Why Aren’t My Dahlias Blooming? 7 Causes and Solutions

Dahlias are a delight. From single to pompom, and cactus to dinnerplate, they are a favorite in flower beds and cutting gardens all over the nation. The beauty and wide variation of flowers across the genus is their main selling point. So, when the flowers don’t bloom, it can mean utter devastation for the long-suffering gardener.

Well, maybe that’s a bit over the top. But I know that when mine did not bloom in past seasons, it was quite a disappointment. Dahlias are not low-maintenance flowers. They have high water needs and need a significant amount of nutrients to produce their large, bold, colorful flowers. 

If you’ve been patiently waiting for what feels like forever, and your dahlias aren’t at least producing buds, you’re probably starting to worry. Don’t get too upset, though. There is still time, and we may be able to get them flowering yet! First, we need to figure out why your dahlias aren’t blooming.

The Short Answer

Dahlias can be finicky, and if things aren’t quite right, they will show it by withholding blooms. It may be because they just aren’t ready yet, but it could be something more complicated. The wrong type of fertilizer, too little moisture, cool temperatures, or a lack of sunlight can all cause your dahlias to hold back.

The Long Answer

Dahlias bloom their best when we meet their specific needs. If they were as easy as zinnias, everyone would grow them. Sadly, they require much more effort. Expect your dahlias to reflect the care they get. Here are some reasons your dahlia may not be blooming. 

Too Early

Depending on your climate, dahlias should bloom approximately two to three months after planting their tubers. It will take longer if you plant them from seeds. If you live in a cool climate and didn’t plant your tubers until May, expect them to flower near the end of July or the beginning of August. 

In my experience, the size of the flower isn’t typically a factor. Dinnerplate varieties can grow and bloom as fast as smaller pompom types. You’ll probably notice that the larger plants grow faster. I’ve had my largest variety bloom first in the past, but it varies. 

In cool climate areas, such as zones 3-7, dahlias can’t stay in the ground during the winter. As a result, you’re wise to wait until there is no more chance of a frost, as their foliage is not frost-tolerant. In this type of climate, they typically begin to bloom in mid-to-late summer. 

In warm climates like zones 8-11, dahlias are perennials, and you can leave them in the ground over the winter. This means that they will sprout as soon as the temperature is right. That will be much sooner in these warmer places, so you can expect them to bloom as early as late spring. My first flower usually blooms around the first week of June here in zone 9.

Too Much Nitrogen

Nitrogen is typically a nutrient associated with positive effects on plants. It is, after all, the main nutrient responsible for green growth. However, an overabundance of nitrogen may be the reason your dahlia is not blooming. If the plant is putting all of its energy into foliage, you’re likely to see delayed or no blooming at all. 

It’s uncommon for soil to contain too much nitrogen on its own. So this is typically something you can control. You should give your tubers some fertilizer when you plant them, and then after they begin to grow. Don’t give them a nitrogen-heavy fertilizer, though. Even a balanced formula can cause this issue. 

Choose a formula that has lower nitrogen and higher potassium and phosphorus, such as a 5-10-10 formula or a similar one. These are the nutrients responsible for vigorous root growth and flower development. 

Overcrowding

Overcrowding your dahlias is another reason they might not be blooming. If you planted a lot of them close together, they could be too close for comfort. Taller varieties can cast shade on smaller ones, and crowding reduces the amount of light that can penetrate the spaces between. 

Another problem that stems from overcrowding is nutrient competition. Dahlias are heavy feeders. They like fertilizer. If there are simply too many plants for the soil to support, they will suffer for it, and a lack of flowering is a common consequence. 

There are a couple of fixes for overcrowded dahlias. You can dig them up and move them so that they are about 18″-24″ apart. If the weather is very warm when you do it, they may suffer a lot of stress from this. I don’t recommend transplanting if it is already stressing them. 

The second fix is to thin out your plants by removing the weaker or inward-growing stems. You’ll get fewer flowers overall this way, but they will be healthier as a result. Any way you can give them more air and light is beneficial in this case. 

Not Enough Sun

Dahlias like a lot of sunlight. About six to eight hours per day, to be exact. For many plants, a lack of flowers stems from a lack of sunlight. Dahlias are in this group. 

Signs of too little light include an abundance of foliage, but no flowers, and tall, leggy growth as the plant reaches for more light. You may also see delayed development and smaller, paler leaves. 

Short of relocating them, there is really only one solution, and that is to cut back whatever is casting a shadow on your dahlias. When you re-plant them in the spring or divide your tubers, move them to a space where they will receive the sun they need. 

Cool Temperatures

Dahlias are native to Central America, so they thrive in warm, humid, tropical climates. Cool air or soil can cause slowed growth and delayed flowering. Soil cooler than 60°F (16°C) and air temperatures below 70°F (21°C) are a bit too cool for rapid growth. 

For the most part, patience is the most effective cure for this. If you’ve had a particularly cold season, you just may have to wait longer for them to flower. You can top dress with a layer of dark compost or mulch to offer some insulation to the roots. This often speeds growth a bit. 

Watering Issues

Both overwatering and underwatering can cause blooming issues for your dahlias. Both situations cause stress and interfere with nutrient uptake and flowering. An underwatered plant will exhibit wilted, drooping leaves, weak, spindly growth, and few flowers. 

While dahlias do enjoy consistent moisture, it’s still possible to overdo it. If you overwater your plants, and the soil stays soggy and muddy, you run a serious risk of root rot or other fungal issues. Your tubers may rot, and as a result, there are no nutrients traveling up to the flowers. 

Consistently watering your dahlias is the key to maintaining healthy plants and flowers. Generally, watering deeply two to three times a week is about right. However, it’s a good idea to pay attention to the soil. If the soil is dry a couple of inches down, water your dahlias. 

Lack of Deadheading

Did your dahlias have blooms earlier in the season, but are not blooming now? This last issue is related to plants that start to bloom, but then taper off and underproduce throughout the season. A healthy dahlia will produce many flowers over a period of several months. If they stop blooming early, it could be that you’re not deadheading and need to clean things up a bit.