There are dozens of dahlia varieties to choose from, and most of them are stunning. They range in size from so-called “dinner plate” varieties down to small and compact, but they can only reach their full potential with the correct potted dahlia care. They go from simple to bold colors and forms, including small pompoms or tight geometric designs to cactus ones with flower petals that have spidery, long tentacles.
Potted dahlia care will allow you to get luxurious blooms that work wonderfully as cut flowers and perennials. While you typically plant them in the ground, they can play the role of a filler or thriller plant in a mixed container. Most dahlias will start to bloom from mid-summer through fall, so your container plants won’t have color for some periods during the year. However, the foliage provides a nice structure when you mix it in with other plants.
Dahlias are wonderfully colorful flowers that will bloom again and again, and there are dozens of varieties to choose from.
Potted Dahlia Care – Quick Overview
|Bloom Time:||Summer and fall|
|Botanical Name:||Dahlia spp.|
|Flower Color:||Pink, red, purple, yellow, orange, and white|
|Hardiness Zones:||8 to 10|
|Mature Size:||One to six feet tall and one to three feet wide|
|Native Area:||Central and North America|
|Soil pH:||Acidic or neutral|
|Soil Type:||Well-drained and loamy|
|Toxicity:||Toxic to cats and dogs|
Potted Dahlia Care Elements
Dahlias prefer it to be warm, so make sure you’re well beyond the final frost date of the season before you put them outside. They grow best when the soil is 60°F or warmer, so it’s common to have them in greenhouses. You can also put them right in containers and set them out as the season warms up. Potted dahlia care requires a few key elements, and we’ll outline them below for you.
Potted dahlia care requires that you meet their fertilizer requirements, and they’re very heavy feeders. The more food they get, the bigger they grow, and the more flowers they produce. You’ll want to get a fertilizer that has a higher phosphorus level at a 10-30-20 ratio to help promote blooms. For this amount, you’ll follow the instructions on the label. Don’t use a fertilizer with a higher nitrogen percentage as this creates foliage with few flowers. If you want to dig up and store the tubers during the winter, you’ll stop fertilizing them at the end of August. This will stop growth late in the season and get the tubers ready to go dormant.
In order for the plants to produce a lot of flowers, potted dahlia care requires full sun. They should get between six and eight hours of sunlight a day at a minimum. In climates that are similar to growing zones eight and up, potted dahlia care requires midafternoon shade, especially when the sun gets hot.
Dahlias prefer loamy, rich soil that has a lot of organic matter and drains very well. So, you can find a lot of different potting soil types that fit this description. You want to avoid going toward the denser clay-based soil, or you can add in manure or peat moss to loosen the texture and offer better drainage. They like the pH to be around 6.5, so neutral.
The soil your dahlias prefer is a well-draining and loamy one, and this is much easier to reproduce in a pot than it is in the ground.
Temperature and Humidity
Timing is very important when it comes to planting dahlias as they hate the cold. You get a little more leeway with your potted dahlia care when you plant them in pots though. If you plan to move your pots outside, you should wait until the last frost of the spring has gone and it stays above freezing out. Ideally, they thrive in 60°F temperatures. You can easily start tubers in containers inside in your greenhouse or garage. You can move them outside when the frost danger has passed, and you want to store them inside in the winter with a little humidity.
Plant your dahlia tubers in the spring and allow them to grow until they start to sprout. Don’t water your tubers until the green growth is above the soil’s surface as they don’t need it until the root system develops. Once they sprout, water them a few times a week, and you want to water them deeply as they need to be six inches in the soil. Since pots tend to drain faster, you want to water frequently enough that the soil doesn’t dry out and make sure there is adequate drainage.
Starting Dahlia Tubers Inside
Once you buy the tubers for your dahlias, you can plant them anytime during the spring months as long as the pots stay inside. If you plan on moving them directly outside, wait until the frost recedes for the season. You want to clean out your container very thoroughly before you plant them to prevent bacterial or fungus infections.
When you start your tubers inside, count back four weeks from the frost-free date in your location. Pick out a pot that is wider than the tuber. Since you’ll transfer the seedling to a bigger pot when it’s time to move it outside, you won’t need to worry as much about the pot’s depth.
Fill the bottom of the pot with a lightweight potting mix that drains very well. Put the tuber in the pot horizontally on top of the soil with the eye facing up. This is where your dahlia will sprout. Cover it lightly with soil and use a mister to lightly water it if you haven’t pre-moistened the soil. Put the pot under grow lights or on a sunny windowsill. You’ll want to harden off the dahlia seedlings as you would veggies before you plant them right into the garden.
Starting your tubers inside gives them a jump start on the blooming time, and it’s common to have them start blooming much earlier in the summer months.
Propagating Dahlias as Part of Potted Dahlia Care
You can propagate your dahlias as part of your potted dahlia care. The most popular way is to use overwintered tubers or cuttings. Propagating using cuttings requires that you wait until the tubers sprout in the spring. However, you can start easier by dividing the tubers and planting them in pots inside before the outdoor temperatures reach the correct level. Come summertime, your plants might flower and mature earlier. Also, dividing your tubers gives you more plants and more flowers.
- Get a sharp knife, potting soil, alcohol pads, a four-inch pot, and rooting hormone powder.
- Wait until your tubers are a minimum of three inches tall. Take your knife and clean it using the alcohol pads and allow it to dry. Next, cut just below the sprout and partially into your tuber.
- Lay the cutting on a hard surface and carefully trim away the lower leaves. Prepare the pots by adding your soil to them and pot three or four small holes along the pot’s edges.
- Dip the end of the cutting into the rooting hormone powder and put it in the hole before backfilling it with potting soil. Repeat with the other cuttings and holes.
- Water the pot and let it drain before putting it in a sunny window. Leave it and keep the soil moist.
- In two or three weeks, the cutting should develop roots. Once they are growing well and the temperatures warmed up, you can repot them into other larger containers or put them outside.
You can grow dahlias from seeds you buy at your local nursery or from seeds you collected from last season’s plants. To do so, you’ll need a seedling tray that you fill with seed starting mix and sow the seeds inside. They should go right into the medium between four and five weeks before the final frost. Move the tray to a sunny location and make a point to keep the soil moist.
Once the seedlings sprout, you’ll wait for them to form the one true set of leaves before you transplant each seedling into a small pot or cell. Again, keep the soil moist. You will eventually move them to larger pots or plant them directly outside in the garden when temperatures reach between 65°F and 70°F.
It is possible to start dahlias from seeds, but most people choose to use tubers or cuttings because it takes weeks off of the propagation process.
- Get your overwintered dahlia tubers, garden pruners or shears, a trowel, peat, potting soil with vermiculite, a five-gallon bucket, and a large growing container or two.
- Mix the peat and soil in the five-gallon bucket and water it until it’s barely moist. Transfer the soil into different growing containers.
- Look at the clump of tubers and find those that have eyes. If you can’t see any, you’ll put them in a moist, warm area for several days until the eyes start to sprout or swell. Cut those tubers from the clump right at the neck. Depending on the clump’s size, you can remove several tubers from each.
- Dig a hole in each container’s soil between two and three inches deep for small tubers and six to seven inches deep for large ones. Lay single tubers horizontally in the planting hole, and the eye should point upwards. You can plant the clumps vertically and upright with an inch of soil covering last year’s stem.
- Let the tubers sprout in a sunny space while making sure the soil never totally dries out. Once it sprouts with three sets of branches, pinch the top off.
- You can then transplant them into bigger containers or outside in the garden between three and four feet apart or with two to three feet between rows.
Potting and Repotting for Potted Dahlia Care
For potted dahlia care, the bigger the container, the better. A good rule of thumb to follow is that the container should be a minimum of 12 inches wide and deep. If you use containers that are this big to start, you won’t have to repot them during the season. Bring your containers outside in the summer to ensure they produce a lot of blooms and reach their full growth, and stake the stems on bigger varieties to ensure they stay upright. You can also grow compact varieties that need smaller containers and less space overall.
Potted Dahlia Care – Overwintering
You need to dig up your dahlia tubers and store them for the winter. To do so, you should pick the healthiest plants from your garden and wait for the first hard frost to come through before cutting back the plant to four inches above the ground. Allow the tubers to stay in the ground for a week before you dig them up. Dig up the root ball starting a minimum of a foot away from the stem. Carefully remove the tubers and clean off any excessive dirt before allowing the root ball to air dry in a place that is out of direct light and sheltered from any further frost.
At this point, it’s safe to store your tubers in a bag or the whole root ball. You want to carefully separate the tubers and store them individually. You can put them in boxes, pots, or bags in a dark, cool place with higher humidity and temperatures between 40°F and 50°F. A root cellar or basement works well, but they should never freeze.
Common Pests and Plant Diseases
Common pests like earwigs, slugs, thrips, and caterpillars love this plant. Slugs are very problematic when the foliage is tender and young. However, once the plants mature, slugs won’t be a problem. Some gardeners have issues with deer while others claim that they’re deer-resistant. This can depend on the variety, so you want to protect the flowers, just in case.
Dahlias will also develop issues with fungal diseases and powdery mildew. Keep the foliage on this plant as dry as possible as part of your potted dahlia care and space them out to allow for great air circulation. If you notice issues, treat it with neem oil.
Five Secrets to Potted Dahlia Care
Generally speaking, potted dahlia care isn’t difficult, even for brand new gardeners. However, there are some care considerations you should keep in mind to ensure you get the plants you want with pretty flowers. The following five are the biggest secrets to potted dahlia care:
1. Choose the Right Variety
Dahlias are not something that is one-size-fits-all. Some flowers may look like tiny pom poms and others are dinner plate size. To make this easier, most dahlias get divided into small, medium, or large varieties. Large dahlias can get up to four feet high, and you grow them in the back of garden beds. Medium-sized ones are roughly half the size, and they top out at one to two-feet tall. Small dahlias are very compact, and they usually max out at 20 inches. Picking the right plant for your wants and needs is more difficult than potted dahlia care. However, when you’re planting exclusively in containers, you won’t have to worry so much.
Larger dahlias grow in bigger containers, but they’re simply not practical because of the structure and size. For successful potted dahlia care, you want to stick with the medium or small cultivars that have enough room to happily grow in the pot. If you can’t decide, the following are good starting points:
- ‘Happy Single Romeo’
- ‘Impression Festivo’
- ‘Jan van Schaffelaar’
- ‘Park Princess’
- ‘Pulp Fiction’
2. Pick the Correct Pot
Once you’ve picked out your dahlia, you’ll need to pick out a pot or container. Dahlias will sprout from buds that form on tubers, and those tubers should fit comfortably in a pot when you plant it. Pick a pot that is a wider diameter at 8 to 12 inches, depending on the tuber’s size. Try to match the pot’s depth with the potential plant height to ensure that it doesn’t look too big or small for the pot you have it in. Also, make sure your container has plenty of drainage holes. In the early growth stages, the tubers are very prone to rotting if the soil stays too wet.
If you don’t have enough drainage holes in the pot, you want to drill a few to ensure that the water goes through your well-draining potting soil and out the bottom. Before you pot anything, it’s a good idea to thoroughly clean the container. Even if you bought it from the store brand-new, especially if you want to reuse an older container from the garden, you should clean it with water and soap. Dirty pots are great places for bacteria to lurk, and it can spread diseases to the newly potted plants.
Picking the correct pot is setting your plant up for success and making sure that you don’t have nearly as many issues with your potted dahlia care as other people.
3. Be Careful When it Comes to Watering
Dahlia plants that are mature and fully-grown like moist soil. However, many gardeners who are new to potted dahlia care may think that they like moist soil all of the time. This leads to the death of the plants before they get a chance to form leaves. The tuber is the plant’s food source, and it’ll rot if the soil stays moist for too long.
In the early growing stages, you don’t want to water them too much. In fact, you can leave the soil to dry out completely before you water it again. Once the plants establish themselves and you fill the container with your soil, you can start watering them regularly to keep them healthy.
4. Consider Staking Bigger Varieties
Most of the more compact dahlias won’t need you to stake them. However, if you choose a medium or large cultivar, you’ll need to stake them as part of your potted dahlia care. This helps the plant grow in an upright manner without falling over, and it also stops the stalks from snapping in stronger winds. You want to put the stakes in the pot before the plant starts growing to avoid disturbing the plant’s roots later.
While you’re drilling extra holes for drainage in the container, add two to four holes in the sides of the pot close to the rim to help anchor the stake. Put the pole the size of the plant’s maximum height right next to the tuber in the center of the pot. Use string or wire tied to the holes in the side of the pot to stabilize it. As your dahlia’s stalk or stalks grow taller, secure them using gardening wire to the stake.
Deadheading is an important part of potted dahlia care, and it involves removing spent flowers from the plant. If you want your plant to produce as many flowers as possible, deadheading is a way to achieve this. By taking flowers off that aren’t looking good, you keep the plant tidy. It also forces the plant to focus any energy on making new flowers.
To deadhead your dahlias, all you have to do is remove any spent flower heads using scissors or with your fingers. Be careful as you do this so you don’t damage the nearby flowers or stalks. You can cut the stems from the main branch to encourage new stem and flower production.
Even though potted dahlia care isn’t difficult, it is something that you should learn before you get your dahlia plants. This way, you can ensure that you get stunning plants that produce a host of blooms into the later fall months.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.