In article , "Martin" wrote:

Greetings all,

The soil in my training pots seem to repel water instead of absorb it. I'm
using commercial grade 'standard' potting mix with added coarse river sand
(about 10-15%). Each time I water, the water either wells around the top
without being absorbed by the soil, or it just seems to run down the insides
of the pot. When the water _does_ seem to be absorbed, it only penertrates
about 5mm down, leaving the rest dry. Additionally, a dry 'crust' of about
5-10mm tends to form on some of the newly repotted plants.
I've tried soaking the pots in buckets of water for 30mins or so, which
_seems_ to help.

I've seen that with my non-bonsai houseplants. It's a symptom of
under-watering. When potting mix gets too dry, it tends to repel water.
It also happens to a lesser extent with potting mix fresh from the bag.

My solution is to use a spray bottle to moisten the whole surface just a
little. Wait half a minute for the spray droplets to be absorbed, and then
water normally. After half an hour, check the soil and water again if it
needs it.