Sphagnum - Loose or Packed Tight?

[Ray]

Whenever I use sphagnum alone as a medium, I tend to keep it a bit loose in the pot - packed enough to support the plant, but not tightly compressed like we see from large nurseries.

I have never understood the "physics" or "mechanics", or whatever you want to call it, of tightly packed sphagnum. (Those of you who know me well must understand my consternation at that!). When saturated, there is absolutely NO free air space in the pot, so it seems to be a great way to kill roots, yet the plants I acquire that's are potted that way seem fine. Is is due to the growing conditions they were in? I suppose that's it, as those plants do not remain "fine" if I don't repot them.

What is it that makes it "good" for some?

I have heard some speculate that the highly-compressed moss simply cannot hold much water, so between plant absorption and evaporation, dries out quickly, but if that's the case, what must the growing conditions be to result in that fast drying. It sure doesn't happen out on my deck.

[WaterWitchin]

Good question. I've always wondered that myself. Especially wondered how the grower got the moss so tightly packed in there to begin with. Maybe just barely had roots going to start with that grew down in?

In my care, with one packed in moss, the plant does "okay." But when I repot, the roots at outside may look great but the middle is usually rotted roots and barely surviving roots. I always thought that was because of lack of air flow. But if, as Ray says, speculation says the tightly packed moss quickly dries, it may be the individual's culture... if I have something in moss, I soak the heck out of it each time I water, then wait until pot is light before resoaking. Sometimes two or so weeks plus before resoaking. Perhaps that's where my rotten middle of pot roots is initiated.

[Paul]

I have grown a number of plants in pure sphag -- including phals and catts. In all but one case, I leave the sphag only lightly pressed into the pot. ( I will note, I never tightly pack down my media ... even with bark/coco chunks.)

I firmly believe, though have never tested my theory, that the tightly packed sphag is a leading cause in root (and consequently plant) death. As has been mentioned, often the roots in the center of a tight sphag ball are dead. Likely due to lack of air. instead the living roots tend to all be along the inner side of the pot or just beneath the sphag.

How do the professional growers do it? My guess is that it comes down to their growing conditions and culture. Most sprinkler/spray systems do not drench the plants. Instead, the short duration sprays likely just moisten the media -- particularly when it is densely packed. In addition, greenhouses generally have very good air circulation which most certainly helps.

The one and only time I had a plant in tightly packed sphag was when some friends had bought a cheap one in bloom from Costco. After it was done blooming they gave it to me. When I went to unpot it, the entire plant with its pot shaped mass of sphag came right out of the pot. Since it was not a plant I cared much about (standard white phal) I decided to experiment for kicks. I did not free it from the moss block. Nor did I return it to the pot. Instead, I set it on a large pot saucer. When I watered, I just poured some water over it. Most of the water ran off the sphag and into the saucer. I let it sit in that run off, absorbing the water that was there. There was not enough water for the sphag to get fully saturated. The plant did just fine. After about a yr, I donated it to an orchid society -- still growing as an unpotted plant in a sphag block.

[SaraJean]

Unpopular opinion: I love sphagnum moss for Cattleyas. There I said it.

Confession #2: I do pack it pretty firm.

Confession #3: It rarely gets a chance to dry out in my rainy summers.

Now for the context. Sorry, this is going to be long winded.
This all started when I was talking to Dr. Courtney Hackney when he came to speak at my orchid society. I had some questions about the Rupicolous Laelias and some mini Catts. I was struggling with them and he mentioned trying sphagnum with some reasons behind it. I looked up an article from the St. Augustine Orchid Society, read about it some more, and gave it a whirl.

If the sphag is in a basket or a very shallow pot I usually don’t pack it. I do not use sphag on any of my blooming size, or near blooming size, standard Catts (that are not recent divisions). I also do not use sphag in plastic pots.

I do use it packed pretty darn firmly, it’s definitely compressed, for many of my orchids- My few potted Phals, some of my Sarcochilus, rupicolous Laelias, my two mini Catts, and basically anything else that is in a 3” clay pot or smaller, though I am still using sphag from some orchids in larger pots. I love it for getting my divisions started. I like using for the usual suspects like Bulbos and Catasetums, but those are moisture lovers anyways.

I’ve tried it a few ways and they all seem to work. One is wrapping the entire root ball in sphag, I wrap it till it’s larger than the pot size and then “gently” cram it in the pot. Or I collar it by wrapping the strands of sphag around only the top half of the root system till it’s bigger that the pot opening and cram that in as well. For my Phals that are in larger cylinder shaped pots, I stuff some peanuts in the center of the roots, wrap sphag around the roots and stuff that in the pot...

None of this sounds very gentle, but it has been working great. I do make sure to wrap the moss, like you would if you’re wrapping a Neofinetia, and not just stuff wads of moss in the pot with my fingers. The moss is not rock hard once I get it in the pot, but it is definitely very firm. It holds the orchids upright and if the pots are smaller (I.e. lighter), I can lift the whole thing by the base of the plant. All of my things get watered every day in the summer. Sometimes all day, for several days, with our rain. I will try to remember to take some photos of the root systems next spring (and when I start repotting my Sarcs this fall) and post some pics. These have had some awesome looking root systems with no signs of rot.

This is speculation, but the only reasons I can think this works in my environment are: It’s hot. Very hot. Day and night. Most of my orchid get pretty annoyed at me if they get dry in 100° heat, even with the high humidity. Moss keeps things pretty hydrated. With the moss being constantly damp throughout the summer, that makes the clay pot wet, the wet clay pot keeps the roots slightly cooler, the Catts and Sarcochilus seem to especially appreciate that. Clay pots are breathable, I figure that can help keep things from getting too soggy by wicking some moisture out. That’s why I don’t use plastic. My stuff gets watered way too frequently for that.


Supposedly, the fibers of the moss are better supported when used more tightly. Too lose and the fibers can hold too much water and collapse on themselves. I’ve seen this in my baskets where I have used sphagnum moss loosely; it breaks down quick, turns into slim, some moss falls apart and the rest of the fibers can actually become a sludge brick if I wait too long to replace and refresh it. When I repot my firmly packed pots, the very top part of the moss has some algae on it, but otherwise the integrity of the rest of the moss throughout the rest of the pot is great. Even if I wait a more than a year to repot. I also soak my pots first for a good hour or two before repotting. Again, the very surface of the moss is pretty wet, the rest of the moss is damp like it would be if you soaked some moss and then wrung it out.




I apologize for the long post and a summary is: These are just my observations. I like using it packed tightly in clay pots, where it doesn’t seem to hold too much water, and remains just airy enough to not rot the roots. here is that article I mentioned for anyone who hasn’t read it https://staugorchidsociety.org/PDF/S...ySueBottom.pdf

[SouthPark]

Originally Posted by Ray

I have never understood the "physics" or "mechanics", or whatever you want to call it, of tightly packed sphagnum. (Those of you who know me well must understand my consternation at that!).

Absolutely. It is interesting that some situations appear very counter intuitive. I often wondered about that too in the past. I recall once reading somewhere - that the firmly packed spaghnum itself can behave on-the-whole a big wick.

If air-circulation is very good, then the water in the tightly packed spaghnum can disperse - wicked around through the mass. And if air circulation is good around the plant and also through maybe many big holes in the pot at the bottom, then a slow flow or movement of water and air etc can be maintained.

The grower must provide a suitable amount of water during the watering, and must have a suitable frequency of watering. They have to sort this out, or work it out for themselves under their own growing conditions. Too much water will definitely lead to saturation, and undesirable things that follow from that.

Too little water, and the water might not get down into the depths (middle and lower part) of the pot.

Catasetum nursery growers use this tight spaghnum method. Some do it for Cattleya - seedlings and all.

The tightly packed spaghnum 'system' is a system. How it all works and how it is controlled is often up to the grower. If the spaghnum is primed (pre-wetted), then one way to keep this system under control is to periodically add maybe suitable amount of water, to keep the system moist. Good air circulation is beneficial as always. An important thing is to know roughly what might be going on inside at the different layers or levels of the pot. This applies to any kind of growing media.

For myself, I've only recently begun to grow catasetum in scoria - 5 mm average diameter scoria. I haven't grown for long enough yet in this media. My current method with my catasetum is fairly tightly packed scoria, with big scoria rocks piled below the spaghnum mass, and around the sides of the spaghnum mass - all in a pot. So the spaghnum is surrounded by scoria. I don't know if it's necessary to do this, but the catasetum type plants have no problem with it.

I just prefer inorganic - scoria.

[Orchidking]

It does seem to serve a purpose for the shops. Basically with the spagnum packed tight the roots won't dry up. They won't be getting much light, won' be growing much and thus won't be breathing much either.
They are not like animals although even some animals don't need much air either so not much air is needed when the plants are in shop "stasis".
Once the roots are packed that tight the spagnum cannot be wetted - pretty much guaranteed root rot every time.

But without the shop having to worry about watering, the plants will survive for a month without any care and attention so it's beneficial for the shop - not the customer.

Quite important to know this when giving out advice about spagnum which is not a great medium for uk growers anyway

[Clawhammer]

I always just figured the moss became more tightly packed when new root growth compressed the sphagnum. I also figured that roots growing into sphagnum were adapted for that medium and that growers allow the sphagnum to dry between waterings; that the water retentive nature of sphagnum was financially beneficial to growers. The biggest root rot issue I see with sphagnum is when there is a original sphagnum core that was never removed and filled in with bark or less water retentive medium. In this case the core never dries out and rots the roots at the base of the plant.

[Dollythehun]

Interesting post, all. I follow a method similar to SaraJean. My phals, Oncidiums, and zygos are in a moss mix, some in pure moss. Always in clay pots. My theory is that the clay breathes, so the roots get more air. I have a ceiling fan running, so air circulation is good, I often have to water every two days. As Ray has previously mentioned, I will fill the saucer and let the plant suck up the water. More often, though, I water from the top as the moss approaches dryness. I do not pack it in when repotting but, I do press it in firmly. When it's cold, I run the phals drier. I have never had root rot and some of these plants are very old.

[SouthPark]

Originally Posted by Clawhammer

IThe biggest root rot issue I see with sphagnum is when there is a original sphagnum core that was never removed and filled in with bark or less water retentive medium.

Another scenario is change of hands - from one grower to the next. The grower with their new plant - especially a beginner - might not know the details or watering schedule or amount. Or not know how to make the necessary adjustments or tweaks in the new growing conditions. Such as popping in too much water, and drenching the media (without knowing what's happening under the bonnet - aka hood).

[KC Kam]

I have such doubt regarding the topic of this discussion too. Hopefully what i get to know can help out at least a little here.

When i repot, i consulted one of the local nursery here. He says tight moss will help to make sure the water in the moss is distributed evenly within the pot due to the nature of the moss that wicks water. Which will assist in judging when to water.

Loosely pack moss will have issues where the top layer of moss is dried and crispy but the lower moss are still moist. This might leads to root rot if the grower mistakenly continuously water it based on the dryness of top moss.

Therefore finding the balance or correctly compact is important.