The dahlias put on a wonderful display, and it is also possible to grow dahlias of many varieties in containers on the patio to enjoy their colors and sculptural shapes here as well.
Plant dahlia tubers and you’ll discover that their needs are not onerous, but they do require a little care for maximum flower power. We asked experts to share their secrets for keeping dahlias blooming to add color and interest from late July until the first frost.
Basic knowledge of maintaining dahlias
Understanding when to plant dahlias is crucial to enjoying a gorgeous array of blooms, but if you want the best from your plants, there are a few tasks you should perform. This is how horticulturists ensure impressive, long-lasting dahlia displays.
1. Dead dahlias
If you want to keep them thriving for as long as possible, deadheading your dahlias is a must-do. “When cutting back dead dahlias, it is important to remove the old flower head and move down to the top of the next bud because this helps strengthen the remaining stem,” advises Steve Bradley, a dahlia expert. Amateur gardening magazine.
Make sure you remove spent flowers, not buds. “There are always exceptions in gardening, but as a general rule, flower buds are usually quite round as they grow,” Steve says. “Once the petals fall, the rest of the flower head becomes quite pointed and often a little pale in color.”
Steve has written (or co-written) more than 40 practical gardening books, and has been commissioned to update some of the world’s best-selling gardening books, The Expert series, originally written by Dr. David Hession.
Over the years, Steve has also written for most of the popular UK gardening magazines, including Amateur gardening. He is a member of The Garden Media Guild and has extensive gardening knowledge which he enjoys sharing with local BBC Radio listeners. He is the resident gardening expert, answering listener questions during live gardening phone-in shows.
2. Share flowers
Steve Bradley points out that staking of dahlias helps maintain the flower display, but staking is also important because it supports the entire plant.
“Fully opened flowers can become heavy (especially after rain) and drag the entire plant into the soil if the plant is not anchored,” he explains. “Insert canes or sturdy stakes (often three to four) around the plant when it is 12 to 18 inches high, being sure to avoid damaging the tubers.”
3. Plant nutrition
Feed dahlias to keep them flowering, although there is some controversy, explains Susan Brandt, co-founder of Blooming Secrets. “Some people say dahlias are heavy feeders, others say they don’t need anything,” she points out. Her advice? “To get your dahlias off to a good start, make sure the soil is fertile and contains plenty of organic matter. You can fertilize every three to four weeks from bud in mid-summer through early fall.
‘When fertilizing, use a plant high in phosphorus, which promotes flowering. Make sure it is not high in nitrogen as this will create large leaves but few flowers. The recommended fertilizer ratio is 10-30-20. If you plan to dig up your tubers be sure to stop fertilizing at the end of August. If you continue to fertilize your tubers, you are encouraging growth when you should be preparing your tubers for dormancy.
4. Water according to the weather
For gorgeous dahlia flowers, it is important to get the right watering for the conditions. “The amount and frequency of watering depends greatly on the weather,” explains Steve Bradley. “A dahlia plant that is 40 inches tall and 40 inches wide needs about 4½ gallons of water per week in dry weather.”
5. Watch out for pests
If you want to preserve dahlia flowers, it is important to be vigilant regarding dahlia pests and diseases. “One common pest that can affect dahlias is aphids,” says Susan Brandt. “These tiny insects feed on plant sap, causing stunted growth and distortion of leaves. To control aphids, you can use insecticidal soap or neem oil, which are safe and effective methods.
“Another pest is slugs.” This pest is often a problem early in the season when the foliage is tender and easier to eat. Using an irrigation system that soaks the soil and keeps the leaves dry is a good way to prevent them.
“In terms of diseases, one notable problem for dahlias is powdery mildew. I have personally encountered this disease with my dahlias. This fungal infection appears as a white powdery coating on the leaves and stems of the plant, resulting in reduced vigor and flowering. To combat powdery mildew, Ensure proper air circulation around dahlias by spacing them appropriately and removing any infected foliage.
“Another disease that can hinder dahlia flowering is crown rot, which affects the plant’s roots and crown area. Overwatering or poorly drained soil can contribute to this condition. If you notice wilting or darkening of the stems near the soil line, this may indicate Crown rot. To prevent this disease, be sure to plant dahlias in well-drained soil and avoid overwatering.
Will dahlias bloom more than once?
Dahlias will bloom more often if you provide them with a little TLC. This means killing them – in other words, removing spent flower buds. But they are the perfect choice for cut flower gardens too, and having cut flowers ready to arrange indoors also encourages them to develop more flowers. For the best display of flowers in beds, borders and containers, be sure to choose dahlia species that create long-lasting displays as well.
Dahlias can produce one of the most eye-catching sights in a summer garden. However, because they are tender perennials, if you live in zone 7 and below, and if you want gorgeous blooms next year, it is important to overwinter your dahlias. Lift and store the tubers after the first frost ready to replant in the spring.