Cardoon is a member of the daisy family (Compositae) along with sunflower and artichoke. It is a perennial plant originating from the Mediterranean region but has naturalized to parts of Central and South America, and California. Plants are deep rooting and can reach a height of 2m. It’s natural cycle is for the plant to sprout in the autumn, pass the winter as a rosette of leaves and then rapidly grows into a tall bushy plant in the spring which dries and dies in the summer leaving the deep root alive ready to re-sprout.

Agronomy

Cardoon thrives in a light, deep limy soil where subsoil retains water throughout the summer. Biomass production is significantly reduced if precipitation levels dip below 400mm/y. Once the seeds are sown, enough time must pass to allow the plant to develop four basal leaves (1-2 months in Mediterranean regions). At this stage the young plant can tolerate temperature as low as -5oC. A spring sowing after the last frost is recommended for areas that experience early autumn frost. Frost damage is identified as tears in the leaves, but if the root is established the plant will remain alive and will recover post-frost.

Ground should be prepared to a fine tilth free of weeds with an even surface and adequate nutrient balance. Fertiliser should be added to address any inadequacy in soil fertility. Seeds are large (8x4mm) and should be sown into a damp soil with a pneumatic seed drill in lines 1m apart. 3 -4 kilograms of seed should be sown per acre, producing approximately 10,000 plants/ha given adequate water supply. Cardoon requires a considerable amount of nutrients in comparison to other biomass crops. Gonzalez (1998) estimates that for a 20 t/ha/y harvest, the replacement nutrient levels are 277kg/ha of N, 56kg/ha P and 352kg/ha K.

Wide spacing of lines and high nutrient levels make weed competition a problem for establishing plants. Herbicides (trifluralin, alachlor, linuron) can be used to combat this, however, widely separated lines allow weeds to be controlled with a cultivator until the leaf rosettes out compete weeds for light. In subsequent years, once roots are established the plants will immediately dominate weeds.

In Mediterranean regions the capitulum (flowering heads) are often harvested separately from leaves stems and branches with a combine harvester. The seeds comprise approximately 13% of the total biomass of the whole plant and are rich in valuable oils. Commercial production of mature seed in cooler climates is probably not a viable option for cardoon growers, however, all of the plant can be considered as biomass and can be harvested in late summer with a swath mower and baler before the new autumn growth appears. Moisture content at harvest is very low at between 10-15% and yields in Mediterranean regions are around 20-30 t/ha/yr dry matter. This material can be combusted to produce electricity and heat and has a heating value of 16.7MJ/kg.

Cardoon in its native regions does have a variety of pests including aphids, stem and leaf borers and miners, cutworms, flies and moths. These can be treated with insecticides and biological controls although they do not appear to be a problem as yet in the UK.

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González, J.F. (1998) Cardoon (Cynara cardunculus L.). In: El Bassam, N. (ed) Energy Plant species: their use and impact on environment and development. James and James Ltd. London, UK.