orchid roots

[bobc]

I was re-reading previous posts on Renanthera and the discussion wandered into watering aerial roots. Several people mentioned roots turning green. I have noticed that some of my plant's roots turn green instantly and others take a much longer time. Some do not turn green at all. Neostylis, Christieara and Phalaenopsis are in the former group. As soon as water hits them the roots begin to darken. Dendrobium biggibum, Sophronitis cernua and Laeliocattleya Little Stars only get some green patches ( at best), even after fifteen or twenty minutes in a bucket of water. They all look fine, making new growth and flowering regularly. I'm wondering if because of the low relative humidity in my conditions, the velamen on certain plants becomes less permeable, protecting against water loss? With the consequence of making it harder to absorb water? Neostylis, Lc and the Phals are potted in bark, while Den. and Soph. are on bark mounts with a wee bit of sphagnum moss. The Christieare is in a basket with several large chunks of bark. I'm wondering if those of you with greenhouses also observe this phenomenom? What about Those of you who grow outside all year? ( I'm not angry because you can - I'm angry because I can't! --- LOL) Thanks for letting me share! Bob Campoli - Philadelphia, Pa - growing plants on a windowsill.

[Ray B]

An interesting question, Bob.

I see something similar, and I grow in a greenhouse, so the humidity is usually quite good. I have always chalked it up to individuals, rather than type of plant, but maybe I just didn't catch the connection.

The velamen is supposed to capture water, and I had never heard of the "prevent moisture loss" concept applied to it.

Might it have something to do with age, or maybe what the conditions were like when the roots grew? The concept there is that maybe - if the plant was watered well during the time of the growth of those specific roots - the velamen was not a crucial part of the uptake mechanism, so didn't develop to absorb as readily as that that grew under drier conditions.

[Kye]

I always found that a few of my Aussie native dens have a very interesting velamen in that they turn splotchy when wet. They appear as mostly white, but have a few green spots.

Kye.

[Diana Kulaga]

Good topic for discussion. I find that among groups of our plants the degree of "greenness" varies. Some of the Phals, notably the ones with thinner roots, green up immediately. But we have some that have much thicker roots, and in order to get them green it takes a good deal more water. I have made the assumption (yes, I know, that's dangerous) that the dark green roots cannot absorb much more. So far, the growth rates in both types are similar.

Bob, with regard to your biggibum, the roots on our superbums green only at the tips. The same goes for reed stem Epis. And the variation in "greening" in our Vandaceous plants is enormous.

We grow outside under screen.

Diana

[bobc]

Hi Ray! I don't know if it's due to age or not. I've always noticed the way my plants roots responded to the application of water, but never questioned it before. I'm going to try and pay closer attention for the next few weeks to see how the various roots on each plant responds. I did notice last night, watering the Den biggibum, that the oldest part of the root darkened rather quickly. And the closer to the growing tip, the whiter the velamen. I'm going to see if that holds true for the other plants as well. Another interesting thing I noticed is the growing tip of the root on the Christieara is reddish ... I believe most, if not all the other plant's root tips are green. Bob

[bobc]

Hi Diana, So apparently this greening isn't due to the low relative humidity in my house. You're in Florida, I believe and Ray has a greenhouse, and you both have noticed the same thing. As does Kye. My general assumption was that velamen, functioning to absorb water, would be very quick to grab it as available. And the green color was due to the chlorophyll in the roots becoming visible. I guessed my relatively dry atmosphere caused the velamen to thicken (maybe), and the root would become green quickly to maximize water intake. Even perhaps going so far as to perhaps develop a one way mechanism - quick on the uptake, slow to evaporate. As opposed to a high RH situation where the velamen didn't have to work so hard. There being plenty of moisture in the air. ( I kind of expected that in a high RH situation orchid roots would be green most or all of the time. There would be no real change of color). When I started to pay attention, however, I didn't see the quick greening of roots like I expected. At least not on every exposed root. Encyclia tampensis is another one in that the greening is so faint that unless I look closely, it appears white. And that has lots of exposed roots. The bigibbum that I thought stayed white really has some very faint green after watering. Well got to go ... my daughter needs the computer for school. Have a great day! Bob Campoli