Optimizing Glycerin-to-water Ratios for Preserving Eucalyptus Foliage

Fresh eucalyptus stems can be preserved via systemic absorption of glycerin, but the optimal rate of glycerin and its effect on foliage color and stem pliability during holding have not been well-described. We harvested stems of Eucalyptus pulverulenta ‘Baby Blue’ and treated them in solutions of 0% (control), 25%, 50%, and 75% glycerin:reverse-osmosis water for 2 weeks. Leaf greenness was measured nine times during this period; the change in stem weights and solution uptake were measured as well. Stem pliability was evaluated after 2 weeks in solution as well as 1 week after holding the stems dry. The 25% and 50% glycerin treatments increased stem weight, whereas the control and 75% treatments decreased stem weight. The glycerin treatments absorbed less than 50 mL solution per three stems during 2 weeks, whereas those in the control absorbed >270 mL water. The color of foliage was similar during the first 5 days in treatment solutions, but stems in 25% and 50% glycerin treatments were less green than those in the control and 75% treatments by day 6, and this trend continued. No difference occurred in stem pliability among treatments after 2 weeks in glycerin solutions; however, after 1 week of holding, the top 9 cm of stems in glycerin treatments were more pliable than those in the control. Based on these results, we recommend a rate of 25% glycerin to preserve eucalyptus foliage for use in botanical artistry.