Dear Carol, I so hope you have some nice weather for it! I could recommend Sissinghurst castle as that has a very famous garden, however it is a bit further on and personally I hate the white garden there.
Leeds castle is awesome, and it is just outside Maidstone, very well worth a visit. The massive old Carp in the huge moat are amusing as well.
I hope that you enjoy some of these I have sent you although there are a lot more to see.
Have a safe journey and a good time.
Regards.
Neil.
p.s. You can get carried away buying things in the Herb garden, I know.