by Elaine Mills, Extension Master Gardener
Photos by Elaine Mills unless otherwise noted
Our newest resource covers gardening techniques with a focus on gardens with native plants. Find information on tasks appropriate to each season and learn about year-long practices to encourage and support local wildlife.
Summer Gardening Tasks
Control height of perennials
- Some native perennials, such as New England aster, New York ironweed, and joe-pye-weed can become tall and leggy over the course of summer.
- Techniques for controlling the height of these plants can promote bushier, more compact growth, prevent flopping, and reduce the need for staking.
- One method is to “pinch off” growing tips and the first set of leaves on each stem by clipping them between the nails of the the thumb and forefinger. Alternatively, the length of stems can be reduced up to ½ by “cutting back” with pruning shears.
- Both types of trimming result in doubled growth of the stems. Either process can be done once or several times from late spring to summer, but it should be completed by early July so as not to prevent later flowering of the plant. July 4 is a handy cut-off date to remember.
- For example, ‘Fireworks’ goldenrod (Solidago rugosa), which normally grows to a full height of four feet, can be pinched back and maintained at 18 inches to 2 feet as an edging around a shrub.
- Refer to the chart on Cutting Back and Deadheading Native Perennials to see which plants can benefit from these techniques and when they should be done.
- See a short video demonstrating “Cutting Back Perennials as They Grow.”
- See also The Well-Tended Perennial Garden: The Essential Guide to Planting and Pruning Techniques, an authoritative book on the topic by Tracy DiSabato-Aust.
Deadhead perennials
- Deadheading, the removal of spent flowers, can be done for several purposes. With plants such as hibiscus and irises, where the flowers each bloom for a short time and become mushy, the practice can improve the appearance.
- The technique can stimulate rebloom in other plants, such as culver’s-root, garden phlox, and spotted beebalm, to extend their flowering season.
- In other cases, as with golden ragwort, goldenrods, and Rudbeckia species, deadheading can prevent aggressive seeding and unwanted spread.
- Small garden snips are the best tool for working in tight spots to remove a single spent stem among others that are still blooming. Shears are preferred for neatly trimming thicker stems of iris. Hedging shears can efficiently cut many spent blooms of Coreopsis at one time.
Do summer pruning
Native Deciduous Trees
- While deciduous trees can be pruned at any time to remove dead or broken branches, summer is the recommended time to prune certain native species.
- The trees pictured below should be pruned after they flower, any time from May to July. Gardeners should avoid pruning after July when new flower buds will be set.
- Although Maple blooms very early in spring, it should also be pruned during the summer to avoid the spring sap flow.
- See VA Tech’s Deciduous Tree Pruning Calendar for details.
- Consult a certified arborist for advice and technical assistance.
Deciduous Trees to Prune in Summer
Native Shrubs
- Shrubs can be pruned at any time to correct damage or to remove diseased material.
- Summer is the time to prune shrubs that bloom old “old wood”; that is those that bloom in the spring from buds that were formed the previous year. This should be done shortly after blooming.
- Slow-growing ericaceous shrubs, such as mountain laurel (Kalmia latifolia), rosebay rhododendron (Rhododendron maximum), and pinxterbloom azalea (R. periclymenoides) will need little pruning, and the only task after they bloom will involve removing spent flowers, so they won’t adhere to the foliage.
- Spicebush (Lindera benzoin) also requires little pruning.
- Common yucca (Yucca filamentosa), a stemless shrub, doesn’t need any pruning. Any young offsets can be separated for replanting.
- Many native shrubs tend to sucker or form shoots or sprouts from the base of the plant. Gardeners can choose to prune these away for propagation purposes by placing them in a container with soil, watering them, and allowing them to re-root. Or they may allow the shrubs to spread, forming a hedge.
Suckering Native Shrubs
- Black Haw, the tallest of the native viburnums, can be allowed to sucker as a large multi-stemmed shrub, or it can be pruned to grow as a single-trunk tree.
- For more details, refer to the chart Native Shrubs To Prune in Summer.
Deal with extreme weather
Drought
- Gardeners are facing new challenges as climate change is bringing alternating periods of heavy summer rainstorms and increased drought.
- During the hot summer months, it’s a good idea to monitor rainfall which should ideally amount to one inch of precipitation per week. Levels less than that should be supplemented with a comparable amount of watering by hoses.
- Water uptake is especially important for newly planted woody plants. Trees need 15 to 20 gallons each week for the first three years, and shrubs need extra water for the first two years.
- Even established plants, including large trees, may need supplemental water during extended periods of drought.
- Use of rain barrels or cisterns for water storage and water bags and soaker hoses to deliver water directly to tree roots without evaporation can help during stagnant weather patterns.
Heavy Rainfall
- At the other extreme are heavy rainstorms in which the rain can hit the ground at 25 miles per hour, eroding soil and carrying it, along with chemicals and sediment from roads, into nearby streams.
- Densely planted gardens with layers of canopy trees and shrubs can help buffer the impact of rainfall, and ground-level plants can as “green mulch” can absorb water and prevent runoff.
- If you use wood mulch in any areas, our local forester recommends wood chips over bark mulch which can tend to mat in dry periods.
- After a period of heavy rainfall, it’s important to refrain from working in the soil so as not to break up the soil structure, causing compaction.
- If ponding occurs in certain garden areas and water is not absorbed within three days, consider a variety of stormwater management techniques. See a series of articles on “Stormwater Management Solutions,” and recording of a presentation on “Case Studies in Stormwater Management,” and a webinar on “Rain Gardens for Homeowners” by the Northern Virginia Regional Commission for more information
Be alert for diseases & pests
Foliar Diseases
- In summer, it’s important to be alert for foliar diseases, such as powdery mildew. This fungal disease that is favored by high relative humidity, causes a white to gray powdery coating to form on plant leaves and sometimes on stems and flowers.
- Herbaceous perennials that are especially susceptible to the disease include plants in the Aster family and the Coreopsis, Monarda, Phlox, and Rudbeckia genera.
Photo © Jessica Walliser
- Several cultural techniques can be employed to keep the disease at bay. Watering early in the day, particularly with a soaker or drip hose can keep excess moisture off leaves. Spacing plants adequately can provide for good air movement to dry moist leaves.
- Should the disease develop, diseased materials should be placed immediately in a plastic bag and discarded to prevent fungal spores from spreading.
- Spot anthracnose, a disease caused by another fungal pathogen, specifically targets dogwood trees, affecting their leaves and sometimes the flowers. It is a seasonal disease prevalent in regions with high levels of humidity and heavy rainfall.
- Spot anthracnose is generally first noticeable on the leaves and may also cause discoloration of the petal-like bracts. Infected leaves may drop earlier than usual, reducing vigor of the tree.
- Cultural practices that can help prevent the disease include:
- Siting dogwoods in locations with afternoon shade rather than full sun
- Planting in moist, rich, acidic soil
- Using mulch to keep roots cool
- Watering during drought to minimize stress
Insect Pests
- Summer may also be a time when gardeners become aware of pest insects on their plants.
- Aphids, sap-sucking insects, seem especially drawn to oxeye and cup plant. Two control technique include knocks the pests off these plants with a water spray and taking advantage of the presence of natural predators, such as ladybeetles.
- Multiple species of milkweed attracts bright orange and black insects called milkweed bugs. While they feed on the seeds by piercing the seed pod, they cause minimal damage, so control other than hand picking is generally not required.
- Red columbine sometimes shows signs of the presence of leafminers, the larval stage of a fly which tunnels through the leaves, leaving patches of dead tissue. The damage they cause is usually only cosmetic, and gardeners can puck off any affected leaves, if desired.
Miscellaneous summertime tips
Control mosquitos
- During the summer months, gardeners may be tempted to spray pesticides to control mosquitos. The use of these chemicals is deleterious to pollinators as the products do not distinguish between unwanted pests and beneficial insects.
- Techniques to control their presence include monitoring for standing water, changing water in fountains and bird baths every three days, and using dunks with Bt (Bacillus thuringensis) in those water features.
- Personal protection can include wearing protective clothing, applying repellents, and using fans in seating areas.
- See the article “Keep Mosquitos & Ticks at Bay without Pesticides” for more details.
Limit light pollution
- When sitting outside in the evening, try to limit light pollution, which has an impact on the navigation of migrating birds as well as the lifecycle of insects and plants.
- Prevent beneficial insects from being drawn to outdoor lights by using shielded lighting and yellow LED bulbs.
Avoid peat-based products
- Peat bogs are non-renewable resources and harvesting this type of organic matter releases vast amounts of carbon dioxide into the atmosphere.
- When potting up plants for use in patio or balcony containers, it is now advisable to avoid potting soil with peat by substituting compost as an amendment.
- Coconut fiber (coir) pots are available as alternatives to peat pots for starting seedlings.
