Volume 14, Issue 32 ~ August 10 - August 16, 2006

The Bay Gardener

By Dr. Frank Gouin

Think Ahead; Dig Ahead

Thriving spring iris need your attention now

To maintain a healthy stand of bearded iris, you need to dig and divide the rhizomes every three to five years. The rhizomes of iris, called pachymorphs, divide every year, and the older rhizome dies. If untended for several years, dead rhizomes become infested with borers. Unless these dead rhizomes are removed at three- to five-year intervals, the population of borers increases to such a level that they begin to invade young rhizomes, resulting in severe decline.

Mid August to late September is the best time of year to dig up and divide iris rhizomes. Since the rhizomes are near the surface, they are easily dug using a garden spade.

After digging the rhizomes, place them in the shade and shake away the soil clinging to the roots. Using a sharp knife cut out the dead rhizomes. Inspect each new rhizome, making certain that it has not been invaded by borers. Borer holes are pencil-size and larger and generally dark brown. Rotting organisms are likely to use their tunnels to invade and eat out the rhizomes.

Dusting the rhizomes with a fungicide called Captan will minimize infestation. Do not trim the foliage on the young healthy rhizomes. That foliage helps new roots form from the rhizomes.

Before replanting the young healthy rhizomes, amend the soil with compost and limestone. Add at least a one-inch layer of LeafGro or Chesapeake Blue or Green and a uniform light dusting of dolomitic limestone (about one large handful per three square feet) and spade deeply. Avoid walking on the amended soil and rake the area smooth.

Plant the rhizomes by pressing them into the loose amended soil. You don’t want to plant rhizomes too deep, for depth increases their susceptibility to rot. Allow six to eight inches of space between rhizomes for future growth. Planting them close together will require digging and transplanting more often.

If you have rhizomes left over, give them or trade them with your neighbors and friends.

Dealing Bermuda Grass Its Death Blow

Q: We are new to Annapolis and have encountered the worst grass weed I have ever seen. I have fought Bermuda grass for two summers. The vicious, stubborn weed shoved its way through our sod. I have pulled and dug, and shot individual sprouts with Round Up. Is there any way to drive this out of my yard?

— Doug Smith, Annapolis

A: The only sure way of get rid of Bermuda grass that has invaded the lawn is to kill the entire lawn. This means spraying Roundup over the entire area now and repeating the spray over the same area one week later. Allow at least two weeks before you top-dress the lawn with compost at the rate of two to four cubic yards per 1,000 square feet and seed a new lawn or lay sod.

