The Ornamental Garden in August
Have you ever wondered about the origin of the expression “dog days of summer?” Actually, the expression has nothing to do with dogs. It refers to the 40-day period, from July 3 to August 11, when the Dog Star, Sirius, rises at the same time as the sun. This period coincides with the time of year when summer is at its sultriest – a time when we humans (and dogs) seek refuge from the heat in the air conditioned comfort of our homes.
But what about our ornamental gardens? We can’t just abandon them to fend for themselves. On the one hand, we want them to look beautiful in the summer. On the other hand, we harbor secret hopes that they will cope with the heat just fine without human intervention. Unfortunately, it doesn’t work that way. Despite the heat and humidity, it’s important to stay alert to the needs of the garden.
Watch for Signs of Drought Stress
In addition to normal summer heat and humidity, we often experience spotty rains, or long stretches without rain, resulting in drought conditions. Even if the soil has adequate moisture, some plants tend to wilt in intense heat because their foliage loses water faster than their roots can absorb it. Normally, they revive by early evening when the sun starts to set and temperatures drop. If they don’t, take pity on them and water them deeply.
Lack of water affects plants in various ways, depending on the species of plant and the level of stress to which they are subjected. In addition to wilting, which is frequently the first sign of drought stress, look for the following signs:
- Premature fall color on trees – This indicates that the leaves have stopped producing chlorophyll and is a signal that the tree may be in trouble. Drought stress may be the problem but not necessarily. Repeated defoliation by Japanese beetles or other insects, for example, can stress a tree. Also, the problem could be caused by damage from weed eaters and lawn mowers or from lack of oxygen at the root level if the tree was planted too deeply. Some detective work may be required to properly diagnose the problem.
- Leaf Scorch – This condition appears as a browning of leaf margins and tips.
It is commonly observed on deciduous trees, such as maples, oaks, lindens, horse chestnuts, dogwoods and Japanese maples, and on broad-leaved evergreen plants such as magnolias, rhododendrons, hollies, and Japanese Andromeda (Pieris japonica). Leaf scorch may be the result of a combination of factors, including high temperatures, drying winds, and low soil moisture.
- Shedding of leaves – Some trees sacrifice their older leaves in an effort to conserve water. By shedding the older leaves, trees can then divert moisture to new growth and buds. TIP: Pay attention to evergreens. Although water stressed, they often do not provide any clues to their condition and may stay green until it’s too late.
- Shoot dieback – Drought may make some woody plants (trees and shrubs) more susceptible to canker diseases, which are localized fungal infections that can cause the dieback of twigs and branches. Typically, a canker appears on a tree branch or twig as a sunken, slightly discolored lesion. Prune the twig or branch several inches behind the lesion. Do not cut into the lesion. Otherwise, you may renew or spread the fungal activity. Use rubbing alcohol or a 10% bleach solution to sterilize pruners after each cut.
A drought this year may affect the health and vigor of next year’s plants. For example, water-stressed shrubs that are forming flower buds for next year’s display may produce fewer buds and smaller leaves. Fruiting shrubs, such as winterberries, may drop their berries.
Don’t take a Break from the Ongoing Battle with Weeds
While all our ornamentals are gasping for water and respite from the heat, weeds just merrily roll along, none the worse for wear. In a perverse sort of way, weeds thrive on heat and humidity and need to be controlled before they set seed. Naturally, every weed that produces seed means more weeds and more work for you next year.
Stay alert to plant pests and diseases
Just as weeds appear to thrive in sweltering heat, bugs and diseases don’t seem to be impeded by it either. Stay on the alert for such problems as:
- Rust – This fungal disease occurs when relative humidity is high and moisture stands on leaf surfaces for extended periods of time. Rust fungi produce masses of yellow, orange, brown, or rust-colored spores as part of their life cycle. Like powdery mildew, rust is an unsightly disease but it rarely kills a plant outright. It will, however, stunt a plant and reduce its vigor. Rust is particularly common on ornamental plants such as asters, daylilies, dianthus, irises, hollyhocks and phlox. For mild infections, remove infected leaves to contain the disease. For severe damage from rust, apply an appropriate fungicide.
- Fall Webworms – A widely distributed native pest of shade trees and shrubs, fall webworms appear in mid- to late summer through early fall. They skeletonize and consume leaves inside the protection of a tent-like silken web, which they spin over the foliage they are consuming. See Virginia Cooperative Extension Publication 2808-1013, Fall Webworm, for additional information on the life cycle of this pest and methods for its control.
- Spider Mites — These tiny pests are common in the ornamental landscape and can inflict serious damage to flowers, shrubs and both evergreen and deciduous trees during hot, dry weather. Spider mites have needle-like mouthparts, which they use to pierce the leaves of host plants so that they can suck out the fluids from individual plant cells. This results in a stippled or flecked appearance on leaves. Prolonged damage may cause leaves to yellow and drop off, similar to the damage caused by drought stress. It may be too late to eradicate spider mites this year, but note their symptoms so that you can use safe and effective controls in the future. Remove them with a strong stream of water or apply a miticide as necessary.
- Scale Insects –
The accompanying photo represents just one of more than 1,000 armored (hard) and soft-bodied scale species that exist in North America. Many species of scale are difficult to detect unless you know what to look for. Immobile, these insects attach themselves to twigs, leaves, and stems of plants. They use their piercing-sucking mouthparts to extract fluid from twigs and branches, causing loss of vigor, yellowing of foliage, and branch dieback to a range of trees, shrubs, and other ornamentals as well as houseplants. The scale species most commonly found in Virginia include euonymous scale, cottony camellia scale, obscure scale, white peach scale, and wax scale. At the newly hatched or juvenile stage, scale insects are called crawlers. Depending on the species, more than one generation may be born per growing season resulting in crawlers during May and June and then again in August and September. Camellias, hollies, dogwoods, beeches, oaks, and maples are just a few species that are susceptible to scale. Ladybugs, lacewings, and parasitic wasps are natural predators of scale insects. At the crawler stage, scale insects are also vulnerable to insecticides. VCE Publication 2808-1012, Scale Insects (ext.vt.edu/2808/2808-1012) provides additional information.
Tasks for the August Garden
In addition to the usual deadheading, watering, and weeding, concentrate on:
- Dividing – Identify perennials that need to be divided in your garden. Many perennials benefit from being divided every 3 to 5 years. Either divide them now or wait a few weeks until the weather cools a bit in September. If dividing results in more plants than you can use, pot up any extras for spring plant sales or for sharing. Sink the pot into the ground or use a cold frame to overwinter. Just remember to water newly divided plants until they become well established.
- Fertilizing – Cut back and fertilize leggy annuals in beds, containers, and hanging baskets to produce a new flush of growth. Don’t, however, fertilize perennials, trees, or shrubs at this time. Late summer fertilizing produces tender new growth that will probably be damaged by cold weather.
- Cleaning up – Remove fallen rose and peony leaves. They can harbor disease and insect pests over the winter if allowed to remain on the ground.
- Planting – Plant trees, shrubs and perennials later this month so that they have time to settle in before winter. Prepare the hole in advance so that the plant can be transferred from its container and into its permanent home as quickly as possible. Water immediately and monitor closely while the plant is getting established.
- Maintaining – If you have a pond, keep it topped off and free of algae.
Now that you’ve got the August garden under control and looking its best, take a break from your labors and begin thinking about next season’s garden. Autumn is just around the corner. Soon, it will be time to plant spring bulbs. For best selections, order bulbs now while supplies are plentiful.