Holly shrubs and trees, known botanically as Ilex, are a genus containing in excess of 400 species and cultivars. Many are evergreen, but some species are deciduous, and most female plants produce seed carrying berries in the late summer, fall and winter when pollinated by male flowering plants in the spring. The berries self sow naturally when they fall from the shrub in winter or are distributed by animals and birds. According to North Carolina State University, holly seeds are notoriously tricky to germinate due to their hard seed coat and slow developing embryo taking upwards of two years even under good outdoor conditions. Indoor cold storage and greenhouse planting can speed this process up to some degree.
Harvest your holly berries in the winter when they are fully ripe. Clean the flesh from the seeds by hand and place the seeds in a fine mesh sieve to wash the remaining tissue from the seed coat with running water. Harvest and clean two to three times the amount of seeds than you want in eventual plants to allow for germination failure.
Soak the cleaned holly seeds in a glass or bowl of tepid water, indoors for roughly 24 hours to hydrate and soften the seed coat.
Place the clean, hydrated seeds inside a thin plastic bag filled one quarter of the way with moist and sterile peat or sphagnum moss and coarse sand in equal measurements. Alternatively, nestle the seeds into a seed tray filled with the same sterile medium. Keep the medium moist, but not wet, at all times.
Store the seeds in the refrigerator at temperature between 37 and 40degrees Fahrenheit allowing at least four months to pass before removing from the cold. Check on the medium every two to three weeks to ensure it is not dry, adding water as necessary to maintain an evenly moist feel.
Plant the cold stratified seeds into small seed trays or seedling pots filled with fresh, sterile and light potting mix. Nestle the seeds in the top 1/8-inch of soil but no deeper. Moisten the soil with water and never allow it to dry out.
Cover the seed trays or pots loosely with clear plastic or plastic bags to create a greenhouse effect, but not tightly in order to allow some fresh air entry.
Keep the seed tray or pots in an indoor location where ambient temperatures remain between 75 and 95 degrees Fahrenheit and overnight temperatures are at least 5 degrees lower than the daytime temperatures.
Move the sprouted seedlings carefully into larger growing pots when the plants attain two to four leaves.