Heresy, you say. Every known work on orchids stresses the necessity of ventilation. But let us consider in more rigorous detail what ventilation actually does for us and our plants. As you would expect, it does some good things and some bad things, and we put up with the bad to get the necessary good. But what if the good things it does could be done another way? Then we wouldn't have to put up with the bad things. which could, all considered, save us a lot of time, money and grief.
Good things brought by ventilation:
Bad things brought by ventilation:
Well, the good news is that we can. Taking them one by one, this is how we can easily
do the good things of ventilation — air movement, carbon dioxide food, open air factor
All I can say is that non-ventilation works for me — my heating bills are kept in check and the plants seem to love it. In the days when I ventilated, I was forever having trouble with black spots and moulds and rots, whereas now I have hardly any (and those are probably my own fault as I almost never sterilise anything). My use of insecticides and fungicides is near zero, and my fertiliser use is very low, but my plants mostly grow OK. Rather than forever trying to heal sickly plants, I now have time to titivate and admire them.
I still have the essential automatic roof vent. but, as there is no through flow, only the hottest air escapes and is replaced with cool air from (importantly) a decent distance above the ground (away from the coldest and most contaminated air).
Obvious, but how well do most of us manage to do it?
First, as any home energy adviser will tell you, it is essential to eliminate all draughts. as the smallest leak can carry away a lot of heat, especially when it's windy. You also should seal all gaps just to keep the bugs out (I failed to properly seal my house as it was being built, and have regretted it ever since!). Sadly. many greenhouse designs are almost impossible to seal effectively, but it's important to do your very best on this.
I used to use horticultural bubble-thene, the one with two skins, but it was a lot of
hassle and not that good. On the sections where I need light to get in. I have now put
secondary glazing of polycarbonate twinwall, and on the sections where I don't need
light I have put one-inch polystyrene insulation board (could be better, but chosen for
ease of handling, cutting and installation, and minimum loss of useful space).
Polycarbonate glazing is a boon here, as you can easily put screws and so on through
it for fixing — glass glazing would provide quite a few challenges!
We all know that humidity is vital, but providing it in the right way and at the right time is also vital.
Since I run my hobby on a shoe-string (as an engineer I have always enjoyed the challenge of doing the maximum with the minimum, and much as I might admire the products of Simply Controls, I can't see me ever shopping there), most things come from chain-stores. A fountain pump drives a home-made cascade with an ultrasonic mister in it and I have two more ultrasonic misters in the form of personal room humidifiers all are turned on by an ordinary room thermostat wired to come on with rising temperature and placed where it catches the sun. Effectively. I am humidifying whenever the sun is shining, but not otherwise, The trace from my data-logger tells me that this system works well, and often the house gets misty enough that it looks like a real cloud forest! On a hot sunny day the cascade will get through 5 to 10 litres of rain water (quite a lot is used up by splashes) and the misters will use 2 to 3 litres, but my RH stays above 50% and is more usually 70, 80 or more. Perhaps surprisingly, condensation doesn't seem to be a problem.
A word here about rain and rain water. The two are not the same. Rain (after the first bit) is mostly pure and clean and sterile, and maybe still retains some slight sterilising properties it does a good job of cleaning plants and keeping them healthy.
Rain water, in contrast, is contaminated with all the rubbish and dirt and spores that have fallen on your roof and gutters, and dissolved or bred in your rain-butt. No surprise, then (if you think about it) that spraying or misting your plants with rain water is a pretty sure way to infect them with all the moulds, rots and bugs you can imagine. Also, if you leave rainwater lying around, as in a sprayer or a mister reservoir, it will quickly grow films of algae, bacteria and the like.
My own solution to this problem is to add a biocide to any rain water that is going to reach the green parts of plants (I don't add it to water for the compost, as I might kill off good bacteria arid fungi there). I use Corsodyl Original mouthwash. about a teaspoon to a bucket and left a while to do its work. This product was recommended to me (as a mouthwash! !!) by my doctor decades ago, and has been my personal general purpose antiseptic of choice ever since (they use the same stuff to ''preclean surgery). The water in my sprayers and misters stays clear, and any residual sterilant no doubt helps to keep my plants free of nasties.
© Ronald Lamont November 2011