Oncidium / miltassia moisture requirements

[Mo Boggie]

Hi, I need some advice on which orchid media would satisfy oncidium/ miltassia needs. I'm guilty of multiple counts of overwatering , and I'm hesitant to use sphagnum moss ( which takes a long time to dry.) I live in nyc; my orchids are in a small 5 foot portable greenhouse, with a small fan and a humidifier.Help please! I just can't crack the orchid watering code thanks

[estación seca]

They need constant moisture. With inadequate moisture the new growth develops pleats, and then the plant might dry up and die. They are tough, though, and if you resume proper watering, they usually survive and grow. They will only make new roots from new growth.

Sphagnum works fine for Oncidiums and kin, if it doesn't stay soggy wet. You don't need to soak the sphagnum when you water. Run some water over just the top of the moss. It will distribute through the moss and be just moist. Water again before it becomes crisp.

If you use bark, be sure the roots don't dry out completely. Many Oncidiums are sold in 3.5" / 8cm pots in large bark. You can water Oncidiums in this every day. Some people here have written they must stand their Oncidiums in large bark in dishes of water during the growing season, or the new growth pleats.

[Ray]

Change your focus slightly... Instead of figuring out "what holds moisture", consider "what allows lots of air flow around the roots, while maintaining moisture".

[rbarata]

I think a good mix, that allows water retention and air flow, would be bark (size of it depends on plant/pot size and coconut crisps with a ratio of 1/2.
You can also use sphagnum with bark but I would change its ratio in the mixture to something between 1/3 and less than 1/2 to assure a good air flow.
With this mixture you need to water a little bit more, depending on your relative humidity/temp but it's better to water more then too much.

[MrHappyRotter]

Oncidiums are incredibly variable in their care requirements and needs. There are species and hybrids that need to dry out thoroughly before you water again, some that need a dry winter rest, others that need even moisture year round, and some that like almost as much water as you can give them for all or part of the year. Not only that, but the ideal frequency of watering is also determined by the size of the plant and the size of the pot or potting situation. I guess what I'm getting at is, without any information about what kind of Oncidium(s) we're talking about, we're all giving you very generalized advice that's guesswork because we don't actually know what you're growing. That's especially true since "Oncidium" is often used in an ambiguous fashion to mean "anything in the Oncidium alliance including the dozen(s) of related genera and intergeneric hybrids".

For the Miltonia, I'd say that's a little more straight forward, but it would still be nice to have some photos or more exact ID if possible. I'd also prefer if you could clarify whether you're referencing Miltonia or Miltoniopsis, as those are very commonly confused genera. For either of those genera, if all other growing conditions are good, for instance the plants are getting an appropriate amount of light, good temperatures, and decent air flow, over watering shouldn't be too big of an issue since the bulk of Miltonias and Miltoniopsis require consistent moisture. For these, sphagnum moss is acceptable for smaller plants, and for larger plants, a typical bark based mix should suffice.

If you're over watering a Miltonia or Miltoniopis, to me that's a signal that you've got bigger problems to address. That's not meant to be critical of you or your care, just an observation that might help guide the advice we give. As an example, during the warm growing season, I find that some of my Miltonias do better if I let them stand in a small amount of water almost the same manner that I grow my Phrags. So that suggests to me that over watering might not be your problem or if it is, then it's the fact that other growing conditions need attention and it may be worthwhile to address those instead of focusing on the watering part.

So, consider whether you need to increase the amount of light your plants are getting. Consider increasing the air flow with a higher fan setting or more ventilation. Think about whether you need to keep your plants warmer or cooler for part or all of the year. Also, try to figure out what kind of plants you've got so you know whether the issue isn't over watering in general, but perhaps it's simply watering when the plants should be getting a dry rest. If you're assuming that over watering is the problem because your plants' roots are dying, there could be other causes too, such as poor quality water or feeding too heavily.

As for potting mixes, the general rule of thumb is that plants with thin roots need more moisture and smaller sized bits of media. Plants with thicker roots need a more thorough and rapid wet-dry cycle, which is usually easier to achieve with a chunky mix. If over watering is a problem for you, then it is especially crucial that you do not over pot your plants (i.e. put them in a pot that's too large), and keep them in as small a pot as possible -- one that just barely fits the size of the root mass. If they have no roots, you can use the psuedobulbs as a guide, and use a pot just barely big enough to contain those. If you have a rambling plant like a Miltonia, then it may be helpful to switch to a shallow bulb pot or even basket culture.

If your problems persist, you may want to consider some alternative growing methods. Mounting your plants may be an option. Growing them semi-hydroponically may be an option.