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Four o'clocks (Mirabilis jalapa), sometimes called 'pretty-by-nights', are named after their tendency to open only in the late afternoon or on cloudy days. Cool temperatures cause the flowers to open when their insect pollinators are most active. The plants can grow to around one metre high and are shrub-like.
Each plant may have hundreds of two-inch, trumpet-shaped blossoms that will last throughout the summer until the first frost. Even on a single plant, these blossoms may be pink, yellow, white, salmon, red, or striped or blotted with any of these colours. Because of their variety of shades, though, they are hard to co-ordinate with other garden flowers and are best used as bedding, border, background, or in containers.
Perhaps the best thing about four o'clocks is that it often says 'Easy to Grow' on the seed package. Seed packets and young plants should be available at any greenhouse or garden centre.
Four o'clocks are drought resistant and can be grown in almost any soil. They can survive in fumes, dust, and smoke and will even do fairly well in high wind or direct sunlight. To get superior plants, one must really only provide enough water.
They are a warm-season annual, meaning they will usually live for only one year; however, they can produce tuberous roots that lie dormant through the winter and make them act like perennials.
After becoming established, in fact, four o'clocks can be extremely difficult to remove. Their durability and tuberous roots make them last even after being 'weeded'.
Four o'clock seeds are hardy and can self-sow even after being simply scattered onto wet soil. Most gardeners recommend soaking the seeds for a day before planting, and others have had success with 'nibbling'1 the seeds with fingernail clippers. Seeds should be planted a half-inch deep and kept well watered and in full Sun. The first seedlings should sprout after 12 days or so at an optimal temperature of around 75° Fahrenheit.
If started early enough indoors they can be transplanted at four to six weeks and should be spaced about a foot apart. Transplanting should be done after the danger of frost has passed and after the plants have become accustomed to outdoor conditions.
Because of their hardy nature, four o'clocks can be found and grown almost anywhere. The genus Mirabilis contains 350 species in 34 classifications. Other members of the family are used in the Orient and South America in medicines, cosmetics, and dyes. The cultivated four o'clocks were transported from Peru to Spain in the 16th Century.
Wild four o'clocks (Mirabilis nyctaginea), however, were originally native to the Dakota Prairie, but spread quickly, especially after their 1792 discovery by French botanist Andre Michaux.
Their fragrant flowers attract butterflies and birds and are, oddly enough, deer repellant. The seeds of the four o'clock resemble pepper grains and are extremely poisonous2; they can cause vomiting and diarrhea and, in large quantities, death.