Do Lupines Need to Be Cold-Stratified?

Characteristics

• Several different species of lupines grow wild in the United States, but the most commonly cultivated plants are hybrids developed especially for home gardens. Many groups of hybrid lupines exist, including one called the Russell hybrids, named after its English developer, that's an especially good choice. These plants grow year-round as perennials in U.S. Department of Agriculture plant hardiness zones 3 through 9. They are about 3 feet tall, producing erect spikes of densely packed flowers that resemble sweet pea blossoms. They come in shades of blue, purple, yellow, pink and red and several bicolors.

Dormancy

• Like many hard-coated seeds, those of the lupine seeds are dormant when released from the mature seed pod, a situation that prevents development of a seedling until the seed encounters the proper conditions. Lupine seeds exhibit a type of dormancy called seed coat dormancy, because the coat covering the seed is impermeable to water and oxygen, preventing germination. Plants like lupines that grow in areas with cold winters have seeds that naturally break dormancy when exposed to cold for a period of time, so that they're ready to grow in spring when warmth arrives. A gardener can mimic this preparation for germination with a process called cold stratification, which helps the seed break dormancy and begin growing.

Cold Stratification

• By cold-stratifying lupine seeds, you simulate the conditions seeds would normally encounter in soil during winter. Moisten some potting material such as peat moss or vermiculite, and add seed, using a ratio of one part seed to three parts moist material. Place the seed-material mixture in a sealed plastic bag, and store it in a freezer at about 28 to 32 degrees Fahrenheit, which mimics subfreezing outdoor temperatures. Check the bag periodically to ensure that it remains moist, but don't let the mixture become soggy, with visible pooling of water. Also check to see whether tiny root tips are forming on the seed, and continue the stratification process until these are evident on most of the seed, a process that can take several weeks or more. At this point, sow the cold-treated seed in moist potting soil or soilless mix, and keep the mixture moist until seedlings appear.

Scarification

• You can also force lupine seeds to break seed coat dormancy by mechanically scarifying the seed coat, causing it to rupture and allow water and oxygen to enter. An easy way to accomplish this is to place seeds between two rough metal files or two pieces of sandpaper and pass the files or sandpaper back and forth several times, until you can see some dulling of the seeds' surfaces. Seeds treated this way need immediate planting to prevent drying of the embryo underneath the seed coat. Whether you cold-stratify or scarify seeds, once the seedlings have two sets of leaves and danger of spring frost has passed, move your new plants to a semishaded spot for a week or two to acclimate them to the outdoors; then, transplant then into a sunny garden spot.