Lobelia Guide: How to Grow & Care for “Lobelia Erinus”

Read our guide to Lobelia flowers for everything you’ll ever need to know! Tips for planting & caring for “Lobelia Erinus”

Lobelia erinus is a gorgeous annual herb that pops up in the spring and continuously blooms throughout summer. If you want your garden to start wearing purple, or blue, red, pink, or white, Lobelia should be your top pick. Besides being highly attractive, this flower is also low-maintenance. It effortlessly adds a splash of colour even in cool or shady areas of your garden.

True blue flowers are a rarity in the plant world. The colour blue is known to promote calmness and increase morale, as well as lower blood pressure. If you choose the cobalt Lobelia variety, your garden will become a unique, tranquil relaxation spot.

Lobelia erinus comes in many cultivars, including ‘Cambridge Blue’, with soft, blue flowers, the white ‘Snowball’, ‘Paper Moon’, and ‘White Lady’, ‘Hamburgia’, and ‘Sapphire’ that are suitable for hanging baskets, purple ‘Sapphire’, and ‘Rosamunde’ with a white eye. Lobelias are a must-have for spring containers or flower beds, so make sure this year you add some to your garden.

Keep on reading below to find out everything there is to know about growing and caring for edging Lobelia!

About Lobelia

  • Lobelia erinus has two different growth habits: compact varieties with an upright growth habit, suitable for flower beds or edging, and lush trailing varieties with a spreading habit that look amazing hanging in baskets or cascading over retaining walls.
  • A member of the bellflower or Campanulaceae family, Lobelia comprises over 400 different varieties, as well as numerous hybrids and cultivars. The most popular species is Lobelia erinus, also known as the common annual Lobelia or edging Lobelia.
  • Lobelia erinus is native to southern Africa and was first introduced into Holland in the 1680s. Around 1760 it made its way to England where it became a staple piece due to the Victorian colourful bedding craze. Lobelia arrived in North America in the mid-1800s, thanks to its popularity with the Victorians.
  • True blue flowers make up less than 10% of the plant species. Blue lobelias are the queens of the gardening kingdom, alongside the blue daisy (Felicia amelloides), blue sea holly (Eryngium planum), Lily of the Nile (Agapanthus africanus), Siberian larkspur (Delphinium grandiflorum), and Texas bluebonnets (Lupinus texensis).
  • According to ASPCA, Lobelia is highly poisonous for cats, horses, and dogs if ingested. Typical symptoms include vomiting, abdominal pain, diarrhoea, excessive salivation, drooping ears, nasal discharge, and heart rhythm disturbances.

Lobelia Features: An Overview

  • Lobelias are fast-growing, easy to propagate from seeds, and virtually pest-free, making them the ideal plant for beginner and seasoned gardeners alike.
  • Their flowers have an interesting tubular, two-lipped shape with 5 petals that grow 0, 5 inches (1 cm) long. The 3 lobes of the lower lip are more prominent than the 2 lobes of the upper lip.
  • Lobelia erinus is an annual plant, hardy in USDA zones 10 and 11. However, other Lobelia perennial species can survive hardiness zones 2-8 where temperatures remain above freezing.
  • Annual Lobelias grow to a maximum height of 12-14 inches (30-35 cm) with a spread of 8 to 16 inches (20 to 40 cm). Perennial varieties grow taller, some reaching even 3-4 feet (100-120 cm) in height, so they can be used as borders and for wildflower gardens.
  • Plants bloom from mid-spring to early autumn and are highly attractive to pollinators such as butterflies and bees. They are a great choice for areas with light shade.

Growing Lobelia

Edging Lobelias and their hybrids are tender perennials in zones 10 and 11 but they can be grown as warm-weather annuals. Most Lobelia species grow best in cooler weather. They can tolerate partial shade and may need it in hotter climates. In the North, it is grown as an annual and sometimes chosen instead of sweet alyssum, as it is more versatile and performs better in low light conditions. If you live in the South, it’s recommended to grow it in partial shade to enjoy maximum flowering. In the North, choose a location with full sun and make sure to water it when needed.

Lobelia grows equally well in containers and in garden beds, but keep in mind that most varieties prefer locations with high moisture levels. Native Lobelias grow happily alongside other pond plants. They also thrive in wetlands, so you’ll want to avoid planting them in a dry spot. They are the perfect plants to grow around a water feature. Nevertheless, you can find cultivars that are more tolerant of dry growing conditions (make sure to check the label or seed packet).

1000+ Lobelia Seeds – Sapphire (Blue Basket), From Amazon

Lobelia erinus is a low-maintenance plant, as it is self-cleaning and does not need to be deadheaded. Moreover, it is deer-resistant, and it is avoided by rabbits and other rodents as well. However, lobelia can suffer from too much sun during hot summer days. If this happens, you can bring it back to life by cutting it back and watering it regularly. A radical pruning will encourage new growth, so by fall, your plants should be in full bloom again. If you prefer a bushier appearance, you can pinch back plants at any time.

Most mature Lobelias are healthy and not bothered by pests or diseases. The most common problem is heat-induced dieback in midsummer which can cause it to stop blooming or die out. Sometimes perennial plants will have problems with root rot, rust, or leaf spot. Seedlings can suffer from damping off, a fungus that causes the stem to rot below the soil surface. If you notice any disease, immediately remove infected plants to prevent it from spreading. Make sure to space plants properly to promote air circulation.

Planting Lobelia

Lobelia erinus should be planted in early spring after the danger of frost has passed, but when the weather is still cool. You can plant perennial varieties in the fall. Start by digging holes that are slightly wider than the plant’s root ball. Break up any clumps and add in compost or other organic material to provide more nutrients and better drainage. Most Lobelia varieties prefer slightly acidic soil.

Perennial varieties will need to be spaced 1 or 2 feet (30 to 60 cm) apart as they tend to get larger. Compact annual Lobelias can be spaced 4-6 inches (10-15 cm) apart. Cover each plant with soil so that the top of the root ball is close to the surface. Press the soil with your hands to firm it and water thoroughly.

We recommend adding a light layer of mulch to help retain moisture and prevent any weeds from growing. Keep the mulch about 1 inch (2, 5 cm) away from the stem to prevent rot. Perennial varieties are happy with a yearly application of compost or fertilizer in the spring. Annuals need to be fertilized more frequently. You can apply a continuous-release fertilizer to help them throughout the growing season.

If you are growing Lobelia erinus in containers, choose a potting mix rich in organic matter. If you feel creative, team up Lobelias with other moisture-loving flowers that can tolerate shade such as sweet alyssum, balsam, and violas. To create an eye-catching display, plant Lobelias in small masses around the container with plants of increasing height in the centre.

Watering Lobelia

Edging Lobelia grows best in moist soil, so you must water regularly to keep the plants healthy and blooming. Perennial Lobelias need regular watering during the first year. Afterwards, the plants become drought-tolerant and require watering twice a week during dry periods. The top 6 inches (15 cm) must remain moist at all times.

Annual Lobelias need frequent watering during growth phases, as their short roots stay close to the surface Water slowly with a garden hose or use a drip system to avoid spraying the foliage. The soil must be saturated to a depth of 6-8 inches (15-20 cm).

Before watering again, allow the top 1 to 2 (2, 5 to 5cm) inches of soil to dry. Soggy, poorly drained soil can promote root rot and other fungal diseases. Container plants might need daily watering, as they tend to dry out faster than plants in the ground.

Blue violet Lobelia erinus
Blue violet Lobelia erinus

Propagating Lobelia

Although perennial Lobelias are short-lived, propagating the plants from seeds is easy and can be done by beginner gardeners. Alternatively, you can buy transplants at your local nursery and plant them directly into the garden.

Both perennial and annual Lobelias can be started from seed. We recommend sowing indoors instead of outdoors into your garden. To start seeds indoors, you’ll need a seed starting mix and cell packs. The best time to sow the seeds is 8 to 12 weeks before the last frost in your area.

Lobelia seeds are very tiny so you don’t need to cover them with soil to germinate. Sprinkle the seeds on top of the mix and gently press them down with your fingers. Water carefully so that you don’t wash them away. Place the tray in a warm location with a temperature between 65-75°F (18-24° C) and keep the soil moist at all times.

In 14-20 days, the seeds will start germinating. Make sure the seedlings get lots of light for the next few weeks. When they have 2-3 pairs of leaves, you can move them into larger pots. One week before moving the seedlings outdoors, start leaving them outside during the day and bring them back at night to harden them. Plant into the ground after the danger of frost has passed.

In Conclusion

Lobelia erinus is a beautiful, low-maintenance flower that can be grown as an annual or perennial even by beginner gardeners. Its colourful flowers pop up in the spring and bloom throughout the summer. True blue flowers are a rarity in the flower kingdom, as they make up less than 10% of the plant species. Adding blue Lobelias to your garden will promote calmness and relaxation.

Lobelia is easy to care for, all you need to do is to find a suitable location in your garden or house and water it regularly. In return, it will reward you with the most vibrant splashes of colour that will bring life and joy to your home.

Miruna is an experienced content writer with a passion for gardening. She is the proud owner of an outdoor rose garden and an indoor collection of tiny succulents. She bought her first succulent 10 years ago - an adorable Echeveria Setosa. Now she owns more than 100 succulents and cacti of different colors, shapes, and sizes. Miruna is a versatile writer and, as you might have guessed, her favorite topic is gardening. Contact

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