Crop Growth and Development for Irrigated Chile (Capsicum annuum)

New Mexico Chile Association: Report 32
Jeffrey C. Silvertooth, Paul W. Brown, and Stephanie Walker
College of Agricultural, Consumer and Environmental Science, New Mexico State University

Authors: Respectively: Professor/Department Head and Extension Specialist, Department of Soil, Water and Environmental Science, University of Arizona; and Extension Vegetable Specialist, Department of Extension Plant Sciences, New Mexico State University

Crop Phenology

Plants vary tremendously in their physiological behavior over the course of their life cycles. As plants change physiologically and morphologically through their various stages of growth, water and nutritional requirements will change considerably as well. Efficient management of a crop requires an understanding of the relationship between morphological and physiological changes that are taking place and the corresponding input requirements.

Heat units (HUs) can be used as a management tool for more efficient timing of irrigation and nutrient inputs to a crop. The thermal environment affects the development of all crop systems, including chiles (Capsicum annuum). Plants will develop over a range of temperatures, which is defined by the lower and upper temperature thresholds for growth (Figure 1). Heat unit systems take into account the elapsed time that local temperatures fall within the set upper and lower temperature thresholds, and thereby provide an estimate of the expected rate of development for the crop. Heat unit systems have largely replaced days after planting in crop phenology models because they take into account day-to-day fluctuations in temperature. Phenology models describe how crop growth and development are affected by weather and climate and provide an effective way to standardize crop growth and development among different years and across many locations (Baskerville and Emin, 1969; Brown, 1989).

Graph of the typical relationship between the rate of plant growth and development and temperature.

Figure 1. Typical relationship between the rate of plant growth and development and temperature. Growth and development cease when temperatures decline below the lower temperature threshold (A) or increase above the upper temperature threshold (C). Growth and development increase rapidly when temperatures fall between the lower and upper temperature thresholds (B).

The first step in developing a phenological guideline for chiles is to look for critical stages of growth in relation to HU accumulation. Figure 2 describes the basic phenological baseline for New Mexico-type chile, which was developed from field studies conducted in New Mexico and Arizona between 2003 and 2010. Use of HUs to predict chile development is considered superior to using days after planting due to the simple fact that the crop responds to environmental conditions and not calendar days. This approach, using phenological timelines or baselines, works best for irrigated conditions where crop vigor and environmental growth conditions are more consistent than in non-irrigated or dryland situations where irregularity in year-to-year rainfall patterns can alter growth and development patterns significantly.

Graph of basic phenological guideline for irrigated New Mexico-type chiles.

Figure 2. Basic phenological guideline for irrigated New Mexico-type chiles.

Phenological guidelines can be used to identify or predict important stages of crop development that affect physiological requirements. For example, a phenological guideline can help identify stages of growth in relation to crop water use (consumptive use) and nutrient uptake patterns. This information allows growers to improve the timing of water and nutrient inputs to improve production efficiency. For some crops or production situations, HU-based phenological guidelines can be used to project critical dates such as harvest or crop termination. Many other applications related to crop management (e.g., pest management) can be derived from a better understanding of crop growth and development patterns.


Baskerville, G.L., and P. Emin. 1969. Rapid estimation of heat accumulation from maximum and minimum temperatures. Ecology, 50, 514-517.

Brown, P.W. 1989. Heat units [Bull. 8915]. Tucson: University of Arizona Cooperative Extension.

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December 2011