Stage 3 

It is advisable to subdivide stage 3 into an elongation stage (3a) and a root induction and pre-acclimatization stage (3b).
Stage 3a: elongation
  • In many cases elongation is a prerequisite for adequate rooting; 
  • Elongation media do usually not contain cytokinins or a weaker cytokinin than the one used in stage 2; 
  • It might also be necessary to add charcoal to neutralize the remaining cytokinin effect from stage 2; 
  • Depending on the type of plant, elongation can take place on singulated shoots or in clusters.
Stage 3b: root induction 
and pre-acclimatization
  • Most often auxins are used to induce rooting. Too often it is forgotten that auxins inhibit root elongation. Best rooting is usually achieved on media with a low salt content (e.g. Knop 1/2). 
  • In vitro developed roots are not always adapted to greenhouse conditions and long roots might create planting problems. 
  • Root induction can take place on singulated shoots and on clusters. 
  • Apart from root induction this stage should also favor acclimatization. Possibilities are: favoring autotrophy, loading the plants with carbohydrates, lowering of the relative humidity in the container, mycorrhization, use of inert substrates (e.g. rockwool, cellulose plugs, polyurethane foam, ...