A fun thought experiment.

[ChrisFL]

I'm a climate guy, so it's fun to think of orchids with respect to climate.

So, in regions of Papua New Guinea, Borneo, etc., it's not uncommon for a total of 3 meters (9.84252 ft) of rainfall to occur in a single year.

Let that sink in.

Now, lets take a sample, a hobby greenhouse. 8' x 12'

Let's do a simple calculation to see how much average daily "precipitation" it would require to give you a similar annual total.

8' x 12' x 9.84252' = 944.88192 cubic feet of water, or 7068.21 gallons. Divide that by 365.25, that comes out to 19.35 gallons of water being dumped into this hobby greenhouse daily, on average.

Let that sink in.

Now with all that dilution and washover, how much "fertilizer" are these orchids, assuming epiphytes like Bulbos, REALLY getting?

You could also easily model a seasonal cycle in rainfall as well, but the places mentioned above rarely have one of any significance.

 

[gonewild]

Look at how many cu' of water you actually used in the greenhouse in one year and see how many inches of rainfall that compares to.

 

[mormodes]

Yikes, I really need to water more

 

[Rick]

that comes out to 19.35 gallons of water being dumped into this hobby greenhouse daily, on average.

Let that sink in.

Now with all that dilution and washover, how much "fertilizer" are these orchids, assuming epiphytes like Bulbos, REALLY getting?

You could also easily model a seasonal cycle in rainfall as well, but the places mentioned above rarely have one of any significance.

I came up with similar conclusions looking at the papers on nutrient flux in rain forests, and then my epiphany of tracking pot EC to watering frequency (and water quality).

I was moving about 1-2 gallons a day in my 12X12 gh and attributed (by convention) root rot to overwatering. But then when measuring EC found that I was concentrating salts by underwatering/evaporation cycles.

So now I'm watering at 2 x what I used to, fertilizing even less, and getting roots like crazy. I don't think I can afford to go to 20 gallons a day, but I'm completely in aggreement with your point.

 

[keithrs]

I can't agree more with mimicking nature... After all, it is the best teacher!

I'm a firm believer in misting(heavy) orchids for longer periods, possibly several times each watering.... Rather than watering by hand with a heavy dump of water.

On the idea of how much diluted fertilizer do epiphytes really get is the reason way I cut my fertilizer from 125 PPM N down to 30 PPM N and I'm going to cut it even more starting next spring down to 10 PPM N.

 

[keithrs]

I came up with similar conclusions looking at the papers on nutrient flux in rain forests, and then my epiphany of tracking pot EC to watering frequency (and water quality).

I was moving about 1-2 gallons a day in my 12X12 gh and attributed (by convention) root rot to overwatering. But then when measuring EC found that I was concentrating salts by underwatering/evaporation cycles.

So now I'm watering at 2 x what I used to, fertilizing even less, and getting roots like crazy. I don't think I can afford to go to 20 gallons a day, but I'm completely in aggreement with your point.

4 GPD for the amount of plants you have..... Are you crazyoke:

I would of thought you would be in the 10-15 range for sure!!!

I waste 15 GPD, some times more watering the small amount of plants I have and they could use more.:evil:

I guess a greenhouse makes all the difference!!!

 

[Rick]

4 GPD for the amount of plants you have..... Are you crazyoke:

I would of thought you would be in the 10-15 range for sure!!!

Part of it is based on the nature of the collection. Probably ~1/3 - 1/2 is mounted or in baskets with very little substrate. So it doesn't take much water to spray them off and end up with most of it hitting the floor.

And then with all the potted stuff we all are cautioned for years that "overwatering causes root rot", and just water to keep things moist (not dripping wet) between waterings. So with 70%+ humidity it doesn't take a lot of water to keep pots damp.

Before I put an auto fill valve on the sump to the wet pad/humidifier, I used to add about 5 gallons a day to keep up with humidification.

So my total water budget could actually be rated at 5 or so gpd more than what I actually squirt on the plants on a daily basis.

 

[Rick]

In one of my earlier cooling/humidifcation itterations using simple misting I did go through at least 20 gal/day, and ended up having water seep under the foundation of my house, (and pooling up under the laundry room).

Anyway when I spray much more than a few gallons at a time, most just ends up on the ground and has no impact on the orchids whatsoever.

 

[Stone]

If we assume that many paphs recieve 100 inches of rain over the growing period (in round figures) over say 6 months, thats 1/2 inch of water per day but obviously not every day. Sometimes they may get nothing and other times 4 inches. When I water my seedlings (especially) I dunk them 3-4 times. When I use the hose, I give the same amount. So for a tube 3 inches deep, thats around 10 inches of water each time.....(about every 3 days) so in fact they are getting lots more water than habitat. BUT with all that leaching its desirable to have a very low but constant supply of nutrients. Thats why comming up with a system of low-level slow release nutrient supply always seems to give me the best results.
Unfortuately no one has come up with a good controlled release fertilizer for paphs. Although Osmocote is working exeedingly well with all my epiphytes along with the roths, phillpis and lowiis etc. Maybe when my seedings are mature it might work well for all. I only worry about the left-overs when dormancy comes around.

 

[NYEric]

Yay watering!!!

 

[Ray]

So let's consider the impact this heavy water supply has on nutrient availability.

Chris mentions "dilution and washover", which certainly are factors, but there are other things to consider.

Plants exude all sorts of nutrients through their leaves, and a heavy rainfall may actually leach more, even thought the plants have mechanisms that try to slow that. There have been lots of studies that have shown the large nitrogen flux associated with drippage from the canopy. I suppose it's possible that the total mass of nutrition might be greater in a "high water volume x more dilute" scenario than one in which the rainfall is lower, even if the nutrient concentration per rainfall is higher.

For plants that live in humus and leaf litter on the forest floor, a lot of rain keeps it moist, freeing ions and making them more available - dry media = no absorption. Again, likely more dilute, but possibly still available in greater total mass.

And....I suppose we can add the elimination of conflicting solubilities. A drier substrate means less solvent. Try mixing calcium nitrate and Epsom salts as a concentrate - or Pro-Tekt and a fertilizer, for that matter. No go. Mix them in a dilute fashion and "no go" becomes "no problem", avoiding precipitation, hence making the minerals available to the plant.

Speculation.... (sigh).

Data, please.

 

[Rick]

Plants exude all sorts of nutrients through their leaves, and a heavy rainfall may actually leach more, even thought the plants have mechanisms that try to slow that. There have been lots of studies that have shown the large nitrogen flux associated with drippage from the canopy. I suppose it's possible that the total mass of nutrition might be greater in a "high water volume x more dilute" scenario than one in which the rainfall is lower, even if the nutrient concentration per rainfall is higher.

This thread is somewhat resurrecting the old K lite ideas from last year. I have some papers on nutrient flux in rainforests from that work and a couple more abstracts have trickled in since. Bottom line is that the total amount of nutrients cycled through a rainforest system is very low compared to an agricultural setting (with applied fertilizer). And given the rainfall amounts and the fact that water flows downhill, the creeks, rivers, and streams, are the final recipients of all this wash down. The amounts of nitrogen phosphorus and potassium at "the bottom of the hill" are negligible (by are heavy feeding agricultural standards), but easily able to support plant growth. When I get a break I'll dig out one of those papers to provide a number, but the wash down water collected as it came down off of the leaves and tree trunks was pretty dilute in the papers I looked at.

I wasn't able to get the whole paper of something I was recently trying to get hold of, but it quantified the amount of leaf litter accumulated in a canopy (available as a nutrient sink for epiphytes) and found that only about 1% of total leaf fall actually stayed in the trees.

 

[ChrisFL]

Any papers you'd like full copies of, pm me. I likely have access.

 

[gonewild]

Plants exude all sorts of nutrients through their leaves, and a heavy rainfall may actually leach more, even thought the plants have mechanisms that try to slow that.

Just throwing out thoughts about this......

Perhaps plants exude nutrients through their leaves in an effort to get rid of internal excesses?

Any exuded nutrient washed from the leaves to the root zone would /could be reabsorbed by the roots if needed. But the "if needed" assumes plants know what they need to absorb and are selective. More likely the roots absorb the maximum possible and then the leaves throw off the excess.

 

[Rick]

At least with regard to K there is no excess.

If you recall the paper on uptake of K by bromiliads, this was an energetic process to capture small amounts of K from "very dilute sources".

There already is a link on this forum to a paper on Panamanian epiphyts that shows that lots of the nutrients in leaves is reabsorbed by the plant before leaf drop.

 

[bullsie]

Seems to me that the natural areas of these plants have some of the greatest numbers of 'high' dwelling critters of all shapes and sizes. How do orchids react to a 'windfall' of fertilizer passing through every now and again? Not that I can see this as a daily regimen but in a week or month or year everyone surely must get this fertilization.

 

[Rick]

Seems to me that the natural areas of these plants have some of the greatest numbers of 'high' dwelling critters of all shapes and sizes. How do orchids react to a 'windfall' of fertilizer passing through every now and again? Not that I can see this as a daily regimen but in a week or month or year everyone surely must get this fertilization.

The only significant imput from aboreal critters appears to be ants that nest around some orchid species (like Gongoras, Coryanthes, and some Catesetum). In these cases the ants are bringing/trapping leaf debris and mulching it in the form of their nest around the roots of the plants.

But things like monkey bird or frog poop wash out pretty fast with the heavy rains noted in a rain forest. And poop from random critters is also a pretty rare and random event given amount of plant density in the forest.

 

[gonewild]

And poop from random critters is also a pretty rare and random event given amount of plant density in the forest.

Correct but as the water containing the washed out poop runs down the tree it is washing nutrients over the roots of all plants below and also dissolving more poop on the way to the ground.
Consider that the rainforest canopy may be several hundred feet tall, that is a lot of collective surface area to accumulate poop between rainfalls. The runoff water becomes a nutrient "enriched" irrigation. Note that I said "enriched" and not "rich".

 

[Cheyenne]

I remember seeing pictures of cattleya and pictures of paphs(I think lowii) in a tree, both from different parts of the world. The plants leaves were so covered in bird or some other animal droppings that they didn't even look green. They looked like there was paint dripped on them. Both the plants were huge. I am sure alot of this runs to the roots when it rains. Especially since most plants are designed in structure to sent water to the roots. If it does was off I am sure it doesn't take that long to accumulate again. In the rainly season the concentration might be less and stronger in the dry. This was one of the reasons I started adding some organic fertilizers like bat guano and worm tea. Plants did great but the smell was a little much indoors.

 

[Rick]

I remember seeing pictures of cattleya and pictures of paphs(I think lowii) in a tree, both from different parts of the world. The plants leaves were so covered in bird or some other animal droppings that they didn't even look green.

Granted there's not a ton of insitu pics out there, but at least 9 of 10 of the pics of epiphitic plants I see have pretty clean leaves.

I promise I'll dig it out later, but the washdown water data is pretty dismal in terms of finding large concentrations of nutrients.

As noted from much of the leaf tissue and leaf litter data, epiphytic plants are masters of conservation and recycling because the total nutrient availability is so low (certainly compared to domestic agricultural crops).