Have small sized basswood tree in front yard. What annual would be best to plant under this tree, as has a fair amount of sap. Lots of black ants attracted to it. Have not had much success with annuals in past.
from Vancouver, BC
The basswood (Tilia americana) is a lovely shade tree. The ants you describe are not attracted by the sap but to the gathering aphids, which ARE attracted by the sap and might spread to your flower beds if not controlled. So the ants are actually working for you!
When full grown, the basswood will cast dense shade, so you will not be able to grow many annuals directly under it. My suggestion would be to review the list of perennials for shade that we have provided here.
Meanwhile, if the tree is still quite small, you can consider several types of annual flowers, such as those we have listed here. That link leads you to a Gardening Guide that will also provide lots of information about how best to grow the annuals, which may help solve the problems you have experienced in the past.
Please note that our Guides were written for Toronto gardens. In Vancouver, you have more rain, so please bear that in mind when choosing among the plants described.