Planting suggestions

single as opposed to double blooms are better for insect life. plant nectar rich plants and those that produce berries. when you say courtyard are you planting in containers only? Bergamots, scabious, knapweeds, cornflowers, eschloschia [calafornian poppy], sweetpeas, snapdragons all bring insects into mine. shrubs budleia,blackthorn, cotoneaster, pyracantha, laurel, ivy, small trees Rowan, crab apple, Hawthorn.

thats all i can come up with off the top of my head. i am sure you will get plenty more suggestions.

I am a little confused by the question, as normally ecological diversity is described in context of quite large areas of land rather than an area as small as a courtyard garden. I associate it with the existence of differing habitats which are self sustaining. The planting is only one small part of the habitat as much depends on the aspect, summer and winter temperatures, shelter from wind, soil type and drainage and also the area of ground.

In a courtyard garden you might be able to create several mini habitats with different soil types, say a well drained rocky area in the sun for alpines, a shady damp area for hostas and ferns, a sunny area with fertile soil for bedding plants and a pond and wetland area. These mini habitats will all create ecological diversity. The planting will need to be done in context of what does well in each habitat.

If instead you are looking for biological diversity then the plants named by Seaburngirl are good at attracting a wide variety of insects and some are liked by birds also. Yarrow, chives, and mint, are others that insects like.

If you are asking the question in context of attracting a lot of wildlife, it is worth knowing what wildlife is particularly prevalent in the area in question, in order to know how best to attract them. For example, I would love to have common lizards in my garden, and I could set up stone walls in my garden, long grass, crevices, and various plants attracting the insects they eat to attract them but in the absence of any in my neighbourhood I could try all I liked but I won't get any!

I saw an interesting web page on bees and on which gardens tended to have the most visiting. They do prefer some flowers over others, they also like a moderate area of the same kind together minimum 1.5 x 1.5 metres as this is more efficient for them . Therefore if you have a relatively small area to play with then if there are flowers the neighbours have which the bees already like, it might be better putting the same ones in as they don't seem to go for individual marginalised plants to the same degree.

What I am trying to say ( and probably not doing very well) is that by providing ecological diversity if the areas of each habitat are too small , you may be cutting down on the wildlife more than if you just had one or two habitats that mirrored what was already part of the neighbouring landscape.

There is a book which talks about garden ecology regarding insects called

" Insects and Gardens: In Pursuit of a Garden Ecology "
by Eric Grissell. I haven't read it but if you are interested in the subject it might be interesting.

Good luck with the garden, it sounds like an interesting project!