Groundwork for June 23, 2013

Some herbs thrive in our Louisiana heat and humidity. If you are new to herb growing or are unaware that herbs will grow during summer, give some of these a try.

Basil is the star of the summer herb garden. The smooth-leafed types that grow 2-3 feet tall are the best known for culinary use. These are typically called sweet basil. Flavorful crinkled- and ruffled-leaf types, as well as some with purple-colored leaves, also are available. All make superb pesto and double as outstanding additions to the landscape.

Mexican tarragon (Tagetes lucida) is native to Mexico and Guatemala. It loves the heat and humidity, providing abundant leaves for cooking all summer. The flavor is remarkably similar to French tarragon, but more intense so you should use less in cooking. Mexican tarragon is also called Mexican mint marigold.

Mexican oregano (Poliomentha longiflora) has an intense oregano flavor. This herb makes an attractive, small woody shrub with small, bright-green leaves. In early summer, it is covered with a profusion of tubular flowers in shades of pale lilac and lavender.

Garlic chives (Allium tuberosum) don’t mind the summer heat at all. Larger and more robust than chives, the flavor is somewhat milder but will do in a pinch. Garlic chives produce stalks with round clusters of white flowers that are attractive and edible. This evergreen, perennial herb is attractive year-round, easy to grow and a great addition to your herb garden.

Perilla (Perilla crispum) produces a plant with purple, ruffled leaves in its most common form, similar to purple-leaf basil. Easily grown from seeds or transplants in part shade to full sun, the flavor of the foliage is unique and is used in Oriental dishes and teas. It’s so attractive, try planting it in your flower beds.


I have five thornless blackberry plants that are growing out of control. They are 6 feet high. How do I prune them?

Blackberries produce vigorous shoots that shoot skyward during harvest season. These vegetative shoots should be cut about 36 inches high. They will branch and next year will have flowers and develop fruit. Remove all old growth — growth that had fruit this year — by cutting back all the way to the ground. The alternate method reduces yield but is easier. Cut all growth back to the ground immediately after harvest.

My crape myrtles have a little fungus on them — a white powder that gets on the leaves and left untreated kind of withers them. I think it is powdery mildew. Fungicides keep it to a minimum, but never cure it. Will the yard treatments help or should I do something additional?

Several applications of a fungicide should deal with a current infection, but will not prevent future infections. If by cure you mean the trees don’t ever get powdery mildew again or at least not again in the same season, well, that’s just not how these diseases work. It’s like catching a cold. You can get over it, but it doesn’t mean you won’t get another one next year (or next month).

My neighbor unhappily pointed out a mass of poison ivy growing from within a large camellia and up the side of his house. Any advice for him on how to kill the ivy but keep the camellia?

Tell him to cut the poison ivy off a couple of inches above the soil line and physically remove the vine from the camellia and side of his house. Immediately after cutting the poison ivy stem at ground level, apply a herbicide with Triclopyr to the freshly cut stems.

I am in need of soil in my yard because of low spots that cause drainage problems and flooding in certain areas. We have St. Augustine grass and want to know if it would be all right to have 12 yards of river silt spread on our grass this time of year. My husband thinks that it might not be the right time to fill the yard. We have a sprinkler system set in place so we could water every day if you suggest this.

Now is an excellent time to fill over lawn grass. This can be done anytime the grass is in active growth, generally from May through early August. Remember that grass will not reliably grow through more than about 2 inches of fill. If you have to fill deeper than that in some areas, you will have to replant grass in those spots. Skip a week mowing the St. Augustine before spreading the soil.

Every summer, my river birch tree practically defoliates, losing half of its leaves. The leaves are covered with spots. I planted this tree to shade my kitchen window and when I need it most the tree is practically leafless. What can be done to solve this problem?

The leaves are infected by a fungal leaf spot, probably Discula betulina, Gloeosporium or Septoria. Other than replanting with a less susceptible tree species, you will need to schedule a preventative fungicidal spray program to prevent this disease. This will require numerous applications and I seldom recommend this approach due to cost and practicality. Leaf spot is more noticeable during rainy summers.

I love the spreading crape myrtles growing in my neighborhood park. How do I prune my tall crape myrtles to look like these spreading trees?

You can’t change the plant’s genetic growth characteristic, so a tall growing variety will always grow vertically and can’t be made to change into a spreading growth habit. Selecting the proper variety of crape myrtle is important when designing the landscape. Since 1980, many new crape myrtles have been released by the USDA and nursery industry, many of them with a spreading growth habit.

Slime mold

A few homeowners have recently asked me about gray powdery stuff showing up in small areas of their lawns. This slime mold on turf looks like burnt wood ashes that have been scattered in small spots on a lawn.

In most cases, only one or just a handful of slimy patches are found scattered across a lawn. After a few days, the slime mold usually disappears without a trace.

Mowing, light raking or washing the affected patches of turfgrass with a hard stream of water breaks up the slime mold and restores the lawn’s beauty. Since slime molds may be more common on heavily thatched or poorly drained portions of a lawn, renovation of the affected areas should reduce the incidence of disease. Applying a fungicide isn’t recommended.

Got a gardening question? Write to Bob Souvestre, horticulturist with the LSU AgCenter, at Burden Center, 4560 Essen Lane, Baton Rouge, LA 70809, or email to bsouvestre, or call Master Gardeners at (225) 763-3990.