This section is from the book "Commercial Gardening Vol2", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The plants may be had in blossom at almost every season of the year, and seeds are sown at different times to keep up a succession. There are, however, two principal sowings - early in August and early in March. The soil used is light gritty loam enriched with well-rotted manure and a little; mortar rubble or, better still, a sprinkling of basic slag. - The seeds are sown thinly in 5-in. (48's) or 6-in. (32's) pots, and when the young plants are large enough to handle easily they are thinned out, leaving about half a dozen in each pot. They are kept in frames or greenhouses, and given plenty of air and light to induce sturdy growth. Cool treatment is best, as the plants are not then inclined to go blind, but will come into blossom in February and March. Too moist an atmosphere must be guarded against; otherwise many of the plants are likely to damp off during the winter. Besides thinning out, the young plants may also have the tips of the main shoot pinched out to induce a more bushy habit and several columnar spikes of bloom. Some growers allow only one plant to a pot, pegging down the stems to secure several growths. Weak liquid manure may be given when the plants are coming into blossom, as this helps to make foliage deeper in colour and the flower spikes larger. Mignonette raised from seed sown in spring may be treated in the same way, but will come into flower more quickly than the autumn-raised plants. When packing for market, two or three small sticks are inserted round the edge of the pots, and a piece of raffia is tied round to keep up the shoots.
Over twenty varieties of Mignonette are known, but the "Machet" strains may be, regarded as the most generally useful.