Crops Pot marigold (Calendula officinalis)

Young plant

Plants are normally of annual habit, developing a strong taproot. The vegetative parts are mid-green in colour, the stems being succulent and angular, and covered in fine hairs; the lower leaves are paddle- shaped, the upper leaves being smaller and more pointed. Plants branch very freely, and will grow extensively if there is sufficient space: some types tend to straggle, while others are more erect, attaining up to 70 cm in height.

Plants in flower (single)

The composite flowers are borne singly on the stems and may be up to 10 cm across, the colour of the ray florets varying between light yellow and deep orange; some varieties have dark-centred flowers, both single and double forms being common.

Unripe seedheads

Ripe seedheads

When the heads are ripe, the seeds become grey or light brown in colour; the seeds vary in shape, decreasing in size towards the centre of the head. Marigolds thrive best in open, sunny situations and on light, easily warmed soils.

Seeds

For oilseed production it is suggested that a seedrate of about 6 kg per ha is used, sowing in 25 cm rows, to establish a population of 50-60 plants per square metre; sowing is probably best during early spring. No more than 50 kg per ha of nitrogen fertiliser is necessary, together with maintenance dressings of phosphate and potash. Weed control is very important, both to encourage a vigorous establishment and to reduce harvesting difficulties, and several herbicides have been suggested as being suitable. Research suggests that desiccation prior to combining may result in lower seed losses than windrowing; seed yields in excess of 2 t per ha have been achieved. Research and development work is continuing, particularly in the United Kingdom, the Netherlands, Germany and Spain, both in the agronomy of the crop and the technical handling of the oil. Breeding work also continues, particularly directed towards improving seed yield and 8 uniformity of maturity; the first varieties intended specifically for oilseed production have just been listed in Germany.