The Ornamental Garden in July

  • By Pat Chadwick
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  • July 2015 - Vol. 1 No. 7
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  • 0 Comments

Mid-summer heat and humidity can overwhelm even the most experienced gardener.   But take heart!  The following basic strategies will help keep your July ornamental garden looking its best.

Plant the right plant in the right place.  Yes, you’ve heard this old adage before, but it really is the best strategy for combating July’s challenging weather. Select tough-as-nails annuals such as Melampodium, Globe Amaranth, annual Salvia, and mildew-resistant varieties of zinnia.  Some good drought-tolerant perennial choices for the sunny border include Rudbeckia, Penstemon, Helianthus, Sedum and Salvia.  They will keep things looking fresh and interesting when many gardens are suffering mid-summer meltdown.  

In the absence of sufficient rainfall, water plants early in the morning.  Be water-wise!  Use drip irrigation or a hand-held hose or watering can to water slowly and deeply at the base of each plant.  About 1 inch of water per week should be adequate.   If needed, add mulch over the root zone of each plant to help hold moisture in the soil.  Avoid using overhead sprinklers.  Much of the water evaporates in the air. See http://pubs.ext.vt.edu//426-713/  on Creating a Water-wise Landscape. 

Pay attention to the moisture needs of newly planted perennials, shrubs, and trees.  Their root systems are too small to cope with drought conditions initially.  Even drought-tolerant plants require ample moisture during their first year or two in the garden. 

Check containerized plantings daily for sufficient moisture levels.  Potting soil dries out at the surface but it may be wet deeper in the pot.  Stick your finger about two inches into the soil.  If the soil at the tip of your finger feels dry, then add water.  Water the soil – not the leaves.  Bear in mind that plants have different moisture needs.  Succulents and cactus, for example, prefer to be kept on the drier side whereas many annuals prefer evenly moist soil.  How often you need to water will depend on the planting medium used, the type of container, the amount of sunlight, and the plants themselves.   

Inspect ornamentals frequently for fungal diseases, such as powdery mildew.  This easily recognized fungus appears as white or grayish talcum powder-like spots or splotches, usually on the upper sides of leaves. Powdery mildew affects a wide range of plants including crape myrtles, lilacs, garden phlox, sunflowers, zinnias, and dahlias, just to name a few.  To avoid the problem in the first place, buy healthy plants.  Select mildew-resistant varieties if possible.  For example, ‘David’ garden phlox (Phlox paniculata) has a higher tolerance to powdery mildew than ‘Franz Shubert,’ which is highly susceptible to the disease.  And ‘Jacob Cline’ bee balm (Monarda) is more resistant than ‘Cambridge Scarlet.’  Space new plantings far enough apart to allow good air circulation. Provide adequate moisture and nutrients to keep them healthy.  Remove any diseased plant material in order to minimize the spread of fungal disease.  If only a few leaves are affected, there may be little, if any, action required.  But if the problem is severe and a fungicide is called for, follow the manufacturer’s directions carefully before applying the product to the affected plant.     

Remove weeds promptly.  They compete with ornamentals for moisture and nutrients.  

Deadhead daylilies (Hemerocallis) to keep them looking tidy.  Snap off each spent blossom at the base but be careful not to snap off adjacent flower buds by accident.  After all buds on a scape (stalk) have bloomed, cut the scape all the way back to the ground.    Deadheading is particularly important for re-blooming daylily cultivars.  ‘Stella de Oro’ and ‘Happy Returns’ are the two best known re-blooming daylilies but many more re-blooming cultivars have been developed for the home garden. They start blooming early in the summer and continue blooming until fall, particularly if they are consistently deadheaded during the growing season.  Deadheading diverts the plant’s energy from making seeds to pushing out blossoms.   

Shear or pinch back the spent blossoms of Lavender, Scabiosa, snapdragons, garden phlox, and thread-leaf Coreopsis so that the plant will develop more blossoms.  

Divide and transplant bearded Irises in July or August, but do it on a day when the temperatures are below 90 degrees.   Irises grow from rhizomes, which are elongated stems that grow horizontally below ground and have roots attached to them.  Snap off or use a sharp knife to cut off the vigorous ends of the rhizomes.  Make sure that there are roots attached to each portion.  Before re-planting, inspect each portion and discard any that indicate the presence of Iris borers or soft rot.  Cut the foliage on healthy rhizomes to about 8 inches.  They prefer dry feet, so replant them 18 inches apart in well-drained soil just at or slightly below the soil line.  Don’t pile mulch over the roots.  Mulch can retain more moisture than the rhizomes can handle.     

Pinch back new tip growth on chrysanthemums and asters by early to mid-July.  This will keep the plants compact and full of blooms.  Caution:  Do not pinch back these plants after the middle of July.  Otherwise, the plant will not have time to develop flower buds for the fall.

Stake tall plants, such as asters, that are susceptible to wind damage.  Loosely tie the plant to the stake with soft twine or twist ties.  Note:  Make sure the tip of the stake is flat and not pointed.  Otherwise, the pointed end might pose a safety hazard.

Inspect plants for red spider mites.  Pale, green coloration on foliage may be an indication of spider mite damage.  Roses, evergreens, and marigolds in particular are prone to spider mite damage.  Hold a white sheet of paper underneath a leaf and briskly tap it.  Tiny, crawling mites will drop onto the paper if they are present on the leaf.  If infestation is light, discourage mites with a forceful, direct spray of water from the hose.  Severely infested annual plants should be removed and destroyed.  

Minimize Japanese beetle damage by removing flower blossoms as soon as they begin to fade and all fruit as soon as it is ripe.  Japanese beetles are especially fond of overripe fruit and deteriorating flower blossoms.  Also, take a wide-mouthed jar of soapy water to the garden each daily and knock any Japanese beetles into the jar. 

To the extent practical, hand pick slugs, stink bugs, and other pests and drop into a jar of soapy water.  For Aphids, try a sharp spray of water from a hose to knock them off plants.  If it is necessary to resort to the use of a pesticide, water plants several hours in advance so that they are well hydrated.  Drought-stressed plants have less water in their plant tissues.  The chemicals that enter the leaves will consequently be more concentrated and may burn the leaves.  Be sure to read all pesticide directions carefully and take steps to prevent killing beneficial insects.  For more information on pesticides, go to http://pubs.ext.vt.edu/ 426-706/ – Choosing Pesticides Wisely and http://pubs.ext.vt.edu/ 426-710/ – Applying Pesticides Safely.   

Control mosquitoes by eliminating all sources of stagnant water.   Mosquitoes require only a very small amount of water to breed.  Stagnant water in saucers under potted plants are excellent places for mosquitoes to breed.  

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