Lobelia in Zone 4B — Mountain West

Lobelia, with its vibrant blue flowers, adds a splash of much-needed color to our Mountain gardens. It's perfect for edging, containers, or cascading from hanging baskets. Here, the intense sunlight intensifies the blooms, and the cool nights even in summer help keep them going strong.

Our short growing season and alkaline soil present challenges, but with careful timing, you can enjoy Lobelia’s beauty from midsummer until the first frost. Knowing that we have about 128 days, starting at the right time is key.

Starting Lobelia indoors in the Mountain West is an option, but honestly, given the tiny seeds and slow early growth, you might prefer buying starts from a local nursery. If you do start indoors, aim for mid-March through early April, giving you about 10 weeks before transplanting.

Use seed trays and a good seed-starting mix. Provide warmth with a heat mat and plenty of light with grow lights. Keep the soil consistently moist by bottom watering to avoid disturbing the tiny seeds. Remember, spring can be late here, so don’t rush things.

Transplant Lobelia outdoors in late May through late June after the danger of frost has passed. Harden off your seedlings for about a week, gradually exposing them to the outdoor conditions. This is especially important given our intense UV.

Space them about 4-6 inches apart. Be mindful of potential late frosts or even hail storms that can occur even in early summer. Protecting your young transplants with row covers can be a good idea.

Lobelia needs consistently moist soil, which can be a challenge in our dry Mountain climate. Water deeply whenever the top two inches of soil feel dry to the touch – use the finger test. Typically, this will mean watering a few times a week, aiming for about an inch of water each time.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases, though our low humidity helps minimize this risk. Signs of underwatering include wilting and browning leaf edges. Overwatering can lead to yellowing leaves and root rot.

Mulching around your Lobelia plants with organic matter like compost helps retain moisture and keeps the soil cool during the warmer parts of the summer. This is key given our dry rainfall.

Lobelia doesn't require a lot of pruning, but a little maintenance can keep them blooming longer. 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 down again. As the first frost approaches in mid-September, remove any dead or damaged foliage, but otherwise, let the plants be.

Lobelia is grown for its beautiful flowers, so there isn't really a "harvest" in the traditional sense. Expect the first blooms to appear in early August through mid-September, about 65 days after transplanting.

Enjoy the masses of tiny blue flowers in your garden. To encourage continued blooming, deadhead spent flowers regularly. Simply pinch or snip off the faded blooms just below the flower head.

As the first frost approaches, you can either let the plants die back naturally or try to overwinter them indoors in a cool, bright location. However, most gardeners in our zone treat them as annuals.

Here are a few problems you might encounter with Lobelia in the Mountain West:

Dies back in extreme heat

• What it looks like: Wilting, browning, and overall decline during the hottest part of the summer.
• What causes it: Lobelia prefers cooler temperatures. In our moderate-at-altitude heat, even 85°F can be stressful, especially with intense UV.
• How to fix/prevent it: Provide afternoon shade, especially during the hottest days. Ensure consistent watering. Mulch to keep the soil cool. Shear back to encourage new growth when cooler weather returns.

Damping off from overwatering

• What it looks like: Seedlings suddenly collapse and die, often with a fuzzy, mold-like growth at the base of the stem.
• What causes it: Overwatering creates a favorable environment for fungal diseases, especially in poorly drained soil.
• How to fix/prevent it: Use a well-draining seed-starting mix. Avoid overwatering, especially in the early stages. Ensure good air circulation. Bottom watering can help 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: 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: The combination of intense sun and low humidity can be tough on Lobelia. Consistent watering is essential, but avoid overwatering. Providing some afternoon shade can help prevent heat stress.

Lobelia makes a great companion plant for several vegetables in our Mountain gardens. Planting it near tomatoes and peppers can attract pollinators, boosting fruit production. The bright flowers also help deter some pests.

Lobelia also complements lettuce by providing shade and helping to retain moisture in the soil. Avoid planting Lobelia near plants that prefer very dry conditions, as its need for consistent moisture could be detrimental to those companions.