Fir bark uneven moisture level

[MrHungx]

I grow my cattleya alliance orchids in plastic pots with medium grade for bark with a top dressing of sphagnum moss. I water my cattleyas in the morning and the sphagnum moss is dry by evening. I find that the top half of the medium in the pot is usually bone dry and the bottom half is very moist. As such, I tend to underwater out of fear of rotting the roots. However, the new growths tend to be smaller and not as developed as the older pseudobulbs. How can I make the medium dry out more evenly? I'm considering switching to a sphagnum moss/bark mixture as this currently works well with my other orchids.

[Ray]

1) Moisture does not cause root loss. Excessive water, coupled with too fine of a mix - whether selected, or arrived-at due to decomposition - traps water in the spaces between the particles, and suffocates the roots, so they die.

Use a coarser mix and water the hell out of it. Once the plants have grown roots accustomed to that, they'll thrive.

2) Smaller subsequent growths suggests that the plant is not getting a lot of what it needs. Water is certainly part of that, but so is nutrition, light , temperatures, etc. Without knowing more about the specific plants and how you're treating them, it'll be hard to come up with meaningful suggestions.

[MrHungx]

Originally Posted by Ray

1) Moisture does not cause root loss. Excessive water, coupled with too fine of a mix - whether selected, or arrived-at due to decomposition - traps water in the spaces between the particles, and suffocates the roots, so they die.

Use a coarser mix and water the hell out of it. Once the plants have grown roots accustomed to that, they'll thrive.

2) Smaller subsequent growths suggests that the plant is not getting a lot of what it needs. Water is certainly part of that, but so is nutrition, light , temperatures, etc. Without knowing more about the specific plants and how you're treating them, it'll be hard to come up with meaningful suggestions.

I realize moisture doesn't cause root loss. It's because the bottom half of the medium is constantly moist so I tend to avoid frequent waterings. As such, I tend to underwater. I think the problem is that I use too coarse of a medium as the top half dries out so quickly.

My temperature is constantly above 70F, which is not exactly ideal for flowering, but should be sufficient for growth. I grow under lights and the leaves are a light green color, so I know that's not a problem. Thus the only concern that I have right now is watering. Some of my other orchids potted in smaller 3 inch pots in a sphagnum moss/bark mixture require watering twice a week, so I suspect my cattleyas potted in 6+ inch pots are under watered.

[silken]

I know your conditions are likely different than mine. But I think by putting moss on top, you may be preventing the bottom from getting enough air to dry out quickly. For my cats I use only med fir bark in clear pots with good holes. The top does get dry, but if the pot is the right size for the amount of roots, the bottom won't be real long getting dry. I use bamboo kebabs and I don't water until it is mostly dry when I pull it out to test. That is usually around once a week. In the heat of summer it is more like 5 days. I do like to use seaweed which really promotes root growth too.

[ALToronto]

LAVA ROCK.

Catts love it, and you can water every day. Touching rocks wick and disperse moisture, so you won't end up with too much moisture at the bottom of the pot. Top dress with sphagnum only if you want to be able to skip a day.

[Leafmite]

Lava rock/LECA and basket pots! That is how I grow nearly all of my orchids and I never need to worry about uneven drying or buying replacement medium.
I tried growing some Cattleyas one year in bark (I was already using lava rock for a noID den and the first Cattleyas but everyone kept telling me that I had to use bark) and I discovered what you are seeing. Even though most orchid growers do very well with bark, it just did not work in my conditions. I will stay with either LECA or red lava rock when my orchids are not mounted.

[bil]

Like Ray says, it's the lack of air that causes the problem. Mine are in an open fir bark mix and I drill a line of 1 cm diam holes round the side of the pot with a hot rod.

In future tho, my fat root epiphytes will be going into very shallow trays so as to ensure that the air can't be kept away from the roots.

I think that sphagnum and fat roots is a very dangerous combination, and the more sphag, the greater the risk.

[Leafmite]

Bark tends to compact as it gets older. The wetter it stays, the faster it decays and, thus, the more quickly it becomes compact. I really don't like the stuff for that reason.
Sphagnum moss has its place. It is great for very young seedlings when a shallow layer is spread in a tray or Vanda basket as it does help to stimulate root growth. For seedling orchids that I think will need adjusting to the LECA or red lava rock, I put sphagnum moss around the roots and set the little orchid on top of the other medium in the pot. When the roots have grown into the LECA or lava rock, I remove the moss. It is the only thing that works with my Angraecum leonis (it is in a tiny basket).
However, it is not something I use otherwise.

[bil]

Originally Posted by Leafmite

Bark tends to compact as it gets older. The wetter it stays, the faster it decays and, thus, the more quickly it becomes compact. I really don't like the stuff for that reason.
Sphagnum moss has its place. It is great for very young seedlings when a shallow layer is spread in a tray or Vanda basket as it does help to stimulate root growth. For seedling orchids that I think will need adjusting to the LECA or red lava rock, I put sphagnum moss around the roots and set the little orchid on top of the other medium in the pot. When the roots have grown into the LECA or lava rock, I remove the moss. It is the only thing that works with my Angraecum leonis (it is in a tiny basket).
However, it is not something I use otherwise.

I'm not saying that moss doesn't have its place, just that I don't see it as helpful when it comes to adult fat root epipiphytes, that are evolved to be 'mounted' with all their roots exposed. OK we pot them for our convenience, but the further away from the naked root system that we go, the more likely we are to have problems.

[Leafmite]

I agree with you.