To make your garden a good habitat for moths it is important to try and provide food for the caterpillars, as well as nectar-bearing flowers for the adult moths. Some moth caterpillars will eat the leaves of a fairly wide range of plants, but most are restricted to a few types of plant or even just one plant species.
A garden with a greater variety of plants is likely to provide a home for more types of caterpillars. Many species eat the leaves of native trees, especially willow, birch and oak, so they are particularly good if you have enough room. If your garden has native trees nearby for caterpillars to feed on, you will probably get the adult moths visiting your garden, especially for nectar, even though the caterpillars can't live in your garden.
If you want a boundary hedge, plant a mixture of native species, particularly hawthorn, blackthorn, hazel, barberry, beech, spindle and privet. This can support many species of caterpillar, but it will be much better if not trimmed too often. Fruit trees and fruit bushes are also good, especially apple, plum, cherry and currant. If there is a wall or fence for climbers, the best choices are roses, native honeysuckle (Lonicera), clematis, hop and ivy. Honeysuckle and ivy are also good nectar sources.
Many caterpillars eat the leaves and roots of native grasses and plants generally considered weeds. It can be very beneficial to have an area with a mixture of native grasses (left to grow long) as well as docks, bramble, plantains, dandelions, nettles and bedstraws. Some native plants favoured by caterpillars are suitable for including in flower beds and herbaceous borders, such as foxglove, primrose and thyme. The native plants which are most likely to attract caterpillars are those which already occur in the locality, so it is worth noting what plants grow in nearby fields, hedgerows and verges, or on local urban brown-field sites.
Although a few caterpillars will eat exotic plants (for example the Elephant Hawk-moth is very fond of Fuchsias) most are restricted to native species. However, some cultivated plants which are related to native plants may be suitable. The Mullein caterpillar normally feeds on the native plant of the same name, but it also likes the closely related garden Verbascums. It's worth trying the many garden plants that are related to our native and naturalised species, such as saxifrages (Saxifraga), dead-nettles (Lamium), yarrows (Achillea), knapweeds (Centaurea) and valerians (Centranthus). Some of these are also good sources of nectar for adult moths. For more information on nectar plants and moth-friendly gardening, see the links on the left.