Some stocks are grown as annuals (the "Ten-week Stocks"). These varieties are sown in spring (generally from March onwards in colder areas, earlier in regions with mild winters). They give a good summer flower display. Other varieties take longer to develop and are treated as biennials. These are often referred to as "Brompton stocks". In cool temperate regions they are generally sown in summer to flower in the following spring. The extra trouble of overwintering the plants is compensated for by the showy spring floral display. In hard winters there may be some mortality and a well-drained sheltered site suits them best. Intermediate varieties (sometimes called "East Lothian" stocks as they originated in southern Scotland) may be treated either as annuals or biennials. If treated as annuals they give a fine late summer and autumn display.
Double-flowered stocks are prized by gardeners for their floral display but are sterile. They therefore have to be produced from the seed of single-flowered plants. The double-flowered form is caused by a recessive gene variant (allele) in the homozygous condition. Therefore, according to the Mendelian laws of genetics, heterozygous single-flowered stocks should produce [ "throw" ] one quarter doubles in their offspring and one third of the singles should be pure breeding singles incapable of throwing doubles. Selection over the centuries has greatly improved these ratios, resulting in the so-called "ever-sporting" stocks, in which pure-breeding singles are absent and the proportion of doubles is one half or greater.
This post is part of the Floral Friday Fotos meme.