The primrose is an easy-to-grow perennial that grows 6 to 12 inches high and up to 18 inches wide. The plants thrive in USDA hardiness zones 4 through 9 and prefer moist, cool soil. Primroses bloom mid summer and should be propagated by division in the fall after blooming ends. To start from seeds, sew indoors in January for an outdoor spring planting.
Propagation through Division
Prepare the soil by tilling compost and peat into the new planting location. Do this prior to dividing so the plants can be placed in the soil before the roots dry out.
Remove the primrose by digging a circle around it 3 to 4 inches wider than the plant itself. Carefully lift it from the hole, taking care not to tear the root structure.
Remove as much soil from the roots as possible. Use a garden hose to spray the roots and clean off remaining soil. The more soil removed at this point, the easier it will be to divide the roots.
Divide the primrose by cutting vertically through the root-ball, making sure that each section has at least 2 plant stems. Use a gardener's saw to cut hard roots of larger plants.
Dig a hole in the prepared soil that is large enough to accommodate the divided root section. Keep the plant at the same depth it was prior to dividing. Plant each section at least 6 to 9 inches apart. Fast-growing varieties should be planted as much as 40 inches apart.
Water immediately after planting and for the next 2 to 3 days. Keep the soil moist but not wet throughout the growing season.
Apply mulch around the new plants to help keep the soil cool and moist.
Do not fertilize the plants until the following spring to avoid damaging the roots.
Propagation through Seeds
Prepare a seed starting tray by combining equal parts of peat, sand and soil. Add the mixture to the seed starting tray, leaving room for a 1-inch thick layer of starting medium.
Prepare an even mixture of sand and peat moss for the seed starting medium. Place a 1-inch layer over the soil mixture and sprinkle seeds on top of it. Cover the seeds with a thin layer of seed starting medium, approximately 1/16 inch.
Once the second set of leaves has grown, transplant the seedlings to a growing flat filled with a mixture of garden loam and peat.
Prepare garden soil by tilling in compost and fertilizer. Do not plant seedlings immediately after applying fertilizer.
Plant the seedlings outdoors in the prepared soil after the last killing frost.