I read in a gardening calendar that I should be dividing my perennials now. I'm not sure what this means. G.J.
Perennial plants re-grow from the roots every year (peony, daylily, hosta, daisy, aster, iris, etc.) getting wider and fuller each season until the roots fill a given area. Once there are too many sprouts per square inch and individual roots run out of space to grow seasonal "feeder" hair roots, the crowded plant's performance begins to diminish. Stems are weaker, flowers are smaller and fewer, and starvation rations weaken tissues so they are more prone to infection and insect damage.
Problems specific to a plant species tend to increase over time, too. Diseases and insects that live over the winter in soil near the plant become numerous and entrenched so the plant is sickly every season, where once it was bothered significantly only in "bad years."
Dividing means to lift the plant out of the ground, rinse the soil away so you can see what kind of roots you're working with, and cut or pull the plant into sections. Then replant about one quarter of each clump into soil that's been loosened and renewed with a generous helping of well-rotted manure, compost or peat. Add a volume of compost at least as great as the root ball you lifted out for dividing. For best results, rotate "crops" occasionally, moving perennials to areas where that species has not grown for several years.
Dividing might better be called "multiplying," since every clump produces one part new division, three parts excess. Avoid the most common mistake in dividing -- put back only small divisions taken from the vigorous, outside edge of the original clump. With more rooting space available to each sprout or "eye," small divisions grow more rapidly and out-perform larger divisions in stem strength and flower size and quantity.
April and September are great times to divide because cool air suppress top growth while warm soil encourages root growth -- divisions reestablish quickly. A simple rule is to divide spring-blooming plants in fall and fall-blooming plants in spring, but gardeners successfully break that rule all the time. For instance, We often have more free time in September than in April, so in fall we may divide everything in a garden we're tending.
Some perennials live for a long time without becoming too crowded -- peonies, daylilies, and hibiscus may not reach the point of diminishing return for ten years -- but others such as daisy, aster, bee balm, and iris may begin to after two years. If you want to see for yourself whether division is worth the effort, lift just one perennial in an area where there are several of the same species, the same age. Divide that one and then compare its leaf size, flower size, and growth rate to the older plants. The difference can be dramatic.
What causes African violets to grow up out of the dirt? Mine has a stem about two inches above the soil. It's blooming beautifully. Should I reset it deeper? Also, how do I separate them when they become doubled? Can one cut them apart? D.B.
Natural loss of lower leaves causes many African violets to develop "necks." The plant gets a better return for foliage produced higher, on younger wood -- these leaves tend to get more light and better air circulation, for instance. So lower leaves fade, drop off, and are not replaced.
Repot and set the plant deeper, where the neck's fortunes will be reversed. Remove any old leaves still attached to the neck, scrape the old stem lightly, and slice off the bottom 1/4 or 1/3 of the root mass to allow deeper planting. This is not as unsettling as it sounds -- placed into good contact with moist potting mix, the wounded stem will grow roots and these roots will be highly productive since they are growing in fresh, uncluttered soil. You will probably even see new top growth within a week.
You can divide African violets. Spring is an excellent time to do this, as lengthening days stimulate a growth spurt. Unpot the plant, loosen the soil around its crown, and gently pull apart the individual plants. Give daughter plants their own pots, or if you already have enough of that type, keep a young, vigorous daughter and discard the mother plant.