Traditionally, a courtyard is a paved section of garden with walls on at least three sides. It feels like an outdoor room and this is why it is so attractive for those seeking a more 'outdoorsy' home life. These days the take on what constitutes a courtyard is not so strict. It is generally paved, or at least partially paved, and has some sort of enclosure like brick walls, metal sheet fencing, trellis panels or brush fences. But the walls need not be 'dead'. You can grow climbers up them, or use tall hedges or rows of trees to enclose a space and create a courtyard feel.

Planning Your Courtyard

When planning your courtyard, decide how you are going to use it. Will it be mainly a place to rest and dine, or is it going to be a secure area for children to play? Do you want a haven for wildlife, or maybe you'd like it to be primarily a kitchen garden where you can grow your own produce? Of course, there's no reason why you can't include several different uses provided you have the space, but for the most part a courtyard is only large enough to have one main theme. Other necessities like clotheslines, garden sheds, and compost heaps can be worked into the design with some forethought so that they are unobtrusive or, if space permits, they can be separated from the courtyard using hedging or walls.

Begin by looking at the area under consideration. Try photographing it from different angles and from different windows of the house from which the courtyard will be visible. Draw a sketch plan to scale on graph paper and along with your photos work out where the 'walls' and other fixed components will be. If there are views you want to hide, like an ugly building or neighbouring garden, you can plan for this now. As you begin to map out your design look at where the main axes run through the garden and the location of the vistas (views) you want to create. This will help you to decide where to lay paths and position garden features. Having done this, you can concentrate on what you're going to include in the remaining space.                

Courtyard Plants

Regardless of how your courtyard is arranged, you absolutely must have plants and flowers. It may be an extra room, but it is an outdoor room and so you need to tie it in with the house using plants.     
You will most likely choose to have plants growing in different areas of the courtyard. Permanent plantings can include shrubs and perennial plants in paving pockets, hedgerows, garden beds at ground level, raised beds or large containers - and perhaps even a tree or two. Temporary plantings, which are chiefly annuals and bulbs, are used to add colour where needed.  These can be used to enliven a garden bed or enhance a garden feature and, for instant impact, they are also well-suited to pots, window boxes and hanging baskets.

Think about what plants make the most sense in your locality under your climatic conditions. If you inherited a courtyard with a mature tree growing in it, it is probably there for a reason such as provision of shade. Consider this a blessing and incorporate it into your design. Don't be too quick to remove any other mature plants either, especially those which are growing well since these are clearly well-suited to the locality. If you're not happy with their positioning, ask yourself whether they could be relocated.
The most important thing when planning your plants is to get the large shrubs and any trees installed first because these provide the main plant structures and take longer to establish. Thereafter, you can experiment with temporary plantings and change these to suit the seasons.