Greetings, A mix made mostly of granite or volcanic fines would certainly be a problem as these materials accrete and dry into very a rock-like substrate (though no doubt rich with nutrients!). I find, however, that a mix with a 1/5 addition of fines does not have that problem and indeed gives better results for seedlings and adult plants. The fines have an enormous surface area from which mineral nutrients can be leached by plant roots. If you have other course components in your mix or amendment (gravel, pumice or sand), I would be sure to include, rather than exclude, fines. -|<ipp ________________________________ From: pbs <pbs-bounces@lists.pacificbulbsociety.net> on behalf of R Hansen via pbs <pbs@lists.pacificbulbsociety.net> Sent: Friday, February 5, 2021 11:29 AM To: 'Pacific Bulb Society' <pbs@lists.pacificbulbsociety.net> Cc: R Hansen <bulbnut@hansennursery.com> Subject: Re: [pbs] Red volcanic sand usage Re: fines in red cinders or white pumice. I agree that the fines are very important, particularly since they're not graded. I use 1/4 10 gravel, with fines, and find that when this is mixed into my container mix, it does not pack and my plants grow much better. The biggest issue for me is simply that it's heavier than red cinders or white pumice. Try picking up a standard Anderson flat that's full of newly potted plants using 1/4 10 and you'll know one of two things: you need to start lifting weights to strengthen your muscles or you need to change to pumice... Robin Hansen Sunshine in Coquille! _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net https://na01.safelinks.protection.outlook.com//… Unsubscribe: <mailto:pbs-unsubscribe@lists.pacificbulbsociety.net> _______________________________________________ pbs mailing list pbs@lists.pacificbulbsociety.net http://lists.pacificbulbsociety.net/cgi-bin/… Unsubscribe: <mailto:pbs-unsubscribe@lists.pacificbulbsociety.net>