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An evening primrose with a single deep taproot cannot be split without cutting that root, and a plant cut that way rarely recovers. For these kinds, collect seed and raise new plants, or let them self-sow and move the seedlings while they are small. Showy evening primrose is different: it spreads underground and forms new crowns, each with its own roots, which can be lifted and replanted.
| Kind | Best method | Notes |
|---|---|---|
| Showy evening primrose (O. speciosa) | Division | Spreads by running roots; divides readily |
| O. tetraptera, O. stricta, O. rosea | Seed | Often self-sow in gravel |
| O. glazioviana | Seed | Dies after flowering; always keep seedlings coming |
| Sundrops, Missouri evening primrose | Seed | Taprooted; do not divide old plants |
| O. acaulis, O. caespitosa | Seed | Raise in gritty alpine mix |
Saving seed
After flowering, each bloom leaves a narrow capsule on the stem. Let the capsules ripen on the plant until they turn brown and dry and begin to split at the tip in autumn. Cut the stems into a paper bag, let them finish drying indoors for a week, then shake or crush the capsules to release the small seeds.
Sift out the chaff, put the clean seed in a labeled paper envelope, seal that inside a jar, and store it in the refrigerator until you sow in late winter or early spring. Seed from species comes true; seed from plants growing near other kinds may be a little variable, which is part of the fun.
Dividing showy evening primrose
Divide in early spring as new growth appears, or in early autumn once the heat has passed. Because the plant runs, you are really lifting well-rooted pieces from the edge of the patch rather than splitting a single crown.
- Lift a section Push a spade in around a young crown at the edge of the clump and lift it with a good ball of soil and plenty of running roots.
- Trim and separate Pull or cut the section into pieces, each with at least one shoot and a length of healthy root. Discard old, woody center pieces.
- Replant straight away Set the pieces at the same depth in sunny, free-draining soil, 12 in (30 cm) apart, firm them in and water once. Keep them just moist until new growth shows.
Letting evening primroses self-sow is the easiest propagation of all. Leave a few seed capsules in autumn, and in spring move any seedlings you want while they still have only a few leaves.