14 Tips For Growing Beautiful Delphiniums This Season

Looking to grow some beautiful delphiniums this season but aren't sure where to start? Garden grown delphiniums can be a beautiful addition to any garden. In this article, certified master gardener Laura Elsner shares her top tips for growing beautifully blooming delphiniums!

delphinium growing tips

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Delphiniums are one of my all time favorite flowers in a garden. As one of the few blue flowering plants, some delphinium varieties have a color that is hard to find elsewhere in nature. They also come in pink, purple, white and even red.

There are varieties that grow up to 6 feet tall and some that grow only to 1 foot in height. The versatility in these flowers makes them easy to add to any garden. They can be added as a perennial border plant, or as edging to areas of your garden that need a fine line of separation between plants, or gravel.

Delphiniums however, aren’t the easiest flowering plant to grow. They can be picky about soil conditions, and require a little more hand holding compared to other flowers. So, to help you make the most of your delphiniums, I’ve outlined my top tips to get them growing and keep them strong all season. Ready to learn more? Let’s dig in!

Know Your Zone, Annual Vs. Perennial

Purple blooming flower
Delphiniums prefer a cool and humid climate.

I am starting with the most important thing you need to keep in mind when growing delphinium. They like cool and moist climates. They grow perennially, meaning they come back every year, in USDA Hardiness zones 3-7. Sometimes they will come back in zone 8.

If you love in zones 8 or higher, it can still be grown, but only as an annual. It is easy to check your zone online and see if your climate is suitable for growing delphiniums as perennial flowers or annuals.

Check Your Soil

Hands Holding Soil
Before planting delphinium, test your soil.

Before planting, check to see if the soil in your garden has the right soil quality. I don’t bother with expensive soil lab tests, or chemical test kits. I just use my eyes and hands to determine soil quality.

Start by just looking at the soil. Is it grey, or a rich dark brown color? Grey soil means that there is not enough rich organic matter in the bed.

Now grab a handful of the soil. Squeeze it together in your hand. Does the soil stay in a ball like putty? This means you have heavy clay soil. This is not good for drainage. While delphiniums like to be kept moist, they do not tolerate being in heavy wet soil.

If the soil in you hands just fades away, you have sandy soil. This is also not optimal for growing delphiniums. It has no nutrients in the soil to sustain the large amount of growth a delphinium undergoes in a single season.

Amend Your Soil When Needed

Gardener amending soil in the garden.
Delphiniums grow well in light soil with plenty of organic matter.

Now that you’ve looked at and determined the type of soil you have, it should be amended to make ideal growing conditions for delphinium.

Delphiniums like to grow in light soil with lots of organic matter, here’s how to achieve this.

If you have heavy clay soil, you will need to amend it with peat or coconut coir to lighten the soil and allow drainage. Work the peat or coir into the beds to lighten the soil.

If you have sandy and grey soil, you will especially need to add organic matter. I recommend adding organic matter to all your garden beds once a year, or every two years. This is my secret to growing success. I top dress my bed in compost.

I do this in the fall, covering the leaves in to add extra nutrients. Then next spring the snow will melt and all the compost nutrients will seep into the beds. You can use compost, worm castings, or manure.

Amending soil so it is light and rich with organic matter is a great place to start when creating a garden. Many of our favorite garden plants favor these conditions.

Provide Plenty of Sun

Blooming perennials in flower garden
Delphiniums prefer to grow in full sun.

Delphiniums are full sun plants. They will not grow in shady conditions. That being said, they are also a cool season flower. They won’t tolerate harsh beating rays on them for prolonged periods of time.

Full sun is defined as 6+ hours of direct sun a day. If you live in an area with harsh hot sun, the quality of that sun will matter. Morning and/or late afternoon sun is not as strong as the midday afternoon sun. Try and position your plants in an area of the garden that offers some shade protection. Dappled sun from a tree works great (as long as it is not too shady). A west or east exposure might also work better than a full south exposure as a spot for planting.

 I also find putting plants in a garden offers protection. Plants are meant to be planted together, a patch of delphinium out in the open will fry whereas ones planted in a garden with lots of other plants will thrive (check out companion plants down below for ideas).

Water Evenly & Regularly

Garden perennial getting watered.
Delphiniums need regular watering to keep the soil moist.

Water is equally as important to get right alongside soil and sun. Delphiniums like to be kept in evenly moist soil. They don’t like drying out completely. They also don’t like sitting in water.

If your soil is right water should be able to absorb and drain and keep your delphinium moist but not wet.

Depending on the rain you may have to add supplemental water. If you don’t get at least an inch of rain a week you will need to water. My preference is to use a soaker hose that is snaked through the garden bed and turned on for a few hours a week if there is no rain. This provides water straight to the soil and roots of the plant without soaking the foliage. This helps prevent powdery mildew.

After their initial planting, be sure to provide extra water for the first season (if you’re in an area where it’s perennial). Water it in very well when it is first planted and then provide water every couple of days (or more if it is really hot and dry). Really let the water soak in to help it establish long deep roots.

Plant Where it’s Not Windy

Flowers Blooming in Garden
Since they are quite tall, it is preferable to plant them in the back row.

Location is key for delphiniums. They are long and tall and need to be planted in the right area of the garden to provide impact and to stay intact.

When planting a bed I think of it in 3 layers. The back garden, mid garden, and then ground level. In the back of the garden bed is where most varieties belong. Dwarf varieties can be planted in clusters throughout the mid range of a garden.

I often see the mistake of buying a delphinium from the garden center and thinking that is its full height. Read the tag to determine how tall it grows. If you plant them in the front of the garden they will block out all the plants behind them.

The next aspect to consider when choosing a location is wind protection. Try and plant them in a less windy area of the garden. Against a house or tall fence can offer protection from gusting winds. Strong winds can bend and snap off the long stalks of flowers in a delphinium. This is a garden tragedy.

Choose The Right Variety

 'Sunny Skies' variety
Delphinium “Sunny Sky” is a beautiful variety that produces double flowers of light blue color with a white center.

There are hundreds of unique varieties of delphinium. Take into account what you want your delphinium to do. Do you want them to be a big showy display in a back garden? Are they going to be planted in pops throughout the garden? Do you have a color theme? Do you want cut flowers?

For planting in the back of your garden, choose the large tall varieties. These are the classic English garden flower that I feel like are most often associated with delphinium. ‘Black Night’ is a popular variety. It grows up to 6 feet tall and has dark indigo-colored flowers.

If you are planting for pops of color throughout the beds, choose a smaller dwarf variety. Some of these only reach 1 foot tall. They still have the lovely star shaped flowers, but are more compact. Try Delphinium ‘Summer Cloud’ for a sweet dwarf variety.

Delphiniums come in a wide variety of colors. Not just blue and purple that are most often associated with tis plant. They come in dark indigo blue, light blue, pink, purple, white, and even red. It’s easy to find a delphinium in a color that will match your garden’s theme if you have one.

Garden designers will often play with colors to make gardens appear a certain way. For instance,  If you want to bring the garden closer and make it appear smaller, choose a red variety such as delphinium ‘Red Lark’. If you want to make your garden appear more expansive, choose a cool blue variety such as delphinium ‘Moonlight Blues’.

For excellent cut flowers, you may want a spectacular double flowering variety. The New Millennium series of delphinium produces gorgeous double flowers on tall stalks. ‘Sunny Skies’ has to be my favorite in the series. They are a striking light blue color with a white eye. Perfect for a bouquet!

Plant Them Properly

Adding plants to garden soil
To plant a delphinium, dig a hole twice the size of the pot.

When initially planting, it is important to plant correctly to give them the best start.

If you buy an already established plant from the garden center, gently remove it from its pot. If the roots are huge and still in the shape of the pot you will need to break up the roots before planting. Scruff the roots or use a knife or clippers to break them up.

Now it’s time to plant. Dig a hole twice the size of the pot. Dig it nice and wide so that the roots have an easier time spreading out. At this time I will fill the hole with water. Plant the up to the crown and fill with a mixture of the soil you dug out, and some fresh compost. Then press firmly into the ground. Water it in again.

Plant about 18 inches apart if they will be perennial in your area. This allows them to grow and have ample airflow through the plant that will prevent diseases like powdery mildew. If you are planting them as annuals in your area, you can pack them in tighter a foot or less apart is fine.

Don’t Skip Maintenance

Pink flowering plant in garden
To make delphiniums bloom longer, prune already faded flowers.

Delphiniums are a fairly low maintenance type of perennial flower. But, they do require a few things to make them grow their best.

I start by trimming off any flowers that have finished blooming. I do not let the seed pods mature, this allows all the energy to go back to the plant and not into seed production. You can let them self seed, but quite often they will not come true to their parent plant. Also, you can’t guarantee where the seedlings will land.

You might be constantly digging them out and moving them to the back of your beds. I would only let them seed if I had a very large garden where they can roam around and do their thing.

If you live in a longer growing season (zones 5-7) you can actually chop them right back after it’s finished blooming and it will flush up and flower again.

Stake Them Early

Flowers with support stakes in garden
Support your delphinium with stakes, cages, or half-moon hoops.

To protect those huge long stalks of flowers, I highly recommend staking your delphiniums.

If you have a very tall variety of delphinium you will definitely want to stake it. There are many different ways to stake them. They make cages that are like tall versions of peony cages. Place these cages on when they are just starting to grow.

It is too complicated putting them on once they are full grown. Bamboo poles and string work great to prop up their stalks. Place the pole in the back so it is not visible. They also make stakes that are squiggly and wavy.

These allow the delphinium to grow up and be cradled in the nooks to provide stability. There are also half moon hoops that can be placed in front of and behind a delphinium to provide support.

Deal With Pests Right Away

Worms on flowering plant
The most common pests of the delphinium are aphids and cyclamen mites.

Dealing with pests is important to ensure lovely stalks of flowers every year. If you keep your delphinium growing under its ideal conditions you are far less likely to have problems with pests. Pests are usually a sign that something is not quite right with your plant.

If your delphiniums do have pests, it is best to treat them and then try and determine what caused the plant to be in a weakened state that left it vulnerable to pests in the first place. It’s normally a sun, soil, or water issue.

Now to get rid of pests. If you are growing them as annuals and they are infested, sometimes it is better to pull them and replant something else. But if they are perennials I would take the time to treat the pests. The most common pest to affect delphiniums will be aphids. Spraying them with an insecticidal soap should deal with them. Do this weekly (or according to the product directions).

There is a far less common pest, cyclamen mites. Signs of cyclamen mites include curled leaves, stunted growth, and withered and blackened foliage and flowers. Unfortunately there is no treatment for this pest. Dispose of any plants affected with it and clean up all leaf litter in the fall. Make sure to inspect plants before purchasing them so you’re not introducing this pest into your garden.

Deal With Disease Right Away

Flowers damaged by disease
Powdery mildew is the most common disease that affects the delphinium due to its humid habitat.

As with pests, diseases on delphiniums are a sign that something is amiss with their growing conditions. The most common disease associated with delphinium (in my experience) is powdery mildew. Powdery mildew occurs when the conditions are just right. So avoiding these conditions will help avoid mildew on your plants.

Powdery mildew thrives in damp dark environments. Check the soil to see if it is soggy and not draining. Also check to make sure the delphinium is getting enough light. Finally, see how close together they are planted. They should be around 18 inches apart. They need to have airflow through the plants to prevent the mildew from thriving.

Once you have the mildew treat it with a copper fungicide. Then work on fixing the conditions so as to not have it every season. Clean up all the leaf litter in the fall and dispose of it.

Always Companion Plant

Plants growing in flower bed
Since the flowering period of Delphiniums is not long, plant it with other plants that grow at different times.

Delphiniums are beautiful plants. But they only bloom for a 2-4 week window in the summer. To create a beautiful gardenscape plant them with other plants that bloom at different times to create a symphony of blossoms.

They are generally the taller perennial flower in the back of garden beds. I like to layer things underneath. They provide a lovely leafy background to other plants then they steal the show with their big stalks of blooms. Then they become a green backdrop again.

My favorite things to layer underneath delphiniums are peonies and/or shasta daisies. Peonies are perfect because they bloom before the delphiniums do and they are just the right height to be a perfect step down from taller delphinium. They also have the same soft color palette that the delphiniums bloom in. It’s a classic combination.

Shasta daisies are native wildflowers that bloom around the same time as delphiniums and they are a perfect cheerful white flower to grow at the feet of delphinium. One of my favorites combinations.

I also like mixing in monkshood in between my delphiniums. They have a similar height and foliage. But the monkshood blooms later in the summer, so once the delphinium blooms fade, monkshood takes over.

This just scratches the surface of companion plantings for delphinium. They are a versatile and easy plant to blend into garden beds. Daylilies, iris, geraniums, roses, and more will blend beautifully into a perennial bed.

Don’t Skip Winter Prep

Plant frozen with ice
Prepare your delphinium for winter: water well until frost, cut off long stems or to the base, and pile the leaves at the base of the plant.

If you live in zones 3-7 where delphiniums are perennial then take some time to prepare your delphiniums for wintersleep to ensure they come back bigger and more beautiful next spring.

Where I live fall is often a dry time of year. I think people forget about gardening once late September to early October start rolling around. But things haven’t frozen up yet and plants still need some attention. Water your well up until your first freeze. This is especially important if it is the first year you planted them. Plants don’t fare well when they go into winter dry.

I cut down my delphiniums in fall. It’s not necessary but I find the long stalks just fall over and don’t look particularly attractive in the winter. If you have pests or diseases on your delphinium, then cut them to the ground and dispose of the leaves to avoid having them reinfected next season.

At this time I would also spread compost on my garden. I would also pile my leaves onto the base of the delphiniums (and my entire garden). This insulates them, and it will retain moisture into the spring. Some people believe gardens should be clean like our houses and strip their gardens of all the leaves.

While this might be more aesthetically pleasing, it is not the way nature intended gardens to be. Leaves on the ground protect perennials, hold in moisture, and house all the beneficial insects that will help protect your garden (a single ladybug can eat 50 aphids a day!). The only time I do not recommend piling leaves on your garden is if they are diseased or have pests.

Final Thoughts

Delphiniums are a fairly fuss free plant in the garden. If you can get them growing in their ideal conditions they will reward you with the most beautiful flowers in the summer. Their beautiful blue blooms are very unique, and can add colorful interest to just about any garden space.

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