| Lilacs require a cold winter to flower well and perform much better in full sun. Beautiful flowers - I have several in different colours. All are old plants but nowhere near 4m high - and certainly much wider than 1m. The dimensions you want are a bit of a problem. At 4m you want something that you don't want to be pruning to maintain the 1m width (unless you built a permanent scaffolding around it). The only thing that springs to mind is a conifer of some kind. But make sure it's going to stay within the 4m limit. An Irish yew (Taxus baccata 'Fastigiata') might fit the bill. Ultimately, it would grow somewhat higher than 4m but not in your lifetime. It does eventually widen out at the top but, again, this is a feature of maturity. What you would be looking at for at least the next ten to twenty years or so would be a very formal looking "punctuation mark". The leaves are very dark green and, unlike most conifers, are soft and feathery. The branches are very dense and upright. Small red berries are produced, rather than cones, and these tend to be hidden away in the foliage. Altogether, a highly desirable conifer. There is a photo of a pair of yews on this site. Unfortunately, the photo doesn't really do the tree justice. You have to see one in real life to appreciate the beauty of the foliage. There is also a golden variety but the few that I have seen growing tend to be quite yellow on the side exposed to the sun and green on the southern side. The timber itself is very attractive and is highly desirable to wood-turners. And you could make your own longbow. | 
