Growing medium

Jane McGary
Tue, 10 Jul 2012 11:39:11 PDT
Sujit asked,
>What is the importance of putting a thin layer of coarse grit? I see that
>im many of the photos posted.

It keeps the surface of the soil from drying out too fast and keeps 
it from forming an impervious layer, which can be a problem if the 
mix contains peat and it gets dry. It also keeps the seeds from 
washing around when watered overhead. The best sort of grit is 
granite, but many people use aquarium gravel, which is more widely 
available, and I sometimes use plain pumice if I don't have any 
grantie grit on hand.

My preferred seed mix has always been 2 parts coarse, sharp sand, 1 
part pumice, and 1 part sphagnum peat, but that type of sand is not 
available everywhere, so some other kind of grit could be substituted 
rather than use the kind of fine, eroded sand found in the lower 
parts of rivers and near beaches. People who can't get pumice usually 
use Perlite instead, but it is inferior to pumice in every respect 
except weight (a large flat of 4-inch pots with my mixes is pretty heavy).

Jane McGary
Portland, Oregon. USA

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