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Offering towering flowers and vivid colours, Delphiniums command their space in the garden with ease. These plants grow in beds and borders but can also be grown successfully in large pots. They may look like a lot of work, but they are quite easy to grow, as I will show in this guide. These perennial plants come in a wide range of varieties with differently coloured blooms as we as different eventual heights so sometimes choosing slightly smaller cultivars for pots is better.
Delphiniums have intricate root systems that require adequate space to thrive therefore you have to pick a sizeable container to grow them successfully in pots.
Below, I will point out how to pick the right container and follow with how to plant and how to take care of your Delphiniums as well as a few issues to look out for.
Choosing the right container to grow delphiniums in
Delphiniums have a widespread root structure when it comes to their root system; therefore, the container has to be wide and deep too. The container needs to be of strong material whether it is plastic or ceramic as this will allow the plant to grow for a long period without any disturbance. If planter taller varieties, I like to use ceramic such as clay pots as there heavier and easier to keep upright when they become top-heavy.
Once you have a sizeable container, layer it with some broken crockery to prevent the holes from becoming blocked and then use a soil-based potting compost as this is heavier and less lightly to dry out too quickly.
What is the best compost for growing delphiniums
You want your plants to get all the nutrients hence; your compost should be a potting compost with long term fertiliser in which most have.
I personally like to use a potting mix that contains perlite or grit mixed in with the potting compost for moisture retention and better drainage. The grit and perlite help the soil get rid of excess water, thus, maintaining a healthy root system. Remember the compost should not be too acidic because the plants thrive better in neutral to alkaline soils so just avoid ericaceous compost as this is more for acid-loving plants which delphiniums are not.
You can always carry out a soil test to determine the PH of the soil before planting to avoid stressing the plant.
How to pot delphiniums into containers
There is the option to grow these herbaceous plants from seeds but unless you are very keen I would avoid this. I like to divide them every 2-3 years and replant these or take cuttings depending on your preference. Obviously if you don’t already have delphiniums you can you can also buy potted plants, usually in a 2 to 3-litre pot and transfer them to a permanent pot which is how most people will probably start out.
The method below is for already established delphiniums grown in pots from garden centres and nurseries:
- Remove the plant from its container making sure to be careful so as not to damage the roots. Detangle any matted roots to enable them to spread easily in the new compost.
- You want to place the plant with its roots above the soil, and then use the remaining compost to cover up the roots around the pot carfully compactinhg teh soil around the roots with your fingers to make sure there is no air gaps.
- Press the top compost gently to stabilise the soil and remove any air pockets without compacting the soil too much. Make sure you don’t plant it any deeper than it was in its orginal pot.
- Once this is done, water the plant and place it in an area where the sun can shine through for about 5-8 hours a day as they like a sunny position.
- Give the plant some supporting structures such as sizeable stakes arranged in a pyramid shape. You can also use bamboo canes just make sure they are well placed in order to support the plant and its flowers.
Read next: Growing hydrangeas in pots
How to water delphiniums and feeding
Water is crucial for most plants thus ensure you water them at least once a week, especially when it is dry. This helps the plant retain its healthy foliage and prevents wilting. To check if the soil is moist enough, stick your finger down the soil and if the soil below is dry, the plant needs more water. It is advisable to water in the morning to give the leaves a chance to dry through the day and avoid mildew.
Apart from water, they need a constant supply of nutrients because they are hungry feeders. Feed the plants using all-purpose fertilizer occasionally during the summer and in autumn before the plants die down.
What to do with Delphiniums over winter
Since you are growing your Delphiniums in pots, it gives you the option of moving them around whenever possible. These perennial plants do not do well if left out in winter if grown in pots. Place them indoors preferably in a greenhouse or conservatory where temperatures are constant. However, if you are unable to move the plants, wrap bubble wrap or burlap sacking around the pots to protect the root system from the cold over winter.
Delphiniums planted in the ground have more protection from the cold because the ground absorbs heat from the sun and stores it.
Deadheading delphiniums to promote more flowers
Delphiniums need deadheading to remove spent flowers and extend the flower display in the summer. Once the flowers complete the blooming, perennial Delphiniums should be cut back to promote better growth in the coming flowering season. Sometimes when you cut back flower spikes after flowering they produce new flower spikes.
Delphinium problems to look out for
Mildew loves delphiniums
I find that delphiniums are prone to attacks from mildew but it is nothing serious and preventing is better than trying to treat it with fungicides. Mildew manifests as white powdery patches on the leaves and stems. Spray the plant with a non-toxic fungicide at the very first signs of mildew. Before spraying the fungicide, remove all severely damaged sections to avoid re-infection.
Slugs and snails also love to eat delphiniums
Snails and slugs also enjoy chomping on Delphiniums’ stems, leaves, and flowers, which leaves an unsightly appearance. To prevent slugs and snails from attacking your plants, introduce birds or frogs that prey on them without harming the plants.
Alternatively, spread gravel or eggshells around the base of the plant to hinder the slug’s movement. You can also try to stick copper tape around the pot in a ring. Nematodes are also a viable option for a long-term solution, and they are harmless to the environment.
Have ago at dividing them every few years for even more plants
With proper care, Delphiniums can last for long and they can be easily propagated through division and then replant in the same pot and plant the other section of the delphinium into new pots or in the ground if you have space.