Lobelia in Zone 5B — Mountain West

Lobelia is a fantastic addition to any Zone 5B Mountain West garden. The masses of vibrant blue flowers provide a delightful pop of color, and the plant's spreading habit makes it ideal for borders, containers, and hanging baskets. Plus, in our intense sunlight, those blue hues really pop.

Growing Lobelia in our short season, high altitude environment does present some challenges. The 149-day growing season means starting early or buying starts is key. With careful planning and attention to watering, you can enjoy these beauties all summer long.

Starting Lobelia from seed indoors is possible, but it requires patience. Begin in early to late March, about 10 weeks before you intend to transplant. You'll need seed trays, a warm location (around 70°F), and a good grow light, since our spring sunlight can still be weak.

Because Lobelia seeds are tiny, bottom watering is essential to avoid disturbing them. Place your seed trays in a shallow dish of water and allow the soil to absorb moisture from the bottom. Given our late springs, indoor starting gives you a jump on our short growing season.

Transplant your Lobelia seedlings outdoors from mid May through mid June, after the danger of frost has passed. Be sure to harden them off for about a week beforehand by gradually exposing them to outdoor conditions. This helps them adjust to our intense UV and fluctuating temperatures.

Space your plants 4-6 inches apart to allow for their spreading growth habit. You'll often find these for sale as bedding plants, and that can be a great option for our climate. Given the tiny seeds and slow growth of Lobelia, buying starts can save you a lot of time and frustration.

Lobelia needs consistent moisture, so watering is crucial in our dry Mountain West climate. Aim to keep the soil consistently moist but not waterlogged. During the peak of summer, you may need to water daily, especially if they're in containers.

Use the "finger test" to check soil moisture: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Generally, Lobelia needs about 1 inch of water per week, but adjust based on weather conditions. Given our low humidity, watering at the base of the plants is preferable to overhead watering, which can encourage fungal diseases.

Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to yellowing leaves and root rot. Mulching around your Lobelia plants with a layer of organic matter, like shredded bark, helps retain moisture and regulate soil temperature in our variable climate.

Lobelia requires minimal pruning, making it a low-maintenance choice for our busy Mountain gardens. The main goal is to encourage continued blooming throughout the season. When flowering slows down in midsummer, shear back the plants by about half.

This encourages fresh growth and a new flush of flowers as the weather cools in the fall. Don't be afraid to be a little aggressive – Lobelia is resilient. As the first frost approaches around early October, simply let the plants die back naturally.

Lobelia is primarily grown for its ornamental value, so there's no traditional "harvest." Just enjoy the masses of tiny blue flowers from late July through early September, about 65 days from transplanting. The vibrant blooms provide a beautiful display in your garden.

Deadheading spent flowers can encourage continued blooming, but it's not strictly necessary. The plants will naturally produce new flowers throughout the season. To keep them producing those beautiful blooms, keep them watered.

As the first frost approaches in early October, the plants will naturally decline. There's no need to harvest anything; simply enjoy the last of the blooms before the cold weather sets in. You can collect seeds for next year, though germination can be a bit tricky.

Lobelia can face a few challenges in the Mountain West. Here are the most common issues and how to tackle them:

Dies Back in Extreme Heat

• What it looks like: The plant wilts, leaves turn brown and crispy, and overall growth stalls.
• What causes it: Lobelia struggles in prolonged heat, especially combined with our intense sun and low humidity. The plant effectively goes dormant to conserve energy.
• How to fix/prevent it: Provide afternoon shade, especially during the hottest part of the summer. Ensure consistent watering and consider mulching to keep the soil cool. A location that gets morning sun but afternoon shade is ideal.

Damping Off from Overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a fuzzy mold around the base.
• What causes it: Overwatering creates a damp environment that encourages fungal growth, especially in poorly drained soil. This is more common when starting seeds indoors.
• How to fix/prevent it: Use well-draining soil and avoid overwatering. Ensure good air circulation around seedlings. Bottom watering can help prevent damping off.

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, combined with low humidity and dry rainfall, means Lobelia needs consistent watering and protection from the intense sun. The key is to find a balance between providing enough moisture and avoiding overwatering, as well as positioning them in a spot where they get some relief from the hottest afternoon sun.

Lobelia makes a great companion plant in the Mountain West garden. Planting it near tomatoes and peppers can be beneficial because it attracts pollinators, which are essential for fruit production. The bright blue flowers also create a visual contrast that can deter some pests.

Lobelia also pairs well with lettuce. Its spreading habit can help provide some shade to the lettuce during the hottest part of the day, preventing it from bolting prematurely. Avoid planting Lobelia near aggressive, sprawling plants that might outcompete it for resources.