There are many situations when planting a hedge where the requirement is for plants without thorns or spikes, for instance in an area where children have access and along public rights of way. It is perfectly possible to plant a thornless hedge either as a single species or as a mixed Native Hedgerow. Thorns, spines and prickles have evolved from different parts of the plant deterring animals from eating them, for example the thorns on Quickthorn are modified branches, the spines on Cacti are modified leaves and the prickles on Roses are extensions of the stem rather like hairs. These are obviously the types of plant to avoid when choosing a hedge where thorns etc are undesirable.
For a Thornless Mixed Native Hedge to encourage wildlife, depending upon the conditions of the area to be planted a combination of plants such as Beech or Hornbeam, Field Maple, Dogwood, and for interest with berries, flowers, and nuts Hazel, Spindle, Wild Crabapple and Guelder Rose which is actually from the Viburnum family. Common Alder will provide catkins again for attracting wildlife, and Dogwood provides pretty stem colour to add further interest. The hedge of course does not have to be of mixed variety, most of the aforementioned species can be planted as single varieties, especially Beech and Hornbeam which give fantastic winter leaf colour.
For informal hedges without thorns but with most attractive blossoms look no further than Mock Orange, Escallonia or Viburnum Tinus all of which can reach heights of between 200-250cm. If just a straightforward evergreen hedge is required then Common or Portugal Laurel would suit or the beautiful apple green Griselinia. There are numerous plants suitable for hedges without thorns it is just a question of choosing the ones suitable for the site.