How to Grow Dahlias in Pots

Dahlias are stunning flowers that come in a wide range of vibrant colors. Many gardeners are hesitant to grow dahlias in pots due to their tall and heavy nature, but with the right pot size and support stakes for larger varieties, dahlias can thrive in containers. With the proper growing conditions and a bit of care, you’ll be able to enjoy beautiful blooms throughout the summer.

Choose the right variety of dahlia for your space. You can purchase dahlia tubers online or from nurseries. Dwarf and slow-growing varieties are the best suited for pot cultivation. Some dahlia varieties can grow up to 1.5 meters, so if you opt for a taller variety, make sure to select a much larger pot.

• Smaller to medium-sized dahlias include Bednall Beauty, which grows up to 60 cm, and Bishop of Llandaff, which reaches 90 cm. Larger varieties like Hadrian’s Sunlight and Twyning’s After Eight can grow to 1.2 meters or more.
• Each dahlia tuber requires a space of 30-60 cm, so you may need to plant each one in its own pot.

Choose a pot with a minimum size of 30x30 cm. You will need a heavy pot that has a minimum depth of 30 cm and a minimum diameter of 30 cm. A pot of this size can hold between 20-25 liters of soil.

• For the largest dahlia varieties, choose a 60x60 cm pot, which typically holds around 95 liters of soil.

Opt for a heavy pot if you want to grow tall varieties. Dahlias that reach 0.9 to 1.5 meters in height tend to be top-heavy, so lightweight pots may not be sturdy enough to support the plant’s weight. Additionally, taller varieties require stakes for support, which adds more weight.

• It’s best to use a solid ceramic or terracotta pot, as plastic pots are generally too light.
• Keep in mind that unglazed terracotta and ceramic pots are porous, meaning they absorb moisture. This can cause them to freeze and crack if left outdoors during the winter.

Drill drainage holes if needed. This may not be necessary if the pot already has multiple drainage holes. However, if your pot only has one hole at the center of the bottom, you should drill additional holes to improve drainage.

• Dahlias grow best in well-drained environments. While they require a lot of water, their delicate roots can rot if the soil becomes waterlogged.
• To enhance drainage, place a 5 cm layer of gravel at the bottom of the pot.

Wash the pot with warm water and mild soap. Dirty pots can spread diseases to your plants, and insect eggs may still be lurking at the bottom. To eliminate these risks, clean the pot before planting. A mild soap and warm water solution is enough to clean the pot.

• Be sure to rinse the pot thoroughly to remove any soap residue.
• This step is particularly important if you are reusing a pot that has previously housed other plants.

Choose a nutrient-rich and well-draining potting mix. Standard garden soil is often too loose and may hinder the plant from flowering. For the best mix, combine two parts potting soil with one part peat moss or well-rotted manure.

• Note that garden soil is not suitable for container plants. You should purchase a potting mix specifically labeled for container gardening.

Plant the bulbs in mid-spring. It is best to plant dahlias in spring, from April to early June in the northern hemisphere. Dahlias are very sensitive to frost, so you should only place the pot outdoors once the risk of freezing temperatures has passed.

• If you live in an area where frost is common in spring but want to plant immediately, you can start the plants indoors and then move them outside later.

Place a thin layer of gravel at the bottom of the pot. A layer of gravel at the bottom of the pot can be helpful, but make sure not to exceed a thickness of 1.3 cm.

Fill the pot with soil, leaving a gap of about 13-18 cm from the rim. Don’t pack the soil too tightly. Simply fill the pot with soil and leave it loose to maintain good aeration. Remember, dahlias prefer soil that is light and well-draining.

• Finally, bury the bulb to a depth of about 10–15 cm, then cover it with soil, leaving about 2.5 cm from the rim of the pot.
• To plant the bulb at the correct depth, start by filling the pot with soil, leaving a gap of about 13-18 cm from the rim.

Water the soil lightly, but avoid overwatering. You need to water just enough to keep the soil moist, but not to the point where it becomes compacted. A watering can works better than a hose to moisten the soil.

Mix fertilizer into the top layer of soil. Dahlias require plenty of nutrients, and incorporating fertilizer into the soil where the roots will soon grow will give the plant a good start. You can use a slow-release all-purpose fertilizer or organic options like bone meal or seaweed-based fertilizers.

• Any fertilizer recommended for flowering plants is suitable for dahlias.
• You can purchase fertilizers in stores with N-P-K numbers, which stand for nitrogen, phosphorus, and potassium. Suitable fertilizers for dahlias include 5-10-15, 5-10-10, and 10-20-20 formulations.
• Use a higher-nitrogen fertilizer early in the season, and then switch to one with a lower nitrogen content later on.
• Be sure to read and follow the instructions on the product packaging.

Place a stake in the pot to support taller dahlia varieties. If you choose a variety that grows over 90 cm tall, you will need to support the plant with a sturdy wooden or metal stake. Insert the stake into the soil before planting the bulb. The bulb and its root system may be damaged if you insert the stake after the bulb is planted.

• Position the stake near where you plan to plant the bulb. Choose a stake that will stand at least 90 cm above the ground once inserted into the pot.
• For a 30 cm pot, use a stake that is 1.2 meters tall.
• As the plant grows, loosely tie the stem to the stake for support.

Plant the dahlia bulb horizontally. Place the dahlia bulb horizontally in the pot, with the eye (the spot where the stem will emerge) centered in the pot. The eye is the point where the stem will grow, so make sure it’s slightly tilted upward, pointing towards the surface of the soil.

• The eye of the bulb looks like a small bud and is opposite the root area on the bulb.

Cover the bulb with a thin layer of moist soil, about 2.5 cm deep. At this stage, avoid covering the bulb with too much soil. Simply add a thin layer of moist soil, about 2.5 cm thick, over the bulb to allow the sprout to emerge.

Water lightly for newly sprouted shoots, but avoid overwatering. You can check the soil moisture by sticking your finger into the soil. Don’t water further if the soil feels moist. If the soil is dry, water gently to moisten the surface.

• Don’t let the soil dry out completely, but overly wet soil will rot the dahlia bulb.
• You may not need to water until the shoots break through the surface and the first leaves appear, unless you live in a hot climate.

Gradually add soil as the stem grows. Be cautious during this step to avoid damaging the plant, as the stem remains quite fragile at this stage. Add soil around the newly sprouted stem until it reaches the first pair of leaves; make sure not to bury the leaves.

• As the stem grows taller, continue adding soil gradually to fill the remaining space in the pot, leaving about 2.5 cm from the top of the pot.
• Dahlias grow rapidly, and you’ll see plenty of leaves appear within two weeks. Flowers typically bloom 8 weeks after planting.

Place the pot in a location with full sunlight. Dahlias thrive best under direct sunlight for 6-8 hours daily. For optimal growth, choose a spot that receives full sunlight from morning to mid-afternoon. If possible, select a spot with some partial shade to avoid intense afternoon sun, especially if you live in a hot climate.

• If growing indoors, supplement natural light with fluorescent grow lights.
• If you start growing your plants indoors early in the spring, provide additional lighting. Place the light 15 cm above the pot when you first plant the bulb, and gradually raise it as the plant grows.

Water deeply once the stem is taller than the pot's edge. Water the plant thoroughly 2-3 times a week. Dahlias in dry, hot climates may need daily watering. Although it’s important to water deeply to maintain soil moisture, make sure the soil doesn’t become waterlogged or overly saturated.

Tie the stem to a stake when it reaches around 30 cm in height. Use twine or nylon string to secure the stem to the stake. As the stem continues to grow, tie it to the stake at intervals of about 30 cm.

Fertilize the plant every two weeks throughout the blooming season. Choose a liquid fertilizer with higher phosphorus and potassium content. Suitable N-P-K fertilizers include 8-24-16 and 0-20-20.

• High phosphorus helps encourage flowering, while potassium stimulates root development.
• Follow the manufacturer's instructions on the fertilizer packaging.

Prune and deadhead regularly to encourage new growth. Dahlia flowers last 4-6 days before wilting. Remove spent blooms to promote fresh flowers. Trim lower leaves in mid-summer or around mid-July in the Northern Hemisphere.

• When the plant reaches about 40 cm in height, pinch the tips of the stems before buds form to encourage fuller growth.
• Removing lower leaves improves air circulation, reducing the risk of mildew.

Apply fungicides or insecticides as needed. Dahlias are susceptible to pests such as mildew, earworms, slugs, red spider mites, aphids, and cucumber beetles. To prevent infestations, alternate insecticides and miticides every 7-10 days when the plant reaches about 15 cm.

• Look for specialized insecticides and miticides for flowering plants at your local garden center and follow the directions.
• If you prefer natural remedies, use organic pesticides like horticultural soap or neem oil.

Store bulbs in a cool, dry place during winter. The first frost will kill the foliage and stems. When this happens, trim the stems back to about 15 cm. Wait two weeks for the bulb to harden in the pot. Then, carefully dig it up, rinse it clean, allow it to dry for a day, and wrap it in newspaper, sawdust, or vermiculite.

• Store the bulb in a dry, dark place with temperatures between 4-10°C during the winter and replant it in spring.

• When cutting dahlia flowers, dip the cut ends of the stems in hot water. This method helps retain moisture inside the stems, keeping the flowers fresh for a longer period.

• Dahlia tuber
• Large and heavy plant pot
• Garden spade
• Potting mix
• Fertilizer
• Wooden or metal stake
• Twine
• Pruning shears