For Release On Or After 02/04/11

By Dan Gill
LSU AgCenter Horticulturist

Most Louisiana landscapes contain a variety of perennials, and February is a good time to transplant or divide them. Now through April also is an excellent time to add new perennials to garden.

Perennials are plants that live for three or more years unlike annuals, which die after flowering and setting seeds. Technically, trees, shrubs and lawn grasses are all perennials, but gardeners use the term “perennial” as shorthand for “hardy, herbaceous perennial” – a group of non-woody plants that reliably survive winter’s cold and are grown for their attractive flowers or foliage. Some perennials are evergreen and never go completely dormant; others lose their leaves and essentially disappear at certain times of the year, usually winter.

Growing perennials is not necessarily more difficult than growing annuals, but it is different. Because they will become a part of your garden for a number of years, using perennials effectively requires learning more about each variety. Keep in mind that when an annual is finished blooming, it’s pulled out and replaced with something that will continue producing flowers. When a perennial finishes blooming, however, it’s left in place, and other plants in other locations must continue the floral display.

Transplanting

If they’re transplanted now, most perennials will barely miss a beat if you’re careful to dig up most of the root system and replant it immediately in a new location. If you wait until later on in the year, warmer weather makes it more likely perennials will suffer increased transplant shock. Don’t transplant perennials if they’re in active growth at this time, such as Louisiana irises, acanthus, calla lilies and Easter lilies.

Dividing

Some perennials are best divided every year or two, but most can be left alone for two to three years or even longer. Dividing helps control the size of the plant and the space it occupies, as well as rejuvenate it. Dividing perennials is also a good way to create more plants you can share with friends or transplant to other areas of your landscape.

To divide a perennial plant, first dig up the entire clump using a shovel or garden fork. Study the clump carefully, noting the crowns or shoots, and decide how many pieces to divide the clump into. Generally, each division should have several crowns or shoots. Decide where to make cuts so you avoid cutting through crowns or damaging shoots. Finally, cut apart the clump with a large, sharp knife. Be careful and wear leather gloves. Replant or pot the divisions immediately.

Planting

Early spring is a good time to plant perennials, but they may not look like much when you purchase them in late winter or early spring. This is a reason newer gardeners, who are accustomed to buying annuals in full bloom, are slow to appreciate perennials. You must be able to imagine how they will look when they bloom in two or three months – or even at the end of the summer – to value them in February.

Plant perennials into well-prepared beds, and space them according to information on the label, in reference books or from local advice. Most perennials will grow considerably larger than the size of the young plant you purchase. Don’t crowd them.

When you plant a perennial, make sure the top of the root ball is even with or slightly above the soil of the bed. Many perennials will rot if they’re planted too deeply. If the roots are in a tightly packed mass, pull them apart and spread the roots out somewhat when planting. You may add a small amount of slow-release fertilizer in the planting hole. Firm the soil around the plant, then water newly planted perennials thoroughly. Mulch the bed to control weeds, but don’t cover the plants.

Selecting perennials

Success with perennials in Louisiana depends largely on proper selection, beginning with a general rejection of varieties that only grow well north of hardiness zone 8. To survive here, perennials must be able to endure the heat, humidity and rain of summer and the diseases that season brings.

Also note the growing conditions that exist in your landscape and select perennials that will thrive in those conditions. Consider plant and stem heights. And don’t forget to choose perennials with a variety of textures and growth habits to create interest and contrast in the visual composition.

Flower colors also are very important. Decide on a color scheme and select perennials that bloom at various times of the year for extended displays of color.

For more information and recommendations of perennials that do well in Louisiana, you can consult “Perennial Garden Color” by William Welch and “Perennials for the Coastal South” by Barbara Sullivan.

Rick Bogren