The seeds are ripe when the hip changes colour and softens. The hip is opened up. The seeds are taken out, cleaned, immersed in water and well rinsed to remove any hairs clinging to them. Generally, all seeds which float are sterile (empty) and can be thrown away. Seeds should be sowed quickly or placed in a labeled small jar or a sealable plastic bag where some soil is added (about three time the volume of the seed) and stored in a cool moist place (a refrigerator at 4°C, a cold greenhouse, a cellar or a gel-free cold layer) for two to five months: this is the stratification.

Stratification is a natural process. In nature, the seeds fall to the ground in the fall in a wet and cold environment and germinate in the spring when the weather gets warmer. Artificial stratification therefore seeks to replicate the natural conditions to which have adapted different species. When roots appear, the seedlings are ready for planting.