Response of ornamental Eucalyptus from acidic and alkaline habitats to potting medium pH

Seedlings of 35 Eucalyptus species were grown in a peat-based growing mediu m amended with limestone and dolomite (1:1) to provide an experimental pH r ange of 5.1-8.9. The species were largely of the multi-stemmed (mallee) gro wth habit, relatively new to commercial cultivation, and known to occur nat urally on alkaline, neutral or acidic soils. Growth was generally greater u nder acidic (pH 5.1-5.6) than under more alkaline conditions in all species , regardless of natural soil occurrence of the parent trees. Above pH 5.6, species showed a range in the degree of response to pH. from those that wer e unaffected even at pH 8.9 (e.g. E. erythrocorys and E. extensa), to those for which growth was reduced at pH 6.8. There was generally good correspon dence between pH response and the pH of the soil in which parent plants occ urred naturally, i.e. accessions from trees growing on alkaline soils tende d to exhibit less growth reduction at high pH. Leaf elemental analyses of s elected species indicated that tolerance of high pH was associated with an ability to maintain relatively low Ca/Mg and P/Fe concentration ratios (<<s imilar to>5). Eucalyptus species from alkaline as well as acidic soils can be best grown in the nursery at a pH in the range 5.1-5.6. (C) 2001 Elsevie r Science B.V. All rights reserved.