Answer: Roses prefer all day sunshine and can be more prone to diseases and infrequent blooming if they're stressed by only half-day sunshine. It sounds as though a fungal disease may have gotten started with your plants. I'd prune back the obviously diseased buds and stems to prevent spread to the rest of the plant. If possible, move your roses to a sunnier spot. Correct pruning can go a long way towards enhanced bloom. Roses are pruned differently depending on the type of rose you are growing. Some are pruned only lightly and some are pruned very hard so it is important to identify the type you have.
Some roses will bloom off and on all season while others bloom only once in the spring. Again, this depends on the type of rose you are growing, but adequate water and fertility combined with a full sun location will maximize performance of all types of roses.
You might wish to look at a basic book on rose care. One I particularly like is "Roses for Dummies" by Lance Walheim. ISBN 0-7645-5031-4. In it you will find a straightforward discussion of the different types of roses, general care instructions, excellent pruning diagrams and other helpful information about feeding, mulching and spraying.
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