Rose hips are the "fruit" of the rose, and are in essence a swollen ovary containing the genetic material of the rose in the form of seeds. Rose hips develop in bunches of varying size on all forms of roses at the site of a spent rose bloom. Harvesting flowers on the stem or deadheading flowers after bloom will prevent rose hips from developing, so discipline about pruning is the key to growing rose hips. Good cultivation practices including generous watering and feeding will also help to develop a large and healthy crop of rose hips.
Water your rose plants deeply one a week to every 10 days depending on your climate and season. Keep the soil around the roots evenly moist at all times but not soaking wet which can cause rot. Never allow the planting soil to dry out, as this can disrupt bloom, which will limit hip development.
Feed your rose plants with a high quality organic rose fertilizer several times during the growing season beginning in early spring after the last frost has passed. Feed again in the early summer and once again in the early fall. Use rose tone, fish emulsion or another commercial rose food. Apply according to label directions and water the fertilizer in well after each application.
Harvest mature and ripe rose hips in the late fall or winter when the hips have swollen to a plump round shape, deepened in color to a rich red, coral or orange and give slightly when pressed with your fingertip. Cut off the bunches of hips for use in flower arrangements, for seed collection, tea or preserves.