Why new leaves v. new air roots?

[Newby phal grower]

Just curious - one of my phals is putting out a lot of new air roots, while another, about the same size, has only put out one new air root recently and is starting a new leaf.

[jkofferdahl]

Just curious - is there a question in there?

Your Phals are not doing anything out of the ordinary.

[Newby phal grower]

Is there an answer here? Was curious as to what stages of growth the different productions represent.

[estación seca]

Welcome to the Orchid Board!

Plants decide what to make next based on what they think they need. The plant making roots thinks it needs to take in more water. The other plant thinks it is fine in that department, so it is making a new leaf to make more food.

[Newby phal grower]

Thanks, estación. I understand needing more water, but not sure what it means for plant to need to "make more food." Can you please explain how the new leaf will allow it to make more food.

[estación seca]

Good question.

The green pigment in plants (called chlorophyll) captures the energy in sunlight. The plant uses that captured energy to convert carbon dioxide it takes in from the air into sugar in the plant tissues. The plant uses the sugar to make new plant parts, including stems, leaves, roots and flowers.

The plant needs to make a fair amount of sugar to use to make flowers, so the more leaves a plant has, the more flowers it can make. Plants try to keep growing to make as much leaf surface as they can, so they can make as many flowers as possible, in order to have the best chance to make seeds and reproduce themselves.

[Newby phal grower]

Good answer! Watching my phals grow is fascinating - thank you for helping me understand their behaviors a bit better!

[Ray]

Another thing that can affect a plant's "decision" is its mechanical stability.

Based upon my observations, I have concluded that aerial roots - at least in part - function as "guy wires" to provide mechanical stability to an otherwise wobbly plant.

That's a lot of mass above a small base in a phal, and if it was unprotected, those big leaves would serve well as "sails" in the wind, potentially tearing the plant off its base. By grabbing hold of some structure from a bit higher in the plant, it is now better braced against that.

One of the things that make me think that way is that phals in smaller pots tend to put out more aerial roots than do those in bigger pots (relative to the pant size). I went so far that I put plants into pots having a diameter equal to-, or greater that the leaf span. Those sank all their roots into the medium.

NOTE: I only did that with plants in S/H culture, in which the LECA medium wicked moisture uniformly throuout the pot. With organic media, you end up with a soppy, root-suffocating mess right in the middle of the pot and root mass.