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The ideal way to divide a perennial is to dig up the entire plant using the drip line of the plant for guidance – most plant root will reach all the way to the drip line. Look at root health and only keep those that look nice and healthy. Use vigorous sections of plants 1st. The size of the division depends on the species. Hosta, iris and daylily grow pretty quickly after being divided. Other plants like peony grow better if the divisions are bigger. The smaller the division the smaller the root system and the longer you’ll wait for new blooms (which typically is 1 to 2 years).
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