Answer: Foliage with a reddish tint can indicate a lack of phosphorus in the soil, a reaction to a cold snap, or water stress (too much or too little). Oenothera cultivars can be perennial or biennial. If you've had your plants over three years, they are the perennial type and they might come back; if they are on their second year in your garden, they could be the biennial type, which will flower, set seed and then die.
Best wishes with your evening primroses!
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