Fertilizing via the automatic misting system? Good or bad idea?

[treefrog]

My shadehouse is equipped with a misting system. The system has enough coverage and water flow to keep the substrate of the plants humid year long without any manual watering. So far, I've been using this system mostly to keep humidity during the dry season or make sure the plants are watered when I'm absent. For the last few month, I've been thinking about injecting the fertilizer through the misting system water line so that twice a day, for 2 min, the mist would contain very diluted fertilizer (20ppm N?). What are your thought about this idea? Isn't it the way professional nurseries feed their plants (but via sprinklers?). I'm attaching small (and bad) videos of the misting in action.
Cheers,
Mathieu
View attachment WhatsApp Vidéo 2024-07-14 à 09.56.22_2f6953d7.mp4
View attachment WhatsApp Vidéo 2024-07-14 à 09.56.23_5a1610f4.mp4

 

[spujr]

You might run into algae problems which may cause misters to become clogged.

 

[gonewild]

I recommend you do it. For many reasons. I've been growing that way forever.

 

[Ray]

Foliar feeding depends, to some degree, on the type of plant and its maturity.

Some plants, such as paphiopedilums, phalaenopsis and many vandaceous types, develop thick, waxy cuticles on the leaves, likely an evolutionary adaptation to slow water loss. They tend to be thin on immature plants and thick on mature ones. Such barriers slow movement in both directions.

That said, if the setup you're using is keeping the medium moist, then obviously some of the fertilizer is going to end up in the potting media where it can be taken up by the roots. As @spujr stated, be prepared for a lot of algae growth.

 

[My Green Pets]

I would also suggest that a nutrient solution that sits in crowns and crevices, especially in a warm, bright location, could lead to problems.

 

[gonewild]

I would also suggest that a nutrient solution that sits in crowns and crevices, especially in a warm, bright location, could lead to problems.

I have never found nutrient solutions sitting in the crowns to be a problem any more than pure water.
A properly managed automatic mist system would not provide so much water that it sits in the crowns too long.
It's just my opinion but I suspect the soft leaf tissue at the crown is the point where nutrients can be absorbed through the foliage.

 

[cnycharles]

Sometimes you can get mineral and as stated algae; but 20ppm seems very light. The Utica city water used at first greenhouse upstate was 32ppm and we had to inject fertilizer to help prevent nutrient loss from pure water over leaves

 

[gonewild]

Exactly.
Because leaves can have nutrients leached by pure water application it's reasonable to assume they can also absorb nutrients through the leaves.

 

[Ozpaph]

i suspect you will clog the misters.

 

[Ray]

Who says nutrients can be leached by the use of pure water? I have never seen evidence of that or anything documented. Any reference I have seen relates to leaching of nutrients from soil, resulting in deficiencies and/or root damage. As orchids have evolved getting little beyond rainwater, I don’t see that last thing being a factor.

The absorption of a nutrient ion into a plant is part of a chemical reaction that results in the dumping of an equally charged ion into the environment, and once brought into the plant, it is incorporated into other chemicals. How is pure water going to leach them?

Back to the foliar uptake thing, it isn’t a matter of there being none, it’s just that it’s inefficient.

 

[Sky7Bear]

Who says nutrients can be leached by the use of pure water? I have never seen evidence of that or anything documented. Any reference I have seen relates to leaching of nutrients from soil, resulting in deficiencies and/or root damage. As orchids have evolved getting little beyond rainwater, I don’t see that last thing being a factor.

The absorption of a nutrient ion into a plant is part of a chemical reaction that results in the dumping of an equally charged ion into the environment, and once brought into the plant, it is incorporated into other chemicals. How is pure water going to leach them?

Back to the foliar uptake thing, it isn’t a matter of there being none, it’s just that it’s inefficient.

But as the expert on semi hydro, do you see this as a good way to avoid salt buildup in the inorganic substrate or is that problem overstated?

 

[Ray]

But as the expert on semi hydro, do you see this as a good way to avoid salt buildup in the inorganic substrate or is that problem overstated?

Buildup is related more to drying than it is to what is being applied. If I soak a sponge with a 10% "whatever" solution and seal it in a ziplock bag, it will ALWAYS contain that same 10% solution. If I let the solvent evaporate, however - which happens at the surface, moving inward, concentrating the solute - it will eventually reach the toxicity level.

Unfortunately, once fertilizer minerals get that "embedded" in media - organic or inorganic - it's hard to extract it again, even with pure water.

 

[gonewild]

Who says nutrients can be leached by the use of pure water? I have never seen evidence of that or anything documented.

Not all horticultural knowledge has been published.
A personal contact at UC Davis did research back in the 70s that determined that to be true. Although probably not significant. His research was conducted for a large nursery operation looking for all ways to increase productivity.

Personally a few years back I inadvertently tested the theory rooting single node vanilla cuttings. Cuttings were stuck in individual pots of silicone fiber fill containing no organic matter. Water source was rain water.
One bench of cuttings was misted automatically throughout the day with pure rain water(4 ppm). Another bench was similarly misted with 400 ppm of nutrients added to the rainwater.
The resulting difference was dramatic. Cuttings with rainwater unevenly sprouted roots at 4 weeks. The single leaf on the stems became yellowish.
The cuttings receiving nutrients remained green and root initiation began in 3 weeks and shoot initiation and growth was more rapid resulting in 25% faster time to final size.
Since the cuttings were rootless during the time the leaves became yellow receiving pure rainwater and stayed green with nutrient water I think supports that some nutrients, minerals or compounds may have
been leached from the foliage.
Definitely addition of nutrients to mist water on orchid foliage (Vanilla) aids plant growth.

 

[gonewild]

Unfortunately, once fertilizer minerals get that "embedded" in media - organic or inorganic - it's hard to extract it again, even with pure water.

If the minerals are embedded so tight in the media that they don't dissolve in water what is the need to remove them?

 

[Ray]

Not all horticultural knowledge has been published.
A personal contact at UC Davis did research back in the 70s that determined that to be true. Although probably not significant. His research was conducted for a large nursery operation looking for all ways to increase productivity.

Personally a few years back I inadvertently tested the theory rooting single node vanilla cuttings. Cuttings were stuck in individual pots of silicone fiber fill containing no organic matter. Water source was rain water.
One bench of cuttings was misted automatically throughout the day with pure rain water(4 ppm). Another bench was similarly misted with 400 ppm of nutrients added to the rainwater.
The resulting difference was dramatic. Cuttings with rainwater unevenly sprouted roots at 4 weeks. The single leaf on the stems became yellowish.
The cuttings receiving nutrients remained green and root initiation began in 3 weeks and shoot initiation and growth was more rapid resulting in 25% faster time to final size.
Since the cuttings were rootless during the time the leaves became yellow receiving pure rainwater and stayed green with nutrient water I think supports that some nutrients, minerals or compounds may have
been leached from the foliage.
Definitely addition of nutrients to mist water on orchid foliage (Vanilla) aids plant growth.

Lance, what you described is not the leaching of nutrients by the pure water, it is starvation because the plants had no source of nutrition other than their own tissues, and that eventually ran out.

If the minerals are embedded so tight in the media that they don't dissolve in water what is the need to remove them?

In my book, replacing the medium is needed. That, or a very, very long soak in copious amounts of pure water.

 

[gonewild]

Lance, what you described is not the leaching of nutrients by the pure water, it is starvation because the plants had no source of nutrition other than their own tissues, and that eventually ran out.

Maybe so. But then that proves leaves absorb nutrients from the mist water.

 

[Ray]

Maybe so. But then that proves leaves absorb nutrients from the mist water.

Not necessarily. Misting is not limited to foliage.

 

[gonewild]

Not necessarily. Misting is not limited to foliage.

For perspective my mist system was carefully programmed to humidify the leaf surface without runoff into the non absorbent silicone fiber. But even if a significant amount of nutrients entered the substrate the cuttings had no roots and only a very short piece of stem. Realistically the only way for the nutrients to benefit the leaf was to be absorbed through the leaf. Whether through the epidermis or through stomata the nutrients were most likely absorbed from frequent foliar applications.

 

[Ray]

Certainly possible as foliar uptake by orchids is generally poor, not nonexistant.

Also, if your unspecified fertilizer contained urea, that is also favored in foliar uptake to nitrates and ammoniums.

 

[gonewild]

Also, if your unspecified fertilizer contained urea, that is also favored in foliar uptake to nitrates and ammoniums.

No urea. My fertilizer was my own formula comprised of Calcium Nitrate, Potassium Nitrate, Magnesium Sulfate, Phosphoric Acid, Micro Nutrients mix and Citric Acid.
The formula fluctuates somewhere between MSU and KLite.