Tidewater Gardening - August 2013

August Gardening Angst


K. Marc Teffeau

August is the height of vacation season for most of us. It’s also the time when numerous problems pop up in the garden. On the vegetable side, a garden that weeds itself has not yet been developed. However, by mulching as much as possible and controlling the weeds before they go to seed, you can reduce your weeding time.
With the hot, humid weather comes disease problems. Two different kinds of mildew ~ downy and powdery ~ will affect vine-type vegetable crops at this time of year.
Downy mildew will be a problem on beans, cucumbers and cantaloupes. This fungus disease causes yellow to dark areas on the upper surface of older leaves. Turn the leaf over and you’ll see a whitish- or gray-colored mold in patches on the under surface. The mold may also occur on bean pods. Affected vines may be scorched and killed.
Powdery mildew appears as a white or brownish talcum-like growth on leaves and young stems of squash, pumpkins, cantaloupes and cucumbers. Look for it, especially on the upper surface of leaves. It will also sometimes affect fruit. Severely infected plants will turn yellow, wither and die.
There are a few measures you can take to control either downy or powdery mildew. Use resistant plant varieties whenever possible. Don’t plant non-resistant varieties in the shade. Improve air circulation by thinning and pruning. Overcrowding keeps the humidity high around the plants and favors the development and spread of the diseases. Destroy the affected crops in the fall, since they may serve as a source of new infections next year.
For control it is also sometimes necessary to use fungicides. Check the garden center shelves for fungicides specifically for vegetables and that list mildews on their labels. Be sure to read the label of any pesticide before using it to insure proper application.
It is important to remember, whenever you apply pesticides, to not spray when temperatures are over 85° or when it is windy. Certain insecticides like Sevin© will burn plant foliage when applied in high temperatures. Other liquid pesticides contain a solvent that will also burn if applied in high temperatures.
Powdery mildew also affects a number of ornamental plants in the landscape, especially lilacs and annual flowers. This infection occurs when the day temperatures are hot and the nights cool. As with control in the vegetable garden, growing mildew-resistant cultivars of plants is your first line of defense. Good culture and sanitation are also important for control.
Avoid use of high nitrogen fertilizers at this time of year as they promote lush foliage growth the is very susceptible to mildew. Treat the plants with a fungicide on an as needed basis.
Fruit plants also need your attention now. Fertilize your strawberries in August. For plants set out this past spring, apply 4 to 6 ounces of ammonium nitrate, or 12 to 18 ounces of a 10-10-10 complete fertilizer per 25’ of row. Spread the fertilizer uniformly in a band 14” wide over the row when the foliage is dry. Brush the fertilizer off the leaves to avoid leaf burn.
For plants in the second year of growth, increase the application rate to 6 to 8 ounces of ammonium nitrate or 18 to 24 ounces of 10-10-10 per 25’ of row. Strawberries set their fruit buds in the late summer to early fall for the next year, so they need plenty of fertilizer now. If you do not want to use an inorganic fertilizer, there are some organic, slow release fertilizer products available. Just follow the label directions as to application rates.
It is very important to maintain adequate water for strawberries, blueberries and bramble crops in August. A slow, long soaking with the water hose around the plants during the dry spells of August will ensure good fruit bud production for next year’s crop.
Don’t forget to prop up branches of fruit trees that are threatening to break under the increasing weight of ripening fruit. Be sure to make a mental note now to thin next year’s fruit crop in June to reduce the number of fruit the tree is carrying so as to improve the size and quality of the remaining fruit.
Watering is also critical for fruit trees at this time, especially for late-season peaches. To get the flesh to swell and to produce large fruit, be sure the trees get adequate water about two weeks before the fruit is to be harvested.
Make sure you pick up and compost all fallen fruit to reduce the pest population next year. Worms hide in the fallen fruit and then pupate in the soil, ready to lay eggs next year. If you shred or cut up the fruit before composting, you will speed the process and also physically destroy the pests.
If slugs are a problem in your garden, here is a quick and easy method of reducing the population, especially if you are squeamish about the critters. Put out squares of cardboard in your garden each night. In the morning, pick them up, and if slugs are clinging to the underside, discard the whole square in the trash. The number and size of the squares depends on the size of your garden and how heavy your infestation is. This eliminates the process of hand picking each one.
Late summer is not the time to prune your ornamental trees and shrubs. The removal of large branches, unless they are dead, will tend to stimulate new branches to grow. Because of their late start, these new branches will not be able to acclimate themselves before the first frost and subsequent cold weather. The results will be winter injury and dying of these new branches, as well as injury to the whole tree. If your hedge is looking a little shaggy, however, there is still time for a light summer trim.
Now is also not the time for any extensive fertilizing that will stimulate growth. This new tender growth is soft and easy to kill with the first frost. Fertilizing now can also stimulate the plant into growth if we have an Indian summer later this fall. If this happens, you can almost guarantee that your plants will not be able to survive the winter. If you must fertilize, wait until sometime around the first of November or after the first or second hard frost.
Avoid deep cultivation in your flower beds. Loosening the soil under hot dry conditions reduces water uptake by increasing the loss of soil water and damaging surface roots. Plants often look much worse after cultivation than before.
Some unusual flowers that you may see thriving in the heat of August include acidanthera (also called Abyssinian Gladiolus) which bears fragrant white flowers with dark lilac centers and resemble gladioli; crocosmia, 24- to 30-inch tall yellow, orange or scarlet flowers; and Galtonia candicans (summer hyacinth) with a loose white hyacinth-like inflorescence.
Mums will start to appear at the garden center in late August. The best time to buy chrysanthemums is in late summer, as soon as they become available. For a longer blooming period, choose plants that are just coming to bud, instead of those already in full bloom.
If your cutting garden is looking bedraggled, clear out the annuals that have finished blooming or are overgrown. Don’t let your hybrid, annual flowers go to seed. This weakens the plant and reduces bloom. In addition, the seed is not desirable to save because the resulting seedlings usually will be very different from the parent and often of a poorer quality. Mulch the empty areas to deter weeds.
Oriental poppies can be safely planted, transplanted, or divided this month. Plant these hardy, long-lived perennials in well-drained soil and in full sun.
Take cuttings or favorite annuals, or sow seeds in pots for winter-flowering indoors. The following bedding plants root easily: coleus, geraniums, impatiens, wax begonias, and fuchsia. Plant calendula, ageratum, marigold, stock, impatiens, and snapdragon from seed.
Petunias vary their growth habits according to temperature and day length. At 62° and below, petunias will be branched, bushy, compact and multi-flowered. From 63° to 75°, day length affects growth. If plants receive less than 12 hours of sunlight at these temperatures, petunias will be single-stemmed and have a single flower. With more sunlight, petunias branch and increase flowering. At over 75°, day length has no effect and the plants will be tall, leggy and bear few flowers.
Plant autumn-flowering crocus, sternbergia, colchicum, and other fall-flowering bulbs as soon as they become available at garden centers. Crocus and sternbergia need full sun; colchicum can be planted in areas receiving light shade.
Colorful plastic golf tees can be stuck in the ground to mark the location of dormant plants, such as spring bulbs or perennials.
For the chrysanthemums that you already have in your landscape, disbudding ~ removal of multiple flower buds ~ will limit the number of flowers per stalk and produce larger blooms. Most mums, except spray types, respond well to disbudding.
Happy gardening!

Marc Teffeau retired as the Director of Research and Regulatory Affairs at the American Nursery and Landscape Association in Washington, D.C. and he now lives in Georgia with his wife, Linda.