UK Edition
Delphiniums are the King’s favourite flower – here’s how to grow them
Everything you need to know about growing your own majestic display of these regal blooms
There are very few garden flowers that can come anywhere close to matching the majesty and unadulterated presence of a delphinium in full splendour. It just so happens that King Charles is particularly fond of delphiniums, so why not help to celebrate this special year by growing a few in your garden from cuttings?
The process of taking delphinium cuttings is a little unusual, but not difficult. I’ll take you through it step by step to help you not only grow some wonderful flowers for your garden, but also to mark the Coronation in a way that the King would surely approve of.
Other ways of growing delphiniums
Delphiniums can be grown from seed, although most named varieties will not come true from seed and you’ll end up with a range of colours. This suits some people, but if you want to grow a specific colour, the only method to ensure a carbon copy of the mother plant is through division or cuttings.
Dividing a delphinium involves digging around the plant to loosen the soil and lifting it out of the ground. Place two garden forks back-to-back through the centre of the crown and lever the sections apart. The clump will split, ideally into equal pieces; take this opportunity to remove any rotten areas. Replant into fresh soil and water well for the first month, until fresh roots have formed.
A guide to growing delphiniums from seed
Sow the seeds thinly on the surface of peat-free compost, in small seed trays or pots, adding a little compost on top, just enough to cover the seeds evenly. Thoroughly saturate the compost by standing the tray or pot in some shallow water, so that the water rises up through capillary action without disturbing the seeds.
Place the tray or pot in a clear plastic bag to maintain humidity, and position it in a room where the temperature remains reasonably constant at about 15C. As soon as the seeds start to sprout, remove the plastic bag, as that excess humidity is now likely to cause rot. When a second pair of leaves appears on each seedling, they can be pricked out into small pots and grown on, ready to plant in the garden around early June.
Soil
Delphiniums are dormant during the wintertime, with no visible growth, but from early spring the plants start to push their shoots up through the soil, and from that point they need our help to supply nutrition and water. The only way to grow a spectacular delphinium is to give it a fertile garden soil, which holds moisture but doesn’t sit waterlogged, and is in full sun for most of the day. Soil conditions that delphiniums enjoy often elude many gardeners, but vegetable plots can be ideal, as they give delphiniums the space and quality of soil that they need to grow successfully.
Feeding and watering
Delphiniums are hungry and thirsty plants, and we need to supplement their food and water to get the best from them. As soon as the shoots start to appear in the spring, scatter two or three large handfuls of fish, blood and bone, or Growmore, around each plant, and lightly fork it into the surface. I would repeat this process after flowering, which may encourage a second flush later in the summer. Delphiniums will generally become quite lacklustre in poor, dry soil and be prone to mildew; keep them well watered throughout the summer. Grey water from washing-up bowls and baths is perfectly acceptable for your delphiniums; just make sure that there are no harsh chemicals in the water before you apply it.
Mulching and staking
Once you’ve applied your fertiliser in the spring, put on a thick mulch of well-rotted manure or garden compost, trapping the winter moisture and suppressing any weed growth.
As you can imagine, a well-fed and hydrated delphinium will become rather large and will require staking to prevent it flopping. There are a number of different techniques used to stake delphiniums. At West Dean, I use a cylinder of stock fence (one metre in height) to support the growth and stems, but four bamboo canes about a metre and a half high in a square around the clump, with string running between the canes at 30-centimetre intervals, will support the young growth adequately. It is also worth staking the flower spikes as they emerge to prevent them from snapping.
After flowering
Once the main flower spike has faded, you’ll find that side shoots will sprout smaller but equally beautiful flowers. Once those side shoots have finished flowering, the main spike should be cut off at the base of the flower, unless of course you want to collect the seed, which can be sown either immediately after collection or in the new year.
Once all of your flower spikes have finished, the entire plant can be cut down to ground level and given a second application of fertiliser, which should stimulate a second crop of flowers later in the summer and into the autumn.
In the autumn, when all the flower stems have faded and are beginning to die down, the top growth should be cut off and taken away to be composted, leaving stems at about 5cm long, so that you can see where your delphinium clump is during the winter. Ensure that all leaf debris and weeds have been cleared away, as this material tends to harbour and encourage slugs and snails, which can damage your delphiniums during the winter.
Slugs and mildew
Look around the base of the delphinium for any clusters of slug and snail eggs in early spring and remove them; this will go a long way to reducing the population of the hungry molluscs. A layer of sharp gravel around the base of the delphinium will also deter slugs and snails. For more control, try an upturned grapefruit skin, which will act as a hiding spot, so that you can collect and dispose of the slugs and snails, or if you can part with any of your beer, a jam jar of it at an angle in the soil will often attract a number of them, too. Over the years, I have learnt that introducing some of this slug control from, say, the middle of February onwards will prevent slug populations building up to levels that can be detrimental to such plants.
Powdery mildew can be a problem for delphiniums from late July onwards, which often manifests itself as powdery white deposits on the upper surface of the leaves. Mildew can be suppressed by good cultivation, watering your plants at the base during the summer and allowing a reasonable amount of air circulation between the plants. I have found that bicarbonate of soda mixed with a little vegetable oil and gentle soap, applied once a week, will raise the pH on the surface of the leaf and reduce mildew infestations. The recipe for a homemade mildew-prevention spray is as follows:
- 1 tablespoon of baking soda
- ⅓ tablespoon of vegetable oil
- A drop of eco-friendly/gentle washing-up liquid
- 4½ litres of water
- Mix well and agitate as you apply
Step by step: Propagating from cuttings
During the early spring, delphiniums are full of life and charged with lots of energy, which we can harness to create brand-new plants for our gardens. When the basal shoots are about 10-15 centimetres long, these young stems can be detached from the crown of the old plant, which will be enough to form the foundation for a new plant in the future.
The following guide will show you how to take cuttings from delphiniums that have been grown in pots. Most garden centres will be stocking them at this time of year, so why not pop down to your local nursery and buy a pot to experiment with?
If you have delphiniums growing in your borders (or you’re taking cuttings from a friend or neighbour’s plants), the process is exactly the same, but you will have to remove some of the soil around the crown of the plant to expose the woody union at the base of the shoots.
1. Tip the delphinium plant out of its pot and tease away the topsoil or compost to reveal the union, where the young stem meets the woody part of the root and crown. I use a kebab skewer, but a small green garden cane works just as well.
2. Remove the cutting just below the swelling in the stem where the fresh growth meets the woody crown; this swollen area is known as the waist. It’s vital that we remove a little of the woody stem, as we need to retain some of the dormant buds located here.
3. Tidy the basal cut with a knife and remove any lower or damaged leaves, as well as any excess leaf stalks that may cause rotting while the cutting forms roots.
4. Wash your cutting under a cold tap to remove any soil and debris.
5. Use a cane or pencil to make a hole in a pot of moist perlite, insert the cutting three-quarters of the way into the pot, and firm around it with your fingers. Plant five or six cuttings in each pot.
6. Label your cuttings and stand them in a saucer of water to keep the perlite hydrated. Position the pot in a cool, bright place, such as an unheated greenhouse, conservatory or porch. Keep the saucer topped up with water at all times until roots emerge from the base of the pot.
7. Separate the rooted cuttings, usually within five or six weeks, and pot each on individually into a small pot of peat-free compost. Plant out into the garden at the end of May.