Wettability of Fresh and Aged Pine Bark Substrates from Different Sources

Bark has been an important component in horticultural substrates for years (and is rapidly increasing in greenhouse professional mixes and in retail potting soil mixes), and in the nursery industry bark is the most common substrate component used in the United States. Bark is obtained as a byproduct of the timber industry (pulp mills, saw mills, pole peeling operations, etc.) when it is striped off logs after harvest. The objective of this work was to determine the wettability and initial hydration of pine bark substrates from different suppliers. Aged pine bark substrates (duration of aging varied among the suppliers) from four sources/suppliers were used to conduct and compare wettability. They were compared at two different moisture contents (MC; 50% and 25%) and two different levels of wetting agent (none and standard rate according to label). Each pine bark was tested as follows: 1) 50% MC with no wetting agent; 2) 50% MC with standard wetting agent; 3) 25% moisture content with no wetting agent; and 4) 25% moisture content with standard wetting agent. Each pine bark was wet up or air-dried to obtain the desired testing moisture content before wettability was tested. Results varied across each source. Source 1 reached container capacity with the first hydration event at 50% MC regardless of the presence of wetting agent. At 25% MC, container capacity was never reached, also regardless of the presence of wetting agent. Source 2 reached container capacity with the first hydration event at 50% MC regardless of the presence of wetting agent. At 25 % MC, it took 5 hydration events to reach container capacity without the addition of wetting agent. With wetting agent, it took 4 hydration events at 25% moisture. Source 3 took 2 hydration events without wetting agent and 1 event with wetting agent to reach container capacity at 50% moisture. At 25% moisture, it took 7 hydration events without wetting agent and 4 hydration events with wetting agent to achieve container capacity. Source 4 took 3 hydration events without wetting agent and 1 hydration event with wetting agent to reach container capacity at 50% moisture. Container capacity was never reached, regardless of the presence of wetting agent, at 25% moisture. Difference among suppliers is likely due to differences in aging practices and timing.  Differences in bark processing and handling also are likely reasons for the variability in wettability.