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The spectacular appearance of delphiniums is well worth the time and care needed to look after them. From choosing their best location in your garden to preparing them for the winter months, you’re rewarded in the summer with glorious color for the effort you put into their care and maintenance. Did you know, you can even grow smaller varieties of delphiniums in containers and pots which I cover here.
- Sow seeds, if using: March, April
- Plant: any time of year if grown in pots but spring or autumn is best
- Flowers: June, July, Aug, Sept (cut back after flowering to encourage a second flush of flowers)
Choosing the best position
The first step in the care of your delphiniums is to choose a sunny, open location for them. They’re tall plants, growing up to 2 meters high (200cm) and with a 90cm spread. They fit well at the back of a border and don’t like to be in a crowd of other plants and shrubs. Avoid anywhere that receives gusts of winds as these plants can easily be blown over so staking is also a must, especially when the flower spikes develop. Make sure that these flowers are not over shaded by other equally tall or taller plants as this can lead to very few or no blooms.
Sun and soil
Delphiniums like full sun but not hot locations. They also grow well in light shade, which gives them the sun they need but in a cooler environment.
These flowers like moist but well-drained soil. Prepare your soil with extra grit or sand so that it isn’t waterlogged. Add some organic material such as well-rotted compost or organic fertiliser, perhaps manure, to give the plant adequate nutrition for its growth. Delphiniums need feeding after they flower, so set up a schedule to apply fertiliser or use a slow release feed.
Use a mulch on top of the soil to keep the water in the soil from evaporating. Organic mulches such as shredded leaves or chipped bark also provide nutrients for the soil and the plant. But be sure to keep the mulch away from the stem of the plant. The cool, damp environment of the mulch encourages pests and diseases. You can also learn more about pests and diseases that affect delphiniums in my guide here. Mulch also keeps down the weeds which would compete with the plant for water and nutrients.
As some taller varieties of delphiniums grow to 2m tall and even higher, it’s essential to stake them to keep them upright. If they’re unsupported, even moderate winds could blow them over. The best time to stake the plants is when you plant them. But you then need to increase the height of the stakes as the plant swiftly grows. There are several methods for staking the delphiniums from simple cans to specially designed cage rings. Read my How to stake peonies and delphiniums for best growth article for detailed information about this.
Delphiniums bloom in the summer, from June to sometime in August or September. Water them regularly or when the soil is dry about 3cm down. Make sure to water early in the morning before it becomes hot. This ensures the cool uptake of the water by the plant and also gives the plant time to absorb the water before it starts to evaporate.
If it has rained about 3cm or more in a week, you don’t need to give extra water to your perennial plants unless the ground does appear dry. But make sure that the soil doesn’t dry out completely as these flowers like a cool and moist environment.
If you’re careful about deadheading all the flowers when they’ve finished blooming, you can get a second series of blooms. Cut back the stalks to just above the leaves when the flowers die. If there’s enough time left in the growing season, you then see another round of flowers. For details on how to do this, check out the When and how to cut back and prune delphiniums article.
Problems and overcoming them
Delphiniums can suffer from a few problems including pests and diseases, one issue some people have is with their delphiniums not flowering. I have an entire article on why your delphiniums might not be flowering here.
Powdery mildew is a problem for many gardeners as well as rust but both can be treated with a garden fungicide and I usually remove the worst affected leaves straight away. I have had success with spraying them at the very first signs of mildew and rust. Slugs and snails also love the new fresh growth so I usually also put down some slug traps or a few organic slug pellets as a last resort.
If you have an issue with your delphinium leaves going yellow and brown, check out this guide here with some causes and now to help them recover.
Delphiniums struggle in the long and cold winter. Starting in the late autumn, you need to prepare them for the wet and often freezing months ahead. This involves cutting them back to an inch about the ground and mulching around the base but I give details on how to do this in the How to keep delphiniums over winter article.
Finally, let’s talk about propagating delphiniums, this can be done in late winter or early spring by sowing seed in pots, trays or directly in the ground which I have covered here. My two favourite ways of propagating delphiniums are by taking basal cuttings, also covered here as well as dividing them every 3 years which I covered in this guide.