I reminded her of the lightweight composts now available. I've been trying Miracle-Gro's expand'n'gro. Dry, it weighs almost nothing, but add water when you get it home and it swells up to three times its size (and gets heavy). It’s said to contain enough nutrients for six months, and to require less watering, which would be a bonus for an exposed windowsill or terrace.
The sample I had came in a plastic bag (left). I added an equal amount of water, and it quickly swelled to fill the 12cm pot included. I’ve used it for a small aloe which has just been joined by an offspring, and am waiting to see how they fare.Some feedback on another product I’ve been trying, Vitax’s NeverGreen, designed to protect outdoor surfaces against mould and mildew. The concrete of our small courtyard regularly turns green and has to be scrubbed and bleached every few months – a task I loathe. I applied some NeverGreen at the beginning of March, and despite all the rain, the surface is still clear. I’ll report back on this again in the autumn.
Both products can be found in the UK at garden centres, DIY outlets and on the internet.
http://expand-n-gro.co.uk/how-it-works
http://www.maxnevergreen.com/what-is-nevergreen