Horticulture Magazine

How To Grow Delphinium In Pots

blue upright delphinium flowers

Delphiniums usually do best when planted in the ground but they can also be grown in suitable containers.

One challenge when growing delphiniums in pots is that they have sensitive root systems and very much dislike overcrowding. Another challenge is that these plants can grow rather tall, and so can be vulnerable to falling over, or being toppled by strong winds.

However, if you make the right decisions, they can look spectacular in a container garden, and some may even be suitable for use as attractive (though rather high maintenance) houseplants.

There are two main types of delphinium grown in UK gardens, and both can potentially be grown in pots or containers.

The first type is perennial delphiniums, which flower in early summer and come back year after year. Some are very tall – over 2 metres – but there are also smaller cultivars that work well in pots.

The second type is annual delphiniums, also known as larkspur. These are annual crops, and so flower only for a single season. But their flowers will bloom throughout the summer months and since they are smaller, they may be easier to grow in pots.

One thing to note about all delphiniums, however, before you decide to grow them, is that they are poisonous.

All parts can cause severe discomfort if ingested, and touching the plants may irritate your skin so always use gloves when handling them. 

Choosing Delphiniums to Grow in Containers

'Magic Fountain' Delphinium
‘Magic Fountain’ Delphinium

If you decide to grow perennial delphiniums, then it is a good idea to opt for the Magic Fountains series. These are smaller delphiniums that will grow to an eventual height of 75-90cm tall, and spread to create clumps of 0.1-0.5m.

There are a number of different colours within this range that you can choose from.

If you decide to grow annual delphinium, or larkspur, you might consider:

  • Delphinium grandiflora
  • Delphinium ajacis

These are easy to grow from seed and are a cheap and cheerful way to fill your patio containers, window boxes or even hanging baskets.

They tend to be a little tougher and easier to care for than their perennial cousins.

Where to Position Your Delphinium in Pots

blue delphinium in a garden container

Both perennial and annual delphinium like a sunny and sheltered position. It is important to think carefully about the best place to position your potted plants so that you can maintain them easily, and also so that they are not damaged by wind.

Be sure to think about sunlight and shade, prevailing wind direction and also about the water needs of your plants and how you plan to meet them.

Be sure to think about other plants in your garden – as well as man-made structures and how these affect conditions.

You might grow delphiniums in their own containers, or in larger containers as part of mixed planting schemes.

If you are growing delphiniums in containers alongside other plants, make sure that the position is also suitable for them, and that they have similar requirements when it comes to their growing medium, water needs etc.

Even if your delphiniums are being grown in their own separate container, it can be helpful to think about other plants which will look good in containers positioned nearby. The containers should be thought of holistically and it is key not to think about each container in isolation.

Even when plant roots do not have the chance to communicate, you should still think about how each container plant you choose works in relation to the other plants, and the wildlife, in your garden.

Containers for Delphiniums

Containers for delphiniums, especially taller perennial types, should be heavy and stable.

Even in a sheltered spot, it is important to make sure that any pots and containers you choose will not tip over with tall plants like delphiniums within them.

Remember to choose a pot of sufficient width and depth to accommodate your plant(s) and pot up as necessary until you have your delphiniums in a suitably large container.

Delphiniums do like moisture during dry periods, but it is also important to create free-draining conditions in a container.

That means choosing a container that has good drainage holes at the base; it may also be beneficial to raise containers up off the ground so water can always drain out freely.

Growing Medium for Delphiniums

As well as requiring a moist but free-draining growing medium, Delphiniums are also hungry plants that will require plenty of nutrients. So it is important to choose a fertile growing medium.

Choose John Innes No. 2, or any good quality multi-purpose peat-free compost with added John Innes, or another loam-based mix. Add grit added to improve drainage, and place crocks at the base of the pots.

Sowing and Planting Delphiniums in Pots

Perennial delphiniums are usually purchased as plug plants in spring, or as potted plants in summer ready for planting out. There are also seeds available for sale, but not all cultivars of perennial delphiniums can be propagated from seed.

Plant out these types into your containers in spring or early summer to give them the best chance. However, you can plant out at any time as long as you ensure adequate water and the growing medium is not waterlogged or frozen.

Replant at the same level as the plants were at in their previous pot, and water in well.

Annual delphiniums (like some perennials) can be grown from seed.

The seeds can be sown in spring or in autumn for earlier flowering, then potted up in spring and placed into their containers for blooms over the summer months.

Caring for Delphiniums in Pots

immature delphinium plant in a terracotta pot

Support for Delphiniums in Pots

One important thing to think about when growing perennial delphiniums in pots is that some varieties will require support.

It can be a good idea to insert canes or stakes into the soil in your containers, and to tie in the delphiniums to these supports as they grow.

Watering

Delphiniums will need to be watered during dry periods over the summer months – remember, watering is more crucial, and more frequent, with container-grown plants.

Keep the growing medium moist but not damp or soggy.

With perennial types, remember to reduce watering as temperatures cool, and over the winter if you are overwintering your plants.

Feeding

Delphiniums need good fertility. One important step to maintain that fertility is adding a good quality organic mulch to the top of the pots or containers that you choose.

When growing in containers, it is also a good idea to add an organic liquid feed regularly over the summer months.

Choose one that is rich in phosphorus and potassium and avoid adding too much nitrogen as this can encourage leafy growth at the expense of flowers.

Deadheading

Perennial delphiniums should be cut back after flowering and annual types should be deadheaded to prolong the summer flowering display.

Just remember to leave some to set seed if you wish to collect your own seeds for next year.

Overwintering

Perennial delphiniums in pots should be moved undercover or into the rain shadow of a wall in winter to prevent waterlogging.

Repotting, Propagation and Division

Re-pot delphiniums before they become too crowded. And divide perennial delphiniums every 2-5 years.

Of course, dividing mature clumps is one way to obtain new plants. You can also take cuttings or raise from seed as mentioned above.

Pests and Problems

Delphiniums are very attractive to slugs and snails, so be vigilant for these pests. Make sure you protect your potted plants and attract plenty of slug and snail predators to your garden to keep their numbers down.

Powdery mildews can also be a common issue. Avoid overcrowding, and under watering, to reduce the chances of issues like this taking hold.

But delphiniums, when cared for correctly, are usually relatively trouble-free plants. They are often much easier to grow in the ground, but where there is not space, growing them in a container garden can be a good idea.

For more detailed growing advice see our Delphinium plant care guide.

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