The effect of intense hydrofogger use in the greenhouse

[Lars Kurth]

Hi,

I went for a 7 days on holidays with nobody being able to water the greenhouse. To avoid that the orchids would become too dry, I left the hydrofogger on 100% on a timer. The fogger is connected to a water tank, which I was feeding through an RO system. I had the fogger from 4-5 AM and from 8 to 16:00's. In terms of weather, the first 2 days of the holiday were sunny, the rest largely grey, rainy and fairly cold. As a consequence, the plants did get more moisture than I bargained for. And that in somewhat cooler conditions than normal.

When I got back today at 7pm and inspected the greenhouse, some plants were quite wet, indicating that the fogger regime created too much moisture (when it is on, it creates a dense mist, which if the weather is not sunny soaks mounts and the top inch or so, of the growing medium in pots.

Here is what has happened.

1) Most plants have gone into an absolute riot of growth. Practically all Vanda's and Angraecous plants have started to rapidly grow both in terms of leaves and new root growth. The same is true for my Dendrobiums, Cattleys & co, which have thrown out masses of new roots. Some roots have grown 2 cm's in a week!
2) Nothing has rotted or been damaged.

The lesson to take away is that simulating a few consecutive rainy days in the greenhouse, can have an incredible effect. The effect of the fogger essentially compares to a few hours of light but persistent rain in a cooler environment. I would guess that using the fogger this way, but maybe more carefully (maybe limit the usage of intense fogging to 2-3 days in a go and then switching to a drier regime) may be extremely beneficial.

I'd be interested to hear your views. Will experiment a little with the fogger during the summer and keep you posted.

Lars

[Call_Me_Bob]

awesome

[johnblagg]

sounds like a plan if done maybe once every other month I know that when I used misters outsid in the yard I get that effect with common garden plants too esp in dead of summer when they love a fine mist all night to cool them down

[Eyebabe]

I believe your observations are excellent and point out the very important difference between environmantal humidity and watering a plant.
Many make the mistake of looking at a dry plant with dry roots and think it needs a good watering or soak when in actuality, it need more humidity.
Thus, if we do not realize this, overwatering occurs and rots the root systems.
Attention to humidity levels is more important than we think

[Lars Kurth]

Many make the mistake of looking at a dry plant with dry roots and think it needs a good watering or soak when in actuality, it need more humidity.

I have been doing this in the past myself and am tending to water potted plants much less than I used to (actually only 3 days or so in hot and sunny weather). Soaking too much, can create a downward spiral. The roots in the bottom half of the pot will rot, in turn the substrate in the bottom of a pot will dry out less quickly, the plant looks as if it needs more water, etc.

Attention to humidity levels is more important than we think

I fully agree. I am wondering what effect that treatment would have had, had the weather stayed warm, or even hot.

Checking this morning more closely, after switching the fogger off, I observed the following:
1) All the mounted or plants in baskets had completely dried by morning
2) The surface of some pots were still quite moist
3) Some corners of the greenhouse got much more moisture than others

I earlier said that I observed no damage: that was not quite true on closer inspection. One new shoot of a Stanhopea and one of a Gongora had wet rot and had to be cut off. These were plants which were in the area of the greenhouse where moisture accumulated. The mist probably condensed and kept the fresh shoots wet over night.

In any case, it seems that with this approach I can go away for a few days, without anybody looking after the greenhouse. At least if the weather is not too hot. Maybe it is possible to use better humidity controls, e.g. use a weekly timer which allows the plants to dry after 2 days of more intense fogging. Or combine the timer with a thermostat such that the fogger switches on less frequently when the weather is bad.

[orchidsamore]

I think you were lucky.

Cool damp conditions are the perfect breeding ground for Phythion fungus. As you noted later you had a little.

The main thing going for you was that your plants were healthy at the start and strong plants resist disease. Also orchids can adapt to most anything for short periods.

I grow outside under shade cloth and it has been under 30 degrees 16 times in the past two winters. I have used non-stop water sprinklers to heat my plants all night these winter nights.

My total result was about 20 leaves lost to pythion over the two years out of 10,000 plants. No plants dead from cold.

However, when I buy plants from other growers and add them to my stock the first week or two I can get lots of problems. They are not hardened off like my regular stock.

Your rapid growth especially on the Vandaceous suggests you are not watering enough. The plants responded to the additional water.

Foggers and watering are no different. Foggers just put less water on over a longer period. The biggest advantage to foggers is that the fine mist spreads more across the greenhouse and 'dead' areas that may be blocked from watering by plants overlapping etc get watered as well.

Most important this thread discusses the greenhouse as if every plant needs the same care. Cattleya need to dry their roots regularly and Vanda need water every day. They should be zoned for best results.

There are a lot of things going on here and they should be dissected before applying the results to all orchids.

[Lars Kurth]

Jerry,

you are of course right. As I only have a fairly small greenhouse, zoning the greenhouse is no ption. I have had to make compromises or stop growing some species.

This year, I have been erring on the side of caution with regards to watering and fogging, so probably my Vanda's and mounted orchids did not get enough moisture.

I have been using the fogger since summer 2008, and have used it too much last year. The increased humidity in the greenhouse (and that is without the holiday treatment described earlier) meant that Cattlea pots were too wet and were not drying out that quickly. I had quite a bit of root damage. So I changed the substrate to be much more open this spring (the aim was to ensure that pots would dry out within a day), using a tiny bit of CHC at the bottom to encourage roots to grow down, then a layer of styrofoam topped with a mixture of CHC, Epiweb and very coarse bark. So far with good success.

So it all comes down to the right balance of conditions. What this has taught me though is that well grown plants are quite resistant to differing conditions for short periods. This year I opted for "more moisture" as I lost quite a few mounted plants in a similar situation last year when I went away for a week and had nobody to check on them. The consequence were some totally dried plants.

Maybe one lesson is that the occasional "strategic" use of more extreme conditions may be beneficial: if used with care. For example there may not be any harm in using extreme fogging on a few (3-4) consecutive days in late spring when the weather is nice, to spring plants into action with the aim of giving them a boost at the beginning of the growing season. While not damaging plants that need drier conditions.

[RosieC]

Hi Lars,

Can I ask what sort of fogger you use?

I'm tying to work out what I need to use in my greenhouse to keep the humidity high and I've found a few products on the market but I'm not sure what to buy. (I'm also in the UK so thought whatever you are using may be available for me).

[Lars Kurth]

Rosie, I use the Hydrofogger 240 (you can get them from Simply Control in the UK, but you can get them more cheaply from other suppliers occasionally). The fogger is connected to a water butt, which in turn is connected to an RO unit to keep it topped up.

[RosieC]

Thanks Lars.