Production of blue hydrangea flowers without aluminum drenches
1997
Handreck, K.A.
Hydrangea 'R.F. Felton' plants were grown to flowering in a soilless potting medium that had been amended with aluminum nitrate [Al(NO(3))(3).9 H2O], Kaolite (a calcined clay mineral, of which about 70% is amorphous cristobalite, tridymite, and mullite), or an aluminum (Al)-rich water clarification sludge, or left unamended. Inclusion of 10% Kaolite (v/v) in the medium led to a marked increase in the Al content of the flowers and a corresponding increase in their blueness. Flower phosphorus (P) content was negatively correlated with blue color. High calcium (Ca) and potassium (K) contents of the flowers also contributed to blueness. High concentrations of manganese (Mn) had a small negative effect on blueness. Media that produced blue flowers had pH values of less than 4.9. DTPA extracts (2 mM; 1:1.5 v/v) of these low-pH media contained at least 12 mg Al L-1 at potting, rising to about 21 mg Al L-1 at harvest.
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