Answer: If the shrubs have been there and survived somewhat on their own for a long time, there may not be too much you need to do. Your approach of adding a topdressing of compost and mulch is a good one, apart from that you might consider trying to identify the shrubs when they bloom. In some cases an area becomes shadier over time because the nearby trees grow larger. This then changes the growing conditions from sunny to shady and can really affect the shrubs planted nearby if they are sun lovers. A symptom of lack of light is wispy and sparse foliage -- although it can also indicate low soil fertility. If they are sunlovers it might be worth replacing them or possibly carefully pruning the trees to allow more light to reach them. Another possibility, and this too really depends on what type of shrubs these are, is renewal or other corrective pruning of the shrubs themselves. Again, identifying the plants is really a critical step.
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