How to Grow Dahlias in Pots

Dahlias are beautiful flowers with a variety of colors. Many gardeners are skeptical about growing dahlias in pots because they are quite tall and heavy, but actually dahlias can grow well in large planters and have support poles for large varieties. With the right growing conditions and a little care, you will be able to see the beautiful flowers all summer long.

Table of Contents

Create the right environment for plants

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Choose the dahlia variety that’s right for your space. You can buy bulbs online or at nurseries. Dwarf and slow-growing varieties of dahlias are best suited to potted conditions. Some dahlia varieties can grow up to 1.5 meters tall, so you will need to prepare a much larger pot if you choose a tall variety. ^{[1] X Research Source}

Small and medium-sized dahlia varieties include Bednall Beauty, which grows to 60 cm, and Bishop of Llandaff, which grows to 90 cm. Larger varieties include Hadrian’s Sunlight and Twyning’s After Eight, which can grow to 1.2 meters or more. ^{[2] X Trusted Source Royal Horticultural Society Go to Source}
A dahlia tuber requires 30-60 cm of space, so you’ll probably need to plant one pot each. ^{[3] X Research Sources}

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Choose a pot with a minimum size of 30x30cm. You need to choose a heavy pot, with a minimum depth of 30 cm and a minimum diameter of 30 cm. Pots of this size can hold 20-25 liters of soil. ^{[4] X Research Sources}

For the largest varieties, choose a 60x60cm pot, which usually holds about 95 liters of soil.

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Choose heavy pots if you want to grow tall plants. Dahlia varieties that grow up to 0.9 – 1.5 meters tall often have heavy heads, so light pots may not be strong enough to support the weight of the plant. In addition, tall varieties require poles to support and add weight. ^{[5] X Research Sources}

You should use sturdy ceramic or terracotta pots because plastic pots are usually very light.
Remember that unglazed terracotta and ceramic pots have the property of absorbing water, so they can freeze and crack if left outdoors during winter. ^{[6] X Research Sources}

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Punch drainage holes if necessary. This step may not be necessary if the pot already has multiple drainage holes. However, if the pot has only one hole in the center of the bottom, drill a few more holes to increase drainage. ^{[7] X Research Sources}

Dahlias grow best in well-drained environments. Although dahlias are water-intensive plants, their delicate roots are susceptible to rotting if the soil becomes soggy.
Spread a layer of gravel about 5cm thick on the bottom of the pot to improve drainage.

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Wash the basin with warm water and mild soap. Dirty planters can infect plants, and insect eggs may still be lying in wait at the bottom of the pot. Eliminate these risks by washing pots before planting. Mild soap and water are enough to clean the basin. ^{[8] X Trusted Source University of Georgia Cooperative Extension Go to Source}

Be sure to rinse thoroughly to rinse off the soap.
This step is especially important if you are using a pot that has previously grown other plants.

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Choose a soil mix that is rich in nutrients and well drained. Standard potting soil is often too porous and can prevent the plant from budging. For the right soil mix, mix 2 parts potting soil with 1 part well-rotted peat moss or manure. ^{[9] X Research Source}

Note that garden soil is not suitable for potted plants. You need to buy potting soil labeled for potted plants.

Plant a tree

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Plant the bulbs in mid-spring. You should plant dahlias in the spring or from April to early June in the northern hemisphere. Dahlias are very sensitive to frost, so you should only put the potted plant outdoors if there is no longer a risk of the temperature dropping to freezing. ^{[10] X Research Source}

If you live in an area that often experiences spring frosts and want to plant them right away, you can plant them indoors first, and then move them outside.

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Spread a thin layer of gravel on the bottom of the pot. A layer of gravel on the bottom of the pot will also help, but you should not lay a layer of gravel thicker than 1.3 cm. ^{[11] X Research Source}

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Pour soil to about 13-18 cm from the top of the pot. Do not compact the soil too tightly. You just need to pour the soil into the pot and leave it like that to keep the porosity. Remember that dahlias prefer loose, well-drained soil. ^{[12] X Research Source}

Finally, you will bury the flower bulbs at a depth of about 10-15cm, then cover with soil up to about 2.5cm from the mouth of the pot.
To plant the flower bulbs at the right depth, you should initially pour the soil about 13-18 cm from the mouth of the pot.

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Lightly water the soil, but do not over-water. You need to water so that the soil is moist but not so wet that the soil is compacted. Try using a watering can to moisten the soil instead of using a hose to spray the soil. ^{[13] X Research Source}

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Mix fertilizer into the top layer of soil. Dahlias need a lot of nutrients, and mixing fertilizer into the soil where the roots are about to grow will give the plant a good start. You can use a slow-release all-purpose fertilizer or an organic fertilizer, such as bone meal or a seaweed-based fertilizer. ^{[14] X Research Source}

Any fertilizer recommended for flowering plants is suitable for dahlias.
You can find fertilizers sold in stores with NPK numbers, representing nitrogen, phosphorus and potassium. Fertilizers suitable for dahlias include 5-10-15, 5-10-10, and 10-20-20.
Use a fertilizer with a higher nitrogen content early in the season, then use another fertilizer with a lower nitrogen content.
Read and use according to the instructions on the product packaging.

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Bury stakes in pots to support tall dahlia varieties. If you choose a plant that grows over 90 cm tall, you need to support the tree with a sturdy wooden or metal stake. Plug the stake into the soil before planting the bulbs. The flower tuber and its root system are at risk of damage if you stake the bulb after burying it. ^{[15] X Research Source}

Insert the stake into the soil next to where you plan to place the flower bulbs. You should choose a stake with a height of at least 90 cm above the ground after it reaches the bottom of the pot.
For a 30 cm pot, you need to use a 1.2 meter high stake.
Loosely tie the stem to the stake as the plant grows.

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Bury the dahlia tubers horizontally. Place the dahlia tuber horizontally and the eye of the tuber in the center of the pot. The bulb’s eye is where the stem will grow, so you should place it slightly up so that the bulb’s eye is facing up. ^{[16] X Research Source}

The tuber looks like a bud and is located opposite the roots on the tuber.

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Fill a layer of moist soil about 2.5 cm thick on top of the tubers. At this time, it is not advisable to fill in a lot of soil. You should only spread a layer of moist soil about 2.5 cm thick on top of the tubers for the shoots to grow.

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Lightly water the newly sprouted shoots, but don’t over-water them. You can poke your finger in the soil to check. Do not water more if you feel the soil is moist. If the soil is dry, sprinkle with enough water to moisten the soil. ^{[17] X Research Source}

Don’t let the soil dry out completely, but soggy soil will rot the flower bulbs.
You probably don’t need to water until the buds are in the ground and the first leaves appear, unless you live in a hot climate. ^{[18] X Research Sources}

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Mulch more soil little by little as the stem grows. Take care when performing this step to avoid injuring the tree, as the stem is still very fragile at this stage. Cover the new stem with soil until you reach the first pair of leaves; Remember not to cover the leaves with soil.

As the stem grows taller, continue to cover the remaining space in the pot with a little more soil until it is about 2.5cm from the top of the pot.
Dahlias grow very quickly, and you should see full leaves within 2 weeks. The flowers usually appear 8 weeks after planting.

Take care of plant

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Place the potted plant in full sun. Dahlias grow best in direct sunlight for 6-8 hours per day. For optimal results, choose a location with full sun from morning to midday. Try to choose an area with partial shade to avoid intense afternoon sun, especially if you live in a hot climate.

If you grow plants indoors, you need to supplement the sun with fluorescent grow lights.
You’ll also need to provide extra light if you’re starting to grow houseplants in early spring. Install the light above about 15 cm from the mouth of the pot when the bulbs are first planted and gradually raise them as the plants grow.

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Water deeply when the stem has grown higher than the pot’s mouth. You need to water the plant thoroughly 2-3 times a week. Dahlias grown in hot, dry climates may need to be watered every day. While it’s a good idea to water thoroughly and maintain moisture in the water, care should be taken not to let the soil get soggy or waterlogged.

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Tie the stem to the stake when the plant is about 30 cm tall. Use rope or nylon rope to tie the tree trunk to the stake. As the stems grow taller, tie them in segments about 30cm apart. ^{[19] X Research Source}