What REALLY causes root death?

[Ross]

I think we are in agreement? My point was, that even though one often find these spp in, apparently, wet envirens, the soil is not really without air. My term "air pockets" is to try to describe small areas of air near the roots. I can think of no orchid that lives (or thrives) in the sort of environment as Drosera, for example.

[Mahon]

Originally Posted by rsfrid

I can think of no orchid that lives (or thrives) in the sort of environment as Drosera, for example.

I find Calypso bulbosa (in a high-elevation Montana bog), Calopogon tuberosus, Cleistes bifaria, Cleistes divaricata, and Habenaria repens growing near or next to Drosera sp. and Saracenia sp.... I think there are other genera of orchids, like Platanthera, Arethusa, and Cypripedium which would also be found in that same type of bog habitat.

During watering, you may be correct about the 'air-pockets'... in cultivation, the sand will drip out of the pot, creating "caves" at the bottom, and the sand will work its way down into those "caves". The water usually runs through the sand very fast, as it is silicate-rich. Those "caves" will eventually work their way up to the top of the pot, and more sand is needed. I would assume something like this happens in situ...

-Pat

[Ross]

Actually (if I am correct) Calypso, and other spp., really don't thrive on sans-water envirens, but tolerate them. The major point here (I believe) is the need or not, for oxygen near the roots. It's my belief that all plants need oxygen -- it's just that some, like cypress trees -- have adapted and developed their own way of coping. The Calypso bulbosa I am familiar with grows along the Rogue River corridor in Oregon, near the Rogue River, where it enjoys high humidity, high pH soils, and wet season/dry season regime. This is not same as S/H regime most here are talking about and not the same as low oxygen root contact regime we have discussed. FWIW, this is the best conversation or thread I have participated in, in months! Keep it coming!

[Mahon]

Originally Posted by rsfrid

Actually (if I am correct) Calypso, and other spp., really don't thrive on sans-water envirens, but tolerate them.

I am actually not to familiar with Calypso bulbosa, I have only seen it once in a water-filled bog in MT... a contact of mine who grows this species had said it grows in low pH (acidic) soils... the other species, like Habenaria repens, are rarely found anywhere else but in water or in bogs.

Anyways, yes, I do agree it is discussion about oxygen in roots, but I was pointing out the orchids in which I question how they accumulate oxygen. If Habenaria repens is fully emerged in water, are the root's systematics the same as that of another aquatic plant? I do agree that oxygen is an essential factor for the orchid roots. Also, remember at night, the plants reverse their respiratory cycle... I wonder how mycorrhizal orchid genera such as Hexalectris, Corralorhiza, and others respirate?

-Pat

[Ross]

Pat, I still think we are agreeing!?

Certain terrestial spp seem to grow well on aparantely acidic soils (like Calypso) but prefer neutral to more basic soils. Having said that, the point was water versus air. The areas I have photographed Calypso bulbosa insitu are uplands, moist, acidic to neutral soils, not wet (sans oxygen) and nowhere else.

I have not experienced bog-related orchids so do not have first-hand experience. I have first hand experience with wetland spp such as certain Cypripedium, but not "bog spp". I believe the discussion here was originally about root rot. I think this thread has drifted from that.

[Anglo]

The roots of all plants require air as well as moisture. The differences between how much air and how much moisture they need are in their specializations for life in respective environments. For example, the ideal oxygen-to-moisture ratios in the root zones of aquatic plants and desert plants are entirely different.

Epiphytic and lithophytic orchids are also highly specialized for life under specific environmental conditions. Their roots receive more complete and continuous ventilation along with continuous moisture, at least in the form of humidity. If they experience prolonged sogginess, they smother and die. If they dehydrate, they wither and die.

In its natural habitat, an orchid may not always be perfectly comfortable, but too soggy or too dry don't normally reach fatal extremes. Within the variations of its immediate environment, the orchid's roots are adaptable. Roots that grow in bark fissures or under flakes of bark or enter a pocket of humus on a tree branch adapt differently than aerial roots.

The fact that the properties and functions of an orchid's roots can adapt to the conditions they encounter makes it possible to grow orchids in various artificial conditions. Orchids can be grown in pots or baskets or they can be mounted. But they are only adaptable within the parameters of their design. Mounting them is not practical unless they can be kept in a continuously humid atmosphere. In pots, watering is a critical issue because ventilation is restricted.

The best method depends on the orchid and the greater environment in which it is grown. Pots are more suitable for some genera than others. For example, a Phalaenopsis is easier to grow in a pot than a Cattleya because Phals like a greater level of continuous moisture. Slatted baskets are better for Catts because they permit air to more freely circulate through the medium.

It is true that once an orchid root is established as either an aerial root or an in-the-medium root, it does not always adapt well to a sudden change of condtions. If it grows on its own into or out of a medium, the transition is no problem.

[Ross]

I think the thread is about how we use this info to make better growth of certain orchid spp.?

So... with that in mind, and dismissing the discussion on Calypso bulbosa, since most of us will never grow that spp., I still say that most plants have adapted to their current envirens. Now, the discussion seems to have migrated to how roots adapt. I have a problem with the concept that once a root grows aerially, it won't adapt to sub-surface. (I think that is what some folks are saying). My experience with repotting orchids says otherwise.

[Anglo]

”I have a problem with the concept that once a root grows aerially, it won't adapt to sub-surface.”

A couple of months ago, I received a large Cattleya dolosa division in the mail. The division had nothing but aerial roots, long, thick and straight. They were really long too, ranging from about 6 inches to nearly 18 inches. The seller, a professional orchid grower, recommended coiling the roots up and squeezing them into a pot while trying to avoid any more breakage than necessary.

I didn’t do that. Instead, I cut the roots short enough so that they wouldn’t quite reach the bottom of a 10-inch square wooden basket and put the division in it, using coarse fir bark as a medium. Possibly due to the excellent health and vigor of the division, the roots didn’t seem to mind a bit. Almost immediately, they began to form new tips and then kept right on growing. One of the pseudobulbs had buds on it. They continued to develop and they bloomed. By now, the roots are doing whatever suits them. Some are snaking around in the bark and a few have emerged from it. One new root is growing along the top of the medium.

In that case, the adaptation was no problem at all. It was as if the roots were just looking for something to grow into. Nevertheless, I was not confident that planting in a pot would have been successful. Curling them up and cramming them into a confined, stagnant space might have been harder on them than being cut.

The first time I repotted a Phal, I bent the aerial roots down and put them into the medium along with all the other roots. They evidently had not been wanting to grow into anything because they died soon after that. So it looks like sometimes it works and sometimes it doesn’t. Some of the determining factors may be genus, age of the roots, the function of the roots as determined by the plant, or how the transition is handled. In general, roots anchor the plant and search for sources of water and nutrients, but maybe the primary purpose of some roots is just to breathe.

BTW Ross, I checked out your web site and AGPix Listing. You have a fascinating vocation!

[Ross]

Thanks. I think I agree with all the stuff you post here? First, I have had the same reaction with my Phals as you observed (when I fit the roots into a pot), but in time they seemed to take off. Who knows? Also I have, in the past, cut off roots to have them take off on their own. I really am not sure where this is going, other than there is something here more complex than originally proposed!

[ospylac]

How the roots behave has a lot to do with the orchid in question. Root death or survival depends on multiple variables including: Where is the plant in its growth cycle, how healthy is it and what type of orchid is it? My experience is that Cattleyas do recover and adapt well to having aerial roots stuck into medium. Vandas are very resentful of the same treament, and may experience root death as a result. Hybrids recover more easily than species to less than perfect treatment.