Grow-Boxes - soil mixture and watering

Grow-Boxes - soil mixture and watering

We
always tell folks to use at least 2/3 peat or other organic material -
and as much as 75%. 50% sand allows the water to drain too
quickly. So the first thing I would do, if possible, is add more
peat, sawdust, or perlite.

The next thing to look at is the size of your holes in the PVC pipe.
Did you use a #57 drill bit? Sometimes people ignore the
instructions in this regard, thinking that a 1/16th inch bit is ok,
but it is not! A #57 bit is only .042" in diameter, as compared
to .0625" for a 1/16th. This allows far more water to come out, and
at greater force.

Either or both of those conditions could explain your perceived
problem. If neither of those are the reasons, write again and we'll
take another look at it.