Your Thoughts Have Turned to Vacation, but Don't Go Until You've Done These Chores

By Joel M. Lerner
Saturday, July 26, 2008

There are several important tasks you should tackle in the garden before you leave for your August vacation.

· Now that blooms have faded on bearded irises, it's time to divide these widely hybridized ornamental perennials. Dividing and replanting now gives roots a head start for winter. When they become too large a mass and need dividing, separate them between the end of July and the middle of August.

There are hybrids of bearded irises that have a genetic tendency to repeat blooming. You might lose the fall flush of flowers on these, but the health of the plant will be greatly enhanced next year.

There are varying theories on how often to divide and transplant. After centuries of breeding irises, it's interesting that there is still no single text offering all the correct practices for growing them. We do know that regular removal of old roots on bearded irises controls the iris borer and fungi.

Bearded hybrids have a distinctive fan of leaves that grow from fleshy, rhizomatous roots. They can appear stunted and stressed in compacted clay soil. When this occurs, replant with one-third compost. They can also become so overgrown that the plants don't flower well. That's when transplanting will make a tremendous difference because this plant is the primary attention-getter of the landscape when in bloom.

Bearded irises grow and bloom from shallow root systems and require good drainage. When you dig them, the soil usually falls off the roots, and they divide rather easily, unless the mass is so dense that you need to cut your way in. Regardless, keep only one-year rhizomes (roots that are attached to the fan of leaves). Dispose of all older root pieces and any showing signs of soft, mushy plant parts. This will keep your irises free of borers and soft rot.

The one-year rhizome for transplanting should be about three to four inches long and must have at least one large fan of leaves attached, but it's fine if there are a couple of smaller fans, as well. Cut the fans in half, to about four inches long, and transplant them to a new location in full sun, making sure the eye or bud on the rhizome is at the soil surface or within half an inch of the surface. Otherwise, it won't flower. Use a generous amount of compost to ensure good drainage.

· Sow your biennials in these next weeks. They are easy plants to grow from seeds. Often misunderstood as short-lived perennials, biennials are defined as plants that bloom a year after they are sown, and then go to seed and die. Sometimes they can be propagated from offshoots that grow from the base of the parent plant, but it is better to grow them from seeds now or buy them as started plants at the garden center in spring.

There is a biennial black-eyed Susan ( Rudbeckia hirta) and a hollyhock ( Alcea rosea). Blue Canterbury bells ( Campanula medium) are a knockout the second year after starting from seed. The biennial dianthus ( D. barbatus) displays some of the most striking colors of the genus.

Check with local garden centers to find biennial seeds. You can also buy them through catalogues. Check Renee's Garden ( http://www.reneesgarden.com, 888-880-7228); Burpee ( http://www.burpee.com, 800-888-1447), and Park Seed ( http://www.parkseed.com, 800-845-3369.)

· Butterflies are emerging and actively seeking nectar and mates. They will wow you from now until fall.

If you failed to plant any butterfly-attracting plants this year, find mature ones, like already-blooming hanging baskets or large container-grown specimens, at garden centers. Keep them in the sun, watered and fertilized with water-soluble nutrients every other watering.

Look for verbena, purple coneflower, lantana, butterfly weed ( Asclepias tub erosa), velvet sage ( Salvia leucantha) or any other salvia that's in bloom, butterfly bush, black-eyed Susan, coreopsis, cosmos, zinnia, and other long-blooming plants that will provide nectar for butterflies. These "flying flowers" will feed well into fall.

· Pull weeds when they're small, before they multiply. Every time you pass the beds, pluck a few. Do it while they're young, and many weeds will never self-sow enough to become a major problem. Those that spread by rhizomes that break off in the soil when you pull them and grow back into colonies within days, such as nutsedge, need a little more attention.

If they're too invasive to pull by hand, a control I have used is glyphosate, sold under the names Kleeraway Grass & Weed Killer and Roundup. These nonselective herbicides will kill any plant they contact. You can't use them on the lawn or the leaves of any ornamental plants. Read and follow labeled instructions. Use sparingly.

If you prefer natural weed control, there is an information-packed Web site organized by the Northern Environmental Action Team: http://www.prrrdy.com/garden-weeds.php.

Vinegar has been approved by the Environmental Protection Agency as a nonselective weed control. Use white vinegar off the grocery shelf, undiluted. Be sure to use a plastic sprayer because vinegar is quite corrosive.

Another weed control is mulch, which is any material that can be laid on your beds to act as a protective covering. It reduces evaporation, prevents erosion, controls weeds and can enrich the soil. Spread compost, straw, salt hay, ground corncobs, pine bark nuggets, shredded hardwood bark, licorice root, wood chips, newspaper, landscape fabric or stone.

I prefer organic, partially composted materials. Get organic material from your compost pile or buy it in the form of Leafgro at the garden center or from a county or municipal program. If possible, lightly cultivate the compost into the soil. Nature will do the rest.

Free mulch and compost can be a little raw and contain weed seeds. You might want to finish composting it on your property and not use it until fall.

These counties run excellent composting programs that can provide you mulch:

· Montgomery: Solid Waste Transfer Station, 240-777-6560.

· Arlington: Department of Environmental Services, 703-228-6570.

· Fairfax: mulch information line, 703-324-5995.

· Loudoun: Mulch pile available at the landfill in Leesburg, 703-771-5500.

· Prince William: compost facility, 703-792-6804.

In other areas, call your local Cooperative Extension Service to inquire about programs that offer this crucial soil amendment.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md. E-mail or contact him through his Web site,http://www.gardenlerner.com.