PET Potting Method

[isurus79]

Originally Posted by Ray

A couple of comments here:

Air temperature does not necessarily translate to pot temperature, especially if they're wet and evaporative cooling can occur.

Having the pellets present doesn't mean they are still releasing fertilizer, as they don't work by slowly dissolving.

Instead, they consist of a permeable polymer pellet containing water-soluble fertilizer. Once the pellet has absorbed water, fertilizer solution starts to ooze out. The rate at which it is released is determined by the porosity of the polymer, and as the polymer has a thermal expansion coefficient, the warmer the pellet, the larger the pores and the faster the fertilizer is released. Different release rates are controlled by modifying the polymer and its thickness.

Your remaining pellets might be just plastic shells.

Yet more valuable information! I'll check the shells when I get home. However, it seems like a rapid fertilizer dump would have harmed my Cattleyas.

[Ray]

Originally Posted by isurus79

Yet more valuable information! I'll check the shells when I get home. However, it seems like a rapid fertilizer dump would have harmed my Cattleyas.

That's going to depend on what "rapid" is, isn't it?

Let's say you used an amount in a pot that would give you 50 ppm N over 9 months at a certain temperature. If your true average temperature was sufficient to double the output, the pellets would dump 100 ppm N for 4.5 months, which would not be harmful at all, but your plants would go for an equal time with no food, and you wouldn't know it.

All of the uncertainty is precisely why I don't use these things on my orchids.

• How much to I add to a pot to get my target ppm N?
• How long will it last, and at what temperature?
• What is the true temperature within each individual flower pot?
• At those temperatures, how much will it dump and for how long? (And I'd need to figure this for each and every pot, separately.)

Whereas by using my water-soluble powder, I pretty much know all of that, without being concerned about the temperature.

[isurus79]

Originally Posted by Ray

That's going to depend on what "rapid" is, isn't it?

Let's say you used an amount in a pot that would give you 50 ppm N over 9 months at a certain temperature. If your true average temperature was sufficient to double the output, the pellets would dump 100 ppm N for 4.5 months, which would not be harmful at all, but your plants would go for an equal time with no food, and you wouldn't know it.

All of the uncertainty is precisely why I don't use these things on my orchids.

• How much to I add to a pot to get my target ppm N?
• How long will it last, and at what temperature?
• What is the true temperature within each individual flower pot?
• At those temperatures, how much will it dump and for how long? (And I'd need to figure this for each and every pot, separately.)

Whereas by using my water-soluble powder, I pretty much know all of that, without being concerned about the temperature.

And yet I got the best growth from all genera this summer that I’ve had in 27 years of growing with a fraction of the effort. I’ll stick with the time release 😉😉

[Ray]

Originally Posted by isurus79

And yet I got the best growth from all genera this summer that I’ve had in 27 years of growing with a fraction of the effort. I’ll stick with the time release 😉😉

I would characterize that as "you got lucky" in your relatively blind choice of formula and amount. But could a little more or less have been better?

I know several professional growers who add a small amount of slow-release stuff, but continue feeding with water soluble powders...

[isurus79]

Originally Posted by Ray

I would characterize that as "you got lucky" in your relatively blind choice of formula and amount. But could a little more or less have been better?

I know several professional growers who add a small amount of slow-release stuff, but continue feeding with water soluble powders...

These are all good questions, which I will better answer this coming growing season.

[isurus79]

The fertilizer balls still contain fluid nearly a year later: Untitled by Stephen Van Kampen-Lewis, on Flickr

[Subrosa]

Originally Posted by isurus79

The fertilizer balls still contain fluid nearly a year later: Untitled by Stephen Van Kampen-Lewis, on Flickr

Unless they dry out completely they should still have liquid in them. What that liquid actually contains in the way of nutrients is the question.

[isurus79]

Originally Posted by Subrosa

Unless they dry out completely they should still have liquid in them. What that liquid actually contains in the way of nutrients is the question.

Dunno! I'll add more in April though.

[DirtyCoconuts]

im late to the party and i don't really have the ability to watch videos with the sound on...can you summarize the technique?

[isurus79]

Originally Posted by DirtyCoconuts

im late to the party and i don't really have the ability to watch videos with the sound on...can you summarize the technique?

Long story short, you create a pot with plastic soda bottles (or other types of bottles) and poke drainage holes a few inches off the to bottom to create a water well. Within the water well, you put inorganic media (rocks are common, I use epiweb from Ray), then add a slow rot media in the middle (I use large grade orchiata), and a few inches of long fiber spag on top. I definitely recommend watching the video. Seeing it easier to explain.

FYI- This was the first video I've ever created. I need to a new one and will probably do it this spring.