Several trials have been conducted to determine the optimum amendment level for the production of container foliage plants in a 1:1, V:V, peat:perlite potting mix.
Experiments with various controlled-release fertilizers have shown superior growth and quality with resin coated products in an artificial mix. This appears to correspond to the nitrogen source with those containing nitrate and ammonium nitrogen giving better results than those with other nitrogen sources, such as IBDU or urea.
Trials with variable rates of dolomitic lime resulted in better or equal growth and quality of a variety of foliage plants without added lime even at pH levels of 4.0.
These results suggest the recommendations for the production of container plants in mixes without soil need to be reviewed and perhaps revised.