Planting your own dahlias can be a fulfilling experience.
In this guide, we’ll cover what you need to know to grow your own dahlias.
Planting dahlias seeds
If you are starting your dahlias from seed, the timing of your planting will be a bit different. Aim to plant the seeds with enough time for them to germinate, sprout and mature before you plant them outside.
To plant the dahlia seeds, purchase some potting soil and fill a container or tray with the potting soil. It doesn’t have to be a deep container — even a shallow tray will be fine for dahlia seeds.
You can purchase plastic pots or packs to plant them, or use something you have lying around your home, such as an egg carton.
Once the container is full of potting soil, poke a hole in the soil with your finger no deeper than the first joint in your finger. Then, place the dahlia seed in the hole and cover it up lightly with potting soil.
To initiate the seed’s growth, water the dahlia seed lightly.
Try to keep the soil in direct sunlight as much as possible. You can cover it with some clear plastic to keep the humidity high as well.
Make sure to keep on watering the soil lightly whenever it dries out. The soil doesn’t need to be more than damp, but it does need to be moist consistently for the dahlia seed to germinate.
You’ll soon start seeing a baby dahlia sprout emerging from the potting soil.
Transplanting dahlias seedlings
After the dahlia sprouted, you’ll want to let it grow a little bit to establish a root structure. If the seedling is planted with its own space to grow, you won’t need to transplant it until it grows its own root cube.
However, if the dahlia seed was planted with other dahlia seeds in its own space, it should be planted earlier so that its roots aren’t in competition for limited space.
As long as the roots have room to grow, you’re fine to keep the dahlia in its container.
If you notice that the dahlia seedling is drying up fast, this may be a sign that it’s time to plant it in a larger container. You can transplant a dahlia however many times you’d like before planting it in its final destination.
To transplant a dahlia, pinch the bottom of the container as you gently pull the sprout up. If the seedling is very small, you can turn the pack upside down as you do this for each sprout so that the plant and its early root structure fall out into your hand.
If the dahlia is rootbound, meaning that the roots are tightly wound together forming the shape of whatever container it was in, then you’ll want to gently rip the roots apart once before transplanting the dahlia into its next container.
After you have transplanted your dahlia, water it in and make sure it gets some sunlight for continual growth.
Planting dahlias outside
Whether you are growing your dahlia from seed, or you purchased a young dahlia plant from a local garden center or greenhouse, eventually you’ll want to plant it outside.
To plant your dahlia, gently squeeze the bottom of the container and pull the plant out of its pack.
Then, use a trowel or your hand to remove soil from where you’d like to plant it.
If the soil is hard and packed down, consider using a tiller to break it up, or just push a shovel in the soil a few times to break up the clumps.
Best soil type for dahlias
You can check your dahlia plant’s tag for specific information regarding soil needs.
You may need to mix in some potting soil or other soil additives to get your soil to the ideal consistency.
When to plant dahlias outside
Choosing when to plant dahlias outside is an important consideration. If you plant them too early, there’s the risk of a late frost killing them off.
As a general rule of thumb, typically if you wait until after Mother’s Day you’ll be fine to plant dahlias outside. That being said, in Central PA we have had late frosts later than Mother’s Day, so make sure to check the forecast for your area in the spring to make sure that there isn’t a deep frost on the horizon.
In some cases, planting dahlias outside before Mother’s Day is definitely doable. Some annuals are just more hardy than others, so you’ll want to consider the hardiness of your dahlia, too. For example, the Bubblegum Supertunias that Homestead Gardens sells can often be planted outside as early as mid to late March, which is well before Mother’s Day.
It depends on the plant’s size, maturity, hardiness (did the greenhouse you purchased the plant from “harden it off”?), and spring weather.
Where to plant dahlias
Once you have your dahlia, you’ll need some soil and a spot to plant it. If you’re going to be planting it directly outside from the pack you purchased it in, you have the option of planting the dahlia in the landscape, in a hanging basket, or in a pot. A dahlia will do great in any of these locations.
Sunlight requirements for dahlias
If your dahlia receives too little or too much sunlight exposure, it will likely still live, but may not grow as abundantly and could require more care.
There are general sunlight requirements for all dahlias. For specific sunlight requirements for the variety of dahlia that you purchased, make sure to check the plant tag.
Best temperature and humidity for dahlias
Most areas have plenty of temperature swings, so an easy way to determine if your growing area will work for dahlias is to check your USDA growing zone.
A dahlia will grow well in most USDA growing zones, but the length of its season will vary depending on the region.
One of the most important factors to keeping your dahlia looking healthy is to diligently water it throughout the summer.
For dahlias, you’ll know they need water when the top inch of soil is dried out. To check, you can stick your finger into the soil down to the first joint in your finger. If it’s moist, no need to water the dahlia plant. If it’s dry, you’ll want to water it in.
Be careful that you don’t overwater the dahlia. A dahlia plant can be susceptible to diseases if it gets too much water.
If you planted the dahlia in a container, make sure that it has holes in the bottom for excess water to escape. Otherwise, the water can collect at the bottom of the container and cause root rot, or other diseases.
Another important factor for plant health is keeping your dahlia fed with nutrition.
If the dahlia is planted in the ground, you can lessen the amount of fertilizer it’ll need by building up the soil with compostable material in the year(s) leading up to your planting. Otherwise, you’ll want to fertilize the dahlia throughout the summer.
A good rule of thumb for fertilizing dahlias is to give the plant a water-soluble fertilizer every third watering. This rule helps to account for the change in temperature and weather throughout the season. For example, in May you won’t be watering your dahlia plant as much as in the heat of the summer in August. So feeding the plant every third watering helps to provide dahlias what it needs throughout the season, no matter the weather conditions.
It’s also recommended to plant the dahlia with a slow-release form of fertilizer to feed the plant slowly throughout the summer. You can add this in with your potting soil in a pot.
Growing dahlias in a hanging basket
If you’re growing dahlias in a hanging basket, you’ll want to make sure you don’t overfill the basket with plants. Plants will generally fill in the space you give them, so if the hanging basket isn’t packed full when you first plant it, that’s great.
The more dahlias you plant in your hanging basket, the more you’ll need to water the hanging plants. In general, if you have more plants competing for water and soil, it’ll take more maintenance to keep the hanging basket looking beautiful.
If you’re watering your dahlias in a hanging basket, you can check if it needs water by lifting the basket from beneath. If the basket is noticeably light, it could use some water.
You’ll know you overwatered your dahlia in a hanging basket if water comes dripping or streaming out the bottom of the basket where the holes are.
Growing dahlias in a pot
As mentioned above, be careful you don’t plant too many dahlias in a flower pot.
The answer for how to care for dahlias grown in a pot will vary according to the size of the pot. In general, make sure that it has plenty of room to grow and has adequate sunlight exposure where the pot is placed.
A dahlia that is planted in a container, whether it’s a pot or a hanging basket, will need to be watered more than dahlias grown in the landscape, since they won’t be able to pull natural water from the ground.
Growing dahlias in the landscape
Choosing dahlias for your flower beds or other landscaping is a great choice. They make for great borders and can help add beauty to your yard.
Since you’re planting them in a permanent spot, you’ll want to be extra careful when planting dahlias in the ground outside. Make sure that there’s little chance of frost and that the dahlias are in a spot that matches their sunlight needs.
If you do have a late frost, and your dahlias are already in the ground, you can cover them overnight with a bucket or sheet to protect them in most cases.
How to get dahlias to bloom
If dahlias are not blooming it could be for a variety of reasons.
First and foremost, ensure that the plant is getting enough water, fertilizer, and sunlight. If dahlias are not given the basic necessities, they’ll resort to growing only what they can, which may mean not producing flowers.
Outside of that, dahlias can sometimes get diseases that prevent them from blooming or stops their blooms.
Deadheading and pruning dahlias
You can deadhead your dahlias to promote future blooms.
For some varieties, this isn’t necessary and the plant will continue blooming just fine without any deadheading. For other plant varieties, the spent blooms can look ugly so you’ll want to snap those off or cut them back.
Cutting back or pruning your dahlia can be healthy for the plant. You shouldn’t need to do this more than a few times throughout the summer. It can be good to do this if the plant is overgrowing its area, or overpowering another plant in a container.
Common diseases for dahlias
A dahlia is more susceptible to common diseases, such as downy mildew or root rot when it isn’t cared for properly. That being said, even dahlias that are given the correct care can fall victim to some diseases.
Consult with your local garden center if you notice that your dahlias have a disease.
While it is possible to overwinter your dahlias, this is not common for dahlias.
A dahlia is an annual, meaning that it lives for one growing season and then dies. If you’d like to grow a plant that comes back every spring, you’ll want to grow a perennial.
Pest control for dahlias
Typically, natural predators are enough to take care of bugs and pests that eat at your dahlias. For example, ladybugs will eat aphids and can help control them.
However, in some cases, you will need to take extra measures to kill off plant pests. Again, consult with your local garden center for a specific solution to your pests.
Companion plants for dahlias
There are many other plants that grow great with dahlias. These are what we would call “companion plants.” This means that if they are planted together they will generally complement each other with their colors and growing styles.
When looking for companion plants for your dahlias, look for plants that have similar growing needs. This is an easy way to find plants that grow well. For example, if two plants love the sun, require similar fertilizer needs and one is taller while the other is a spreader, they will probably be great companion plants in a pot or hanging basket.
Varieties of dahlias
There are many varieties of dahlias. In general, their growing needs will be consistent across these varieties, but it’s always best to check the plant’s tag to make sure there isn’t specific instructions for your variety of dahlias.
It’s possible to propagate dahlias.
To do so, you can cut off a small piece of the plant and put it in water for a week or so. Soon, the dahlia should start growing fine roots.
Eventually, you’ll be able to plant the dahlia cutting into soil.
For some varieties of dahlias, propagating and then selling your cuttings as plants once they are established is illegal. Make sure there isn’t a patent on the dahlia variety before you would do this.
Some annuals, such as sun coleus, can be propagated just by placing the cutting directly in potting soil.