I live in Northern Illinois where (unfortunately) the native soils
contain a good deal of heavy clays. This spring I was given a dry root
hibiscus, which I planted, admitted without enough thought of
conditioning the soil in which I was planting it. The hibiscus has,
in my opinion, grown nicely this summer, although it has not
flowered. The three to four foot radius around the hibiscus is free
of other plants or shrubs. The soil in this area seems to be quite
compacted and is showing some large cracks. I was wondering whether
it would be wise to careful dig up the soil in this area and mix in
some peat moss with the soil that is there. Is this is a good idea?
Would be benefit the hibiscus? Can it be done without disturbing and
damaging the hibiscus? Any one have an idea for the best method for
doing such a thing?
That's not a misfortune; clay is very fertile (compared with sand, or
This spring I was given a dry root
The reason your clay developed those big cracks in summer, is because
its water content dried out. That shows you how much water clay holds.
In winter the clay gets wet from rain or snow and expands again so the
cracks disappear.Peat also holds water like a sponge. Hibiscus don't
like wet boggy soil in winter so by adding peat you would be creating
the worst possible conditions for it .
When making a planting-hole in clay it's a good idea to mix in sharp
grit/gravel which will help keep a looser texture, which helps roots to
penetrate it and spread. I would not dig the soil near the plant at this
stage.You could dribble some grit/gravel down the cracks to fill them up
and improve drainage in winter.If you also spread some home-made compost
or well rotted FYM all over the surface of the clay soil; first, this
will protect the soil surface from excessive sun drying, helping to
prevent cracking. The worms will take that material down into the clay,
and the humus and worm tunnels will both improve the texture of the clay
Broadcast about a 1/4-inch layer of gypsum over the area. Sprinkle with
just enough water to wet the gypsum but not rinse it away. Wait a day.
Water slightly more generously to start the gypsum dissolving. Wait a
day. Soak the area with a slow hose; that is, let the hose slowly
trickle to start rinsing the gypsum into the soil.
The gypsum will react chemically with the clay, causing it to lose its
stickiness and become somewhat granular. This treatment should be
renewed every spring, before the summer rains. (Contrary to common
belief, there is generally more moisture in the summer rains than in the
winter snows in your area.)
David E. Ross
Climate: California Mediterranean
A friend of mine had great results with gypsum, although she added a step.
She used a pitch fork to poke holes straight down and made sure some of the
gypsum was sprinkled into those holes. After two seasons, the soil's quite a
bit easier to work with.
Garden soil should be about 30%-40% sand,30%-40% silt, and 20%-30% clay.
After treating your clay with gypsum, take a one foot deep core sample
(without the mulch, ect.) and slurry it in a glass bottle with water.
The sand will settle out in a few minutes. The silt in 20 min. and the
clay in a day. The height of each of the three layers, compared to the
total sediment will give you the percentage composition of your soil and
you can amend as needed.
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