Spring Is A Good Time To Divide Plants

From The Fresno Bee, April 29, 2010, by Elinor Teague:

Agapanthus, daylilies and heuchera (Coral Bells) are some of the clumping plants that need dividing every few years when the root systems become crowded and flower production slows. Spring is the best time to divide theses plants. We often put plant division at the bottom of our spring chore list, but we're lucky to have a few extra cooler spring days this year to finally get the chore done.

The technique is simple. Wet the soil and the root system of the plant thoroughly; then use a spading fork (not shovel or spade) to work around the clump and lift it free from the soil. The tines of the fork will slide under the roots rather than cutting through them as do shovels and spades. If you don't have a spading fork, you'll need to insert the shovel further away from the plant to keep as much of the root system intact and undamaged as possible. The roots of heuchera can be pulled gently apart, but the underground tubers of daylilies and agapanthus should be cut apart with a very sharp knife or pruning saw. (I use my mother's Ginzu knife for this).

Place the new sections in damp soil at the same level they previously grew. Big sections will need to be placed further apart than smaller sections; leave at least 8 to 10 inches between agapanthus sections and at least 6 to 8 inches between newly replanted daylily and heuchera sections. Water the transplants thoroughly and sprinkle a couple of tablespoons of bone meal or "bulb booster"-type food (any brand will do) over agapanthus and daylilies or a couple of tablespoons of an acid-type food over shade-loving heuchera.

You may have noticed that some of your spring-blooming bulbs have also become crowded over the years. In milder climate zones, bulbs can be lifted (again with a spading fork) and stored over the summer in a cool, dry place until they are replanted in fall. Few of us have cool outdoor spots for bulb storage in the Central Valley. Our spring-blooming bulbs can be lifted, divided and replanted in late spring after the foliage is nearly completely dead. (We can wait until fall, but it's tricky to find the buried bulbs when they have no foliage). When burying the bulbs, make sure to place them at the maximum recommended depth; usually the hole should be three times deeper than the bulb size--a 2-inch tulip bulb should be buried six inches deep. Burying bulbs at the proper depth helps to protect them from our summer heat. A couple of tablespoons of bone meal or bulb food placed in the new hole will boost the bulb's vigor.

Bearded iris, in glorious full bloom now, are dormant from July until October. Wait until later in the summer or early fall to divide them.