The Ornamental Garden in June

The June garden is alive with color. Perennials are hitting the peak of their first cycle of summer bloom. How can we make sure that color will continue throughout the growing season? And how do we take care of our garden in early summer so that it can endure the demands of a sultry July and August?

ADD COLOR WITH PERENNIALS

June-blooming perennials make our gardens come alive. They are the reward for an ornamental gardener’s planning, work, and nurturing. Perennials usually offer a two-to-three-week bloom period. It takes some careful planning, or perhaps some trial-and-error fortuitous planting, to get a continuous bloom from different perennial groupings.

Nurseries like to sell plants when they are in bloom, so plant shopping can be an overly-tempting experience! Make a mental note and draw up a list or even draw a quick sketch of gaps in your garden. Consider whether you want to fill that space with a current bloomer or a later-season bloomer. In addition to color, consider which foliage textures would be attractive. Do you want taller perennials for the back of the garden, or shorter-to-midsized perennials for the front and midsection?

The website for the Lewis Ginter Garden in Richmond highlights plants in bloom each month and June bloomers include: Magnolia grandiflora; Hydrangea quercifolia or oakleaf hydrangea; Hydrangea paniculata ‘Pink Diamond’; Hydrangea serrata ‘Blue Billow’; Echinacea pupurea or ‘Pink Double Delight’ coneflower; Echinacea paradoxa or yellow coneflower; Papaver somniferum or opium poppy; Iris ensata ‘Ise’ or Japanese water iris; Calopogon pallidus or pale grass pink or swamp pink; Hemerocallis or daylilies, Platycodon grandifloras ‘Sentimental Blue’ or balloon flower; Rosa ‘Julia Child’; Scabiosa columbaria ‘Butterfly Blue’ or pincushion flower; Mondarda didya ‘Jacob Cline’ or bee balm; and Kniphofia triangularis or red-hot poker, and more!

Bloom periods can also be extended by growing different varieties of the same plant. Hydrangeas, for example, offer varieties that bloom from mid-spring to late summer. Wild roses or heirloom roses bloom once in spring but rose cultivars in a spectrum of colors were developed to provide continuous bloom from spring through first frost.

ADD COLOR WITH ANNUALS

Another approach for continuous color is to add annuals as June perennials reach the end of their bloom period.

Lantana is a great option for lots of color ranging from white to orange to yellow, pink, and lavender. As the individual flowers age, they often change color, giving the blossoms a bicolor effect. The foliage can be mildly poisonous to some animals, including deer. See the Clemson Cooperative Extension Factsheet on Lantana.

Angelonia angustifolia or summer snapdragon is an annual that grows 12-18’ in height, in colors that range from deep mauve to lavender, pink, and white. The plant tolerates heat and humidity and is deer resistant. Its leaves are somewhat aromatic. See the Missouri Botanical Garden Plant Finder for more information.

Verbena x hybrida, commonly called garden verbena, is a short-lived perennial in zones 9-11 but is grown as an annual in zone 7. It is noted for its profuse bloom of small five-petaled flowers in rounded clusters (to 3” wide) from late spring to fall. Plants can be mat-forming/trailing (to 10” tall) to bushy/upright (to 20” tall). Flower colors include blue, violet, purple, rose, dark red, yellow, white and bicolor. Some varieties are fragrant. Oblong toothed leaves (to 4” long) are gray-green to dark green. The plant’s deer resistance is rated B by the Rutgers New Jersey Agricultural Experiment Station; that rating means “seldom severely damaged.”

Gomphrena or globe amaranth, also deer resistant, is treated as an annual north of Zone 9. Gomphrena is one of 90 related species belonging to the Amaranth family. Gomphrena globosa is the species most commonly grown in this country. It is a 12” to 24” tall annual bedding plant with 1” to 2” globe-shaped flower heads that resemble clover blossoms. Cultivars come in shades of white, pink, purple, and magenta. Blooms enliven the garden from early summer until frost. This plant was highlighted in the September 2017 issue of The Garden Shed.

MAINTENANCE

Watering

After a rainy spring season, it is hard to imagine the beginning of a summer drought. But June often brings drier weather which means we need to start watering and keep watering newly planted plants, container plants, and any established plants that look wilted after even a short dry period. In times of drought, water infrequently and deeply, about 1” per week. For more info, see The Garden Shed June 2016 article, “Growing Things When the Rains Don’t Come.”

Weeding

Weed. And weed some more. Mulching not only helps retain moisture, but it deters weeds and makes weed-pulling easier. Commonly-seen weeds in June include:

• Crabgrass – The best crabgrass preventer is a healthy, thick lawn, and soil with the proper pH balance (7.0-7.5). Perennial ryegrass is the best competition for crabgrass. Crabgrass thrives in compacted lawns so aeration can be beneficial.
• Pigweed – An annual that reproduces by seeds, pigweed is characterized by its fleshy, red taproot. This weed appears in late spring or early summer and likes warm weather. Try to pull it out before it flowers.
• Chickweed – There are two species of chickweed, one perennial (mouse-ear) and one annual (common chickweed). Common chickweed is easier to control. Both types have shallow roots, so they can often be removed by hoeing or hand-pulling. New plants can grow from broken pieces of mouse-ear rootstock, however, so make sure you remove the entire plant.
• Lamb’s Quarters – This fast-growing annual reproduces by seeds. This summer weed rapidly removes moisture from soil, so extract it with a hoe from your garden as soon as possible.
• Purslane –This weed appears in late spring or early summer and likes warm weather and rich, fertile soil. This annual reproduces by tiny black seeds and stem fragments. Pull out the weed as soon as you see it and destroy the plant; this weed can live in your soil for years.

See the following article for helpful weed identification photos and for more information: “Identifying Common Yard and Garden Weeds.”

Fertilizing

A soil test at the beginning of summer is the best approach for determining how much fertilizer is needed. If the garden soil has been amended nicely, less fertilizer is required. If you apply 1-2” of leaf mold or compost to your garden at the beginning of each summer, you may not need to add fertilizer. Heavy fertilization could increase foliage at the expense of blooms.

What nutrients are necessary? Let’s assume you use a 5-10-5 fertilizer: the first number is nitrogen, the second is phosphorous, and the third is potassium. Some products that claim to increase flowering have higher levels of phosphorous. But if your soil test says your phosphorous levels are adequate, adding phosphorous could be detrimental. You could choose a light application of 4 to 7 pounds of a complete organic fertilizer (3-4-4) per 100 square feet. Spread fertilizer in small rings around each plant in March. Repeat twice at 6 week intervals. Apply another treatment of fertilizer to late-blooming plants in late summer, but make sure you don’t fertilize after 6 weeks before the average first frost. Always water the bed after applying fertilizer. This will wash the fertilizer off the foliage and prevent burn. It will also make fertilizer available to the plants immediately.

Deadheading

As soon as plants are allowed to set seed, chemical messages are sent back telling flower production to stop. Deadheading short-circuits this message so that flowering will continue. Trimming off spent foliage also keeps the garden looking fresh when leaves are spent or have been damaged by slugs or insects.

Disbudding

To gain large blooms from perennials, as opposed to more numerous but smaller blooms, plants can be disbudded. In disbudding, small side buds are removed, which allows the plant to concentrate its energy to produce one or a few large blooms. Peonies and chrysanthemums are examples of plants which are often disbudded.

Staking

As the season progresses, some taller plants or top-heavy plants benefit from staking. If plants fall over, the stem will function poorly where it has been bent. If the stem is cracked, disease organisms can penetrate the break. Stake plants when you set them out so they will grow to cover the stakes. When staked, tall perennials can better withstand hard, driving rain and wind.

Select stakes that will be 6 to 12 inches shorter than the height of the grown plant. Place stakes behind the plants and sink them into the ground far enough to be firm. Loosely tie plants to the stakes, using paper-covered wire, plastic, or other soft material. Tie the plant by making a double loop of the wire with one loop around the plant and the other around the stake. Never loop the tie around both stake and plant. The plant will hang to one side and the wire may girdle the stem. Add ties as the stem lengthens.

PRUNING

There are MANY shrubs that should be pruned in May-June-July. Please see the shrub pruning schedule published by the Virginia Cooperative Extension for a list. Be aware that spring or early summer blooming shrubs such as azaleas, forsythia, viburnums, rhododendrons, and hydrangeas should be pruned after blooming but before new buds are set. These shrubs bloom on old wood, which means the plant forms the flower buds for next year’s blooms during the current year. The buds are carried through winter on last year’s growth – the old wood.

JAPANESE BEETLE

The Japanese beetle, Popillia japonica, can feed on the foliage, flowers, and fruit of over 275 different plant species. Some of the Japanese beetle’s favorite ornamental landscape plants are roses, crape myrtle, linden, hibiscus, crab apple, and elm. Damage called “skeletonization” is caused by the insects feeding on the upper leaf surface and eating tissue between leaf veins. This gives leaves a lacy appearance. Most damage from Japanese beetles is temporary; plants will produce new leaves and flowers when the beetles are gone.

Japanese beetles are active during the day. Morning is a good time to knock the beetles off plants into soapy water. Although traps can be used to monitor the levels of Japanese beetles, they are not effective in getting rid of them. Beetles are good fliers and can detect trap lures from far away. Therefore, traps might actually attract more beetles to a landscape and increase damage.

The larvae, called grubs, are white and ‘C’ shaped with yellow-brown heads. They burrow through the soil, feeding on the roots of grass and shrubs. Areas of dead grass may appear when large numbers of grubs are present, especially during dry spells in September or early October. Japanese beetle grubs rarely do enough damage in a home lawn to warrant treatment.

INVASIVE SPOTLIGHT

Japanese stiltgrass, Microstegium vimineum, is an invasive plant that is now common to the Piedmont area. The following information is from Blue Ridge PRISM (Partnership for Regional Invasive Species Management, www.blueridgeprism.org/factsheets).

Seed germinates from April into June. In mid-to-late summer, flowers form low down on the stems, hidden between stem and leaf sheaths. These hidden flowers do not open but are self-pollinating, assuring seed set. Later, more visible flowers bloom at the stem tips and are wind–pollinated. Flowering begins any time from July into October, and seeds ripen and drop to the ground from August to December.

Treatment: Hand-pulling small infestations before plants set seed is effective but labor intensive. Plants pull easily from moist soil. Consider hand-weeding around desirable native plants before applying herbicide. Mowing and weed-whacking can greatly reduce seed formation. Mowing is feasible only in open areas, not in forest settings. If stiltgrass is cut in June, flowers low on the stems may bloom earlier than usual, so repeat mowing is needed. Mowing is best done just before flowering in August and September and needs to be done only once if you wait until then. Cut stiltgrass as low as possible, scalping the ground, to remove all flowers.

Foliar Spraying: Japanese stiltgrass is easily killed with low concentrations of herbicides. Researchers at Virginia Tech showed that a grass-selective herbicide is the most effective control method. When a grass-selective herbicide is used, more native plants return than when a non-selective type of herbicide is used. This proved true even at the very low concentration that kills stiltgrass and spares many desirable plants. The recommended time for spraying is from July into early September and before a particular area of stiltgrass flowers and sets seed. A broad-spectrum herbicide works best when stiltgrass is actively growing in spring and summer and works less well in late summer and fall or during drought.  Grass-specific herbicides work throughout the season. Where stiltgrass grows in a lawn, treat the lawn in spring and summer with a pre-emergent crabgrass killer to stop stiltgrass seed germination. Two to three years of treatment are usually required for effective eradication.

For more information, see the “Invasive Plants” article in the February 2015 issue of The Garden Shed and “Japanese Stiltgrass Control in the Home Lawn and Landscape,” N.J. Cooperative Extension Fact Sheet FS1237, njaes.rutgers.edu/fs1237 (Oct. 2014).

SUMMARY

June is a busy time, both for enjoying the fruits of your labor, and for preparing the garden for the challenges of mid-to-late summer. You can fine-tune your garden’s color palette and prolong bloom by adding perennials and annuals. Watering, weeding, fertilizing, deadheading, disbudding, and staking are all ongoing tasks to improve the garden’s health and appearance. June is also the time to prune shrubs that bloom on old wood. A garden pest common to June is the Japanese beetle. Although pesky, it is usually not a fatal invader. And finally, an unwelcome garden and yard intruder is Japanese stiltgrass, a problem invasive that germinates seed in early summer.

SOURCES

“Gardening with Perennials: Perennials by Blooming Period,” http://extension.illinois.edu/perennials/specific.cfm?NodeID=3883

“Perennial Flowers Bloom Guide,” http://www.costafarms.com/get-growing/news/perennial-flowers-bloom-guide

“June Blooms,” http://www.lewisginter.org/visit/gardens/whats-in-bloom/june-blooms/

“Growing Perennials,” https://hgic.clemson.edu/factsheet/growing-perennials/

“Lantana,” https://hgic.clemson.edu/factsheet/lantana/

“Landscape Plants Rated by Deer Resistance,” https://njaes.rutgers.edu/deer-resistant-plants/

“Deer Resistant Species,” https://www.wildflower.org/collections/printable.php?collection=deer

“Gomphrena – An Antidote for the Late Summer Blahs,” http://piedmontmastergardeners.org/article/gomphrena-an-antidote-for-the-late-summer-garden-blahs/

“Angelonia augustifolia,” http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=b444

“June Yard and Garden Tips,” http://www.clemson.edu/extension/laurens/yard_garden/06_june.html

“Identifying Common Yard and Garden Weeds,” https://www.almanac.com/content/common-garden-weeds

“Perennials: Culture, Maintenance and Propagation,” https://pubs.ext.vt.edu/426/426-203/426-203.html

“Growing Perennials,” https://hgic.clemson.edu/factsheet/growing-perennials/

“Fertilizing Established Perennial Gardens: Feed ‘em and Weep,” http://msue.anr.msu.edu/news/fertilizing_established_perennial_gardens_feed_em_and_weep

“A Guide to Successful Pruning, Shrub Pruning Calendar,” https://pubs.ext.vt.edu/430/430-462/430-462.html

“Japanese Beetles on Ornamental Landscape Plants,” https://content.ces.ncsu.edu/japanese-beetle-1

Factsheet: “Insidious and Formidable Invasive: Japanese Stiltgrass,” http://blueridgeprism.org/factsheets/ 

“Invasive Plants,” http://piedmontmastergardeners.org/article/invasive-plants-whats-all-the-fuss-about/