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DIVIDING IRISES, PEONIES, AND GRASSES

The best time to divide irises is a month or two after blooming.  Two signs that indicate your irises need to be divided are decrease in blooms or overcrowded rhizomes that are heaving out of the ground.  Lift as much of the root mass as possible out of the ground and brush off the soil.  Each rhizome division should be 3-4 inches long and have at least one fan of leaves.  Discard any section that has no leaf fans or any section that feels soft because of disease or borers.

Trim the leaf fans to 6-9 inches tall and replant in a sunny well-drained location.  Dig a hole deep enough to accommodate the roots, leaving the top of the rhizome at soil level.  If planting several rhizomes near each other, point each away from each other, and plant at least 18 inches apart.  One of the most common mistakes in growing irises is planting them too deep.  The rhizomes like to sun themselves near the top of the soil and should not be covered with soil or mulch.  Mulch only the first winter to help set the roots.

If you discover that your peonies have smaller flowers and crowded stems, it’s time to divide.  The right time to divide is in the fall when they start to go dormant.  Cut the foliage back to the soil line, dig the roots, then  give them a good soaking with a water hose to remove soil from the roots.  Leaving the roots in the shade for a while will soften them a bit making them easier to cut.   Examine the roots to see where they separate easily, and cut.  Each section should have 3-5 eyes for next year’s growth. And about 6 inches of root.   All the fine rootlets need to be pruned away to deter root diseases that can severely restrict the growth of peonies.

The new location should have at least a half day of sun.  More sun means more flowers, but light shade will keep blooms fresher longer.  The hole should be wide, as a mature plant can have roots with a width of 5 feet or more.  Fertilize the hole with bone meal which will take 2-3 years to break down.  To replant, make sure the eyes are facing up and plant no more than 2 inches deep.  Cover with soil, tamp the ground firmly, and water.

Ornamental  grasses rise up from the same root crown or tussock that sits at or just below the soil line.  Each year this root crown generates new blades and stems, expanding with time, and increasing the overall diameter and lushness of the plant.  As new growth occurs on the outside edges, the center begins to die out and it’s time to divide and renew the grass.  The grass can be divided in winter or early spring before new growth begins.

Lifting the tussock with a spading fork, discard the dead center and divide the remainder into sizeable chunks.  Each chunk should be large enough to contain at least 2 growing points, then replant in pots or in the ground.