Even though I have a yard and gardens, I love to plant up ornamental pots each year. I enjoy choosing the color scheme, and figuring out the flowers and foliage combos. It’s nice to include single plants in a container to include in an arrangement of pots, like Spanish lavender or herbs, but there is one flower that can really stand out: the dahlia. I like growing dahlias in pots because they can shine on their own and the foliage generally holds up and presents nicely, too.
Growing dahlias in pots is also a great option for someone with a small space—a small patio, front porch, or deck—provided the area gets at least six to eight hours of sunlight a day.
If you’re at the garden center, dahlias are usually found in the flower bulb section. and online, you’ll also usually find them listed under summer bulbs. However plants are actually grown from tubers. Dahlia tubers look more like an oddly-shaped potato than a flower bulb. But from this non-descript tuberous root you’ll be rewarded with some pretty amazing blooms.
One thing worth noting is that the potted up dahlias full of buds and blooms, generally found in the annuals section of the nursery, are likely grown from cuttings. Growing your own dahlias from tubers opens up a greater selection of flower forms and color options. And it puts you in control of the planting process.
Choosing the right size of dahlia and the right pot
If you’re going to be growing dahlias in pots, you need to be very mindful of the information on the package of tubers or the online description. Dahlias are highly prized as cut flowers, with some plants reaching at least four feet high, not to mention those that are classified as dinner plate dahlias. Those will not work for pots!
It’s best to look for dwarf or small dahlia varieties, paying attention to bloom size, as well as the plant size. They also need about one to two feet of space, so you’ll probably only be planting one tuber per pot.
If you’re planting your tuber directly in its summer home pot, you’ll want to choose a container that is at least 16 inches wide (40 cm). Look at the package to determine how tall the plant will be and choose a pot of the same height/depth. Make sure there are plenty of drainage holes. Drainage is very important when growing dahlias in pots because you don’t want the tuber to rot.
Get a head start by growing dahlias in pots indoors
Once you purchase your dahlia tubers, you can wait to plant them when all threat of frost has passed. Or, you can give tubers a head start indoors. With the former option, you’ll have an empty spot in the container until the tuber sprouts, grows into a plant, and then blooms. With the latter option, when it’s time for dahlias to be planted outside, your tubers will have already sprouted for you, resulting in earlier blooms. Be sure to clean your container thoroughly before planting.
When starting tubers indoors, count back about four weeks from your area’s frost-free date. Choose a pot that’s wider than your tuber. Since you’ll be transferring your seedling to a larger pot once it’s time to plant outside, you don’t need to worry as much about the depth of the pot. Fill the bottom with a lightweight potting mix that drains well. Place the tuber horizontally on top of the soil with the eye facing up (this is where the plant will start to sprout). Cover lightly with soil and use a mister (if you haven’t pre-moistened the soil) to lightly water. Place the pot in a sunny window or under grow lights.
You’ll want to carefully harden off your dahlia seedlings as you would your veggies before planting them directly in the garden.
Starting dahlia tubers outdoors in containers
Wait until your last frost date has passed before planting dahlias outside. Plant them around the same time as you would your heat-loving veggies, like tomatoes, melons, and peppers.
When planting your dahlia tuber in its outdoor container, the same rules apply as when you’re starting one indoors. Fill about one third of the pot with pre-moistened lightweight potting soil. Lay the tuber so it’s horizontal (flat), being sure that the eye is facing up. Make sure no part of the tuber is touching or close to touching the side of the pot. This will ensure the roots have room to grow.
Lightly cover the tuber with about an inch of soil. Let the soil dry out between watering. As the seedling starts to grow, gently add more potting soil around it until the soil gets close to the top of the pot.
Caring for dahlias in pots
Most of the standard container garden maintenance tips apply. While you risk a rotting tuber by overwatering a dahlia before it starts to sprout, once it’s established, you’ll need to water more often. You don’t need to worry about fertilizing your dahlia when you first plant it, as all the energy and nutrients it needs to grow are in that tuber. Once you have more of an actual plant, you can start to fertilize about once a month. Choose an organic fertilizer that’s higher in phosphorus and potassium as too much nitrogen really just promotes more leaf growth, but not blooms.
More container gardening ideas and tips
- Planter ideas: Inspiring design tips for growing gorgeous garden containers
- Container plants for full sun: Choices for colour, foliage, and texture in your summer pots
- Brighten up dark areas of the garden with annual flowers for shade
- Container rose gardening made easy