Tapla said:

"The perlite, in smaller volumes, can't change that balance, but it does
take up some space that would otherwise be occupied by water, so it
reduces the o/a water retention of the soil without significantly
increasing aeration or the ht of the PWT.The perlite, in smaller volumes, can't change that balance, but it does
take up some space that would otherwise be occupied by water, so it
reduces the o/a water retention of the soil without significantly
increasing aeration or the ht of the PWT."

So I'm confused. If perlite reduces overall water retention of the soil, won't that mean more aeration? To me a soil that holds less water should be a good thing in most cases of containerized plants, especially tropicals/succulents etc... I'm just confused.

Also, does anyone make Tapla's 5-1-1 mix and sell it? I would be willing to buy some. Does Tapla sell it? Thanks all!

Z

see this thread. about 1/3 way down al has a good post that might answer your question.

http://forums2.gardenweb.com/discussions/1383968/pumice-versus-perlite?n=40

I think I found Al's comment. He says "In soils, perlite promotes drainage and improves porosity. It's also effective for starting seeds & cuttings."

Now I'm even more confused. In Al's other threads, he specifically says that perlite does not help drainage, and says it will only help drainage when it becomes over 50% of the whole soil/mix.

can you link to the thread where you saw the other quote? small amounts of perlite probably won't do much but a 5-1-1 mix has plenty of perlite

Maybe you are thinking of just some perlite (or any other grainy material) mixed with soil: soil is much finer than perlite. So it will just fill all the spaces between granules of perlite. Al pointed that out: ..."The perlite, in smaller volumes, can't change that balance"...

You can find some perlite in bagged soils - if you look hard enough :) That is not going to help at all. While perlite holds water internally, excess will just drain out from in-between the granules unless that in-between is filled with soil. Soil will absorb this excess water and keep potting mix wet for much longer - how wet, and how long depends on amount of soil.

I use mix of grit and perlite in equal amounts plus some turface for succulents. It drains any excess water fast, and whatever water is retained is released to plants. But that water is held internally, so roots do not sit in wet muck. I use mix like 5-1-1 for tropicals, but have some in gritty mix too.

Gritty or 5-1-1 mixes are not available in stores, we make them ourselves. There are couple/ few on line places you can buy premade mixes, BonasiJack or rePotme come to mind. I never bought from them so check them out first.

My question is why when you add some perlite to a mix, it causes water to drain out the bottom much faster than not. I really like that aspect and it really helps the plants. But you're right. Putting a 1/4 cup of perlite doesn't help. It has to be like 1/2 the mixture.

In any case, I will check out ways to buy the 5-1-1- mix or 1-1-1- mix from someone. Thanks.

z

...because perlite creates 'space' between the particles. Bigger paricles - more space in-between. Fine soil will not do that - particles are very small, so they are much closer together. Leaving no space (or very, very small) between them. When wet, they will stick together further...

Did you check he sellers I mentioned?

I did check those sellers, thank you. They seem to only make the gritty mix. I'm sick of the inferiority of commericial potting soils. Can someone please tell me if I had 50% perlite to any of the general mixes, I will get a fast draining mix?? Thanks. What about if I used 50% vermiculite?

Z

not vermiculite. it is not a substitute for perlite.

Mixing at least 50% of perlite will be better than not mixing it in...or pumice if you can get it.

Hi Z-man!

("In Al's other threads, he specifically says that perlite does not help drainage, and says it will only help drainage when it becomes over 50% of the whole soil/mix.")

I believe Al is referring specifically to trying to improve *potting soil* by adding perlite. Potting soil usually contains lots of fine particles, so it's dense and not well aerated (Al compares it to pudding in his example). If you add perlite to pudding, you don't improve it's drainage unless you add an enormous percentage of perlite. But if you use perlite as one component of a mix that's made from larger, similarly sized particles (think of a bag of peas rather than the pudding), perlite could function well to maintain aeration etc. Does that make sense? It's not that perlite is either good or bad, it just performs differently in different applications.

Al seems to offer an explanation of this principle in each edition of his informative post on container mediums:

http://forums2.gardenweb.com/discussions/1423691/container-soils-water-movement-and-retention-xvi?n=161

"If you start with a water-retentive medium, you cannot effectively amend it to improve aeration or drainage characteristics by adding larger particulates. Sand, perlite, Turface, calcined DE ...... none of them will work effectively. To visualize why sand and perlite can't change drainage/aeration, think of how well a pot full of BBs would drain (perlite); then think of how poorly a pot full of pudding would drain (bagged soil). Even mixing the pudding and perlite/BBs together 1:1 in a third pot yields a mix that retains the drainage characteristics and PWT height of the pudding. It's only after the perlite become the largest fraction of the mix (60-75%) that drainage & PWT height begins to improve. At that point, you're growing in perlite amended with a little potting soil.

You cannot add coarse material to fine material and improve drainage or the ht of the PWT. Use the same example as above & replace the pudding with play sand or peat moss or a peat-based potting soil - same results. The benefit in adding perlite to heavy soils doesn't come from the fact that they drain better. The fine peat or pudding particles simply 'fill in' around the perlite, so drainage & the ht of the PWT remains the same. All perlite does in heavy soils is occupy space that would otherwise be full of water. "

Somewhere in the hundreds of Al's threads and posts I've read he mentioned that coarse perlite aerates by getting between the pieces of bark. That could be an outdated theory, but it made sense to me because bark generally has at least some flat faces.