Every year, Martha and I grow dozens of dahlia varieties. We like to grow them at the farm for their summer and fall blooms, which add much-needed color to the garden in the hotter months when most other blooming plants are spent. Another reason we love dahlias is their variety; in addition to their many colors, they come in a vast array of flower sizes, styles, and shapes.
On the farm, we grow many varieties and plant about three to five plants per type. We have a supply of dahlia tubers that we plant and grow every year, and we add new ones to the collection each growing season. My favorite style of dahlias are the giant dinner plate varieties, which show off huge, impressive blooms. (A single flower can be large enough to fill an entire vase!)
If you’re interested in growing dahlias, ahead are my best tips for how to plant and care for these flowers so that you, too, can enjoy their beauty at home.
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Consider Variety When Planting Dahlias
Dahlias can be used in various ways in the garden. They can be planted in big mixed beds or rows of just dahlias if you’re growing them solely for cutting. They can be added right into the landscape garden in small groups of the same variety or sprinkled here and there throughout.
The type of dahlias you grow will depend on how you want to showcase them. You can get short varieties for edging beds, medium-sized plants to add throughout the flowering landscape or tall giants that you can place in the back of beds for height and structure.
Also, consider the foliage when choosing a variety of dahlias to grow. While most dahlia foliage is green, there are many cultivars that have darker, almost black foliage. These types of dahlias can add extra beauty to the garden, depending on how you use them.
Choose a Planting Location Carefully
Dahlias are heat lovers that need sunlight and thus should be planted somewhere they’ll receive at least eight hours of full sun per day. It’s also very important to provide them with good drainage. Dahlias grow from tubers and can easily rot in wet, poorly draining soil. So make sure the soil is loose and amended with plenty of organic matter. Adding a bit of sand to the soil can also improve drainage.
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Stake Dahlias Early
Dahlias grow very fast, and they will get tall and flop before you realize it, so it’s important to stake them as early as possible. The best time to stake is before they even start growing. At the same time you plant your tubers, pound a stake right into the ground next to them (you can always add a second one later if need be). This way, you remove the risk of smashing or damaging the tuber if you insert the stake into the ground later.
Pinch the Plants to Control Size
Pinching is helpful if you need to control the size of your dahlia plants. Pinching out the growing tips or the side shoots on occasion will help to keep your dahlia plants tight and sturdy as they grow. It greatly helps to reduce the floppiness of the plants—and as a bonus, more pinching means bushier plants that will put out more blooms.
The Martha Blog
Deadhead to Encourage Growth
Deadheading dahlias is important for a few reasons. First, removing the old flowers helps the plant look more clean and tidy. Second, by removing the spent blooms, you’re not allowing the plant to produce seed—this stimulates it to produce more buds and, thus, more flowers. Continually deadheading your dahlias will greatly increase the length of the season that the plant will produce fresh blooms.
Provide the Right Amount of Water
While dahlias are not terribly thirsty plants, I wouldn’t consider them drought-tolerant. They need an average amount of water in order to thrive. Similar to tomatoes (another summer crop), it is better to water your dahlias and then wait until they just barely start to wilt and are a bit limp before watering again. Less is more with dahlias; it is better to underwater than to overwater.
Prevent Mildew or Fungus Growth
Dahlias are generally very disease-resistant. However, mildew or fungus can be an issue in wet, humid weather. This can be prevented by watering dahlias from below instead of from above; that way, you don’t get the leaves wet and create an environment favorable to fungal growth. If the issue persists, treating dahlias with an all-purpose fungicide usually clears up the issue.
Protect Against Insects
Similar to disease, dahlias don’t often have problems with insects. The most common pest to protect dahlias against is Japanese beetles, which chew the flowers and leaves. They are large enough that you can pick them off the plant (if you don’t have too many), or you can use an insecticide or anti-feed on them.
Bees and wasps also love to rest and tuck up inside dahlia blossoms, especially the larger dinner plate type. You don’t want to kill these beneficial bugs, so just shake or move the flowers around before cutting to prevent yourself from getting a bee sting (it’s happened way too many times to me!).
