Reverse PET culture for Catasetums

[Lars Kurth]

A while back kavanaru on this forum mentioned PET culture, which is basically an SH method adapted specifically for Catasetums. The basic principle is to use growing containers with a water reservoir at the bottom (using a coarse anorganic substrate, such as crushed brick or pots), an insulation layer (such that the actual substrate doesn't get in direct contact with the water reservoir - in PET they use cork or palm nut) and on top the actual substrate. This method works perfect during the growth period of Catasetums.

That got me thinking. My biggest problem is always to find the right time to decide when to start watering. The common advice is not to water until the new growing shoot is a few inches tall and the roots are an inch long. Part of the problem is that I can't see into the pots and judge when the roots have reached the right length.

Another problem with the PET culture is that one needs special containers with an inch of water reservoir at the bottom. Which is a little impractical.

This brought me to the idea to reverse the PET culture. The basic idea is to layer the substrate in the following way:

• Instead of having a water reservoir at the bottom, the idea is to use substrate that stays wet for long. For example rockwool cubes or sponge.
• Then one would add a layer of insulant, such as epiweb, cork, etc.
• The actual substrate would follow, e.g. CHC
• The central idea is to use a fast draining substrate such as Hydroleca in the top inch of the pot, or maybe better pumice as heavier. However, this may even work with spaghnum.

This would mean that in spring, one could dip the pots into water occasionally: only enough to wet the bottom layer. The effect would be that the the bottom layer of the sandwich contains some moisture. The insulation would ensure that moisture largely stays there. Through evaporation the substrate above would absorbe some moisture, but that would be minimal. The top layer would be pretty much bone dry. The moisture at the bottom should encourage roots to grow down quickly and accelerate the growth cycle. But roots would never get water until they are long enough (and the plant is ready).

In the summer one would water from the top. The moisture retaining lower layer of rockwool or sponge would act similarly to the water reservoir in PET culture.

I am wondering whether anybody has experimented with similar ideas, or whether long-time Catasetum growers think this would work.

Regards
Lars

[Brooke]

I guess my method is similar to what you are thinking. I use net pots with sphag/tree fern and during the growing season I sit them in a tray of water to keep them very wet.

When fall comes around I take them out of the water and water manually. As the leaves start to yellow I reduce the watering even more.

I already have one Morm x Cyc cross with a growth several inches so I am now watering it manually with some fertilizer twice a week. As the growth matures more I will sit it back in the water.

Using the net pot lets me see the massive roots encircling the net pot and also the ones growing into the water.

When I can't see the roots I judge by the length of the new growth.

Brooke

[Lars Kurth]

@Brooke: maybe worth giving the method a try.

When I can't see the roots I judge by the length of the new growth.

That is something I never quite get right. I suppose it depends on the plants also. I guess, the taller ones (Cycnodes & Mormodes & vigourous Catasetums) would need to be judged differently from Clowesia and some of the smaller bulbed plants.

[isurus79]

Originally Posted by Lars Kurth

That is something I never quite get right. I suppose it depends on the plants also. I guess, the taller ones (Cycnodes & Mormodes & vigourous Catasetums) would need to be judged differently from Clowesia and some of the smaller bulbed plants.

Honestly, it doesn't have to be exactly 3". I used to just time it by saying that I will start watering about 2 weeks after I can no longer see the green part of the roots that have dug into the media. Always worked well for me.

[Oscarman]

Interesting info. This is a group of orchids i am just getting into, so I appreciate the insight into their culture.