that can be shut off for plants in dormancy during the winter, and left on during the summer. Since the watering is an overhead spray, I set the timer for 9:00am, so any water standing in crowns is gone before night. I’ve never had problems with crown rot.

Plant types

I’m surprised at how many different things grow and bloom in my environment. Within a small space I have a variety of micro-climates (much more LUCK than design acumen for sure!), and I’m learning more about how I can use them all the time. Obviously suited to mostly warm to intermediate growers, I really couldn’t do much with real cool growers. Nevertheless, I have had good fortune with a lot of the more warmth-tolerant varieties of cool growers; Cymbidium, Masdevallia, Pleurothallis, Zygopetalum, etc.

I have about 250 plants, ranging from a few cattleyas with a dozen growth leads, in 16” pots (and one “monster” Oncidium), to small, SMALL pleurothallids. Although I love the big specimen plants, things are getting a little crowded (and I do pack them in) so I have been concentrating on the small to mini types lately.

You can see a FEW of the plants in my gallery, and I’ll probably add some more before too long. I have photos of everything that has bloomed for me over the past 6-7 years, and I DO like to let them “show off”.

Ed