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Every Oenothera needs full sun, meaning at least six hours of direct light and ideally a whole day of it. They do not tolerate shade. In even partial shade the stems stretch, flop and produce few buds, and the night-blooming kinds may barely open at all.
Choose the hottest, brightest spot you have: a south-facing bed, a gravel garden, the edge of a driveway or a rock garden. These are plants of prairies, dunes and dry slopes, and they are at their best where many other flowers struggle.
Soil and drainage
Drainage is the other half of success. A taprooted plant sitting in cold, wet soil rots at the crown, especially in winter. Raise the bed a few inches above the surrounding ground, or plant on a slope or mound, so water runs away from the crown.
On clay, dig in plenty of coarse grit or small gravel, not just compost, to open the soil. Sandy and stony soils suit them as they are. Lean soil is fine; in fact it keeps the plants compact and flowering.
- In the ground Loosen the soil deeply so the taproot can go straight down, work in grit on heavy ground, and plant with the crown level with or slightly above the soil.
- In containers Use a deep pot with good drainage holes and a potting mix cut with about a third grit or perlite. Deep pots matter more than wide ones for a taproot.
- For the tiny alpine kinds O. acaulis and O. caespitosa want a gritty alpine mix, a collar of gravel around the neck of the plant, and ideally shelter from winter rain.
Watering and feeding
In pots, water when the surface of the mix has dried out, then soak it and let it drain. In the ground, established plants usually need no watering at all; their taproots find moisture deep down. Water only during long dry spells, and then deeply rather than little and often.
Feed sparingly. Too much fertilizer, especially nitrogen, gives you a mass of soft leafy growth, weak stems and fewer flowers. Plants in the ground need none. Container plants can have a light dose of a balanced slow-release fertilizer in spring and nothing more.
| Where | Water | Fertilizer |
|---|---|---|
| In the ground | Only in prolonged dry weather | None |
| In containers | When the surface dries, then thoroughly | A light slow-release dose in spring |
| Alpine kinds in troughs | Sparingly; keep dry in winter | None |
Staking, tidying and winter
Tall kinds such as O. stricta (1 to 3 ft, 30 to 90 cm) and the large-flowered O. glazioviana (3 to 5 ft, 90 to 150 cm) can lean or topple in wind and rain. Put in a stake or a ring of twiggy supports early in spring, before the flower stems lengthen. The low, spreading kinds need no support.
Most evening primroses are hardy and need only light protection in cold, exposed spots: a loose layer of evergreen boughs or a little straw over the crown during the coldest weather. Remove it in spring. Wet is a bigger threat than cold, so never smother the crowns with heavy, soggy mulch.
Showy evening primrose spreads by running roots and can take over a small bed in rich soil. Grow it where it can roam, edge it firmly, or keep it in a container.