Answer: Potentilla shrubs bloom on new growth. Trim them back quite hard in early spring to remove winter damage and restore a symmetrical shape, taking off about two thirds of the plant. This should cause them to grow back dense and bushy and produce a strong flush of flowers in early summer. Once those flowers fade, trim the plant lightly to shear off the faded flowers. This should encourage rebloom later in the summer.
These plants do well in full sun and soil of average fertility. You may find they bloom better if watered deeply and slowly during dry spells so the soil never dries out completely. Flowering slows when summer temperatures turn hot, so some years you may have longer flowering than others.
You should not need to use a water soluble fertilizer on these shrubs. Instead, use a slow release or general purpose granular fertilizer per the label directions in early spring and again in early summer. Apply a top dressing of good quality compost in spring and early summer. Also use a two to three inch deep layer of organic mulch over the root area year round. This will help to feed the soil as it breaks down slowly over time.
You might also want to run some basic soil tests to make sure there is nothing severely lacking. Your county extension should be able to help with the tests and interpreting the results with an eye on growing potentillas. I hope this helps.
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