Return to the Professional Gardener Forum | Post a Follow-Up

advantages of perlite?

Posted by cassiope 03/WI (My Page) on
Fri, Feb 16, 07 at 14:14

I'm in charge of a couple of small greenhouses housing several hundred diverse species. The tradition here has been to mix our own soil. We use a ratio of 1:1:1 of peat moss, sifted top soil, and perlite. (then we pasteurize it) I find that the perlite tends to work it's way to the top and is often rinsed away. Can anything be substituted for the perlite? I'm not happy with our mix at all - I think it dries out too quickly and with time compacts too much (and the perlite seems to have disappeared). I appreciate any advice! Thanks, Cassiope

Follow-Up Postings:

RE: advantages of perlite?

Try using a larger grade of perlite. Or substitute pumice or turface or other high-fired, pelletized clay products. You need something of sufficient pore size to bump up the drainage and provide aeration. Even adding very coarse sand into the mix will help. The compaction is due to the very similar particle size of the peat and soil - with insufficient quantities of perlite, either through initial application or because it is rinsed away, all you are left with is mud. And since heaven only knows exactly what "topsoil" is, you might try purchased humus, screened compost or bark fines in its place. And are you adding ground limestone to counter the pH effects of the peat?

You might find screening through some of the posts or archives of the Container Gardening forum helpful - lots of discussions on seed starting or container mixes and various recipes. Also there is always the option of going with a bulk commercial mix that is already blended.

RE: advantages of perlite?

You could also try adding some vermiculite to keep the soil moister and help with compacting. I would also add some fir bark. I used to make my own potting mix too, probably have some lung disease now from the peat moss dust- awful! Better to leave the mixing to the professionals- buy bulk. The time and manpower you spend in labor mixing your own blend is probably equal to or less than the cost of buying it.

RE: advantages of perlite?

My first impression: You have a heavy dirt mix. There are positives and negatives to that. The heaviness of the media is part of why so much floats to the surface.

My second impression: You have an extraordinarily high ratio of perlite. Again, part of why so much floats to the surface.

How much mixed soil do you use in a season? And how committed are you to using your own blend?

What grade perlite do you use? I'll second the suggestion to find a heavier grade.

I'd question using vermiculite. Yes, it's a substitute for perlite, smaller size and darker it's harder to see when it floats away, but's it just as light.

Are you by any chance able to locate bark fines? It'll help you do all kinds of things, pretty much all very positive.

A great substitute for perlite is grain hulls. I've usd hammermilled rice hulls and am quite satisfied. I've also heard of oat hulls being used, and the results were positive, but have not used them personally, but I would if I had a good local source. One tremendous advantage of grain hulls as opposed to perlite: No dust.

RE: advantages of perlite?

Thanks for your suggestions. What all 3 of you say makes sense - the perlite we use is very fine grade (it's horticultural grade - very dusty). And the top soil is heavy in sand. So, you are right Gardengal - the components all have similar size. I've been mixing soil almost every day since it's spring and lots to repot and seeds to sow. We use the equivalent of about half a cubic yard a week. My concern with substituting perlite, is that many of the plants remain in their same pots for years, and I know bark breaks down (although I prefer it for my own use). Many of these plants have historical value in our collection and are decades old. So I want to take care as I'm repotting them! Honeybunny - I agree about using commercial mixes - I think they're great. And Heptacodium, I will look into grain hulls - they sound ecologically friendly.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Professional Gardener Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here