Propagation of Senna Alata

Timing

• As a tropical plant, popcorn senna requires a long, warm growing season to produce its characteristically spectacular flowering display. Starting the seeds indoors four to six weeks before the last spring frost will give the seedlings a head start, which will allow them to become established sooner and bloom abundantly in cooler climates with a shorter growing season.

Equipment and Preparation

• Popcorn senna shrubs produce very large seeds that must be sown in individual pots to allow them adequate room for growth. Four- to 6-inch pots with two or three drainage holes at the base work best, although larger pots can be used in a pinch. The pots must be thoroughly washed and dried, then filled with sterile medium such as seed-starting compost to provide the right conditions for healthy germination. Don't use garden soil or previously used potting soil because it may harbor pathogens.

Seed Pretreatment

• Due to their impermeable seed coat, popcorn senna seeds must be scarified and soaked before sowing to increase their moisture uptake. The flat side of each seed must be rubbed with coarse sandpaper or a nail file until a pale spot forms; however, it is vital not to make a hole in the seed coat because it will kill the embryo inside. Once scarified, the seeds must be soaked in hand-warm water for 24 hours to further weaken the tough seed coat and hydrate the embryo inside.

Sowing

• Popcorn senna seeds require darkness for successful germination, so it is vital to make sure they are completely covered. Sow only one seed in each pot. Poke a 1/4- to 1/2-inch-deep planting hole in the center of the medium and place the seed inside. The nicked portion of the seed should be facing sideways to allow the radicle, or leafless sprout, to emerge unhindered. Cover the seed with medium and gently firm it. Add water until the top 3 inches of the medium feel moderately moist.

Germination

• Although popcorn senna seeds germinate with abandon in their natural state, they must be kept under consistently warm conditions when grown indoors. Placing the pots on a bottom-heating propagation mat works best, but the pots can also be kept in a greenhouse or on top of a refrigerator where temperatures stay reliably above 75 degrees Fahrenheit. The growing medium must be kept moderately moist in the top 2 inches for the duration of germination, which occurs seven to 10 days after sowing.

Transplant and Aftercare

• Sterile medium is necessary for starting popcorn senna seeds, but they must be transplanted into nutrient-rich soil after germination to encourage healthy growth. Wait until the seedlings reach 1 to 2 inches in height before transferring them into a pot filled with standard potting soil. Grow the seedlings under bright, diffuse light for roughly one month before moving them to a sheltered area outdoors for hardening off. Slowly acclimate them to direct sun and less water for two weeks before planting. Plant popcorn sennas in spring after the first frost in cooler areas, or wait to plant until autumn in areas with hot, dry summers.