Yarrow is an herbaceous perennial that is highly recommended for landscape gardens in many parts of the United States. However, performance data of yarrow produced under limited irrigation conditions is lacking. During 2004 and 2005, we studied the growth and physiology of yarrow (Achillea ‘Moonshine’) maintained as well irrigated controls or irrigated when there was a 30 or 60% depletion of moisture in the growing substrate. Plants irrigated at the 60% moisture level had the lowest predawn water potential, stomatal conductance and transpiration rate. Cell osmotic potential and relative water content data suggest that yarrow might be able to withstand prolonged exposure to drought. In 2005, net assimilation rate of well irrigated plants (0.317 mg/cm2/d) was almost twice as high (0.179 mg/cm2/d) as that of plants maintained at the 60% moisture level. This suggests that a 60% moisture depletion level had a very significant impact on carbon assimilation. In 2005, leaf area of plants irrigated at the 30% moisture depletion level showed only a 15% decline compared to well irrigated plants, while those irrigated at the 60% moisture depletion level showed a 47% decline in leaf area.

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Author notes

Contribution of the New Mexico Agricultural Experiment Station, New Mexico State University, Las Cruces and the Higher Education Commission of Pakistan, Islamabad.

2Former Post Doctoral Research Fellow; currently Professor, Department of Agronomy, NWFP Agricultural University, Peshawar, Pakistan.

3Corresponding author. <rsthilai@nmsu.edu>.

4Regents Professor.

5Professor.