Risk of damage from short-term exposure to extreme heat.

[BrassavolaStars]

Hello All,

I am worried I may have made the dog in the hot car mistake with my plants.

I had just begun to add my plants to my greenhouse. The greenhouse has three roof vents, a powerful fan, and an aluminet shade cloth.

The plants in the greenhouse were cattleyas, brassavolas/rhyncholaelias, a few dendrobium nobiles, one Den Formosum, a vanda, and a few zygos and oncidium type orchids.

Today, the predicted temperature for the morning was 79f and cloudy, however, when I checked my thermometer in the greenhouse, it registered 99f with a previous high of 107!

I immediately took my plants out and put them somewhere cooler.

So far, they appear to be alright. What are the chances they have actually been harmed by these high temperatures?

it could have been above 100f for anywhere between 1hr and 3hrs. Would this amount of time at those temps have been enough to have caused problems in the plants listed above or should they be okay?

Thanks.

[Ray]

100°, by itself, may not be much of an issue. High temperature with bright sunlight increases the leaf temperature far beyond the air temp, and that can result in burning.

Time will tell.

[BrassavolaStars]

Hello All,

I did not see any evidence of sunburn on any of the plants. I think my shade cloth combined with the overcast weather prevented that thankfully.

The best way to describe the conditions that occurred is that the plants were in a sauna temporarily.

My humidistat said the RH was 99% along with a temp of 107f.

However, the light level seemed to remain relatively mild with no bright, direct sun on the plants.

[Orchid Whisperer]

I've had plants outdoors at 108 F ambient (higher with heat index). But they were truly outdoors, plenty of air movement, also under shade.

If yours were under bright sunlight, no air movement, could be a lot more problematic

[BrassavolaStars]

Hello Orchid Whisperer,

That makes me much less worried since my plants were under a shade cloth with a circulation fan.

I guess the best thing to do it be more careful next time.

As an aside, is there a good way to keep the greenhouse from reaching such high temperatures in the future? this extreme heat happened with even three vents and a fan.

I looked at evaporative coolers as an option, but it seems they will be ineffective in my high humidity region.
Is there something else not too expensive that will at least confine the temps to under 95F?

[Roberta]

Shade and air movement go a long way toward protecting the plants. So maybe, at least another fan and more shade cloth. I use a big fogger (Aquafog 900), pricey but it works great - but my humidity isn't too high, usually not much more than 60% at mid-day when I need the cooling. But with air movement, you probably can keep the temperature down pretty close to ambient (which may not be uncomfortable but probably won't hurt the plants - as in Ray's situation. And keep those fans going 24/ 7.

[Ray]

Don't underestimate the efficacy of evaporative cooling. It "works" at anything under 100% RH, but the lower the humidity of the incoming air, the more effective it will be.

Being as you're in NY, I am reasonably confident your ambient RH is not too high. They are supposed to draw outside air in, which is cooled and blown into the greenhouse, but I have seen one in operation inside of a hot, humid greenhouse in Houston, and was stunned when I felt the cooling effect in its fan blast.