Crops Field scabious (Knautia arvensis)

Young plant

Field scabious is a perennial, developing a deeply-penetrating taproot, with lateral roots at some depth.

Well grown plant

Plants may tiller profusely, and well established scabious plants may form clumps of up to 50 cm diameter. The earliest-formed rosette leaves are of a pointed oval shape, with a prominent midrib: later leaves are notched, the notching becoming more pronounced in successive leaves, the stem leaves often being reduced to strap-like structures with little tissue around the midrib. The stems are thin, tough and lightly ridged, often attaining 1 m in height.

Fully open flower

The hemispherical flowers are usually in shades of pale lilac or light blue, occasionally pink or white: the earliest flowers are formed at the outer ends of the main stems, being succeeded by later flowers on branch and secondary stems.

Unripe seedhead

Seeds

The seeds are exposed, and change colour through light green and yellow to tan, falling to the ground when ripe. Established scabious plants are drought-resistant and are found naturally in open, sunny situations. Though it is by nature a perennial, scabious will flower and produce seed if grown as an annual, either autumn or spring sown. Few guidelines for the culture of this species may yet be given with assurance; it is suggested that 40 plants per square metre may be a suitable plant density for annual crops, but much lower populations should be adequate for sowings which are to be retained as perennials. As with many perennial species, establishment and early growth are slow, so weed control is of great importance. Trials with some linuron products, applied pre-emergence, have shown these to be effective without any apparent toxicity to the crop. Well-established perennial crops should suppress weeds effectively The nutritional needs of the crop have not yet been examined, but fertiliser requirements are not expected to be high. The long flowering period, which may extend for several months, together with the exposed seed-beds, makes the timing of harvest very difficult: so far, a succession of harvests has been taken in order to assess yield potential. Recorded yields to date have been disappointing, values of up to 0.35 t seed per ha for annual crops and 0.7 t per ha for perennial ones, though all these measurements are from plots in which the established populations were considered to be substantially sub-optimal. Much work will be required if this species is to become a useful oilseed crop, particularly with regard to crop establishment and harvesting. Results so far suggest that the best method of culture may be to sow in spring a crop which is intended to remain in the ground for some years; once established, crops should require little maintenance. It may prove possible to shorten the flowering and harvesting seasons by the use of plant growth regulators, or, in the longer term, by breeding: observation of wild plants suggests that there is considerable variability in earliness and length of flowering season.