Ceramic metal halide grow

[Steve83]

I just set up a 5'Lx2.5'Wx6.5'H under a 315w cmh, and would like to share what, why, and how I'm doing things, with hopes of learning more about orchids.

I decided to try a 315w cmh for the spectrum, cri (I found a tent with viewing panels), and the heat-to provide a day/night swing. In addition I chose a unit with the ballast in the hood, as opposed to outside of the tent.

I spent the latter part of the afternoon adjusting vents, light height, fan, and taking temp and humidity readings.

Oddly, my best temp and humidity readings so far were with all of the lower vents shut, minimal venting at the top, and the clip on style fan positioned high up, and blowing against the opposite wall to create light turbulence throughout.

I will post my high/low temps and humidity once it has sat like this for a few days.

Of note, having the lower vents open pulled air in and created a strong chimney effect, which in turn dropped humidity. I thought this would be needed to mitigate heat, but it made no difference. This was confirmed via probe 24" directly below the center of the lamp. Most info about cmh suggests a distance of 2.5' to 3' from the canopy, but that info is likely geared to marijuana growing. So, I have my plants a bit further and shrouded with burlap while they acclimate.

I hope to post more info in a few days, in addition to figuring out how to post pics.

[Steve83]

I'm pleased to report that everything is going well with getting this tent dialed in, and with my education about orchid culture.

I couldn't find much detailed info about growing orchids under hid lighting in a smaller enclosed space, and erred on the side of caution with plant distance from the lamp.

Then it struck me to use the variety of bromeliads I was growing on my patio, since I had a feel for their light requirements outside. They're looking even better than from when they were outside, my Neoregelia 'Red Tiger' developed bright pink at the leaf tips and lower edges. I'm chalking this up to higher humidity, and proper nutrient uptake, as I was using organic nutes at feedings (can't have much of a soil food web when there isn't any soil).

Now I'm in the process of moving my mounts and high light/heat plants closer to the lamp so I can better use the space and see how all respond. I'm also trying out different media blends and mounts to find out what works best for me.

A small cheap evaporative humidifier, which I have set on it's own timer, to run most of the day, kick on a briefly during the night.

As currently configured, during the day I have a temp gradient of 74f near the lower vents, 87f approx. 30" directly below the lamp, and if you take that 30" mark and pivot 45 degrees up, it's 81f.

Night temps are around 69f.

Daytime humidity is between 62-75%, at night it jumps immediately as the light, and humidifier go off, then receives little boosts when the humidifier cycles on.

Everything is looking great, and I'm elated at the amount of root and top growth I'm getting. I'll try to post some pics too

[Ray]

Nice description, Steve. I’d recommend you not bother running the humidifier at night.

Many orchids are CAM plants, so open their stomata at night for gas exchange while the humidity is naturally higher, reducing the risk of water loss. However, if the RH is extremely high, it can suppress the exchange process.

[Steve83]

Ray, thank you for the information, it is greatly appreciated. I will discontinue running the humidifier at night.

Also, I am loving the information on your site. It's answering a lot of questions that have popped up.

[Steve83]

Here's a photo update of two that I purchased in bud 8/18/20. I couldn't believe how quickly they bloomed, given the size of the buds at the time, and despite my impatience and repotting the Gomesa crispa.

C. jungle beau2.jpg - Google Drive

C. jungle beau.jpg - Google Drive

Gomesa crispa.jpg - Google Drive

[Steve83]

Here are some pics of the current arrangement. I'm seeing lots of growth, and am settling on a feeding regimen to hopefully keep from yellowing the older leaves too much.

I definitely understand why the only hid lighting my local hydro shops carries are cmh now. Although sunglasses and a wide brim hat are essential.

Mounts.jpg - Google Drive

Top.jpg - Google Drive

Tent.jpg - Google Drive

Corner.jpg - Google Drive

[DirtyCoconuts]

I like the look of the setup.

[Steve83]

Thanks! The rack isn't ideal, but it was cheap on Craigslist, and will work until there's a need to change things up to accomodate more or lower light plants.

[Steve83]

Here are some updated pics.

fireballs.jpg - Google Drive

Dinema.jpg - Google Drive

Encyclias.jpg - Google Drive

Watering is 2-4 times a day at 20ppm N K-Lite via sprayer. KelpMax and Quantum are added as prescribed, and I'm also dosing with a Silicon supplement once a week.

[Steve83]

So, after some time has passed, I've made some observations, and will be making a major change to my grow tent.

The most interesting is that of gas exchange. While all of my plants are growing well, the ones in pots (on a wire shelf, which takes up space and blocks airflow) are at the back of the line. Also of note, are that all of the potted plants require more shading than any of the mounts. I wanted to have mounted most of them by now, but they are in spike, and I am waiting until they flower.

The other issue, and I think it's more due to the 2.5" tent depth, is the 36" long "death cone" that shoots straight down from the bulb. I have my broms as close as I can get them, and it's just a space killer. The cmh reflector is a better fit for square tents, or an open area.

In order to free up space and get rid of the shelf, I'll be swapping the 315w cmh out for 2 HLG Sabers (100w each). These will provide a more uniform light spread, and I probably won't have to actively shade the lower light plants.

I think in terms of overall light quality it's a step back (cmh has nice uv and infrared), but if it appears lacking I can supplement lighting. On a posiyive note, less exhausting will be required, so I should see a little bump in average daily humidity.

Once the Sabers are installed and things settle, I can finally add some permanance for mounting, by using 2x4 chrome wire panels instead of the plastic fencing (which sways a bit when opening/closing the tent.

If I had more space, a 4' or 5' square tent would be ideal for the lamp. To think this is doable with only 315w is an important consideration for the basement growers who use multiple shelves and t5 or led fixtures taking up lots of space.