To keep initial growth rates in control, use a soil mix with just enough nutrients. Mix 2 parts coir (coconut fibre) compost to 1 part perlite, and then add 20 percent worm castings. Test the pH
of any mix, and if it is acidic, add one gram of hydrated lime for every litre of soil mix. Or, you can substitute with vermiculite, which does not need pH adjusting. Finally, add 1 tablespoon of kelp meal for each gallon of soil to add plant hormones and to give beneficial micro-organisms something to feed on. Use this mix whenever you transplant.