Jenkins’ Seed Packets: Wild Senna

Wild senna (Senna herbacea)

Wild senna is a shrubby herbaceous perennial native to moist, open wooded areas and disturbed sites, such as riverbanks and slopes. The yellow flowers attract pollinators in summer and are especially valuable to bumblebees. The seed pods provide a food for birds.

Natural Habitat: Woodlands, riverbanks
Light Requirements: Sun to part shade
Soil Requirements: Moist
USDA Hardiness: Zones 4-9
Size: Height of 4′ to 6′
Wildlife Value: Birds, pollinators
Deer Resistance: Resistant

Germination Requirements

Wild senna seeds require a light sanding followed by 10 days of Cold Moist Stratification (abbreviated CMS in many reference guides). Stratification is the process of pre-treating seeds to overcome the seeds’ natural inhibitors that prevent germination in less-than ideal circumstances. Cover the seeds lightly when you sow them. A general rule is to cover seeds to a depth equal to their height.

To sand the seeds, set them between two sheets of sandpaper and move the top piece back and forth across the seeds that are sandwiched between the two layers. Don’t press so firmly that it is difficult. It is a light motion.

Cold Moist Stratification can be accomplished by sowing the seeds and setting them outside when temperatures are consistently below 40 degrees. Seeds can always be kept cold longer than the required number of days, so it is fine to sow these in December and leave them outside for the entire winter. They will germinate when the soil warms up in spring. A refrigerator can also be used to provide the 10 days of cold conditions.

Plants in the pea family benefit from the use of an inoculant if you have access to some from a vegetable gardening friend. It is not required.