Vandas in semi-hydro?

[Tindomul]

When you say airflow, do you mean constant air movement? I'm having a hard time picturing the air stuck in between the hyrdroton as moving air. Or is it that they simply need gas next to the roots, so they get their O2 and CO2?

Originally Posted by Ray

A couple of comments.

In my opinion, growing in semi-hydro culture is not a substitute for having adequate humidity.

A semi-converse, however, does seem to hold true: If you have very low humidity, it appears easier to grow those plants that we typically think of as needing drying out in S/H culture. Maybe it's because the gradient is steeper, being dry deeper in the pot.

Actually, the more I think about it, the more I am convinced that the "need to dry out" is really a misinterpreted "need for lots of air flow".

Lots of these plants come from regions where there is a LOT of rain for certain periods of the year. During those times, the roots stay saturated literally for months at a time with no issue. (Actually it's not "no issue", it's "thrive" as that's when most of the growing occurs.) So why not in a pot? As long as the medium is sufficiently coarse to provide lots of air flow to the roots, there should be no issue.

[Ray]

I was referring to gas exchange, but if you have any air movement in the growing area, there will be some in the pots, as well.

[Tindomul]

Originally Posted by Ray

but if you have any air movement in the growing area, there will be some in the pots, as well.

Well yes, that makes sense.

[Charles]

I often try to imagine the natural growing conditions too. I use large bark chunks for moisture on my Vandas. Some roots like it and some do not. ( I secretly believe that the plants have two kinds of roots.) Those that find warm wet spots for moisture during dry periods and those that must hang in the air.

[Ray]

Originally Posted by Charles

(I secretly believe that the plants have two kinds of roots.) Those that find warm wet spots for moisture during dry periods and those that must hang in the air.

Actually, I don't believe a plant has more than one type of root, but if you want to interpret it that way, they can have any number of different kinds of roots. Here's my logic - right or wrong:

It is a well-established fact that root cells tailor themselves to the conditions in which they grow. Based upon that, it's easy to view aerial and "submedian*" roots as being "different".

However, in the case of roots that have grown down into the reservoir of a semi-hydro pot, they are now fully submerged, so are easily a third type.

Now then, think of the last time you repotted a plant that was in soppy sphagnum. The older parts of the roots may have mostly died and shriveled up, but there is fresh, new, white growth below that! Two more "types" of roots.

So basically, one might interpret a root grown under any two different conditions as different roots - and that would conceivably even apply to seasonal variations.

* Think "subsoil" or even "subterranian", but with the generalized "medium" replacing soil. If Ben Franklin could coin words, so can we all!

[Charles]

True. And why not? Orchids throw roots everywhere. Some seem to want to be in the air and others want to find dark wet places. Only the plant can decide what it needs. If you see a plant shooting out nothing but aerial roots, what message are we hearing? On the other hand, if a plant is hot and dry, it will grow into the wet areas of some medium or mounting. It's this same need that causes a root to grow away from the light.
All I am saying is that the plant will take what it needs. I agree, submerged soaking wet roots are not the desire.
I also think sphag problems are air movement issues more than moisture issues.

[Ray]

I think you may be "over-interpreting" a bit, Charles.

Plants roots growing down is not an aversion to light, it is gravitropism - an orientation based upon gravity. Moreover, that doesn't really apply that well to orchids, as in nature the roots go in every direction, and usually contain chlorophyll, suggesting they would want to see light, not avoid it.

Aerial roots don't "want" to be in the air, they are "reaching" out from the plant in order to get a better hold on the substrate for stability and to provide additional absorption routes. I have taken plants with aerial roots and moved them into significantly larger pots than one might ordinarily expect, and Lo and Behold! those aerial roots go down into the medium.

Roots serve two primary functions, water- and nutrient uptake and plant stability. Where they go is dependent on those two things only, as influenced by the environment.

Also, I think you misunderstood my comment on the submerged roots - liquid submersion is not undesirable at all - IF the roots grew there. Submerging roots that grew in another environment and then you've got troubles.

[adriponic]

good point ray

I have 2 equitant oncidiums (William Thurston) in sh.
One in a 10cm deep pot and the other in a 17cm deep pot.
Both set from flask to cp then to above pots at the same time and same size Obviously the one in the 17cm pot is
doing better after 5 months... about twice the size.

BTW 15 others were mounted on fir bark and cork and
none of these show better growth than even the 10cm
pot. I agree though that these mounted chids get watered and fertilized about 2 times weekly at best.

[grayowl]

I have been growing a mokara hybrid for several years in a mix of leca and perlite, and water once a week or less top down, in a standard container. Sitting in a moist environent(semi-hydro) they rot quickly. They need a lot of oxygen exchange or air movement at the root zone.

Highly recommend "The world of orchids" by Jack Ross about his extensive research into hydroponic culture.

[Charles]

I have had vandas and others growing in a western window and almost entirely without fail, the roots are looking to grow away from the light. Also grown slightly on the dry side as the A/C is usually on so humidity is low. It would seem that the plant is looking for a shady wet place to draw moisture.
I agree. Roots that are started in a certain environment will prefer to continue in that environment. My point is that giving the plant a choice between dry conditions and wet conditions and letting it use what it needs of each is ideal.
I think you have misinterpreted my point. I agree with you and I am also pointing out that reacting to heat and dry may cause roots to seek moist shade.