Invigorate Perennials with Fall Division

Success with perennial flowers is no accident.  Perennials need some specialized care in the Fall to remain vigorous and full flowering next spring. Top on the Ato-do@ list is the dividing and replanting of clumping perennials.

Division is one of the easiest ways to start new plants.  It=s also a requirement for many perennials every few years.  As they grow clumping perennials form new plants or offshoots that are constantly growing farther out.  Over time, the center of the clump begins to die out from competition with the younger, more vigorous, surrounding plants.  Dividing is a way to space out vigorous plants in the clump to assure their success.

Fall is the best time to divide most perennials because air temperatures are cool and soil temperatures are warm.  That means perennials dug up and replanted are not subject to shock as they would be under our scorching summer heat.   Warm soil temperatures will cause lots of new roots grow out on the newly divided plants. 

Fall transplanting is best for a number of our commonly grown perennials including; gopher plant, penstemon, artemisia, guara, rudbeckia, society garlic, rain lilly, iris, and purple coneflower.  They vary somewhat with the frequency of dividing, but it=s important to do it periodically, even if clumps look healthy.  Waiting too long can cause the clump to weaken.

The first step in the dividing process is to thoroughly water the clump.  This should be done a couple of days prior to division.  The water will plump up the plant to be divided and steel it from moisture loss during the transplanting process.  Watering ahead of time will also make digging easier.

Also prior to transplanting, prepare the soil where the new plants will be installed.  Perennials prefer a soil that is rich in organic matter.  If the young plant divisions are to be located in a perennial bed, prepare the entire bed.  If they are to be planted individually, prepare an area approximately 3 feet in diameter.   Mix in a layer of 3 or 4 inches of organic matter into the top 12 inches of soil.  This organic matter can be sphagnum peat, bagged compost, composted manure, or organic top soil. 

Besides organic matter, mix in a small amount of bonemeal, ammonium phosphate (16-20-0) or other flowering plant fertilizer.  One quarter cup of ammonium phosphate is ample for the 3 foot individual planting spots.  For bed plantings mix in 3 pounds of ammonium phosphate for every 100 square feet of bed area.  Phosphorous is important in the development of new roots and it will promote abundant flowering next spring.

In dividing the clump, use a sharp shovel to dig under the clump starting at the edges.  Assume that the roots will extend down into the soil a minimum of 12 inches.  Use the shovel to undercut the roots. Continue undercutting with the shovel all the way around the clump.

Next, locate the individual plants in the clump.  This is easiest done by lifting the clump out of the ground and pulling the roots apart with your fingers.  Individual plants will usually break off.  If you have difficulty prying the clump apart, cut through the clump using the shovel.

After dividing the clump, replant the individual plants.  If the center plant in the clump is weak or dying, discard it and only replant the young, healthy ones.  Plants should be set in the ground at the same depth they were growing at before the clump was divided.  Planting too deep will cause the plants to die.

Be sure to fill in around the roots with soil.  Tamp soil around the roots and then apply water to settle the soil.   Push soil in and around the roots with your fingers.  Probing in this manner is a good way to detect and fill in air pockets. No air pockets should remain after planting. 

Mulch the soil around the newly planted perennials with bagged bark, shredded wood mulch or course compost to hold in moisture.  Water on a regular basis to encourage the development of a strong root system.   Cut the leaves back some on top-heavy plants to compensate for damaged roots.  Finally, tidy up plants by removing spent flower stalks and old leaves.