That gel stuff you can add to your compost to help retain water is astonishing. However, I advise you in the strongest possible terms to read the fucking instructions before you use it. I have been repotting my amazing migrating pelargoniums for three weeks now, and still haven’t got it quite right – yesterday’s Jubilee Rain swelled the soil so much the plants romped out of their pots again, and my top terrace was covered in what looked like – but was not – frogspawn.
This isn’t a complaint. I foolishly adopted the “just bung some in, how bad can it be?” approach. Do not follow my example. A little goes a very, very long way.
Aside from the fact that it really does retain water very well, the other thing I rather like about this gel stuff is that plants root into it and seeds sprout in it with a readiness I have not seen in any other medium. Presumably it has to do with the consistent wetness of the stuff. However, the gel, when wet, gives soil a – well, a jelly consistency. So the roots formed are fast, nice and deep, definitely good at keeping the plant watered, but not necessarily any use for providing stability for the plant.
I now put a layer of soil with the gel in it under the plants as I pot them, then pot around the plant with normal potting compost. Hopefully this will work – the plants should root down into the gel, and the layer of good compost on top should prevent the gel’s swelling effect from migrating the plants bodily out of the pot whenever we get a good downpour.
You live and learn.