Actually singing with love as intend improves somehow the growth in plants .Lets not forget that the sound is vibration and it also bears energy with certain wave lenght .Sound can travel only through medium (air in most cases ,but it can go through solids too).Plants are energetically sensitive especially as seedlings and while developing roots .This phase is crucial in their life and their survival depends on that pretty much . You do need to do that quiet often to notice some strong improvement .Also they will not like a noise which cause a lot of pressure .
I think that somehow plants have their own understanding what is happening around them and they react to the environment accordingly for good or bad .
I personally talk and sing to my plants not only to make them grow but to strenghten our connection ,because my favorite place to collect energy and meditate is my garden .Beautifull garden make you feel relaxed ,happy and positive .
I agree with Chenny that inviting fae folk and natural spirits in your garden will improve it further more .
Garden always need good maintenance .It is hard work except if you do not grow only local species which can take care off themselves in most time ,except in very extreme situations .
Other than that it needs prunning ,deadheading ,watering ,feeding
,weeding ,planting and some plants need also overwintering in special concitions .