PERLITE

[Bluey]

Thanks to everyone who replied to my first post. I received a diverse response, typifying the different areas where our orchids are grown.
So i thought i'd try this week another thing which i am finding confusing. PERLITE.
Most, but not all growers, recommend the use of it, or peanuts, or something similar. Some say it MUSTgo into the very bottom of the pot, some say the very top. Others say it should be mixed up with the medium.
Is there a right answer? Also, if its function is to retain moisture, isn't that running counter to the advice of using a free draining orchid mixture? Should we be clogging up the mixture around the roots and maybe rotting them?
Hey, I'm new. Maybe i have the kangaroo by the tail. Inform me. Please.
Bluey!

[Zoi2]

I don't quite understand using it on top of the medium. I think most use perlite more for aeration than water retention.
Joann

[Bluey]

Thanks Joann.

[stonedragonfarms]

I agree with Joann on this one, though I have heard anecdotally that a layer of perlite on top of the pot dissuades slugs and their ilk from venturing into the media (supposedly the sharp/rough texture is vexing to them, but I don't know that there's any proof of this, and if the perlite was the fine grade stuff, it would probably either wash out of the pot or float away when watering...)
I generally mix perlite into my mix to aid in aeration and to keep the mix light and less likely to compact.
Keep the questions coming, and we'll try to keep the answers rolling,
Adam

[WhiteRabbit]

Perlite is an expanded volcanic glass - it retains moisture while at the same time "aerating" the mix because it is extremely porous, similar to pumice or lava rock, but because it is expanded, even lighter and airier. Because it is so light, I would imagine if you use a layer on top of your media, it won't be there for long lol.

I do use styro, perlite, pumice in potting mix, and also frequently styro and/or pumice at the bottom of the pot.

[rodrigo]

Originally Posted by Bluey

Also, if its function is to retain moisture, isn't that running counter to the advice of using a free draining orchid mixture?

Hi Bluey!

You need a mix that is free draining, but also that retains moisture and lets oxygen come into the mix/roots.

High water retention and/or porous materials like Perlite, coconut husk, lava rock, pumice stone, baked clay pellets, etc. etc. etc. will give you the necessary moisture needed by plant + enough air to prevent roots from rotting.

Remember, you have to fine tune a mix that will work for you in you climate, and using the materials readily available in your area.

Just my

Rodrigo

[orchids3]

Have used pearlite for all the reasons mentioned but use stalite gravel now instead for the following reasons1) Pearlite is abrasive and gives me astma.
(2) Stalite serves the same purpose and is heavier.
Weight may be a drawback to some but I grow outside. Having heavy pots keeps them from blowing away. My plants stayed on the bench thru the tail end of two huricanes even when trees were blown over right next to them. Some have Santa Ana winds in California. I chased my plants down the street a few too many times when I lived there.

[Cym Ladye]

Originally Posted by WhiteRabbit

Perlite is an expanded volcanic glass - it retains moisture while at the same time "aerating" the mix because it is extremely porous, similar to pumice or lava rock, but because it is expanded, even lighter and airier. ...

White Rabbit is correct on the source but in my experience, it retains very little moisture, drains very quickly and does not break down. Some forms of lava rock will hold onto salts which perlite does not do. Many growers use it for these reasons.

When the term "Peanuts" is used, it refers to the styrofoam, peanut shaped, light weight material made for packing. More and more of it is being manufactured as biodegradable and not recommended for use in the bottom of a pot as it reduces to a mushy mess. A lot of growers have used the older form or non-biodegradable form for a layer of drainage material in the bottom of the pot. I have used it in the past but found it does not really improve the drainage in my Cymbidium pots enough to overcome the nuisance of dealing with it at repotting time. Rather than being able to just cut the bottom 1/3 of the root ball off and consigning it to the compost, I was faced with chasing loose peanuts around the potting bench and then convincing them with their static electricity to go into the trash!

CL

[Ray]

Perlite is actually a very good absorber of moisture. The very first S/H experiments ever done used coarse perlite as the medium, and it worked quite well - until it broke down into root-suffocating sludge, that is.

Where some differences in understanding originates, is that how perlite performs in a mix is dependent, to some degree, upon what other ingredients are present, and the particle size.

For example, the #1 "horticultural grade" perlite, at no more than about 1/4" (6mm) particles will aerate something fine like soil, but in an coarser orchid medium, they tend to fill the larger spaces and provide an easier means for "bridging" water droplets to totally block the spaces between the particles, which can lead to suffocation and root death.

Coarser grades of perlite - often referred-to as "sponge rock" - tend to not fill those voids, and may actually create larger ones, so even if they do absorb thoroughly, the medium remains open and airy.

#4 grade, with particles of 3/4" and up, is the best, but is damned hard to find any more. Even the stuff I purchase wholesale as #4 is really, in my opinion, #3 grade, with pieces generally in the 1/2"-3/4" range.

[RosieC]

I actually found perlite held too much moisture for my use. I had tried using it to airate a mix and it actually made it wetter.

Depends on the mix though, it helped airate my heavy peat based mix for a Ludisia, but it just added to the moisture retention of my course bark mix for Phals.