On 12/09/2012 09:30, stuart noble wrote:
On 11/09/2012 18:00, Jake wrote:

I grow raspberries in 30 litre tubs, 5 canes to a tub with a wigwam of
bamboo canes for support. With three tubs, we have enough for
ourselves and some to give away. I use a mix of John Innes No 3
compost and Perlite (you can use grit but the Perlite does the same
job - helps drainage - and weighs less so tubs are easier to move
around) with 25 litres of compost to 5 litres of Perlite.

Hmm. IME perlite and vermiculite increase the weight of tubs because
they hold so much water. I haven't tested this scientifically BTW :-)

And when they dry out they reduce the weight.