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Ron Finley Teaches Gardening

Delphiniums are herbaceous perennial flowers—meaning that they die back every fall and winter, but their roots remain alive and regrow the plant every spring and summer. Taller varieties of delphiniums can grow up to eight feet tall and can add a beautiful vertical layer of vibrant color to your summer garden.

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Ron Finley Teaches GardeningRon Finley Teaches Gardening

Community activist and self-taught gardener Ron Finley shows you how to garden in any space, nurture your plants, and grow your own food.

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3 Delphinium Varieties

Plants in the Delphinium genus are commonly known as larkspur, a name shared with plants in the Consolida genus; so, when purchasing your delphinium, make sure you're not accidentally buying an annual species of Consolida instead. Delphiniums come in dwarf, medium, and tall sizes, and are commonly found in the following varieties:

  1. Belladonna delphinium: The belladonna group is the hardiest type of delphinium, capable of flourishing in hotter climates than other varieties. This hybrid first-year blooming plant produces flowers in shades of white, blue, indigo, and purple. Belladonnas grow three to four feet tall with one- to two-foot-tall flower stalks.
  2. Alpine delphinium: Also known as candle larkspur, this hybrid breed blooms in shades of blue, pink, white, and purple and produces single, semi-double, or double flowers. Elatums grow up to eight feet tall.
  3. Pacific Giant delphinium: With flower spikes in violet, pink, and several shades of blue, this heirloom variety of delphinium makes a gorgeous cut flower for decorative use. Pacific Giants are mildew-resistant and deer-resistant, and they attract hummingbirds to your garden.

How to Plant Delphiniums

Delphinium seeds are notoriously difficult to germinate, so to make planting easier, start with young potted delphiniums from a garden center. Be careful when planting young delphiniums, as they are toxic to both humans and animals and can cause skin irritation if touched or ingested (consider wearing gloves if you have sensitive skin).

  1. Plant in early spring. To decrease the chance of transplant shock when planting, try to plant on a cloudy day or in the late afternoon. You can plant delphiniums in USDA hardiness zones three through seven, but they grow best in climates with cooler summers. Depending on how mature your young plant is when you transplant it into your garden, your delphinium flowers should bloom between late spring to late summer.
  2. Choose a sunny location protected from strong winds. Delphiniums grow best in full sun areas, though partial shade is acceptable in hotter climates as long as they still receive six to eight hours of sunlight a day. Choose an area that is protected from strong wind to avoid damage to tall flower stalks.
  3. Plant delphiniums in rich, well-drained soil. Soil with exceptional drainage is important to prevent root rot disease. Delphinium plants are heavy feeders and require lots of nutrients, so enrich your soil with organic matter like compost, manure, or leaf mold before planting.
  4. Dig a planting hole large enough to harbor the root ball. A good rule of thumb is to make the hole twice the diameter of your plant's original container. Then, uproot the plant from its pot and carefully loosen the root ball to incite new growth once replanted. Place the plant in your hole, making sure the top of the root ball is even with the top layer of soil. Fill the hole with soil, and gently pat it down with your hands. Depending on the size of your delphinium variety, space your plants one to three feet apart.
  5. Water and mulch after planting. Adding a one- to two-inch layer of mulch over the topsoil will suppress weed growth and lock in moisture. When applying the mulch, leave some space around the plant's stem to avoid rotting.
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How to Grow and Care for Delphiniums

Follow these simple guidelines to provide the best growing conditions for your delphiniums:

  • Keep your soil moist but not oversaturated. If your delphiniums aren't getting enough natural precipitation, make sure to water them regularly to keep the soil moist but not sopping wet; if you see standing water, that means you've overwatered. Water at the base of the plant to prevent the leaves from becoming damp and contracting diseases.
  • Fertilize as needed throughout the growing season. Use a slow-release, liquid fertilizer every three weeks as needed to help provide your delphiniums with the nutrients necessary to thrive.
  • Use stakes to support your delphiniums. Due to their delicate hollow stems, which are susceptible to snapping in strong winds or heavy precipitation, all medium-sized and tall varieties require staking with a sturdy support, such as bamboo garden stakes.
  • Prevent diseases. Delphiniums are particularly vulnerable to root rot and powdery mildew. Symptoms of root rot include wilted leaves and brown lesions on the stem below the soil line. Prevent root rot by making sure you don't overwater or over-fertilize your delphiniums. Symptoms of powdery mildew include white or gray patches on leaves. Prevent powdery mildew by watering your delphiniums with a drip irrigation system and making sure they're planted in a location with good air circulation.
  • Monitor and deter pests. If aphids plague your delphiniums, try to deter them using an insecticidal soap or by adding companion plants that attract ladybugs—a natural aphid predator—to your garden. Cyclamen mites are another common delphinium pest. You can control cyclamen mites using an organic mite deterrent.

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Grow your own food with Ron Finley, the self-described "Gangster Gardener." Get the MasterClass Annual Membership and learn how to cultivate fresh herbs and vegetables, keep your house plants alive, and use compost to make your community - and the world - a better place.

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