Mildew and fungus problem garden border
Problem border I think your best bet is to improve the growing conditions by adding grit, soil conditioner and mulching the border so that there is a barrier between the plants and the spores on the fallen leaves lying on the soil. Good hygenie is paramount. Pick off all leaves that are lying around and burn. You will find that most diseases and mildews are on the whole host specific so they usually will not spread to plants of a different genus. So it sounds that the cultural conditions are favouring all these different fungi added to the fact that the weather last year was ideal for spreading fungal spores.
With the Clematis they are know as ‘gross feeders’ and need to have a good planting with plenty of organic matter as they are very hungry. To avoid Clematis wilt the best bet is to plant them 15 cm to 30 cm deeper that the level they are already at so that if they do suffer from Clematis wilt then they can come back from the roots. Do not plant a Clematis in the same spot where another one has failed.
Next season you should ensure that all your plants are fed with a slow release fetiliser and spray at regular intervals from NOW (March to October) with a systemic fungicide (it works in the plant’s system) like Systhane Fungus Fighter. If you have a regular spraying regime for this season is will reduce the overwintering spores on the plants. The other option is to choose plants evergreens etc.. that are not as prone to diseases and are better suited to the N E situation.
A soil Ph test would be a good idea to do as well! You can get kits at garden centres use distilled water with the soil sample to be tested.