Evaluation of potting media for commercial nursery production of container‐grown plants

A range of peat‐based container media was prepared by additions (0, 25, 50, 75, 100%) of a New Zealand commercial nursery amendment (sand, perlite, pumice, sawdust, bark chips or soil) to the Mataura peat. Physical properties related to air‐water relationships were studied for their suitability as peat substitutes for container‐plant production. Peat and perlite showed water‐release characteristics which approached those most suited for use in container plant production. Increasing additions of sand, pumice, sawdust, or bark to peat resulted in less water relative to air being held in the media at tensions less than 100 cm water. Sand, pumice, sawdust, and bark released a large proportion of their water at less than 50 cm tension. Over 80% of the total pore space in sand and pumice, and about 70% in sawdust and bark, was occupied by the macropore water (0–100 cm tension). Additions of soil to pest decreased the proportion of macropore water and also the proportion of air to water in the media. Total pore space did not measure container aeration as well as did air capacity measurements. Container capacity changes much faster than total pore space after changes in the pore size distribution of peat‐based media from the additions of either pumice, sawdust, or bark to the peat.