foliar feeding
 

hi folks,

as we expand our knowledge and expeience with orchids, the topic of foliar feeding is one that has come up several times, including most recently in our conversations with a much more experienced grower.

in regard specifically to phal gigantea and doweryensis, it seems like the pros do foliar feeding. i always thought the nurseries did it for ease and efficiency sake.

so, the question is, is it really necessary? our plants seem to be doing good overall, but if it helps a couple plants grow better than i am willing to try.

can we use the same concentration we have been using for root zone feeding? should we add a drop or two of soap as i read is often suggested as a binder of sorts?

thanks for any info hivemind!!

a few thoughts-

yes foliar "feeding" can work on orchids however there are a few things that are required for optimal effects. some may chime in and say that the foliar applied nutrient may just be washing to the roots when you water next and that leaf application is not effective. orchids are epiphytes and chances are some of your foliar spray will hit the exposed roots during application this isn't a bad thing. generally, orchids with thick waxy cuticles like Cattleya do not absorb foliar sprays nearly as well as thin leaved orchids.

1. what are you foliar spraying? fertilizer? micronutrients? biostimulants?

While orchids can certainly take in nutrients through the leaves, I think the overall consensus is that the roots are more than sufficient and preferred for taking in mineral nutrition. It is reported that urea is the best for foliage absorption due to its lack of charge and high solubility. Amino acids fertilizers blur the line between fertilizer and biostimulant and can also be applied to the foliage. Again, foliar feeding is not the most efficient to supply mineral nutrition plus its generally not a good idea to apply a single nutrient out of balance with the others unless you REALLY know what you're doing.

In my opinion where foliar application shines is with biostimulants which may present a cost challenge at larger scales. For example, kelpmax (a popular kelp based biostimulant) at a 1:250 dilution could be expensive to a large collection when fertigated but applying the solution to the plants with a spray would allow you to stretch the product much further.

2. what makes a good foliar spray?
if you want to experiment with foliar spraying you need to make sure that you use soft or low TDS water. the water should be slightly acidic pH 6.2-6.5. if applying minerals, apply them more dilute than you would fertigate with.

wetting agents, ect are VERY useful to increase the absorption of biomolecules like plant hormones or amino acids. wetting agents also increase the ease at which the leaf surface can be coated. the internet is filled with people obsessed with using dish soap on their plants but it's not the best tool for the job. dish soap has ionic surfactants which can react and precipitate with fertilizers or calcium and magnesium if you make the mistake of using hard water and increase the risk of burning your plants at worst or render the foliar spray less effective at best. use a non ionic surfactant or saponin to apply foliar things:

cocowet
polysorbate20/tween20
thermx-70 (yucca saponins)

3. how and when you apply foliar sprays is KEY

the main way that foliar sprays enter the plant is through the stomata. applying a foliar spray when stomata are closed can render the application useless. stomata open and close differently for different classes of orchids. foliar spray early in the morning when its cool or in the evening. another reason to apply in cooler low light times is that the wetting agent can cause phytotoxicity and burning at high leaf temperatures. foliar sprays absorb best if you can deliver ultra fine droplets to the leaf underside where most of the stomata exist. the sprays are absorbed much better if the ambient humidity is high especially for more difficult to absorb things like certain minerals.

too long didnt read version:
use pure, or low TDS water, at an appropriate pH and with a wetting agent. apply at the correct time of the day to increase absorption and so you don't burn your plants. your milage may vary depending on the type of plant you are growing. minerals=meh biostimulants=hell yea

I would not foliar feed, just based on the plants in question. In greenhouses, growers usually grow these mounted (so crown hanging) and have very good air circulation. So anything sprayed will drip off, and the rest evaporate quickly.

Phal gigantea is said to be extremely susceptible to rot when water gets trapped between leaves. I think you are growing yours potted and indoors (like I do) and I would not want to get the leaves of my giga wet, especially for a questionable level of benefit.

Some additional thoughts:

In terms of uptake efficiency, urea is better absorbed by the foliar route than are nitrates and ammonium compounds. The opposite is true of the roots.

Orchids can be particularly poor at foliar uptake due to waxy cuticle layers that form on the leaves. It is an evolutionary adaptation to slow water loss, which also slows uptake. I imagine wetting agents could help, as they will increase the percentage of the surface wetted and the length of time they stay on.

That said, the cuticle layers develop over time, so young plants will respond to foliar feeding better than older ones. Their presence and/or development of the waxy layers varies a lot, as well, with catts, phals, and vandas being on the “thick” end, while thin-leaves species on the other.

Solutions are not actually absorbed through stomata, but through areas known as “plasmodesmata” in close proximity to them. Many orchids have the majority of their stomata on the undersides of leaves, making it difficult to wet them down.

hey guys and gals, thanks for the great input.

a couple thoughts in response. first, camille, we have avoided this for the exact reason you say. but now that the weather is getting warmer, like last year we will pretty much keep all the doors and windows open all summer, so we get a very nice cooling breeze. but it still concerns me.

as far as what, i was thinking of starting with only kelpmax this summer. and reducing the kepmax from our normal watering schedule. we are not ready to tackle new nutrients like urea just yet. i read a good article about foliar feeding only once every 4th week in a cycle. that sounded reasonable to me.

@thefish, i am admittedly one of those soap people, i hate to say it! but i cant argue with the last 15 years or so of results with it. so, that was my planned wetting agent :rofl: and i like to avoid strange and harsh chemicals if at all possible.
also yes, i planned to spray at night.

and on an unrelated note, how come none of you have submitted your guess for the latest bloom time?!?! shame on you.... ;)

A professional Phal. grower told me Phals take up fertilizer from their leaves faster than from their roots, and the huge commercial Phal. growers take advantage of this. The research is available online though I've never looked it up.

As Ray mentioned most other orchids don't take up anything through the leaves due to the waxy cuticle that prevents water loss.

For most people raising the temperature and relative humidity of their Phal. growing space will give far better results than any manipulation of fertilizer. I mention this over and over, but home growers have no idea how fast they grow when it's 85 degrees F / 30C and 60% relative humidity.

That’s an interesting observation. I can see that being a possibility when they are very young (lots of leaf surface area, little wax, few roots), but over time I would think that would not hold true as the plants mature.

Something else I just thought of - might plants grown in a humid environment develop less of a waxy layer than ones grown drier? Seems logical, but I don’t know if that’s the case.

I haven't read the literature on this so I don't know the details.

good points. this article suggests that some plants will reduce wax when humidity is decreased...but no orchids were part of this study, so i will have to do more digging....

Just a moment...

well, i suppose then that our middling humidity may finally be looked at as some sort of positive!

there is also a short section on wettibility in relation to the angle of droplets hitting the leaf. might be of interest to any currently foliar feeding

As a general comment, I am against foliar feeding, as the salts all leave ugly deposits.