Production of Biennial Caraway for Seed and Essential Oil

Growing areas

Caraway (Carum carvi L.) occurs as wild plant within phytocoenoses of meadow type, usually in a humid coastal or mountain climate (). Such ecological conditions should be taken into account in the choice of region for caraway cultivation, and also to a certain degree, in the choice of soil type and a sequence in crop rotation. In Europe, where this species has been widely grown for over 200 years, caraway was and usually still is produced in coastal regions of the Netherlands, Germany and Poland as well as in a piedmont of the Czech Republic and Slovakia.

The second factor that must be considered in caraway cultivation is the character of its development, since it could be either biennial or facultatively perennial crop with a distinct juvenile phase (). Besides, there are some caraway properties typical of a wild plant, that favour its adaptation for the development in natural sites, having however a negative effect on its cultivation. Elimination of such traits is difficult, particularly in relation to non-uniform seed germination, uneven fruit ripening on plants and shattering.

Caraway: Soil requirements, sequence in crop rotation and fertilization

Caraway: Soil preparation, setting up of a plantation

Maintenance and care of plantation

Appropriate timing and adequate quality of agricultural practices are particularly important for caraway, considering its as a biennial crop and also, as mentioned before, cultivation often combined with other crops. Such measures include loosening (aeration) of soil, weed control, thinning of cover plants and disposal of their post-harvest residues and, if necessary, thinning of caraway and ridging.

Seedlings emerge usually after 2 weeks and, like in other umbelliferous plants, their initial growth is slow. At that time the young plants are particularly sensitive to shading, and also to insufficient aeration and moisture of the soil. Such negative effects can be reduced through soil loosening as well as by chemical and mechanical weed control. The latter measure clearly differs from the loosening of the soil by the depth of penetration. Whereas weeding is shallow, to prevent the lifting of weed seeds from lower soil layers, the loosening is deeper, even down to 10 cm. Frequency of such practices depends on the soil and weather conditions, and differs for the first and second growing season.

Herbicides are commonly used in caraway cultivation, as it is relatively resistant to these chemicals (). Since new products are being constantly introduced, selection of herbicides suitable for caraway also changes.

A plantation should be free of weeds during the first year in particular. In a pure crop herbicides can be then applied three times: first directly after sowing (linuron, prometryne, metobromuron), next at the stage of 2–3 leaves (linuron, metolachlor) and the final treatment for the first year in late autumn, before the soil gets frozen (propyzamide). In the second season, herbicides may be applied at the beginning of caraway vegetation. In both years monocotyledon weeds can be eliminated with the use of graminicides, regardless of the developmental phase of caraway plants (fluazifop-P-butyl). Chemical weed control in mixed cultivation with coriander follows the rules of herbicidal treatments in a pure crop. When caraway is grown together with flax or pea, Afalon provides good results (). On the case of other cover plants, chemical weed control may begin in autumn of the first year and should follow the principles related to a pure crop.

While caraway is grown together with poppy, the thinning of this cover plant is very essential and should be performed as soon as possible. In late summer and autumn of the first growing season there is the most intensive gain in plant matter, therefore cultivation practices in that period are of a major importance. In mixed crops, post-harvest residues of cover plants should be instantly removed and weeds eliminated. In the case of high stubble (e.g. seed-coriander) such residues can be mechanically finely chopped and left in the field.

Another important measure is harrowing, carefully performed across or askew to caraway rows. Apart of loosening the soil, harrowing is a method for thinning the plants, especially if they are too dense. This procedure frequendy combined with the use of N-fertilizers applied as top dressing, followed by mechanical loosening of inter-rows. Towards the end of the first year, shortly before the soil gets frozen, shallow ridging is often performed to prevent caraway plants from freezing-up during severe snowies s winters, and also from damage caused by hares.

In spring of the second growing season, cultivation practices should be conducted as soon as possible. They mainly include loosening of inter-rows and weed control. Also, harrowing across caraway rows is often carried out at the same time. All these procedures are usually combined with mineral fertilization. If the plantation is intended for the third year, all post-harvest practices are analogue to those recommended for the first growing season, including mineral fertilization.

 

Harvesting, drying, storage

In Europe, caraway is harvested in the period from late June to mid-July. Appropriate time is particularly important, considering non-uniform maturation of umbels and the fruits highly susceptible to shattering. It appears from long-time observations that caraway harvest begin when in most plants the fruits of the main and top lateral umbels change colour from green to brown. A delay brings inevitable losses due to shattering of the most valuable fruits. On the other hand, if the harvest is advanced a lot of fruits will not ripen, being of a lower quality for sowing and row material.

A two-stage harvest brings the best results. Cutting with the use of a mower, reaper or a binder should be performed early morning (with dew) or on a cloudy day. Cut plants should be left in swaths or sheaves for a few (up to 10) days, before they are threshed. This short period from cutting to threshing is very essential, since then the fruits become finally formed and coloured. Warm weather favours this process, however too intensive insolation is unwanted. Observations by the author of the present paper revealed a rather peculiar, positive relation between rainfall over that period and the quality of raw material, expressed by a more uniform, light-brown colour of the fruits and their distinctly smaller contamination with caraway carpophores and with weed seeds. A combine harvester operating in the field is the best method for caraway threshing. Often, such harvesters are specially adapted for this crop (). Threshers are also used, however, transport of dry plants from the field usually increases yield losses. After threshing and mechanical cleaning, the fruits should be redried down to 10–12% moisture content. Then, for some time the fruits should be kept loose in a thin layer, being frequently mixed, within a dry and aerated storeroom to finally establish their moisture content. Such prepared raw material is packed into sacks and, if inadequately stored, it can go musty and mouldy, thus becoming useless as raw material.

Caraway yields widely fluctuate, reaching 1–3 t/ha. In mixed cultivation with cover crops, likewise on a plantation left for the third year, the yields obtained may be 15–30% lower ().

Caraway: Pests, Diseases and Their Control

 

Selections from the book: “Caraway. The Genus Carum”. Edited by Éva Németh. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 1998.