Answer: Rose canes tend to thicken and grow woody as they age, so by periodically removing some of the oldest canes you will be taking out old wood and encouraging vigorous new growth. Removing say a quarter of them each year (cut them off at the base) will maintain a steady ongoing replacement system. Depending on the type of rose you have, it may bloom only on new wood meaning the new growth that spring, or on old wood, meaning wood that grew the previous summer or even before that. On plants that bloom on new wood, pruning is usually done in late winter and is more aggressive. You might want to look at a book or two about rose pruning and care. One I like is Roses for Dummies, ISBN 0-7645-5031-4. It includes descriptions and diagrams and discussions of the different types of roses.
Hydrangeas that bloom on old wood include the commonly seen typical bigleafed hydrangea or Hydrangea macrophylla. These plants bud and bloom only on old wood, or stems that grew the year before (or earlier). Pruning is limited to removal of truly dead stems (eg complete kill by winter damage) and periodic thinning by removing some fo the older stems at the base. The thinning would be done right after blooming and new growth should develop to fill in the plant. If you prune these hydrangeas in fall or spring you will remove flowering wood for the coming season. This also explains why severe winter damage and/or freak late spring frosts can destroy the buds for the entire coming season. I hope this answers your question.
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