Lobelia in Zone 5A — Mountain West

Lobelia, with its profusion of vibrant blue flowers, brings a welcome splash of color to our high-altitude gardens. These delicate blooms thrive in our cool nights and intense sunlight, adding a touch of elegance to containers, borders, and hanging baskets. The cool evenings in the Mountain West actually enhance the floral display.

While our short growing season and intense UV rays present challenges, careful timing and site selection make growing Lobelia entirely manageable. You have about a 138-day window to enjoy these beauties, and with a little attention, they'll reward you with continuous blooms from late summer into fall.

Starting Lobelia indoors can give you a head start, but it's honestly not always necessary. These plants are often available as inexpensive starts at local nurseries. If you do choose to start from seed, begin in early to late March, about 10 weeks before you plan to transplant outdoors.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist by bottom watering to prevent damping off. Provide warmth and plenty of light – a grow light is ideal, given our late spring sunshine in the mountains.

Transplant your Lobelia seedlings outdoors in late May through late June, after the last threat of frost has passed. Before planting, harden them off for about a week by gradually exposing them to outdoor conditions. This helps them adjust to our intense sun and cool nights.

Space the plants 4-6 inches apart in a location that receives full sun to partial shade. Given that Lobelia seeds are tiny and slow-growing, you might consider purchasing established starts from a local garden center.

Lobelia needs consistent moisture, especially in our dry Mountain West climate. Aim to keep the soil consistently moist, but not waterlogged. This is crucial because they don't tolerate drought well and can go dormant during hot, dry spells, even though they often recover when the weather cools.

During the peak of summer, when temperatures can reach around 85°F, water deeply about 2-3 times per week. Check the soil moisture with the "finger test" – if the top two inches feel dry, it's time to water. In our low-humidity environment, watering at the base of the plant is generally best to avoid fungal issues.

Signs of underwatering include wilting leaves and dry soil. Overwatering can lead to yellowing leaves and potentially root rot. A layer of mulch, like shredded bark or compost, can help retain moisture and regulate soil temperature.

Lobelia requires minimal pruning, but a little attention can encourage more blooms. When flowering slows down in midsummer, shear the plants back by about half. This encourages fresh growth and a new flush of flowers as the weather cools in the fall.

Simply use sharp scissors or pruning shears to trim back the foliage. Don't be afraid to cut back quite a bit; Lobelia is resilient. Avoid pruning off any healthy, green growth, focusing on removing spent or fading blooms.

Lobelia is primarily grown for its ornamental value, so there isn't really a "harvest" in the traditional sense. Enjoy the masses of tiny blue flowers throughout the growing season, from late July through mid-September. The flowers are not typically used for culinary or medicinal purposes.

Deadheading, or removing spent blooms, can help encourage continuous flowering. Simply pinch off the faded flowers to keep the plants looking tidy and promote new growth. As the first frost approaches in late September, let the plants go to seed if you want to collect seeds for next year.

Here are three common problems you might encounter with Lobelia in the Mountain West:

Dies Back in Extreme Heat

• What it looks like: The plant wilts, leaves turn brown and crispy, and flowering stops.
• What causes it: Intense sun and heat, combined with low humidity, can stress Lobelia, causing it to shut down.
• How to fix/prevent it: Provide afternoon shade, especially during the hottest part of the day. Water deeply and consistently, and consider using a shade cloth during heat waves.

Damping Off from Overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a fuzzy, white mold on the soil surface.
• What causes it: Overwatering and poor air circulation create ideal conditions for fungal diseases to attack young seedlings.
• How to fix/prevent it: Use a well-draining seed-starting mix. Water from the bottom to avoid wetting the foliage. Ensure good air circulation around the seedlings.

Slugs

• What it looks like: Irregular holes in leaves, especially low-growing plants. Silvery slime trails on leaves and soil.
• What causes it: Moist conditions and readily available hiding spots attract slugs, which feed on Lobelia foliage.
• How to fix/prevent it: Set out beer traps (shallow dishes of beer sunk into the soil). Apply iron phosphate bait (pet-safe). Remove mulch, boards, and debris that provide hiding spots. Water in the morning so the soil surface dries by evening.

Mountain West Specific Challenges: Our intense UV radiation can scorch Lobelia leaves if they're not acclimated properly. Make sure to harden off seedlings gradually before transplanting them outdoors. The dry air can also lead to rapid moisture loss, so consistent watering is key.

Lobelia plays well with others in the garden, offering both aesthetic appeal and practical benefits.

Good companions include tomatoes and peppers. Lobelia attracts beneficial insects like hoverflies, which prey on aphids that can plague tomato and pepper plants. They also pair well with lettuce. The shade provided by taller lettuce varieties can help protect Lobelia from the intense afternoon sun.

Avoid planting Lobelia near aggressive plants that might compete for resources. Also, avoid planting near plants that require very dry conditions, as Lobelia prefers consistently moist soil.