Looking after a window garden is just like any other container. Before you plant, you’ll want to make sure there are drainage holes in the bottom. It seems obvious to say, but worth pointing out as not all containers have them, and it’s not fun to find out afterwards. If yours doesn’t, you can still drill them in yourself – just choose a drill bit that’s right for your container, like one designed for stone or metal.
Getting the compost right is important too, especially if your plants will be in their pots for more than a year. The easiest thing to do is use a pre-made potting compost – we’d always recommend a peat-free one – but if you’ve got an ordinary garden or multi-purpose compost already, that’s fine too. You’ll just want to add something like coir, which keeps hold of water, and grit or sand, which improve drainage – two seemingly opposite things that most plants love. If yours like dryer soil (think Mediterranean plants like lavender and thyme) then leave out the coir and add more sand.
Then it’s just a case of keeping up with the dead-heading and watering. Most plants won’t ask for more.