Producing a spread of vibrant purple and red flowers, the lobelia has been a summer garden staple for generations. Originating from Southern Africa, these beautiful bellflowers are a relatively low-maintenance way to bring color and wildlife to every flowerbed. Lobelias also adapt to various garden layouts, working well as edging and or in outdoor pots. There are many varieties available, but some of the most popular are those that produce "true blue" blooms — a rarity in the natural world.
Lobelia is an outdoor plant, but seedlings need to be sown indoors. Starting with nutrient-rich, well-draining soil, sow your lobelia seeds in pots around eight to 12 weeks before the last frost. After three weeks, you'll see seedlings begin to emerge. Once they've grown several inches, it's time to move them to your outdoor garden. However, before planting them in your flower bed, it's important to "harden" them to the elements by leaving their indoor pots sheltered outside for a week. This prevents the lobelias from suffering transplant shock once they're planted.
Each lobelia plant can grow up to 12 inches tall, though six to nine inches is the average height. Their spread is typically slightly wider, ranging from around 12 to 16 inches in width. So, when it's time to transplant your plants into your outdoor garden, make sure you dig their holes around six to eight inches apart. This will give the roots enough space to grow and ensures a moderately dense flower patch without the risk of overcrowding.
Lobelia may have a prim and proper aesthetic charm, but it's certainly not a fussy plant. No matter where you live, your lobelias should be able to adjust well to your sunlight levels. For optimal blooms, if you live in the south, try to keep your lobelias in partial shade. This will keep your plants flowering profusely throughout the long, hot summers. If you live in the north, full sunlight will typically give you the best growing results.
While lobelias do require well-draining soil, they also need to be kept fairly moist if you want to prolong flowering for as long as possible. Start by giving your plants one inch of water every week. Their soil should always remain moist, so if it dries out before the week is up, you may need to adjust your watering schedule to your climate. That said, be careful to avoid overwatering, as too much moisture can lead to root rot.
Of all the pests lobelia can attract, spider mites are some of the worst. These mites do serious damage by sucking out chlorophyll and replacing it with toxins. Look out for pepper grain-sized bugs, white dots, or webbing on your plants — all signs of a spider mite infestation. If you do have spider mites, use a forceful hose spray to blast them away. Aphids (which feed on leaves and attract ants) can also be washed away with a water hose. Japanese beetles and slugs are best picked off by hand.
Lobelias are susceptible to an array of plant diseases. Leaf blight, for example, creates yellow halos on lobelia leaves, eventually making them wither and die. Likewise, fungal diseases like leaf spot — marked by dark, circular spots — and rust — marked by rust-colored spots — are also common. To rid your patch of these diseases, you'll need to pull up and discard any infected plants before the issue can spread. Other common lobelia diseases are more easily avoidable. You can prevent both root rot and a condition known as "damping off" by avoiding overwatering and overcrowding your plants.
A relatively low-maintenance plant, lobelia doesn't require much special care. Fertilizing isn't essential, but applying liquid fertilizer every four to six weeks can help your patch grow healthy and strong. Just avoid overfertilizing (especially if you're using a nitrogen phosphorus-rich fertilizer), as this can increase the risk of damping off. On top of that, remember that you may need to water your plants twice a week or more if you live in a particularly hot area.
Along with growing lobelias from seeds, you can also propagate new plants from cuttings. When taking cuttings, it's best to work late in the spring season, cutting only the new growth that hasn't flowered yet. Shear off 4- to 5-inch pieces, and remove any leaves. Next, plant them quickly before the cuttings have time to dehydrate. Submerge the cuttings halfway down in wet soil and keep them moist. Once new roots have set, the lobelias are ready to plant in your flowerbeds.
If you want to attract more wildlife to your garden, lobelias can be a big help. These vibrant flowers are like magnets for butterflies and hummingbirds, both of which love to drink their rich nectar. The lobelia has also been used in traditional, herbal remedies for many years, particularly as a treatment for breathing problems like asthma, bronchitis, and apnea. However, the plants are toxic in moderate to large quantities, so it's best not to harvest your own lobelias for medicinal use.
There are several varieties of lobelia available, and many of them are popular in gardens. Trailing lobelia (lobelia erinus) is a compact perennial, typically grown as border edging or used in hanging baskets and window boxes. This variety is often found in shades of purple and blue, but it can also grow in pink and white. Cardinal flower (lobelia cardinalis) is a tall-growing perennial characterized by its scarlet-red, tube-shaped flowers. Other, less common varieties include the upright, lilac Great Blue Lobelia (lobelia siphilitica) and the vigorous, dark violet Vedrariensis (lobelia x speciosa).