This site tells what and when ,but doesn’t state HOW MUCH PER PLANT of fertilizer is to be used Bi-weekly.
How Much( a Cup,a Quart ) Fertilizer Do You Use on Mandevillas Bi-Weekly.
Certified GKH Gardening Expert
It really depends on if this is liquid or slow release fertilizer. Liquids will have their own instructions, but I prefer to feed at half strength every two weeks. If this is granular, or slow release, then once in spring will be fine each year.