Answer: Pinching back to encourage flowering can't be done to all plants. For example, lily of the valley grows from a pip--its leaves originate from that pip and so can't be pinched back. Fern leaf bleeding hearts grow from a crown and can't be pinched back either. Pinching back is only effective on plants whose foliage and flowers grow along a stem. Prolonged flowering can only be encouraged on some perennials. Many do not respond.
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