How to Grow Delphinium | Happy DIY Home

The delphinium is one of the most attractive summer flowers. Its showy, spiky blooms emerge on tall, towering stems. Sadly many gardeners believe the delphinium is difficult to grow and therefore avoid planting it in their garden, instead opting for low maintenance alternatives. However this attractive perennial, which flowers in a range of colorful shades, is, in my opinion, one of the best summer flowers and its showy blooms are well worth a little extra effort.

Also known as larkspur, the delphinium has been a staple of the cottage and mixed flower garden since Victorian times. Equally at home in the cut flower garden, the eye-catching flowers are often used in wedding bouquets alongside chrysanthemums and lilies.

Tall and stately, these long lasting plants flower from early summer until the fall. Popular with pollinators and hummingbirds, if you want to add some delphinium flowers to your garden this guide is designed to take you through everything that you need to know.

1 Tall purple delphinium
Typically tall and purple, larkspur are staples of the summer flower garden.

What are Delphiniums?

Members of the Ranunculaceae or buttercup family, these elegant flowers were originally blue in color. Today you can also find many hybrid varieties which flower in shades of yellow, red, white, pink and lavender. While single flowering types are attractive, you can also find double flowering varieties.

Typically tall plants, they are best used in the back of a flower bed. The flower spikes can reach between 2 and 6 ft. Delphiniums are also a good mass planting choice. Shorter cultivars can be used in the front of a border or in pots. While most varieties are perennial you can also find biennial and annual delphinium plants.

The Elatum delphinium group are amongst the most commonly grown of the many varieties. They are also one of the tallest types, producing spikes of single or double flowers.

Belladonna types are shorter, with a loose, branching habit. Their spikes are filled with colorful single flowers.

The Rising Stars series produces either single or double flowers in a range of colors. These plants provide a dramatic garden display and also make for good cut flowers.

Pacific Hybrids were developed in the 1950 and 60s. These are short lived perennials, or biennials in certain conditions, which resemble the Elatum type but are far smaller. This makes them a good choice for container gardens or the front of a flower border.

Another compact option is the Magic Fountain series. These diminutive plants are ideal for small gardens.

Some of the most popular delphinium flowers include:

  • Amadeaus is an attractive cultivar. Its velvet or deep purple and blue flowers have a distinctive dark brown eye. A reliable plant it makes a good cut flower choice,
  • Faust is another reliable cultivar, producing attractive, tall spikes which, when in flower, are covered with dark blue blooms,
  • Cinderella is a compact specimen producing pale pink flowers on sturdy stems.
  • Blue Bird is one of the most attractive cultivars. When in flower Blue Bird produces attractive violet blue blooms with white centers,
  • King Arthur is an eye-catching, deep purple flowering variety.

2 Variety of colors and size
Larkspur are available in an ever increasing range of colors and sizes. 

You can find delphinium plants for sale from specialist plant nurseries or your local garden centers. While the plants can be grown from seed, it is a lot easier to purchase small plug plants that are ready for transplanting.

When selecting your flowers, try to select plants with lots of healthy green foliage. There should be no visible sign of pests or disease. You should also check the delphinium’s mature size. Make sure that it fits into your growing space and that you can provide the right growing conditions.

Where to Plant

Plant your delphinium transplants in spring either before or just as new growth starts to emerge.

Delphinium plants do best in light, sunny areas. For the best flowering display try to select somewhere that exposes the plants to lots of light morning sun whilst also providing a little afternoon shade. This is particularly important in hot areas. Ideally the plants should receive around 6 hours of light every day.

The soil should be light and well draining. A neutral to slightly alkaline soil is ideal.

Before planting, enrich the soil with 2 to 4 inches of compost. These are heavy feeding plants and enriching the soil beforehand gives the developing seedlings a good boost. Also prior to planting, loosen the soil with a garden fork or tiller to a depth of 12 to 15 inches. This helps the roots to spread and set more easily.

3 Prepare the soil
Before planting, prepare the soil. This helps your plants to quickly settle and thrive in their new position. 

To plant, dig a hole twice the diameter of the pot currently holding the delphinium. Remove the transplant from its container and place in the middle of the hole. The top of the root ball should sit level with, or slightly above, the soil level. In poor draining or heavy soils planting slightly above soil level helps to encourage excess water to drain away from the plant.

When you are happy with the position of the delphinium backfill the hole and gently firm down the soil. Water well. If you are planting more than one delphinium, space the plants 1 to 3 ft apart.

Planting Larkspur in Pots

Growing delphinium plants in pots is easy as long as you have a large enough pot. When selecting the pot, remember that width is more important than depth. Delphinium roots are shallow and wide. Your pot should be large enough to comfortably hold the root system.

Cover the drainage holes at the bottom of your chosen pot with crockery stone or polystyrene. This helps to improve drainage. Add a layer of good quality compost. Next, press handfuls of the potting soil mix into the sides of the pot. You are aiming to fill the sides while leaving a hole in the middle. Potting soil on its own is fine but to further improve drainage you can combine it with some perlite or grit.

Remove the plant from its container by holding the pot on its side and sliding the plant out. Be careful not to damage the roots as you remove the plant.

Gently loosen any tangled or matted roots before placing the delphinium in the pot. The top of the root system should sit above the soil level but below the rim of the container. When you are happy with the position of the plant continue to fill the pot with your chosen potting mix.

Firm down the soil and water well. As the soil settles after watering you may need to add a little more potting soil.

Caring for Delphinium Plants

An attractive plant, the delphinium can be a high maintenance addition to the garden.

Regularly weed the soil around the plants. This helps to keep plants healthy. It also stops fast growing weeds from smothering or stunting the growth of your flowers. If, like me, you find weeding a chore, there are a number of useful tools you can use to keep your garden neat and weed free.

After planting use sharp garden scissors to thin out the growing shoots when they reach 3 inches in height. This encourages good quality flower spikes to develop. Aim to leave 2 to 3 shoots on young plants or 5 to 7 shoots on well established specimens.

4 Thin shoots to encourage flowering
After planting, thinning out growing shoots encourages more flower spikes to develop.

Water

Aim to keep the soil consistently moist. Allowing the soil to dry out can cause plants to wilt or fail. Mulching the soil helps it to retain moisture, preventing it from drying out on warm days. Mulching also keeps the root system cool, prolonging the flowering period during the warm summer months.

Fertilizer

For a long lasting, healthy display, fertilize your delphiniums regularly. Start as soon as new growth emerges. Continue to fertilize regularly until the last flowers fade.

To boost healthy growth, prior to planting, work lots of well composted organic material into the soil. Alternatively, apply a balanced 10-10-10 granular fertilizer. This is easily incorporated into your watering routine. A fertilizer rich in potash can also be applied.

Consult the fertilizer label for the exact dose size and how often it should be applied. This varies depending on the product you are using and what flowers you are growing. In general delphinium plants require fertilizing once every two weeks. Stunted growth or yellowing foliage means that your plants require more fertilizer.

Deadheading Spent Flowers

Deadhead the first blooms as they fade in early summer. This encourages more flowers to form. Deadheading also helps to prolong the flowering period.

Once flowering has finished and the blooms are spent, remove the flower stalks.

https://www.youtube.com/watch?v=Mg8niTVi2eE 

Supporting Growing Plants

Most varieties of the delphinium are tall specimens. This means that they require some support, especially if they are planted in windy or exposed areas. The stems of the delphinium are hollow and can easily break under stress. Supports are best installed when transplanting young plants or as seedlings develop

Hydrofarm Natural Bamboo Stakes provide sturdy support whilst blending into your garden or planting scheme.

Companion Planting

The delphinium is a staple of the cottage garden. The flowers work well in mixed beds alongside many flowers, including:

Tall varieties complement other tall grasses and flowers such as

Medium height varieties work well alongside:

You can also underplant your delphiniums with chamomile, legumes, or chervil. These can all introduce nutritional benefits into the soil.

5 Mixed flower garden
Delphiniums are particularly effective if planted in a mixed flower garden.

How to Over Winter Your Plants

To prepare your delphinium plants for the winter, water regularly during the fall. Continue to water until the ground freezes so hard that the soil can no longer absorb any moisture. Don’t use a sprinkler. A hose or watering can is better because the water is more likely to trickle down through the soil, saturating the roots.

It is important to keep the ground damp during this period to prevent the roots from drying out. Plants continue to lose moisture through their leaves during the winter so ensuring that they are fully hydrated is vital if you want them to survive until the spring.

After the first frost, cut the foliage down to 6 to 8 inches above the ground. You can also cut the foliage back in the spring however cutting back in the fall makes mulching the soil a lot easier.

Remove any leaves or plant debris from around the plants. This helps to prevent disease. It also removes many potential hiding places for pests such as slugs. If these pests are a particular problem, this guide to controlling slugs in the garden has lots of useful advice and suggestions.

Apply a 2 to 3 inch layer of mulch in late fall when the ground is cold but not frozen. An organic mulch such as straw, bark, dry grass or chopped leaves is ideal. As well as helping the soil to conserve moisture, mulching prevents damage caused by freezing and thawing. If you don’t want to apply a mulch, a plant blanket can also be used.

Water your delphinium plants occasionally during the winter if the ground thaws out enough to absorb moisture.

Plants growing in pots can be moved undercover as the temperatures fall. Placing pots on a Metal Plant Caddy enables you to easily move them around your garden or home.

Common Problems and How to Prevent Them

Growing in good soil in a favorable position helps to keep plants healthy.

6 Plant in open light position
If planted in an open, light position these are pleasingly problem free plants.

Regularly check young plants for any signs of problems. You will also need to protect the foliage from slugs and snails.

Try not to overwater the plants. This can lead to them developing root rot.

Cyclamen mites can be a problem as can powdery mildew if the foliage is wet or the plants are over crowded.

Rust, as the name suggests, causes rust colored pustules on foliage. Cut away affected leaves. Weed the area around the plant and remove any plant debris to prevent the problem from returning.

Delphinium black blotch is a bacterial infection which causes large black blotches on leaves. It is particularly common during wet summers. Remove any affected plants to prevent the disease from spreading throughout your garden.

Remember to clean your tools before and after using them. This prevents diseases from easily spreading around the garden. You should never place diseased foliage on the compost heap.

Delphiniums are deer resistant.

How to Propagate

The delphinium can be propagated in a number of ways.

When selecting a plant to propagate, never take cuttings or seeds from unhealthy or diseased plants. Propagating from healthy and productive plants increases the chances that the new plants will also be healthy and productive.

Harvesting and Growing from Seed

Growing from seed can be challenging.

To harvest the seeds, allow spent flowers to remain on the plant. As they fade, seed pods emerge.

After the pods mature and turn dark brown they can be cut from the plant. Carefully open the pods and remove the seeds. The seeds can be stored in a paper envelope in a cool dry place until you are ready to use them.

https://www.youtube.com/watch?v=nIObbWW-8X8 

Delphinium seeds need to be stratified, or exposed to cold temperatures, before sowing. Commercially purchased seeds have often already gone through this process before they are packaged up and sold. You will need to stratify seeds harvested from plants growing in your garden yourself. To do this, place the seeds in a bag in a refrigerator for a week.

Sow the prepared seeds in trays filled with an appropriate seed starter soil mix undercover about 8 weeks before the last predicted spring frost.

You can also sow seeds directly into their final growing position in early summer. To do this, germinate the seeds before planting by placing them on a wet coffee filter and folding it in half. This holds the seeds inside. Place the filter somewhere where it won’t be knocked over or disturbed for about a week. During this time the seeds start to germinate.

Following germination, place the seeds on the soil surface and cover with an inch of soil. Keep the soil moist. The temperature should average between 70 and 75 ℉. Seedlings start to emerge within 3 weeks.

To encourage germination, place them in a light position. If you struggle to maintain the optimal germination conditions, why not try a heated propagator? The iPower Heating Seed Starter Kit comes with a vented humidity dome and heat tray. This enables you to maintain ideal germination conditions around sensitive seeds and seedlings.

Once the seedlings have at least 2 pairs of true leaves, harden them off for about a week before transplanting into their final position.

Dividing Establish Plants

Mature delphinium plants can be divided  every 3 to 4 years. This is best done in the spring as new growth emerges. As well as being an easy way to propagate new plants, making divisions is also a good way to rejuvenate established specimens.

Soak the soil around the plants the day before dividing. This ensures that the roots are fully hydrated and more likely to survive the process.

Cut away any excess foliage. Aim to remove about a third of the foliage from the plant. This makes handling the plants a lot easier.

Use a spade or shovel to dig a 7 to 8 inch wide circle around the plant. This may seem too far away from the center but digging at a distance helps to protect the roots from any accidental damage.

As you dig, try to dig at an angle towards the plant. This enables you to force the shovel under the plant, meaning that you can easily lift it from the soil. If the plant is growing in a pot, simply remove it from the pot.

Brush away any remaining soil and inspect the roots. Delphinium roots are easy to separate, simply pull them apart. You may need to use a knife or the edge of the spade to do this. A decent sized clump should easily divide into 4 healthy sections. Each section should have a good section of healthy roots and some foliage.

Replant the sections as soon after dividing as possible. You can place the roots in a bucket of water to prevent them from drying out as you prepare the hole.

Basal Cuttings

This is possibly the easiest way to propagate delphinium plants. Basal cuttings should be taken in the spring as new shoots appear.

When new shoots appear use a sharp knife and cut a shoot just below soil surface. Take no more than two basal cuttings from each plant.

Place the cuttings in a polythene bag immediately to preserve moisture as you prepare them for planting. Remove most of the foliage from the cuttings,allow just a few leaves to remain in place.

https://www.youtube.com/watch?v=7xVwAAWbWoM 

Plant in pots filled with a combination of perlite and multipurpose compost. Water and cover with a polythene bag or place in a propagator. Place the cuttings in a quiet corner of your greenhouse or on a sunny windowsill. Continue to keep the soil moist. You can also mist the foliage to prevent it from drying out.

Roots should form after a few weeks. To check that roots have formed gently tug the cutting. If you feel resistance it means that roots are developing.

Once roots have developed remove the cutting from its protective cover and continue to grow on. Keep the soil evenly moist. Harden off before transplanting into their final growing position.

7 Elegant addition to the garden
Larkspur is an elegant and attractive addition to the garden. 

An elegant plant the delphinium looks particularly attractive in a mixed flower bed growing alongside purple coneflower, moonbeam coreopsis and yarrow. Alternatively, thanks to the plant’s tall, dramatic flowering spikes mass plantings can look just as effective. An ideal choice for a pollinator garden, with regular care these flowers provide color, height and interest to your garden throughout the summer months.

Delphinium 1 Delphinium 2