| Herbaceous Ornamental Plants - May 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
The frost-free date for Central Maryland is May 10 – think Mother’s Day! Plant all warm season annual plants at this time. Purchase stocky, transplants with healthy, white root systems. Remove any flower buds or opened flowers when you get them home to hasten root establishment. This will help direct the plants’ energies to root development and will result in more productive plants. Gently breakup the roots of root-bound transplants. Summer annual bulbs like gladiolius, tuberous begonias, cannas, caladium and dahlias can be planted now. Perennial plants can be safely divided and moved at this time.
Soluble starter fertilizers can be applied to the foliage or root-zone of spring flowers to get them off to a fast start. These fertilizers have a high percentage of phosphorous relative to nitrogen and potassium. The middle number on the fertilizer label will be highest. Seaweed extracts, fish emulsion, manure and compost teas can be used as well. Sweep or wash granular fertilizers off of plant foliage. Fertilize spring flowering bulbs with a balanced fertilizer like 10-6-4 or 10-10-10. Leave the foliage of spring flowering bulbs alone until the top growth dies back. The green foliage is producing sugars to maintain good bulb health.
Consider planting a groundcover this spring in areas of your yard where the turf is consistently weak. Groundcovers are especially useful on slopes, in shaded areas under trees, and as a border around buildings and garden beds. Before planting a groundcover, work in organic matter and add lime and fertilizer according to soil test recommendations. Groundcovers for sunny areas include creeping tyme, phlox, artemesia, creeping dianthus, oregano, plumbago, and lambs ear. Some good shady area groundcovers include vinca vine, astilbe, epimedium, coral bells, wild ginger, hosta, mazus reptans, sweet woodruff, and lambs ear. Check with local nurseries for other plant ideas and specific cultivars. Groundcovers are also useful as a border around buildings and garden beds. However, do not plant these rapid growers near property lines or woodlands.
This is a good time to lay down organic mulches, like pine bark, to moderate soil temperature and suppress weed growth in flower beds.
Consider growing annual vines like cardinal climber, hyacinth bean, morning glory, etc. to cover fences, gazebos and trellises. Hops are a fast growing perennial that can be planted now and allowed to climb on a fence or trellis. Or try planting a hardy climbing rose in a sunny spot against a building or fence.
Tear-a-thumb, also known as mile-a-minute vine, germinates in early spring and can be seen growing now. The triangular shaped leaves have stems with recurved spines. This invasive, viney weed can quickly take over a garden bed. Control by hand-pulling or an application of a glyphosate herbicide.
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Pests
You may notice streaking in iris foliage caused by young iris borer. The larvae then tunnel down and feed on the rhizome. The leaves and flower stalks may wilt. The best control is prevention. Do not mulch your irises, plant rhizomes high in the planting bed and select full sun sites. If you suspect borers, dig up the rhizomes after bloom, cut off rotted and infested portions and re-plant.
You’ll begin to see slugs on all types of flowering plants. They chew small holes in leaves and can also shred leaf tissue with their rasping mouthparts. Slime trails are a definitive sign of slug activity. They breed in protected, damp areas under boards, in ground covers and under thick mulches. They can be controlled with a directed spray of vinegar and water, with traps and baits and, of course, handpicking. They can be trapped with shallow pans of water and bread yeast or beer. You can also set out boards or half grapefruit rinds to attract and kill them. Diatamaceous earth, sharp sand or ground crab and oyster shell can be applied around plants as physical barriers. Chemical baits are also available. Be sure to carefully read the label.
Four-lined plant bugs are feeding on a wide range of woody and herbaceous plants, especially mint. The adults are yellowish-green with 4 black stripes. The nymphs are bright red. The bugs leave rows of small, round dark spots on leaves. Plants typically grow out of the feeding damage.
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Disease
The fungal disease Phomopsis can show up on vinca which can cause dieback and can be controlled by thinning out beds.
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Aquatic Gardening
Algae growth is rapid in the spring when the pond is fully exposed to the sun before water plants begin to make vigorous growth. Starting up your filtration system will help control algae growth. A biological filter can also help reduce algae growth by absorbing the excess nutrients that feed algae. Biofilters are small boxes with a rock substrate that bacteria grow on. The bacteria will absorb nutrients. Once water plants begin to cover the water surface the algae problem will subside. Be sure to plant a sufficient number of plants to cover about 60% of the pond surface.
Now is a good time to divide and repot hardy water lilies and other crowded aquatic plants. Fertilize your aquatic plants with products recommended for aquatic plants. Wait until June to plant tropical water lilies.
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