Dahlias are a fascinating New World flower, native to Central and South America. It was declared Mexico’s national flower in 1963, and it’s a favorite in the Pacific Northwest as well, being the official flower of San Francisco and Seattle.
The Aztecs grew them for their tubers as a food source before the arrival of the Spanish, who following their conquest introduced them to Europe. They first entered the Western record in 1615 under their original name in Mexico, “acoctli.”
While they have grown in Europe in the centuries since, they do best in areas that are free of frost. True to their warm weather roots, these are not flowers that do well in the cold. They have a royal association, being a favorite flower of Marie Antoinette (who had a variety named after her) and Queen Victoria.
Dahlias are beautiful flowers which can grow up to a foot in diameter — but what if yours aren’t growing at all? If your dahlias have started to droop or haven’t begun to bloom at all, this guide can help restore them to their rightful glory.
Before we get into what can go wrong for dahlias, we should first look at what they’re like when they are going right. The process for planting dahlias differs whether you are planting them indoors or outdoors.
If you are planting them indoors, you’ll want to make sure that you heat the soil up outside first. Remember, these are flowers that are used to warm weather environments, and so you should make sure that their soil is at least 60 degrees Fahrenheit.
When planting them outdoors, you’ll want to make sure that they get a lot of sunlight to mimic the sunny conditions these plants usually receive in their Central and South American natural habitats. They should receive at least six hours of sunlight per day.
They grow and flourish around the same time as tomatoes do. The soil should be rich, and you’ll also want to make sure that it’s well drained. As we’ll see below, if you don’t properly drain the soil, the flower will suffer.
As for the soil itself, it should be on the sandy and loamy side, and more acidic than basic. Dahlias tend to grow well in soil that has compost or other forms of organic fertilizer. A little goes a long way with dahlias when it comes to fertilizer. They are hungry plants with potato-esque tuber roots.
These flowers can grow taller than three feet, so you’ll want to space them out by 12 to 18 inches to make sure that they have enough room for their roots to spread out. If you are growing a larger variety of dahlia, you’ll want to stake the plant, meaning that you’ll want to place a stake behind it to support its stem.
Why Dahlias Might Not Bloom
One potential reason why your dahlias might not be blooming the way you’d hoped is that plague of flowering plants everywhere: pests. While dahlias are actually pretty lucky in this regard insofar as they are freer of pests than a lot of these plants, they still have to contend with them, with slugs being one of the main culprits.
Slugs love chowing down on dahlias. As with termites in a wooden house, they can wreak havoc in no time, so as soon as you identify them, you need to act fast. They aren’t the only ones who enjoy dining on dahlias, however, Caterpillars love eating dahlia leaves, so if you see chew marks all over yours, it’s probably them.
Depending on where you live, other bugs and insects can decide to try and nosh on your dahlias as well. For example, Japanese beetles seem to enjoy them.
As mentioned, dahlias require a lot of sunlight, so if you plant them in a cloudy area, this could cause them to droop or not bloom to their full potential. The same goes for heat, as if the temperature is too cool, your dahlias may not be able to grow well.
Likewise, dahlias do not do well when they are thirsty. They require a lot of water, so droughts can cause them to droop.
Finally, you will want to pay very close attention to fungi and disease. Far too often, new gardeners overlook this to their peril.
This is due in part to the fact that these issues can be more difficult to spot than pests. However, they can be just as detrimental to the long-term health of your plant, if not more so, and thus require immediate action.
For example, sometimes dahlia plants are susceptible to powdery mildew, which is typically a sign of greater fungal or disease trouble. This is typically the result of a pathogen known as Erysiphe cichoracearum, which distorts the leaves before they finally wilt and fall to the ground.
Another, similar issue, Fusarium wilt, poses a similar problem with similar symptoms. The foliage starts to yellow and wilt, climbing up the plant and potentially killing it.
What You Can Do About it
If you see slugs dining on your dahlias, you need to eliminate them with slug bait. In the case of caterpillars, you can and should pick these off whenever you happen to see them. Caterpillars, Japanese beetles, and other bugs can also be dealt with via soapy water.
In addition, you need to make sure that you have an appropriate amount of fertilizer. Too much or too little will overfeed or starve your dahlia.
Nitrogen may stimulate leaf growth but won’t help grow the flowering part, and that’s what you care about. You should thus look into fertilizer with little to no nitrogen.
If your specimen has produced flowers in the past but isn’t blooming now, or its buds aren’t blooming properly, this may mean that you need to deadhead it. This means removing blossoms when they die so that new buds can grow unfettered.
For powdery mildews, you’ll want to make use of Serenade. In addition, you’ll want to be careful about how much you are watering the plants, as this kind of issue can occur when the soil is overly wet. On the other hand, if the soil is dry to one inch deep, you need to water it.
Another way to prevent powdery mildew diseases is to apply neem oil at least every couple of weeks. If your plant is already sick, this should be done every week until it is cured.
However, there is no cure for Fusarium wilt, so you need to act preventatively and destroy it on sight to prevent it from spreading to other plants. Solarize the soil if necessary, or fumigate it with a chloropicrin-methyl bromide solution.
Finally, if your plant is suffering from a viral disease, you’ll likewise need to remove the affected plants. Once again, there is no cure available, so early identification and isolation is essential for making sure that the rest of your dahlias are safe.
Dahlias are a beautiful flower, albeit one which can require a fair amount of maintenance to keep in good condition. Still, with the right information, a little attention and love, the right watering and lighting regimen, and preventative measures, you can make your dahlia blooms better than ever.
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.