Summer is a great time to enjoy the perennial garden. Summer bloomers like daylily, yarrow, butterfly weed, blanket flower and purple coneflower brighten the garden in June and July. Keeping perennials healthy and attractive all season long requires some care during the summer months. In this article, horticulturists with Iowa State University Extension and Outreach answer common questions about the care and maintenance of your perennial garden in the summer.
How often and what time of the day is best to water the garden?
The watering frequency is determined by soil characteristics, weather conditions, type of plant and other factors. Generally, a deep watering once a week in dry weather should be adequate for most flower gardens. When watering gardens, water slowly and deeply.
Early morning (5-9 a.m.) is the best time to water the garden when using a sprinkler, garden hose or any other device that wets the plant foliage. When watering is completed, the plant foliage dries quickly. The rapid drying of plant foliage helps guard against the development of fungal diseases. Additionally, a morning application allows the water to soak deeply into the soil with little water lost to evaporation.
Watering at midday is less efficient because of rapid evaporation. Watering in the evening with a sprinkler or garden hose can lead to greater disease problems as the plant foliage will likely remain wet throughout the night.
Mornings and evenings are excellent times to water gardens when using a drip irrigation system or soaker hose. Watering in the evening isn’t a problem as these methods don’t wet plant foliage.
What perennials benefit from deadheading?
Deadheading is the removal of spent or faded flowers. Deadheading improves the appearance of plants, may encourage a second flush of bloom, and prevents self-seeding.
Perennials that improve appearance with deadheading include bearded iris (Iris), peony (Paeonia), lamb’s ear (Stachys byzantina), perennial geranium (Geranium), daylily (Hemerocallis), hosta (Hosta), and coralbells (Heuchera).
Several perennials benefit from deadheading to prolong the bloom or promote a rebloom, including yarrow (Achillea), tickseed (Coreopsis), blanket flower (Gaillardia), daylily (Hemerocallis), garden phlox (Phlox), perennial salvia (Salvia) and spiked speedwell (Veronica).
Perennials that readily reseed benefit from deadheading to prevent seed set in other areas of the garden. These perennials include columbine (Aquilegia), blackberry lily (Iris domestica), bellflower (Campanula), purple coneflower (Echinacea), garden phlox (Phlox paniculata), campion (Lychnis) and goldenrod (Solidago).
How do I control weeds in my garden beds?
Keeping ahead of weeds and controlling them when they are small is essential for good weed management. This requires persistence throughout the entire growing season to remove weeds as they emerge. There are essentially two types of weeds in the garden: annuals and perennials.
Annual weeds grow rapidly, flower, set seed and die in a single season. New annual weeds, such as crabgrass, purslane, knotweed, lambsquarter and foxtail, germinate from seeds each year. Perennial weeds die back to ground level in fall but send up new growth in spring. Perennial weeds, such as dandelions, quackgrass, thistle, pokeweed and plantain, reproduce by seeds and may spread by creeping above or below ground stems or spreading root systems.
Cultivation, hand pulling, mulches, and herbicides are the primary means to control weeds in the home garden. Annual weeds can be effectively controlled by cultivating, hand pulling, mulching and using pre or post-emergent herbicides. Perennial weeds are best controlled by hand pulling or spot treating with a non-selective herbicide.
Which perennials can be pinched or cut back?
Some perennials benefit from pruning in early summer. Cutting back removes anywhere from 25 to 75% of the total plant. When done after flowering to spring blooming perennials, it can promote fresh regrowth that is more attractive, and potentially a rebloom later in the season. Perennials that benefit from a cutback after flowering include lady’s mantle (Alchemilla), columbine (Aquilegia), pinks (Dianthus), silvermound (Artemisia), threadleaf coreopsis (Coreopsis verticillata), perennial geranium (Geranium), catmint (Nepeta) and perennial salvia (Salvia). 
Summer and fall-blooming perennials can be pinched in late spring to early summer to produce sturdy, compact growth that is less likely to become lanky or flop over. Pinching removes the stem’s upper 1 to 2 inches to promote branching. It may delay bloom by a week or two but can promote more flowers in certain species. Perennials to pinch before flowering for height control include aster (Symphyotrichum), mums (Chrysanthemum), Joe-Pye weed (Eutrochium), false sunflower (Helianthus helianthoides), bee balm (Monarda), tall sedum (Hylotelephium), and balloon flower (Playtcodon grandiflorus).
Should I stake floppy plants?
Some species of perennials, such as peony (Paeonia), delphinium (Delphinium), and dahlia (Dahlia), may require staking, especially as they begin to bloom. Staking materials include wooden, bamboo, metal, or plastic stakes or rings. A gridwork of wire, bamboo or string placed above young plants allows stems to grow up through and receive support. Similarly, twiggy branches can be set in the ground to provide a more natural-looking support material.
Ideally, support materials are placed early in the growing season, and the plant can grow through it. When sized appropriately, the staking material is masked by the plant’s foliage once it reaches its mature size. If perennials need staking after they’ve reached their mature size, then a few stakes around the perimeter of the plant surrounded by an unobtrusive twine or string at various heights can help hold stems upright and still allow movement of the plant. Individual stems can be supported with stakes carefully placed at the base of the stem. As it grows, tie the stem loosely to the stake with string every 10 to 15 inches, leaving a little slack so it can still move in the wind.
Shareable photos: 1. Purple coneflower in perennial garden. 2. Summer garden with tickseed, Russian Sage, globe blue spruce.
