Lobelia in Zone 6B — Mountain West

Lobelia is a charming addition to any Mountain West garden. Its masses of delicate blue flowers bring a touch of cool color, and they’re perfect for spilling over the edges of containers or softening the edges of garden beds. The cool nights we often have, even in summer, really make the colors pop!

Our short growing season and intense sun can present challenges, but with careful timing, you can definitely enjoy Lobelia in your garden. With our typical 163-day growing season, focusing on transplants will give you a head start.

Starting Lobelia from seed indoors is possible, but honestly, it can be a bit tricky given our late springs. If you want to give it a go, start 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, provide warmth (a heat mat is helpful), and give them plenty of light, especially since our spring light can still be weak at this altitude. Bottom watering is a must to prevent damping off. Honestly, though, given their slow growth, buying starts from a local nursery might be the easier option.

Transplant your Lobelia outdoors from early May through early June, after the risk of frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. Plant them 4-6 inches apart in an area that gets full sun to part shade. Keep an eye on the weather, as we can still get some late-season cold snaps or even hail during this time.

Lobelia needs consistent moisture, especially in our dry Mountain West climate. Aim to keep the soil consistently moist, but not soggy. Lobelia is definitely not drought-tolerant, and it will quickly go dormant if allowed to dry out. Don't worry, it'll bounce back when it cools down.

During the hottest part of the summer, when temperatures reach around 85°F, you’ll likely need to water deeply every other day, or even daily, depending on how quickly your soil dries out. Use the finger test – stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. Because our humidity is low, you can generally water at the base of the plant or overhead without worrying too much about fungal diseases.

Signs of underwatering include wilting leaves and a general lack of vigor. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch, like shredded bark, can help retain moisture in the soil and keep the roots cool.

Lobelia needs minimal pruning. However, if you notice that 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 down in the fall. Don't be afraid to cut them back – they're pretty resilient. As the first frost approaches in early October, you can let the plants go. They won't survive our winters, so there's no need to try and overwinter them.

You don't really "harvest" Lobelia in the traditional sense. The real reward is enjoying their beautiful blooms in your garden. Expect the first flowers to appear from mid July through late August, about 65 days after transplanting.

The plants will continuously produce masses of tiny blue flowers throughout the summer and into the fall, provided you keep them watered and give them a little trim if they start to look leggy. Just deadhead spent flowers to encourage more blooms. As the first frost approaches in early October, enjoy the last of the flowers. They won't ripen or produce anything after being cut, so just enjoy them on the plant.

Here are the most 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: Our intense sun and moderate-at-altitude heat, combined with low humidity, can stress the plants, especially if they aren't getting enough water.
• How to fix/prevent it: Provide some afternoon shade, especially during the hottest part of the summer. Make sure the plants are getting enough water, and consider using a mulch to help retain moisture in the soil.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a fuzzy, moldy growth at the base of the stem.
• What causes it: Overwatering creates a damp environment that encourages fungal growth.
• How to fix/prevent it: Use a well-draining seed-starting mix, avoid overwatering, and provide good air circulation. Bottom watering is a good way to prevent this.

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: Use 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 summer heat, combined with low humidity and dry rainfall, means that consistent watering and some afternoon shade are crucial for keeping Lobelia happy. Be especially vigilant about monitoring soil moisture and providing supplemental water as needed.

Lobelia makes a great companion plant for several vegetables in the Mountain West garden. Plant it near tomatoes and peppers to attract pollinators, which will help increase fruit production. Its low-growing, spreading habit also makes it a good choice for planting around lettuce, as it can help to shade the soil and keep the lettuce roots cool during the hottest part of the summer. I wouldn't recommend planting it near anything that needs very dry soil, as Lobelia prefers consistent moisture.