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Oenothera is a genus of taprooted plants. A young evening primrose sends one thick root straight down, and once that root is established the plant sulks or dies if you dig it up and move it. That is why nurseries sell few of them in large pots and why most gardeners start them from seed: a seedling moved early, before the taproot has gone deep, settles in without complaint.
The exception is showy evening primrose (Oenothera speciosa), which spreads by running roots and is easier to divide than to sow. Every other kind in this guide is best raised from seed, and many will also seed themselves around a sunny, gravelly bed once you have them.
| Kind | Usual start | First flowers |
|---|---|---|
| O. tetraptera, O. stricta, O. rosea | Seed in late winter to early spring | Often late in the first summer, fully the second year |
| O. glazioviana (large-flowered) | Seed in late winter to early spring | Second year; the plant dies after setting seed |
| O. acaulis, O. caespitosa | Seed, raised in gritty mix | Second year |
| Sundrops (O. perennis), Missouri evening primrose (O. macrocarpa) | Seed | Second year |
| Showy evening primrose (O. speciosa) | Division, or seed | Divisions flower the same year |
When to sow and how to store seed
Collect ripe capsules in autumn when they turn brown and start to split at the tip. Shake the fine seed onto paper, let it dry for a few days, then seal it in a labeled envelope inside a jar and keep it in the refrigerator over winter. Cold storage keeps it lively and mimics the winter it would get outdoors.
Sow from late winter to early spring, indoors or in a cold frame, when daytime temperatures are around 60 to 70°F (15 to 21°C). The seed germinates readily and usually shows within two to three weeks. Sow thinly on the surface of a fine, free-draining seed mix and press it in lightly; the seed is small and needs only a dusting of grit or vermiculite over it.
Moving seedlings on without hurting the root
Timing matters more here than with most flowers. Move seedlings out of the tray as soon as they have one or two true leaves, while the taproot is still short. Wait longer and the root will already be heading for the bottom of the tray, where it snaps when you lift it.
- Lift from below Loosen the seed mix with a pencil or plant label pushed in beside the seedling, and ease it up with the whole root attached. Hold it by a leaf, never the stem.
- Pot into deep cells Use deep plug cells or 3 in (7.5 cm) pots filled with a gritty potting mix. Drop the root straight down into a hole made with the pencil, so it is not bent.
- Pot up two or three times Each time the roots reach the drainage holes, slide the whole root ball, undisturbed, into a pot one size larger. Two or three moves bring the plant to a size that can go out.
- Plant out as a whole root ball Harden plants off for a week, then plant them in their final spot without teasing the roots. Firm them in and water once to settle the soil.
Sowing direct
Where you want a drift of evening primroses and have a sunny, well-drained patch, you can skip the pots altogether. Scatter the seed in early spring on raked soil, barely cover it, and thin the seedlings to 8 to 12 in (20 to 30 cm) apart. Plants that never get moved grow the strongest taproots and are the most drought tolerant later.
Most kinds make a flat rosette of leaves in their first year and flower in their second. A few, such as O. tetraptera, often give some flowers late in the first summer from an early sowing.