wrote in message
oups.com...
I re-use my potting mix in planters year after year after year, but it
is
NOT "compost", and I wonder if we are writing about different growing
media. Are you in the US or elswhere?

Thanks to everyone for the replies.
I'm in UK where "general purpose compost" is described on the bag as
"peat reduced". Reading on (and maybe I should have done that before
posting the question) it says it contains enough nutrients for the
first 4-6 weeks only, after which you should go and spend more money on
liquid fertilisers, so it looks like this stuff is "soilless".
I'll try recycling with the time release granules. We do get a lot of
ants in our window boxes so it may have to be dumped anyway.

Don't worry about what you didn't read. Soilless Mix simply provides a
medium where nutrient delivery can happen, where roots can have purchase,
and therefore support growth. In the greenhouse environment, watering is
done with a soluble fertiliser that nets out to 20-20-20 NPK, kickstarting
the plant material to pleasing maturity early enough so you'll pay good
money to buy it. There is usually enough nutrient in the mix to carry
your purchased plants for much of the planting season, but you'll have to
supplement the soilless mix with additional NPK for best performance.

Gardening does test the wallet, by design.

Sue
Western Maine