Lobelia in Zone 6A — Mountain West

Lobelia, with its delicate, vibrant blue flowers, is a fantastic addition to any Mountain West garden. Its unique color and spreading habit make it perfect for filling in gaps in beds, cascading from containers, or softening the edges of pathways. Plus, the cool nights we experience even in summer enhance the intensity of its blooms.

Our high altitude, intense sun, and short growing season can seem daunting, but Lobelia is surprisingly well-suited to our climate with proper planning. Starting seeds indoors at the right time, coupled with our long sunny days, gives you a great head start on enjoying these beauties within our 153-day growing season.

Starting Lobelia from seed indoors is a good idea in our region, especially if you want a jump start on the season. Given our late springs, it's a good way to get a head start. You'll want to start your seeds indoors from late February through mid March, about 10 weeks before you plan to transplant them outdoors.

Use seed trays with a good seed-starting mix, and keep them consistently moist by bottom watering. Place the trays in a warm location, ideally around 70-75°F, and provide supplemental light, as our spring sunlight can still be weak and variable.

Transplant your Lobelia seedlings outdoors from mid May through mid June, after the danger of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense sun and cooler nights common in the Mountain West.

Space your Lobelia plants 4-6 inches apart in a location that receives full sun to part shade. Our intense UV light means even "full sun" plants appreciate some afternoon shade here. Honestly, though, these tiny seeds are very slow to grow, so consider buying starts from a local nursery.

Consistent moisture is key for Lobelia in our dry Mountain West climate. While our moderate-at-altitude summer heat isn't scorching, the low humidity and dry rainfall mean you'll need to be diligent about watering. Aim to keep the soil consistently moist, but not waterlogged.

During the peak of summer, you'll likely need to water your Lobelia every other day, or even daily if the soil dries out quickly. Use the finger test: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Water deeply, providing about an inch of water per week, focusing on the base of the plant to avoid wetting the foliage and encouraging fungal diseases.

In spring and fall, when temperatures are cooler and rainfall is more frequent, you can reduce watering accordingly. Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. Mulching around your plants with a light layer of compost helps retain moisture and regulate soil temperature.

Lobelia requires minimal pruning, but a little attention can keep it looking its best. When flowering slows down in midsummer, shear back the plants by about half. This encourages fresh growth and a new flush of blooms as the cooler fall weather arrives.

Simply use sharp scissors or pruning shears to trim back the entire plant, removing any spent flowers and leggy stems. Don't be afraid to cut it back fairly hard; Lobelia is resilient and will quickly bounce back. As the first frost approaches around early October, you can leave the plants as they are, allowing them to naturally die back for the winter.

Lobelia is primarily grown for its beautiful flowers, so there's no need for a traditional "harvest." Simply enjoy the masses of tiny blue flowers that adorn your garden from mid July through early September, roughly 65 days after transplanting.

The vibrant blooms provide a stunning visual display and attract pollinators to your garden. To encourage continuous production, deadhead spent flowers regularly by pinching them off with your fingers. This directs the plant's energy towards producing new blooms rather than setting seed.

As the first frost approaches in early October, you can let the plants go to seed if you wish to collect them for next year. Otherwise, simply enjoy the last of the blooms before the cold weather sets in.

Here are the top 3 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 overall growth stalls or stops.
• What causes it: While our summers are moderate-at-altitude, we can still get periods of intense heat. Lobelia prefers cooler temperatures and struggles when temperatures consistently exceed 85°F, especially combined with our intense UV.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Water deeply and regularly to keep the soil consistently moist. Consider using shade cloth to protect the plants from the most intense sun.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a fuzzy, mold-like growth at the base.
• What causes it: Overwatering creates a damp, humid environment that favors fungal growth. This is especially problematic when starting seeds indoors, where air circulation may be limited.
• How to fix/prevent it: Use a well-draining seed-starting mix. Water from the bottom to avoid wetting the foliage. Provide good air circulation with a small fan. Don't overwater.

Slugs

• What it looks like: Irregular holes in leaves, especially low-growing plants. Silvery slime trails on leaves and soil. Damage worse at night and in wet weather.
• What causes it: Gastropods that feed at night in moist conditions. Hide under mulch, boards, and debris during the day.
• How to fix/prevent it: Beer traps (shallow dish of beer sunk into soil). Iron phosphate bait (pet-safe). Remove hiding spots. Water in morning so soil surface dries by evening. Copper tape around beds. Diatomaceous earth around plants.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall mean you'll need to pay close attention to watering and provide shade during the hottest parts of the day. The alkaline soil can also be a challenge, so amend your soil with compost to improve drainage and nutrient availability.

Lobelia makes a great companion plant for a variety of vegetables and flowers in the Mountain West garden.

Good companions include tomatoes and peppers. Lobelia can help attract pollinators to your tomato and pepper plants, increasing fruit set. Plus, its spreading habit helps to suppress weeds and retain moisture in the soil, which is particularly beneficial in our dry climate. Lobelia also works well with lettuce, providing ground cover and helping to keep the soil cool, which lettuce appreciates in our intense sun.

Avoid planting Lobelia near any plants that prefer very dry conditions, as its need for consistent moisture could create an unfavorable environment for those companions.