ARS | Publication request: Planting depth for oilseed calendula

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 14, 2012
Publication Date: January 1, 2013
Citation: Joly, R., Forcella, F., Peterson, D.H., Eklund, J.J. 2013. Planting depth for oilseed calendula. Industrial Crops and Products. 42:133-136.

Interpretive Summary: Calendula (aka, pot marigold) is not only a popular ornamental plant in northern states, but also a potential oilseed crop. Its seeds contain a drying oil that has important industrial applications. The properties of the oil are similar to those of tung oil and better than those of linseed oil. Thus, a ready market for calendula seed oil is expected. Unfortunately, very little agronomic information is available for calendula, and what does exist is limited to northern Europe, or it deals with ornamental plants rather than agronomic crop types. Therefore, our objective was to examine planting depth and seedling dynamics of the variety known as "Carola," which is one of the few commercial oilseed varieties available. The experiments were conducted for two years, 2010 and 2011, near Morris, Minnesota. Seedlings emerged better when seeds were planted at depths of 1/3 and 2/3 inches than at 1 1/3 or 2 1/3 inches. Half of all seedlings emerged when growing degree days (GDD) in the soil reached 160 GDD, which was approximately 7 days after planting. However, GDD was a better predictor of emergence than calendar days. The results lead to the following recommendations and advice for specialty oilseed companies and growers in northern states: (1) calendula seeds should be planted shallowly (1/3 inch) in early spring, (2) 160 GDD should be expected for emergence to occur, and (3) because shallow soil depths dry easily, delayed emergence of seedlings can be anticipated if rainfall is minimal during the first 7 days after planting.

Technical Abstract: Calendula (Calendula officinalis L.) is not only a popular ornamental plant in temperate climates, but also a potential oilseed crop. Its seed oil has high levels of calendic acid, which makes it a highly valued drying oil with important industrial applications. Much basic agronomic information on calendula is not readily available, is limited in geographic scope, or pertains primarily to ornamental varieties. Consequently, our objective was to investigate planting depth and seedling dynamics of "Carola," one of the few commercial oilseed varieties available. More seedlings emerged from planting depths of 1 and 2 cm than from 4 or 6 cm. Regardless of planting depth, time to 50% emergence was associated with less variability when estimated by hydrothermal time (HTT, 89 deg C d, CV=14) than calendar days (7 d, CV=39) after planting. HTT was calculated best with a base temperature of 5.5 deg C and a base water potential of -2900 kPa. Although shallow planting is necessary, soils at these depths can dry rapidly, which results in slow HTT accumulation, and delayed emergence of seedlings.