Growth and foliar nutrition of Spiraea alba Du Roi and Spiraea tomentosa L. in response to root zone pH

- Three accessions of Spiraea alba and two accessions of Spiraea tomentosa were assessed for growth, appearance, and foliar nutrient concentrations when produced at different media pH.
- Media pH requirements is reflective of the native environment of the accessions: media pH of 7 resulted in chlorosis and reduced growth.
- Chlorosis was correlated only with leaf Ca:Mg ratios and not any other individual nutrients commonly calculated ratios of nutrients.
- There were no differences among accessions in growth response or chlorosis related to media pH.

Spiraea alba and Spiraea tomentosa are native to the eastern and northern U.S. with potential for wider use in urban landscapes. Both grow in acidic soils in their native habitats. To determine their pH requirements in container media, three seed sources of S. alba and two of S. tomentosa were planted in media adjusted to pH 5, 6 and 7. Biomass and leaf greenness were reduced at pH 7 in all seed sources. Foliar P and Ca were higher and Mg and Al lower in plants grown in pH 6 and 7. Foliar Mn was not affected by media pH and Fe decreased with increasing pH only in S. alba. Shoot dry weight was correlated with high foliar N and low Zn and chlorosis was correlated with an increased Ca:Mg ratio. Growth of both species was best in media with a pH of 5 or 6, similar to their native habitats.