Thank you for all your time Pat, it did not work though. The team in Newbury have solved the problem for me now.
vectorworks.net/uk
The reason your quantity column is not showing the correct quantity, is because you have not selected the quantity field in the row header (in cell B2). You have selected the following instead:
='Plant'.'Plants per column'
Whereas, it should read:
='Plant Record'.'Quantity'
You can change it by clicking the arrow in cell B2 and setting it as follows:
You will also need to use Sum Values, to ensure that the quantities are added up.
In cell A2, you also don't have the plants summarised, so you are getting a row for each group instead of a summary of all plants with the same name. To change this, click the arrow and check the box to Summarize Items. You could also have them Sorted in alphabetical order if you wish.