It's still not too late to get a late annual sowing in for this year. Even if you just use cornfield annuals as border fillers, they look great and give a real boost to local wildlife.
They self seed and provide colour and habitat for wildlife for years, with little maintenance. It's well worth it if you have the space.
Remember, native or naturalised species are always best, as they are adapted to our environment and they often provide the best source of food and shelter for our wildlife, as opposed to highly cultivated species or exotic imports.
https://www.rspb.org.uk/get-involved/activities/nature-on-your-doorstep/garden-activities/sowapoppypatch/