Tom writes
Hi, can anyone recommend good sources / brands of plant food that I can
buy online (there are no decent shops where I live and I don't drive).

I have
10 x Cacti
2 x succulents
1 x fatsia
1 x Kucle (citrus) plant.
Lots of outdoor plants on my balcony.

Everything is in pots, I don't have a garden.

There are plant foods carefully balanced to each different type of
plant. Since you don't have a vast number, I'd recommend meeting the
exact needs of the most fussy (probably the citrus) and limiting the
number of types you have. My cacti have been happy for years on tomato
fertiliser.

Ease of application is also important. Things you have to make up with 2
gallons of water are OK when you're watering the whole lot, but a pain
if it's early in the season and only one or two plants need it. You can
get plant foods where you add a couple of drops to about a pint though
they tend to be more expensive than the 'one capful in 2 gals' type.

You can also get slow release pellets which last 6 weeks or so and just
tuck into the soil - useful if you have one or two plants away from the
rest which may get watered separately.
--
Kay