Watering Schedule for Phalaenopsis

[labyrinth1959]

I have a Phal that I repotted from a 4" to 5.5" clear slotted plastic pot 6 weeks ago. I used a mixture of large and very fine bark. It was severely root bound. I left all the roots intact because none were rotten, they looked great. I use bamboo skewers to decide when to water. I have two skewers in this pot, one near the outside and one in the center of the pot. The one in the center remains damp for up to 2-3 weeks. I don't water at all until both are dry.

this is my question. Assuming a humidity of about 40% and room temperature of about 68°F. How long can I safely go without watering. This is a large plant with 6 leaves, the last 3 are almost a foot long.

[rbarata]

Assuming a humidity of about 40% and room temperature of about 68°F. How long can I safely go without watering.

I would do it once a week. The best is to watch the leaves for wrinkles. When you start to see them, you'll know it's time to water it.

[Orchid Whisperer]

Unless you are seeing signs of ill health, I would keep trusting the skewers. I would water when skewers are not quite totally dry.

BTW, for most Phals, "severely root bound" is a good thing. My best blooming white Phalaenopsis has been root bound in a 4-inch clay pot for 3 or 4 years.

[estación seca]

Very fine bark mixed with large bark will greatly slow down the rate at which water evaporates. The fine bark will occupy the spaces between the large bark. It will be almost be as though you planted in fine bark without any large bark.

At 68F it's not using a lot of water. I would not be surprised if it takes more than 2-3 weeks to dry out.

When your central skewer shows there is still water at the roots it's not thirsty. I would just keep an eye on it and take note when it starts to wrinkle. Keep checking the skewers. You will learn how long it takes.

Even if it gets a few wrinkles, those will disappear after the plant takes up some water. This will not set it back at all, and you will have learned a lot about the plant's water needs.

[Orchid Whisperer]

e.s., you are 100% right about mixing the fine and coarse bark. It greatly reduces the porosity, which reduces drainage.

[estación seca]

The same thing happens in any mixture of particles. The smallest component dictates how rapidly (or slowly) things drain and dry out. Another example is when people add sand to soil mixtures thinking they are "improving drainage." Most of the time they are making their mix stay wet even longer. The reason the great English gardeners of the 19th Century used sand beds for rooting was it stays moist much longer than other media, which is more conducive to rooting many cuttings.

Faster-draining and higher-air-proportion mixes have fewer particle sizes in the mix, or the smallest particle permits gaps between any of the particles larger than the distance water can stretch from particle to particle.

[Orchid Whisperer]

e.s., so I'm guessing you are an engineer, soil scientist, or geologist?

[estación seca]

No, but I pay attention. I've been to a number of lectures over the years given by all the above.

I have been growing succulents for a very long time. Planting medium composition is a hot topic on that planet, too.

[Ray]

That's straight out of my talk on semi-hydroponics!

When we water, the liquid has three "destinations" - most pours right through, some is absorbed by the potting medium particles and the plant, and the rest is held in place between particles by surface tension.

If the voids between the particles are small, surface tension can hold enough water to completely fill them, which cuts off air flow to the roots, ultimately suffocating and killing them.

I believe that is the incorrectly-concluded source of the adage that "orchids have to dry out between waterings". If you have a crappy medium that suffocates the roots when saturated, then letting it dry out allows those voids to reopen, which permits the roots to "breathe" again.

If, on the other hand, you have a potting medium that stays open, there is no such thing as too much water.

---------- Post added at 07:51 AM ---------- Previous post was at 07:29 AM ----------

A couple of graphic examples. In the image on the left, the voids are small enough for surface tension to be very effective at blocking airflow. That can happen in too fine of a medium, one having a wide range of particle sizes, or one that has become too compressed courtesy of a lot of overhead watering (think sphagnum) or has begun to decompose and break down.

[NYCorchidman]

As has been already mentioned, you have been growing your phal very well, so keep doing what you have been doing.

I also agree that with that size of pot with fine bark mixed in, once a week watering might be a bit "dangerous". I would leave a bit more interval between watering until the temperature rises and the plant actively grows, but you know your conditions the best, so you have to be your own judge.

Good luck!