Dahlias are likely grown in most gardens, with 1000's of very cultivated forms, many derived from D. coccinea and D. pinnata, with colours of every hue and many types of flowers. Dahlias originate in Mexico to Colombia, with those that we grow having simple flowers, (good for pollinators) and hardy through most of the UK. With these, tubers can be left in the ground over winter, but in a well-drained soil. If your soil retains water well over winter, it will be best to lift the tubers during this season.
As with all 'daisy-like' flowers, the disc-flowers in the centre of the flowerhead produce nectar and pollen that are attractive to insects. The flowerheads of this genus are particularly favoured by bees and beetles, although in some of the more highly bred varieties, with doubled or pompom-like flowers, there may be reduced nectar or structural barriers which prevent insects from accessing it. The foliage is relatively palatable to insect larvae including a range of non-specialist larger moths such as large yellow underwing.