7 Dahlia Care Jobs to Do in August for More Blooms Until Frost
August is when dahlias reach their peak in many U.S. gardens. By now, they’re producing an abundance of colorful blooms, from dinnerplate varieties to compact pompons, and creating one of the most spectacular displays of the growing season. But while they may be at their most beautiful, they also need a little extra attention to keep plants healthy and flowering.
Whether you’re growing different dahlia types in borders, cutting gardens, raised beds, or containers, good dahlia care is essential during this demanding month. Hot temperatures, periods of drought, heavy summer storms, and high humidity can all affect flowering, but a few simple maintenance jobs will keep plants producing fresh blooms for weeks to come.
1. Deadhead Regularly to Keep Flowers Coming
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The single most important job this month is learning how to deadhead dahlias correctly. Dahlias are prolific bloomers, but once flowers fade, the plant naturally begins diverting energy toward producing seeds rather than developing new buds. Removing spent blooms every few days encourages the plant to keep flowering until the first fall frost.
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Look carefully before making the cut. Faded flowers develop a pointed, cone-shaped center where seeds begin to form, while unopened buds remain round and tightly closed. Use a clean, sharp pair of pruners, such as the Fiskars SoftGrip Bypass Pruning Shears from Amazon or the GARDENA ExpertCut Pruner from Amazon, and snip the stem back to the first healthy pair of leaves or a strong side shoot to encourage fresh growth.
If you’re growing dahlias as cut flowers, regular harvesting provides the same benefit, stimulating the plant to produce even more blooms. Keeping a pair of reliable pruners nearby makes it easier to remove fading flowers as soon as they appear and maintain a continuous display throughout late summer.
2. Water Deeply Rather Than Little and Often
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August heat can leave dahlias thirsty, especially during prolonged hot spells or if they’re growing in containers or sandy, free-draining soil. Instead of watering lightly every day, give plants a deep soak once or twice a week, ensuring moisture reaches the root zone. Deep watering encourages stronger root systems and helps plants cope better with heat and dry weather.
For larger dahlia beds, a drip irrigation system can make consistent watering easier. The Rain Bird Landscape and Garden Drip Watering Kit from The Home Depot delivers water directly to the base of plants, helping keep foliage dry while providing steady moisture to roots. For smaller gardens and container-grown dahlias, a gentle hose nozzle such as the Expert Gardener Heavy-Duty Metal 8-Pattern Watering Nozzle from Walmart can help control water flow and avoid washing away soil around the plant.
Water early in the morning and direct the water at the soil rather than the foliage to reduce the risk of fungal diseases such as powdery mildew. Container-grown dahlias may need watering every day during periods of extreme heat, particularly in southern states.
3. Feed to Support Continued Flowering
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By August, dahlias have used much of the nutrients available in the soil, so adding a balanced dahlia fertilizer can help support continued blooms through late summer and into fall. Feeding every one to two weeks gives plants the nutrients they need to keep producing flowers, especially during the peak growing season.
Choose a fertilizer that’s relatively low in nitrogen but higher in phosphorus and potassium. Too much nitrogen encourages lush leafy growth at the expense of flowers. A liquid tomato fertilizer works particularly well because it’s formulated to promote flowering rather than excessive foliage. The Miracle-Gro Water Soluble Tomato Plant Food and Espoma Organic Tomato-Tone Plant Food are both widely available options at retailers such as Amazon and The Home Depot and can be used to encourage flower production in dahlias.
4. Keep Tying In Tall Stems
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Even well-supported dahlias can become top-heavy as flowers increase in size and number. Inspect stakes and supports regularly, especially after summer thunderstorms or strong winds. Supporting plants before stems bend or snap is much easier than trying to repair storm damage later.
For tall dahlia varieties, sturdy plant supports and gentle ties can help keep stems upright without restricting growth. The VELCRO Brand Garden Ties are useful options for securing stems because they are flexible, reusable, and designed to avoid cutting into growing plants.
For extra support, consider using the Vigoro 48-inch Green Steel Plant Stakes from The Home Depot to help anchor taller varieties and large dinnerplate dahlias.
5. Watch for Pests and Disease
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Warm August weather creates ideal conditions for several common dahlia pests and diseases. Earwigs are often blamed for damaged blooms, although they’re usually feeding on flowers that are already fading. Slugs and snails may still be active after rainy periods, while aphids often gather around tender new shoots and developing buds.
Check plants every few days, paying close attention to the undersides of leaves and around flower buds. Catching problems early is usually enough to prevent a major infestation.
For gardeners looking for an easy way to monitor and manage common summer pests, a product such as Bonide Captain Jack’s Dead Bug Brew, available through retailers like Amazon and The Home Depot, can help control a range of insect pests when used according to the label directions.
Also keep an eye out for powdery mildew, particularly during periods of high humidity or when plants become overcrowded. Improving air circulation, spacing plants properly, and watering consistently at soil level can help reduce the risk and keep foliage healthier through late summer.
6. Cut Flowers Often
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One of the easiest ways to encourage more blooms is simply to cut them. Knowing when and how to prune dahlias can help keep plants productive while providing plenty of flowers for indoor arrangements. Harvest flowers early in the morning while stems are fully hydrated, and choose blooms that are almost fully open, since dahlias don’t continue opening much after they’re cut.
Use clean, sharp pruners, such as the Fiskars PowerGear2 Bypass Pruner, to make clean cuts without crushing stems, and place flowers into fresh water immediately. The more flowers you harvest, the more the plant is encouraged to replace them with new buds, giving you an even longer display outdoors while filling your home with fresh bouquets.
7. Start Planning for Tuber Storage
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Although dahlias are still flowering, August is a good time to think ahead to the end of the season and how you’ll protect your dahlia tubers through winter. Label plants now while blooms are easy to identify, as many cultivars look similar once frost blackens the foliage.
Gardeners in colder regions, generally USDA Hardiness Zones 3 through 7, should gather storage supplies before the first frost. A product such as Back to the Roots Organic Vermiculite can help keep stored tubers protected by providing a lightweight, moisture-controlling medium.
In warmer climates where the ground doesn’t freeze, dahlia tubers can often remain in the soil with a layer of winter mulch, provided drainage is good.
Can You Still Plant Dahlias in August?
In most parts of the U.S., August is too late to plant dormant dahlia tubers if you’re hoping for a full season of blooms before the first fall frost. However, gardeners in the warmest regions, including parts of USDA Hardiness Zones 9 and 10, may still have time to plant actively growing container-grown dahlias.
While late-planted dahlias won’t flower for as long as spring-planted specimens, they can still provide weeks of color before cooler weather arrives. Keep new plants well watered as they establish, especially during hot August weather.
The secret to spectacular dahlias in August is consistency. Regular deadheading, deep watering during hot weather, feeding every few weeks, and checking supports after summer storms will keep plants healthy and blooming. Avoid leaving spent flowers on the plant, overfeeding with nitrogen, or allowing containers to dry out, and your dahlias will reward you with a vibrant display right through to the first fall frost.
