Flowers for good insects.

It's good to have flowers in the garden at all times of year. It's not always easy, though. Some seasons are too extreme for flowering plants.
These flowers will attract and maintain hoverflies, lacewings and other useful insects in your garden.
Flowers: daisies, allysum, Queen Anne's lace, mint, thyme, tansy, lemon balm, santolina, caraway.
Vegetables: Gone to see vegies often have good flowers that will attract insects which are beneficial to your garden; such as parasitic wasps, killers of caterpillars.
Veg to let go to seed include: brocolli family of veg, mustards, fennel.
Buckwheat, a grain, is also good for hoverflies. It has blue flowers.