9 Reasons Your Dahlias Aren’t Blooming and How to Fix it
Are you missing beautiful blooms from your dahlias this season and aren't quite sure why? There are a few different reasons this may happen, and your approach to correct it will depend on the reason behind it. In this article, certified master gardener Liz Jaros examines why your dahlias aren't blooming this season, and how to address it.
After dreaming about dahlias all winter, toiling away in the garden all spring, and waiting patiently for them to have their time in the sun, nothing brings a gardener down like a dahlia that blooms poorly. Or even worse, a dahlia that doesn’t bloom at all.
But it can happen, even to the most seasoned dirt digger. And there are plenty of reasons why. Fortunately, there are also remedies for the most common bloom problems and plenty of ways to prevent it from happening again.
Here we look at 9 of the most likely reasons your dahlia blooms are not meeting your expectations this year and offer some suggestions for turning things around.
Not Enough Sun
Dahlias require abundant sunshine in order to bloom fully and repeatedly. As natives to Mexico and South America, dahlias are partial to hot rays and high heat.
If they’re not getting their full share, stems will be leggy, buds will be less plentiful, and flower heads will be less impressive than those planted in full sun.
In order to fix it, choose a location that will get at least 6 hours a day, and take care to avoid locations under tree limbs or shadows. The six hours do not need to be consecutive, but you’ll need six hours total. If you have to choose between morning sun and afternoon sun, morning is preferable.
You Forgot to Deadhead
If your dahlias’ first blooms met your expectations, but the next go-round was disappointing, make sure you’re deadheading them properly. Dying blooms are an indication that seed production has begun, and a flower’s growing system will then divert its focus from creating showy blooms to nurturing its roots and foliage.
Removing spent or fading flowers from a healthy plant will actually trick the roots into sending up more blooms.
In order to fix it, Make it a point to buzz through your dahlia patch every few days to remove blooms that are on their way out. Beginning just beneath the base of your dahlia’s spent flower, slide your fingers down its stem until you reach either a set of leaves, a new bud, or a sidestep.
Make your cut just above one of these points and you won’t be left with unsightly, headless stems. In just a few days, your dahlias will reward you with new growth from the nodes just below these regions, and ultimately new blooms.
Not Enough Water
Regular, even watering is key to growing the dahlias of your dreams. Tuberous roots are prone to rot and fungus, and puddling water is their sworn enemy.
Conversely, nothing impacts bloom quality more negatively than thirsty roots and dry soil, so make sure they’re getting the proper amount of irrigation. Lack of water is easy to spot, with a lack of blooms and yellowing leaves on the stalk.
To fix this issue, you’ll want to address it early on. During early growth, while you are waiting for blooms, keep soil moist but do not overwater. Shoot for about 1 inch of water a week, and use a soaker hose to prevent excessive moisture on foliage. Check soil with your finger to make sure it is moist but not soggy.
Once blooming has begun, dahlia roots will need a bit more water to keep nourishing their flower heads, so bump your watering routine up to about 2 inches per week for the rest of the summer.
Because humidity and precipitation will vary from zone to zone, you’ll need to be mindful of rainfall and/or drought events that may throw your routine off. Most likely you will be watering somewhere between 1 and 3 times a week.
Planted at the Wrong Time
If the dahlia show you’ve been expecting is just not happening, there’s a chance you timed your planting wrong. Dahlias planted too early may have been exposed to cold temperatures in spring.
Freezing ground temperatures may have damaged your dahlias’ tuberous roots and killed their flowering potential. Or freezing air temperatures may have destroyed their sensitive buds.
Dahlias that were planted too late, on the other hand, might still have a ways to go before they bloom. Most dahlia varieties will flower somewhere between 90 and 100 days after they’ve sprouted.
If you started your seeds late or didn’t get the tubers in the ground until mid-summer, blooms will be significantly delayed. And may not come at all.
To fix this problem, Plant dahlias outside immediately after all danger of frost has passed. Check your hardiness zone for the average date of your region’s last freezing temps and add a couple of weeks to be safe. Soil temperatures need to be a steady 60 degrees.
For southern gardeners, it’ll be safe to plant tubers in late March or April. Northerners will have to wait patiently until at least the end of May, maybe a little longer. But don’t wait too long. Timing is everything.
Not Properly Overwintered
In warmer growing zones, where soil does not freeze in winter, dahlias will act as perennials and can be cut back and left in the ground. In more temperate zones, where sub-freezing temperatures are the winter norm, dahlias left in the ground will freeze and die.
You will surely have no blooms at all if you didn’t dig them up at the end of last season. And if you dug them up but did not store them properly during the dormant season, your blooms will likely suffer a similar fate.
In order to fix this problem, you’ll need to make sure you take proper overwintering steps.
In moderate zones, dahlias should be cut back to the ground as soon as their leaves have blackened and withered. It’s not a bad idea to pile mulch, leaves, or dirt generously on top of your tubers to give them the warmest and most protected winter environment possible.
In colder zones, lift tubers from the ground when their leaves have died or right after the first frost. This will be their signal to enter dormancy.
Cut the stems off just above the eyes from which they grew, clean the roots off with a dry towel and lay them out to dry out for a couple of days. Pack your tubers loosely in a basket, box, or burlap bag and cushion with peat moss, newspaper, or sand.
Select a container that is not air-tight, as a little bit of air circulation will help prevent molding. Store in an environment with a temperature that exceeds freezing but does not climb above 50 degrees and wait for spring.
Planted Too Close
Dahlias have extensive root systems and do not grow well when crowded. They also require good airflow to prevent bloom-affecting fungal conditions. If you’ve overzealously crammed 20 different dahlia varieties into a small bed, flowering will be greatly reduced. Some varieties may not flower at all.
This is an easy issue to fix. A one-foot minimum is recommended for dahlia spacing, but again, pay close attention to the variety you are planting.
Smaller pompon dahlias may need slightly less room to grow, while dinnerplate darlings may require up to 2 feet between them and their neighbors.
Using Improper Fertilizer
If your dahlias have thick beautiful stems and rich, green foliage, but little to no blooms, you may be overfertilizing. Or using a product with too much nitrogen. Nitrogen will give you dahlias that are bushy and leggy, but the blooms will play second fiddle to the greenery.
To address this issue, you may want to use a nitrogen rich fertilizer while shoots are establishing. Once blooms have begun, you’ll want to dial it back.
A fertilizer with a ratio of 5-10-10 will give you more potassium and phosphorus, which will lead to more beautiful blooms. Follow manufacturer’s instructions for application, but a good rule of thumb for dahlias is at 30 days of growth and then again at 60.
They Have Powdery Mildew
Grayish or white, powder-like spots are the tell-tale signs of powdery mildew. This fungal dahlia disease will be glimpsed first on leaves, but it might also spread to stems and blooms, negatively impacting your dahlia’s flowering potential.
Look for it when climate conditions are characterized by high levels of humidity, but moderate day and night time temperatures.
While dahlias are particularly prone to powdery mildew, especially in spring and fall, the disease does not have to be fatal. If leaves, stems, or blooms appear infected, prune out the bad parts and leave the healthy growth alone.
If you can live with the way it looks, and fungal growth is not too severe, plants with a little mildew can be left in place until the end of the season. At that point, cut stems to the ground and dispose properly to prevent fungus from spreading or overwintering.
They Are Being Eaten By Earwigs
If your dahlias’ blooms and leaves appear shredded and/or they are dropping petals suddenly, check them for earwigs. These common dahlia pests can cause serious problems with your blooms.
Easy to identify because they are long and brown with rear pinchers that look like forceps, earwigs are not life-threatening to dahlias, but they can do a lot of damage to their blooms.
The key to discouraging earwigs lies in habitat management. Since they prefer dark, moist places to hide, keeping dahlia beds free of rocks, yard art, dense groundcover, and debris is a good place to start.
You can also set traps using wet newspaper stuffed in toilet empty toilet paper rolls to lure earwigs away from your blooms and foliage. Chickens and toads both feast on earwigs, so you might also consider introducing some new animal friends to the yard.
Remember that gardening is a journey, not a destination! With each growing season comes new knowledge and experience. This is especially true when it comes to higher maintenance plants like dahlias, which can be slightly more demanding of your time and attention.
To ensure bountiful, beautiful blooms in future dahlia beds, pay close attention to the genus’ growing requirements and make sure they are diligently met. Plant them in full sun and water them evenly to give your dahlias the best start possible. Follow up with proper maintenance practices and pest/disease monitoring as well as proper winter care, and they’ll reward you with bigger, better blossoms next year!