What do you guys think about foliar feeding?

[ula]

Hello,

I was lately wondering about benefits of foliar feeding- if any (for orchids only, that is). I like to mist my darlings at least once a week with 0.2/0.2/0.2; I just dilute a balanced fertilizer in a weak surfactant solution (0.2% Tween 20) and use that. Are all genera created equal in their foliar nutrient absorption capabilities, or some are more capable than others? Is intake through that route negligible compared to the roots? A penny for your thoughts...

[gngrhill]

Miracle-Gro makes a foliar spray specifically for orchids. If you go to their web page and read the reviews you can see anywhere from "I makes no difference at all." to " My plants are thriving, blooms all over the place." So, who knows

[hanzy08]

I asked this question before from Ray who is an orchid Iconoclast and also a member of this website and he said that orchids in particular are very poor in foliar intake of nutrients and moisture.

[Ray]

Originally Posted by hanzy08

I asked this question before from Ray who is an orchid Iconoclast and also a member of this website and he said that orchids in particular are very poor in foliar intake of nutrients and moisture.

But not all orchids are created equal, in those respects.

Nitrate and ammonium sources of nitrogen are poorly absorbed through the leaves, but preferentially absorbed through the roots. Urea, on the other hand, is preferentially absorbed through the leaves, and far less so through the roots.

Orchids with thick, waxy, cuticle layers on their leaves will be particularly poor at foliar uptake - you have to figure that a plant that has evolved means to slow water loss through its leaves is going to have a hard time taking anything up that way, too.

I heard someone state that the macro nutrients (N, P, K, Ca, Mg) are primarily only up by the roots, while the trace elements are taken up via foliage. I don't know if that is correct or not, as my feeding regimen involves absolutely soaking everything, so how would I tell?

[Orchid Whisperer]

Ray, we continue to disagree on this - of course urea is quite well absorbed by orchid roots and is well utilized in that manner. If anyone is interested, PM me and I can point you to published research on the subject.

To the original question, I would imagine that heavier, waxy orchid leaves will absorb relatively little fertilizer, maybe the less waxy leaves will absorb more, but most of the fertilizer nutrients are best absorbed by the roots.

[Ray]

I don't disagree with you on that at all, OW. My intended point is that it's a matter of degree.

Plants grown hydroponically (i.e., with no media interaction to confound it) with individual nitrate-, ammonium-, and urea nitrogen sources in solution will show nitrogen uptake by the plant in all three cases. The rate of uptake will be slower with urea than the others.

I speculate that the basis of the difference is both mechanical and chemical - in solution, a urea molecule is large, compared to nitrate and ammonium ions, and velamen has a natural affinity to charged entities.

[ula]

Thanks, I'll concentrate on feeding the roots then .