July in the Ornamental Garden

As any gardener knows from experience, July’s heat and humidity can dampen our enthusiasm for working in the garden.  However, a good strategy is to work in the cool hours of the morning or evening.  Just 10 or 15 minutes a day maintaining your garden can make a huge difference in how it looks and performs.  Here are a few suggestions (for new gardeners) or reminders (for seasoned gardeners) for keeping your garden looking perky and well maintained despite the heat:

Deadhead spent blossoms.  Devote a few minutes each day to snipping or pinching off spent blossoms. Just choose one or two plants that need your attention and focus on those.  The result will be a tidier looking garden with less stress and wear and tear on you.  As a bonus, deadheading can trigger the production of more blossoms on many ornamental plant species.

Trim plants of old, tired, or tattered-looking foliage, flower stalks, or damage caused by pests or disease. Large-leaved plants, particularly hostas, look much more attractive if you trim off the leaves that have suffered heavy slug damage.

Selectively cut back or shear plants that have finished blooming to spur fresh new growth and perhaps some re-bloom as well.  For general information on perennial plant care, see the Virginia Cooperative Extension’s (VCE) publication 426-203 on the culture, maintenance and propagation of Perennials.  For the new gardener who would like more detailed information on perennial plant maintenance, Tracy DiSabato-Aust’s book on The Well-Tended Perennial Garden is a useful, well-organized resource on the subject.

Stake or cage taller perennial species to keep them from flopping over or collapsing.  Plants fall over for many reasons, including too much weight from flowers, too much moisture, too much shade, or overly rich soil.  A number of plants may simply be cut back, pinched, or sheared to keep their height under control without loss of blooms.  Goldenrod, asters, balloon flower, tall daisy species, catmint, and Boltonia fall into that category.  Other plants should not be cut back but staked or caged instead to avoid damaging flower buds.  Lilies, hollyhocks, foxgloves, and Crocosmias fall into this latter category.

Pinch back fall-blooming perennials, specifically chrysanthemums and asters, before mid-July to keep their overall dimensions under control and to prevent them from setting buds before fall.  Do not pinch back these plants after mid-July because they won’t have enough time to set new flower buds for the fall.

Neatly edge flower beds and replenish mulch as needed.  This is one of the simplest and most effective ways to make your garden look fresh and inviting.

Monitor moisture levels.  July is often the hottest month of the year and typically one of the driest.  So, in the absence of adequate rainfall, provide supplemental water to plants as needed.  Be water-wise and use drip irrigation or a hand-held hose or watering can to water slowly and deeply at the base of each plant.  Infrequent deep watering is generally best for established plants.  This encourages them to send their roots deeper into the soil, which helps them become more drought tolerant.   Plants that are becoming established in the landscape should receive about an inch of water per week.  Newly installed trees and shrubs may require more water, particularly during their first year or two in the ground.

Keep the garden from looking crowded and overgrown.  Dividing some of those overgrown perennial clumps and thinning them out will improve the overall appearance of your garden.  While fall is preferable for dividing most perennials, some, such as bearded Irises, may be safely divided in summer in the absence of a drought.   If you do attempt to divide your perennials in the summer, choose a cool, cloudy, or overcast day to do it.  Water the plants deeply the day or evening before so that they are well hydrated.  Dig them up, divide them, and plant the divisions right away so that the roots don’t dry out.  Cover the root zone with mulch to cool the soil and help retain moisture.  Give the divisions some protection from the sun while they become established.  Shade cloth or a row cover or even an old umbrella tilted at an angle can provide huge benefits as temporary protection from strong sunlight.  Water early in the day for maximum benefit to the plants and continue to keep them well watered for the remainder of the summer.

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 into the soil about two inches.  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, 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.

Weeding – This task never fails to be included on every “to do” gardening maintenance list during the growing season.  It is one of those never-ending chores that most ornamental gardeners detest. But here’s why it’s important:  Weeds compete with ornamental plants for moisture and nutrients plus they have an amazing capacity for self-preservation.  For example:

• Oxalis (Yellow wood sorrel) – This prolific annual weed is highly successful at reproducing itself. It looks innocent enough with its tiny yellow flowers and clover-leaf shaped foliage.  But the flowers give way to seed capsules, which explode, throwing the seed several feet away.

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  Horse Nettle – This perennial weed reproduces by seed as well as by an extensive root system. If you dig it out of your garden (rather than use an herbicide), remove the entire root.  Any root fragments left in the soil can remain viable for years and will wait patiently to sprout until growing conditions are ideal.

• Crabgrass – A summer annual, this weed certainly qualifies as one of the top ten nuisances in both the lawn and the ornamental garden. It germinates from mid-spring to mid-summer and reproduces by setting seeds and by rooting at the lower joints.  To control it, dig it out by the roots and make sure you get every bit of the plant.

Tackle these and other weeds when they are small, easy to pull, and less likely to require an herbicide to control them.

ORNAMENTAL PLANT DISEASES

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.  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 to help minimize the spread of fungal disease.  If only a few leaves are affected, little, if any, action may be 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.

Aster Yellows – This highly contagious viral-like plant disease is caused by a phytoplasma, a tiny organism that is spread from plant to plant by sucking insects such as leaf hoppers. This disease affects more than 300 ornamentals, vegetables, and weeds.  It is characterized by chlorosis (yellowing of the leaves while the veins remain green), extreme leafy growth, and deformed flowers that often remain green or sometimes exhibit tufts of green foliage within a blossom or in place of a blossom. Some annuals and perennials affected by aster yellows include aster, coneflower, coreopsis, cosmos, chrysanthemum, petunia, snapdragon, marigold, and zinnia.  Other than selecting plants that are immune to the disease, there is no effective cure for it. Remove the entire plant to prevent this disease from infecting other plants in your garden.  The aster yellows phytoplasma organism will not survive once the plant dies.

ORNAMENTAL PLANT INSECT PESTS AND PREDATORS

It’s a bug-eat-bug world out there and keeping insect populations under control is one of the gardener’s biggest challenges in summer.

Red spider mites are a type of arachnid and not true insects. They may be tiny, but they can do a lot of damage.  Pale, green coloration on foliage may be an indication of spider mite damage.  Roses, evergreen species, and marigolds are examples of plants prone to their damage.  To test for spider mites, hold a white sheet of paper underneath a leaf. Briskly tap the leaf to dislodge any suspected tiny, crawling red mites.  If they are present on the leaf, they will drop onto the paper.  A minor infestation can be remedied with a forceful, direct spray of water from a hose.  Severely infested annual plants should be removed and destroyed.

Aphids are a common pest of many ornamental plants as well as houseplants, vegetables, fruit trees and field crops.  These soft-bodied insects prefer succulent new shoots or young leaves. These pests have sucking mouth parts that allow them to suck juices from plant tissues.  While a mild Aphid infestation is not particularly harmful to a plant, a heavy infestation can stunt the growth of a shoot, cause slightly curled leaves, and delay the production of flowers and fruits.  In addition, Aphids secrete a substance called honeydew, which encourages the growth of an unsightly sooty mold on foliage and interferes with photosynthesis.  Fortunately, aphids have natural predators, such as lady beetles, parasitic wasps, lacewings, and damsel bugs, which help mitigate damage to plants.  Also, a sharp spray of water is usually sufficient to dislodge them from plants.   Asclepias tuberosa (milkweed), hibiscus, and Garden phlox are several plants that are often subject to aphid damage.  A fascinating fact about aphids is that they are capable of reproducing parthenogenetically – that is, without mating.  For more information on how that is possible and to learn about the relationship between aphids and ants, see Virginia Cooperative Extension publication ENTO-350NP on Aphids.

Not all bugs are pests.  Ground Beetles, for example, are the unsung heroes in the battle against garden insect pests.  Of this huge family of insects, approximately 2,500 species may be found throughout the United States.  Most ground beetles have shiny, sometimes iridescent, black, blue-black, brown, or green hard shells on flattened bodies with narrow heads.  They are equipped with large mandibles that they use to capture their prey.  These nocturnal creatures feed at night and hide during the day under mulch, leaves, rocks, boards, or logs.  They have wings but seldom fly, opting instead to scamper quickly away when disturbed.  Both the adult and larval forms of ground beetles have voracious appetites and prey on a variety of soil dwelling pests as well as plant and tree pests.

Earwigs are considered to be either beneficial insects or pests or both, depending on your point of view.   Anatomically, they are one of the stranger-looking insects in the garden.  Large pinchers emerge from the tips of their abdomens giving them a ferocious look.  Mostly nocturnal creatures, they feed on plants at night and hide during the day in moist, dark places, such as mulch, soil, plant debris and under rocks and boards. They are regarded as a nuisance because they feed on the flowers and foliage of a wide range of plants, leaving irregular holes or ragged edges.  Despite their destructive eating habits, earwigs do have some useful qualities.  They are omnivorous and help break down organic matter in compost piles.  They are natural predators of aphids, mites, nematodes, insect larvae, slugs, snails, and other slow-moving insects.  For more information, see VCE publication 3101-1527, Earwigs.

INVASIVE ALERT:  Japanese Honeysuckle (Lonicera japonica) is an aggressive, fast-growing vine that is invasive throughout the entire eastern United states. It forms large tangles that smother and kill other vegetation.  Often found at the edge of a disturbance, such as a path or along the edge of woods, it prefers full sun but is highly adaptable and can thrive in shaded environments as well.  It drops its leaves in colder climates but can be semi-evergreen to evergreen in warmer climates.  It reproduces by seed or from runners.  For advice on when and how to control this invasive species, see the Invasive Plant Control Calendar, which was published in the May 2022 issue of The Garden Shed.  Also see the Blue Ridge Partnership for Regional Invasive Species Management (PRISM) fact sheet for information on Japanese Honeysuckle.