It seems to me like you are attempting to gain entry into melb uni via a course that has a low atar requirement. To me that would not be wise, as you will be forced to study in a course which you potentially have no interest in, meaning you will most likely not do well and therefore not be able to transfer into the course you want.
Also breadths only amount to 2-4 for each level. Meaning you will be unable to do a whole years worth of breadths which is required for the uni to consider you on your uni marks alone- you need i do at leat 8 subjects total in order to use them as a basis for a transfet application. (level 1 breadths as i explained above only account for 2-4 TOTAL for your enite course - and level 2 breadths cannot be done unless youve completed the necessary lvl 1 subject).
My advice is for you to apply for a similar course at another uni and apply for a transfer after one year. That way you will be doing a course you enjoy AND as an added bonus, you most likely get to credit those subjects to your melb uni degree - which means you go straight into 2nd year.
I know this first hand as I transferred from rmit after completing my 1st yr commerce degree and into 2nd yr commerce at melbourne. All my 1st yr subjects were credited and therefore I did not have to redo any subjects for my chosen major. However, keep in mind you will need a 75 average MINIMUM to be competitive for a transfer, but it would more or less be the same if you wanted to transfer from horticulture- priority is not really given to internal transfers since you still apply through vtac.
Again this post is purely apeculation on why you posted the question and i can be completely wrong about your motives (if it is, i do apologise). Assuming if i am correct, may i ask why you want to attend melb uni so badly? All undergrad courses are almost identical, and going to melb uni will not help you in getting a job any more easily than another uni (it is really more about your marks you get at uni). I only applied for a transfer as I am looking at getting into the economics honours program which is significantly better (imo) than at any other uni.