The Ornamental Garden in June
It’s that time of year when we ornamental gardeners slip into maintenance mode. The time for planting, transplanting, and seeding is about over. Indeed, if the dry weather pattern of May continues into June, it’s completely over. Transplants really struggle to get established in hot, dry weather. If you notice a plant that should be moved, simply add it to your autumn to-do list. What’s on the list for this month?
For starters, be sure to check the list you’ll find under Gardening Resources, Monthly Gardening Tips — June/PMG.
Pruning perennials? Yes, various types of snipping and pinching fall under the category of pruning perennials. There are a number of reasons why you might prune a perennial: to promote repeat blooming, to delay blooming, to shape a plant, to encourage lush new growth, to increase flower size or numbers, or to prevent excess re-seeding.
Many perennials benefit from deadheading, which is simply removing an old or spent bloom. As soon as plants are allowed to set seed, chemical messages are sent to stop flower production. On many plants (but not all), removing spent blooms short-circuits this message so that the flowers will continue to bloom.
The deadheading rules tend to be species-specific. But if you see new buds or flowers below the old one, it’s a sign that deadheading is in order. Snip off the old growth down to the new buds or flowers. Most perennials should be deadheaded down to a lateral flower, bud, or leaf. Popular plants in this group include yarrow, salvia, daisies, coreopsis, and purple coneflowers (Echinacea).
With some geraniums, you can simply tug at a flower or leaf, and up it comes, little scape and all. That’s what happens when I deadhead my ‘Biokovo’ geraniums (Geranium x cantabrigiense ‘Biokovo’). It also needs the occasional “deadleafing” — a term apparently invented by Tracy DiSabato-Aust — the removal of old, tatty foliage as the season progresses. Deadleafing is all that’s needed to keep all members of the Geranium macrorrhizum clan looking their best.
Flowers with larger blooms can be deadheaded by cutting one spent flower at a time. Such flowers include peonies, daffodils, roses, and zinnias. Another technique is shearing across the top of a plant that has many small blooms. This technique can be used in June and July for either pre- or post-bloom management. Early bloomers such as catmint (Nepeta), mountain bluet (Centaurea montana), and bellflowers (Campanula) can be sheared by about one-third after blooming to encourage a second bloom and to neaten the plant’s appearance.
Later-blooming plants with small flowers, such as sneezeweed (Helenium autumnale), can be sheared by about 6-8” before blooming to encourage strong branching and denser growth.
Late bloomers, such as asters, chrysanthemums, and sedums, can be pinched back until mid-July to encourage a fuller, sturdier shape. This term means that you literally pinch out the growing tip and first set of leaves (about ½ to 1 inch) of each stem between your thumb and forefinger. Pinching back encourages the growth of side shoots; it will delay blooming somewhat, but the fuller plant shape and stronger stems are worth the wait. I’m trying this technique on Helianthus angustifolius, a new addition to my garden last year. Its blooms were lovely and so welcome at the end of summer, but it has a rangy habit, as you can see in the photo at right.
Pinching back also allows you to tweak bloom times. If you have a big grouping of asters, for example, you might pinch one group a little earlier and more frequently than others so that the bloom season is extended overall.
Shrubs that have recently finished flowering can be pruned now if they need it. Also, finish pruning any spring-flowering shrubs. Check the “Shrub Pruning Calendar” at Virginia Cooperative Extension (VCE) for information on which shrubs to prune in June — and which shrubs not to prune in June. And for advice on how to prune, take a look at the Garden Shed article, A Pruning Primer.
If you have a rhododendron whose lower limbs have been “pruned” by deer, now’s a good time to re-shape it a bit. You may need to prune the lower branches; cut these back to the first live buds and leaves that you see. Remove any dead and broken branches. If you prune off some of the upper part of the shrub, new shoots should emerge from the stems below. See What’s the best way to prune large rhododendrons that were damaged by deer?. This Maine Extension article refers readers to Tips for Beginners: Pruning Rhododendrons: How and When/VA Tech.edu for detailed how-to guidance, including photos. It’s important to understand how pruning the upper part of your rhododendron will affect its shape and exactly how to do it. Here’s the critical guidance from the VA Cooperative Extension:
There are two basic types of pruning cuts: heading cuts, and thinning cuts. Heading cuts stimulate growth of buds closest to the wound. The direction in which the top remaining bud is pointing will determine the direction of new growth. Make heading cuts selectively to reduce shrub height and retain natural form. Non-selective heading cuts made indiscriminately will stimulate rapid regrowth from buds below the cut. These vigorous shoots are unattractive and make shrubs bushier, but not smaller. . . . For heading cuts, prune 1/4 inch above the bud, sloping down and away from it. Avoid cutting too close, or steep, or the bud may die.
Fertilizing is recommended at the time of pruning. It’s possible that a badly-damaged rhododendron might need “rejuvenation” or “renewal” pruning — i.e., hard pruning that is done in late winter before bud-break and which might best be spread out over the course of several years. Read more about this at A Guide to Successful Pruning/VA Coop.Ext.
Last month we had an early period of drought. Was it a foretaste of a dry summer? Anything is possible in this era of climate change — including too much rain — but I’m getting out my soaker hoses just in case.
Annuals and Perennials
Monitor your plants for water needs, especially newly-added perennials and annuals. Remember that plants will dry out even more quickly on windy days. The general rule of thumb is one inch of water per week for established plantings. Watering plants more deeply but less frequently encourages them to set deeper roots; this helps plants become more drought resistant. Mulch perennials with a 2-inch layer of compost, pine bark, or pine straw to help keep down weeds and conserve moisture. Avoid overly-heavy mulching that could cause crown rot.
Keep close tabs on containerized plants, including the houseplants which are spending their “summer vacation” on the deck or patio. These plants dry out quickly and may even need daily watering in periods of high temperatures and/or drought. If you’re planning to go away on vacation, group containerized plants together near a hose or other water source so that it will be easier for your neighbor or other helpful person to handle the watering in your absence. Place the plants where they will be out of the afternoon sun; this will help them conserve water. Don’t forget to check all hanging baskets daily, particularly those that are in full sun, and water as needed.
Water trees and shrubs deeply and infrequently to help them get through the summer heat. This is particularly important during the first few growing seasons after a tree or shrub is planted. It’s also important for all plantings during drought conditions.
MONITOR FOR PESTS AND DISEASES
Mildews: Ornamental plants are subject to two common types of mildew that will manifest early in the season, depending on conditions.
Powdery mildew produces white, flour-like colonies, usually on upper leaves. The fungus can cause severe leaf drop, and affects vigor and resistance to stress over time. The fungus can affect many ornamental plants that are favorites in the perennial garden, including: wild bergamot (Monarda fistulosa), bee balm (Monarda didyma), garden phlox (Phlox paniculata), tickseed (Coreopsis grandiflora), purple coneflower (Echinacea purpureum), and zinnia.
Downy mildews, on the other hand, are a completely different kingdom of organisms, more closely related to algae than to fungi. Downy mildews produce grayish, fuzzy looking spores and mycelium on the lower leaf surfaces. The distinction between powdery mildews and downy mildews can be important, because the fungicides effective against one are not usually effective against the other — although, as with every rule, exceptions do exist. Preventative controls for each disease are important and include the following steps: selecting disease-resistant varieties and cultivars, providing good air circulation among plantings, and disposing of diseased foliage. If you decide you need a fungicide, see these pages about powdery mildew and downy mildew for more information.
Inspect rose bushes for insect damage from aphids, mites, or thrips. Aphids may be eliminated simply by directing a strong water spray from the hose on the rose bush. If ladybugs are present in the environment, they may eliminate aphids without any intervention on your part.
My bearded irises are covered with spots, and that’s not unusual for irises. The most common type is caused by Heterosporium Leaf Spot. To reduce this fungus next year, remove the old leaves in the fall. Fungicides can be used for control. Refer to specific recommendations in the appropriate Virginia Cooperative Extension Pest Management Guide.
Daffodils: Leave foliage from daffodils and other spring blooming bulbs in place until it turns brown and begins to dry. Do not braid or tie the foliage. Bulbs store food through the foliage for about 6 weeks after blooming is finished. Not all daffodil leaves will turn yellow at the same time. The foliage of earlier bloomers will be ready for cutting before mid-to-late bloomers. If your daffodils were done flowering in mid-April, they should turn yellow by early June.
If you want to propagate new plants via stem cuttings from woody shrubs, trees or perennials, now is a good time for many species. As new growth begins to mature, softwood cuttings can be taken from trees and shrubs. For expert guidance, read the recent Garden Shed article, Creating New Plants From Cuttings. For more about propagation techniques, see “Propagating by Cuttings, Layering and Division”/VA Coop. Ext.Pub. No. 426-002,
Don’t let the weeds get ahead of you. To avoid getting overwhelmed, pick one defined area each day; weed that small area, breathe a sigh of relief, and you’re done for that day.
Finally, don’t forget to bask in the beauty that spreads from all your hard work and cut some blooms to enjoy at the dinner table!
Featured photo by Cathy Caldwell
The Well-Tended Perennial Garden: Planting & Pruning Techniques (Tracy DiSabato-Aust (2006)
What’s the best way to prune large rhododendrons that were damaged by deer?, Maine Coop.Extension
Plant Problem Image Gallery, Va.Tech.Plant Disease Clinic
“Helianthus angustifolius,” Wildflower.org
Iris Leaf Spot, VA.Coop.Ext.Education Resources,