| Herbaceous Ornamental Plants - August 2008
Please Note: All recommendations are for central Maryland. Time frames shift two weeks earlier in Southern Maryland and the Eastern Shore and two weeks later for Western Maryland. Check publications for further information.
Culture
Annuals and Perennials
Yarrow and salvia can be cut back to encourage re-bloom. Deadhead the spent blooms of annuals like zinnias and marigolds.
Plant hardy mums now so they will become well established prior to cool weather. Late August through September is a good time to transplant, divide and plant perennials.
Perennials such as daylily, liriope, echinacea and others can be divided and replanted at this time. Be sure to keep them well watered during dry periods.
Ground Covers
If turf grasses have failed due to poor location, consider planting appropriate groundcovers this fall. Soil should be loosened and organic matter incorporated prior to planting. Select plants based on the amount of sun they require. Good choices include striped or spotted wintergreen, trailing arbutus, moss phlox, epimedium, sweet woodruff, partridge berry and ferns. Groundcovers are also useful as a border around buildings and garden beds. However, do not plant rapid growers near property lines or woodlands.
Vines
Cut back annual vines that are looking peaked or are growing out of bounds.
For an interesting alternative to traditional vines, try hops. You can plant them in the spring or fall from purchased crowns. Plant them in rich, well-amended soil. The plants grow vigorously if supported, either upward or sideways. Attractive, pleasant smelling cones or catkins are produced through most of the summer.
This is a good time to propagate clematis and other vines by taking stem cuttings with a sharp knife. Dip the bottom end into a rooting hormone and plant in a loose growing medium with at least one node below the soil level. Keep the cuttings moist and out of direct sunlight until new roots develop.
Weeds
Poison ivy foliage can be sprayed with a labeled herbicide now. You will have to make multiple applications through the growing season to significantly weaken or kill the plants. Cut poison ivy plants down to the ground or spray with glyphosate or triclopyr. Do not handle the hairy poison ivy vines wrapped around trees.
Late season is a good time to apply glyphosate to control bamboo shoots and other hard to control weeds because this is when the plants are transferring nutrients to the roots.
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Insects
Sawfly larvae have been observed feeding on hibiscus. They are green and resemble caterpillars. Treat affected plants with insecticidal soap, provided temperatures are not too high.
Irises with leaves that are flopping over may be infested with iris borer, the larva of a clear wing moth. The eggs are laid on the foliage in the spring and the larvae move down to the crown and bore into the rhizome. Dig up infected plants and cut out the larvae and damaged tissue. Re-plant the healthy rhizomes.
Whitefly and spider mites are common pests that may be causing stippling, yellowing and scorching of foliage. Spider mite populations can be high in hot, dry weather. Damage occurs on a wide variety of flowering plants. You’ll notice yellowing leaves that look dusty or dirty on the underside. Mites are pinpoint size sucking pests that can be observed on leaf undersides with the unaided eye. Keep plants hosed down during hot dry weather. Spraying insecticidal soap or horticultural oil on mite damaged plants during hot weather can cause serious leaf burn. If you notice spider mite damage on different types of plants in your yard you might consider purchasing and releasing beneficial mites, which will hunt down and consume the pest mites.
Grasshoppers can chew large, ragged holes in the leaves of many different plants.
Slugs are quite active in wet weather. The three types of slugs found in this area are the spotted garden slug (3-5inches), the tawny garden slug (2-3 inches) and the gray garden slug (2-3 inches). They cause damage (large holes in leaves) to a wide variety of annuals and perennials. Favorite plants include hosta, salvia and marigold. Set out shallow saucers of beer or yeast mixed in water to attract and drown the slugs. Safe and effective baits containing iron phosphate are widely available.
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Disease
Southern blight is a significant disease of annuals and perennials encouraged by hot, humid weather. It is a soil-borne fungal disease that attacks a wide range of perennials including thyme, coneflower, coreopsis and black-eyed susan. Affected lower stems turn brown or black, foliage wilts and plants will eventually dry up and die. Tan colored fungal fruiting bodies, the size of a small seed may be observed on affected stems. You may also notice a white fungal mat growing over the infected stems. In some cases, plants can be cut back to the ground and plants will re-grow. However, the disease may kill crown and roots and plants will need to be removed. Keep mulch away from plant stems and water in the morning to minimize problems with Southern blight. Working organic matter into the soil may help lessen the problem. No chemical controls are available.
Rhizoctonia web blight is a problem on sweet woodruff and other perennials, which produces similar symptoms to southern blight. Foliage becomes matted and brown. Rhizoctonia usually does not kill roots or crowns. To reduce the incidence of disease, remove mulches, work organic matter into the soil and space plants out to improve air circulation.
Powdery mildew may be seen now on many perennials, like roses, phlox and monarda. This is a fungal disease that is favored by low rainfall and high humidity. Powdery mildew may be observed on plant foliage as a grayish, powdery coating on upper leaf surfaces. Select resistant cultivars when possible.
Daylily leaf streak causes spotting and blighting of daylily leaves. Remove damaged leaves.
Periwinkle and vinca are prone to another fungal disease called phomopsis blight that causes plants to wilt and turn brown. Prune out infected plants. No chemical controls are available. Web blight attacks low growing perennials like woodfruff. Foliage becomes matted and brown. This disease only kills the plant tops, not the crowns. To reduce the incidence of these diseases, remove mulches, work organic matter into the soil and space plants out to improve air circulation.
You may have hostas that are yellowing and becoming scorched. In many cases this was caused by a combination of hot, dry conditions and diseases like alternaria and gray mold. Remove badly affected leaves.
Bacterial and fungal leaf spot diseases of English ivy may be observed. You may notice ivy leaf blight on your ivy vines. This fungus will weaken your planting and is most severe in thick, overgrown beds where dead leaves have accumulated. Rake out and thin out infected ivy beds. A fixed, basic copper spray can also be applied.
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Water Gardens –Water lilies are growing rapidly and should be fed with fertilizer tablets regularly according to label instructions. Periodically remove the older, yellow leaves and spent flower heads of tropical lilies. The water lily leafminer is a common pest that produces serpentine mines in leaves. Simply remove and discard affected leaves. The china mark moth larva is another pest of lilies. The larvae live in small pockets of leaf tissue and float on the pond eating holes in the edge of lily pads. Pick off and dispose of the affected foliage. Water lettuce and water hyacinth are tropical plants that can help keep your pond water clean. Tropical lilies should be at peak bloom and will continue flowering through frost. Keep them fertilized to encourage strong blooming. Trim off and remove ragged and dead plant parts. Weak or dying plant parts should be removed to help keep the water clean. Water lily aphid feeding has been observed. Remove heavily infested leaves or direct a strong water spray at the aphids.
Now is a good time to clean out excessive plant growth in your pond and remove dead or diseased leaves. If you have a circulator or fountain, turn it on during hot weather to increase the amount of oxygen available for your fish. Ponds may need topping off. If using public water do not add large amounts of water at one time. The chlorine added to public water systems may kill fish.
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Ornamental Landscape Plant Tips - July 2008
Ornamental Landscape Plant Tips - August 2008 |
