The Ornamental Garden in August
August is the last of the summer months – a time when hot, humid weather can significantly stress or weaken plants throughout the ornamental garden. With the growth spurt of spring and early summer now only a distant memory, your landscape may appear to be slowing down and taking a breather. But that doesn’t mean you can as well. In fact, it’s now more important than ever to maintain vigilance over weeds, pests, diseases, and moisture levels.
As you tend your garden, observe what worked this growing season and what didn’t. Make a list of changes or improvements that need to be tackled. This sometimes means making hard choices about the plants in your landscape. For many of us, our ornamental gardens are perpetual works in progress. Maybe that prized peony that looked so stunning in May now looks crowded by its companion plantings and afflicted by mildew. Or perhaps that cute little Russian sage turned out to be a thug and spread with wild abandon throughout your garden. Whatever the problem, now is a good time to assess your options and decide what course of action to take for next year’s garden.
Speaking of next year’s garden, use a garden journal to document your gardening successes and failures. If you aren’t in the habit of keeping a journal, August is a good time to start one while all the details are still fresh in your mind. That will be a big help to you as you decide what improvements you want to make. For example, are there bare spots that need to be filled in? Do some of your plants need to be divided? Did some of your plants succumb to disease? Was drainage a problem? With a working list of problem areas, you’ll have a head start on creating an even better garden next year.
As for specific gardening tasks to perform now during these hot, dry August days, it’s particularly important to control weeds. Otherwise, your ornamentals will have to compete with them for water and nutrients. In your battle to conquer weeds, don’t make the mistake of deeply cultivating your flower beds. Loosening the soil under hot, dry conditions can damage surface roots as well as reduce soil water that might otherwise have been available to your plants. As a result, your plants may end up looking much worse after cultivation than before.
In the absence of rain, monitor moisture levels and provide water as necessary. Deep but irregular watering is the best strategy at this time of year. Don’t forget your containerized plantings. They can sometimes require water daily or even twice daily.
Don’t prune shrubs or trees this late in the growing season. Any pruning you do now will stimulate new growth which will not be able to harden off before winter sets in.
Tidy up your garden by cleaning up dead or dying daylily foliage. And while you’re at it, cut back any remaining daylily flower stalks. If your daylilies need to be divided, now is a good time to do it.
Divide and transplant bearded irises, but do it on a day when the temperatures are below 90ºF. Irises grow from rhizomes, which are elongated stems that grow horizontally below ground and have roots attached to them. Snap off or use a sharp knife to cut off the vigorous ends of the rhizomes. Make sure that there are roots attached to each portion. Before re-planting, inspect each portion and discard any that indicate the presence of iris borers or soft rot. Cut the foliage on healthy rhizomes to about eight inches. They prefer dry feet, so replant them 18 inches apart in well-drained soil just at or slightly below the soil line. Don’t pile mulch over the roots. Mulch can retain more moisture than the rhizomes can handle.
If you’re into dried flower arrangements, you’ll have better success drying flowers with bright yellow, orange, pink or blue petals. Those colors preserve best. Red and purple become darker and less attractive when dried. White flowers can quickly turn a buff or tan color. If you’re using straw flowers, cut them when the blooms are only half open. Tie them together in small bundles and hang them upside down in a well-ventilated place to dry before using them in arrangements.
If your annuals have finished blooming or if they look overgrown and leggy, remove them from the garden and replace with mulch to keep weeds under control. Or, if you’re really intent on keeping those petunias going a little while longer, try shearing them back, fertilizing and watering them to see if you can coax another round of blossoms from them.
Unless you want to leave seed heads in place for the birds, deadhead purple coneflower and rudbeckia. Also, deadhead garden phlox before it sets seeds. Phlox seedlings do not come true to parent color and may overtake your garden. If you like surprises in your garden, then leave the seedlings in place to see what comes up. If that approach doesn’t appeal to you, just pull them up.
Order spring-flowering bulbs now while selections are good. If you’re buying bulbs from nurseries, choose the largest bulbs available. Be wary of so-called “bargain” bulbs. If the bulbs are small or of inferior quality, they may not be much of a bargain.
Make a list of plants that can be moved or divided this fall. As a general rule of thumb, spring or summer-blooming plants may be divided in the fall. Fall-blooming plants should be divided in the spring. Keep in mind that some plants, such as peonies, bleeding heart, Baptisia, and Oriental poppies grow better if left undisturbed.
Many self-sown seedlings of hollyhock, larkspur, columbine, sweet William, etc., are appearing now. If the parent plant is a hybrid, the seedling may not come true to type. Remove any unwanted seedlings now.
Sow seeds in late summer for cool-weather annuals such as calendulas, Iceland poppies, primrose, pansies, violas, snapdragons, stock or forget-me-nots.
Monitor all ornamental plants for adequate moisture levels during the hot summer months. While this is important for all new plantings, it is particularly relevant for newly planted trees or shrubs. Those first few growing seasons are critical for the overall health and development of vigorous root systems. If you need advice on strategies for watering the landscape, check out the Virginia Cooperative Extension’s Publication 426-713, “Creating a Water-Wise Landscape,” http://pubs.ext.vt.edu/426/426-713/426-713.html.
Remain vigilant throughout the growing season for fungal diseases on roses, particularly black spot. Just as its name suggests, this fungus appears as round black spots on the upper sides of rose foliage. The spots are often surrounded by yellow halos. As the disease progresses, the leaves turn yellow and fall from the plant. If you leave the leaves where they fall on the soil or mulch, the fungal spores will overwinter and infect next year’s roses. To contain the disease, remove all fallen rose foliage and dispose of it in the trash. Do not put it in your compost pile.