Lobelia in Zone 3B — Mountain West

Lobelia, with its profusion of vibrant blue flowers, adds a delightful pop of color to our Mountain West gardens. The cool nights we experience here, even in summer, intensify the flower color, making them truly stunning in hanging baskets, containers, or as edging along garden beds. Plus, their long bloom time provides beauty throughout our short growing season.

Growing Lobelia in our region presents some challenges. The intense sun and alkaline soil can be tough. However, starting seeds indoors and timing your transplant carefully will set you up for success during our 108-day growing season.

Starting Lobelia indoors is definitely an option, though many gardeners here find it easier to buy starts. Lobelia seeds are incredibly tiny and the plants are slow to get going. If you choose to start your own, aim for late March through mid April. This gives you about 10 weeks to get them established before transplanting.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist (bottom watering helps prevent damping off) and provide plenty of light. A sunny windowsill or grow light works well. Remember our late spring means you'll need to keep them indoors for a while.

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

Plant them 4-6 inches apart in well-draining soil. Even in June, we can still get some surprisingly cold nights, so be prepared to cover them if a late frost threatens. Given how tiny the seeds are and how slowly they grow, many of us in the Mountain West opt to buy established starts from a local nursery.

Lobelia needs consistent moisture to thrive, which can be a challenge in our dry Mountain West climate. They are not drought-tolerant and will quickly suffer if allowed to dry out. Aim to keep the soil consistently moist, but not soggy.

During the hottest part of summer, you'll likely need to water daily, especially if they're in containers. Use the "finger test" – if the top 2 inches of soil feel dry, it's time to water. Generally, give them about an inch of water per week, either from rainfall or irrigation. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our low-humidity environment.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, indicated by yellowing leaves and a mushy stem. A layer of mulch around the plants helps retain moisture and regulate soil temperature, which is especially helpful in our fluctuating climate.

Lobelia requires minimal pruning, but a little attention will keep them looking their best. When flowering slows down in midsummer, shear the plants back by about half. This encourages fresh growth and a new flush of blooms.

Use sharp scissors or pruning shears to make clean cuts. Don't be afraid to cut them back fairly hard – they're resilient and will bounce back quickly. As our first frost approaches in early September, stop pruning and let the plants naturally die back.

Lobelia isn't really a plant you "harvest" in the traditional sense. Instead, you enjoy their masses of tiny blue flowers as garden flowers throughout the season. Expect the first blooms to appear from mid August through early September, about 65 days after transplanting.

The flowers will continue to bloom prolifically if you keep the plants watered and shear them back when they start to look tired. To encourage continued production, deadhead spent flowers regularly by pinching them off. As the first frost approaches in early September, enjoy the last of the blooms. The plants are annuals and won't survive our cold winters.

Here are some common problems you might encounter growing 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: Lobelia struggles in extreme heat. Our intense sun and moderate-at-altitude summer temperatures can be too much for them, especially if they're not getting enough water.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Ensure consistent watering, especially during heat waves. Mulch around the plants to help retain moisture and keep the soil cool.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die. The stem may appear thin and water-soaked at the base.
• What causes it: Overwatering creates a damp environment that encourages fungal growth. This is more common when starting seeds indoors.
• 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. Avoid overcrowding seedlings.

Slugs

• What it looks like: Irregular holes in leaves, especially on low-growing plants. Silvery slime trails on the leaves and soil.
• What causes it: Slugs thrive in moist conditions and feed at night.
• How to fix/prevent it: Use beer traps or iron phosphate bait (pet-safe). Remove hiding spots like mulch and debris. Water in the morning so the soil surface dries out by evening. Copper tape around beds can deter slugs. Diatomaceous earth sprinkled around plants can also help.

Mountain West Specific Challenges: The combination of moderate-at-altitude heat, low humidity, and dry rainfall can make it tricky to find the right balance for Lobelia. They need consistent moisture but don't like to be waterlogged. Pay close attention to the weather and adjust your watering schedule accordingly. The intense UV can also scorch the leaves, so providing some afternoon shade is beneficial.

Lobelia makes a wonderful companion plant for several vegetables in our Mountain West gardens. They thrive alongside tomatoes and peppers. The lobelia's delicate flowers attract pollinators, which can improve fruit set on your tomatoes and peppers.

Lobelia also pairs well with lettuce. The lobelia's spreading habit can help shade the soil, keeping the lettuce roots cool and moist. There aren't any specific plants to avoid planting near Lobelia.