Soils and potting mixes

J.E. Shields
Fri, 26 Jul 2002 16:20:29 PDT
Hi all,

I doubt that we have decomposed granite available around here.  Most of our 
rocks are limestone, and about 100 - 200 ft straight down, below the soils, 
subsoils, sand, gravel, and whatever.  As you may guess, I'm no geologist!

Garden soils tend to be clays.  If you are fortunate enough to have some 
original topsoil left where you live, it is probably a sandy loam, loam, or 
clay loam type.  As former agricultural lands are converted to 
subdivisions, the original topsoil may be sold off or may merely be buried 
as the areas are graded for construction.  Those poor folks in brand new 
homes have their expensive sod laid on top of pure clay subsoil.  When they 
come to my garden for daylilies, I always advise them to hire a landscaper 
with a backhoe to dig out the top 12 - 18 inches of clay and replace with 
high quality blended topsoils, about $15 - $25 per cubic yard, 
delivered.  A few of them really do so.  We can get a great triple-mix 
topsoil here, composed of loam, local black peat, and sand (1 : 1 : 1).

In my pots, I use two basic mixes:  One, my "sandy mix," is a Promix - sand 
(2 : 1) mixture.  The other one, my "gritty mix," is Promix - sand - 
granite chick starter grit (ca. 2 : 1 : 1).  These two do pretty well for 
most of my plants.  For starting small seeds and daylily seeds, I usually 
use straight Promix, which is manufactured in Canada and is based on brown 
Canadian peat mixed with a little perlite, vermiculite, and some rough 
shredded twigs.  You could probably use ordinary brown peat at 1/3 the cost 
of something like Promix.

Pen Henry in the Clivia group suggested using a concrete mixer to make 
these potting mixes up, and I finally follower her advice, thank god!  It 
works far better than mixing by hand.  We bought an electric concrete mixer 
at Lowe's, for about $250.  It has never had cement in it and never 
will.  It has two wheels on one end, and I  can roll it around.  It is 
stored in the garage, right beside the propane grill.

I grow my Hippeastrum, Cyrtanthus, Nerine, Haementhus, Clivia, and Crinum 
bulbs in the the gritty mix.  I start their seeds on the sandy mix.  Both 
mixes are indeed heavy in large containers.  But since a large Clivia plant 
in a 3-gallon container outdoors will be blown over in a typical summer 
thunderstorm here, the more weight in the bottom, the better.

Because of the weight involved, I usually haul my potted bulbs around on 
carts. Irma, my wife, found a neat 4-wheeled cart with a removable second 
story in a garden supply catalog a couple years ago.  It hitches to the 
back of our riding mowers and is great for moving multiple big pots between 
back door or greenhouse and the outdoors areas in spring and autumn.

In summer here in central Indiana, we can have anything from very wet to 
very dry weather, anything from mild to hot temperatures, and almost always 
high relative humidity.  It can be tough to get clivias through a wet, 
rainy summer outdoors.  Some of my Haemanthus are not very happy in the 
humidity too.  Almost all my Haemanthus carneus are on strike this summer; 
it looks like they would rather rot than grow.  H. humilis hirsutus and H. 
montanus, however, are apparently doing pretty well.  If I ever get the 
montanus to bloom, I will certainly cross it with hirsutus to pursue my 
quest for another Haemanthus besides albiflos that it is humanly possible 
to grow here.

Jim Shields
in central Indiana, where it is a mite warm and humid after a quick mid-day 

Jim Shields             USDA Zone 5             Shields Gardens, Ltd.
P.O. Box 92              WWW:
Westfield, Indiana 46074, USA                   Tel. +1-317-896-3925

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