Here's a guide to planting Alisma subcordatum (American Water-plantain) from seed in the USA:
Site Selection
Sunlight: American Water-plantain prefers full sun to partial shade. It will do best with at least 6 hours of sunlight, but can tolerate some shade, especially in very hot climates.
Soil: This plant thrives in moist to wet soils. It's commonly found in shallow water, along shorelines, and in swampy areas. It can tolerate a range of soil types, including clay and loam, as long as the soil is consistently moist or submerged.
Soil Preparation
Amendments: Since it grows in wet areas, amending the soil is usually not necessary. If planting in a container, you can use a heavy garden soil or a specialized aquatic planting mix.
pH: American Water-plantain prefers a neutral to slightly alkaline soil pH.
Planting
Direct Sowing (Fall or Spring)
Timing:
Fall: Fall sowing is often preferred as it allows for natural stratification over the winter.
Spring: Sow seeds in the spring after the last frost.
Depth: Plant seeds very shallowly, barely covering them with soil. They need light to germinate.
Location: For direct sowing, it's best to sow seeds in a location where they will naturally experience the fluctuating water levels they prefer. This could be a muddy shoreline or a shallow area of a pond or stream.
Starting Seeds Indoors (Spring)
Timing: Start seeds indoors 6-8 weeks before the last expected frost.
Containers: Use small pots or seed starting trays filled with a moist soil or aquatic planting mix.
Depth: Plant seeds very shallowly, barely covering them with soil.
Water: Keep the soil consistently moist or even slightly submerged.
Light: Provide ample light. A sunny window or grow lights are suitable.
Stratification and Scarification
Stratification: Alisma subcordatum seeds benefit from stratification. Cold, moist stratification for 4-6 weeks in the refrigerator can improve germination rates. Place seeds in a moist paper towel or in a bag with slightly damp sand or vermiculite.
Scarification: Scarification is not typically necessary for this species.
Watering
Keep the soil consistently moist or even slightly submerged during germination and seedling growth. Once established, American Water-plantain can tolerate some fluctuation in water levels, but it prefers consistently moist to wet conditions.
Maintenance
Weeding: Remove any competing weeds, especially when the plants are young.
Pest and Disease Control: Generally, Alisma subcordatum doesn't have serious pest or disease problems.
Division: Established clumps can be divided in the spring or fall to propagate more plants.
Invasiveness
Alisma subcordatum is native to North America and is generally not considered invasive in most areas within its native range. However, it can spread locally by rhizomes (underground stems) and seed. In some regions, particularly where it's introduced outside its native range, it might be considered potentially invasive. Check with your local extension service or native plant society to determine if it's considered problematic in your area. It's always a good idea to monitor its growth and prevent it from spreading aggressively if necessary.
Important Considerations
American Water-plantain is an important plant for wetland ecosystems, providing habitat and food for wildlife.
When planting near water, avoid using any fertilizers or pesticides that could harm aquatic life.
