Deer are considered reproductive hosts for blacklegged ticks (a.k.a. deer ticks). This means that adult female ticks feed on the deer to get enough protein to lay eggs. The deer do not pass on any pathogens to the tick (the mice do that).
So, if you live in an area where deer have any kind of presence, chances are that there will be fairly large tick population, as well. And, besides being a reproductive host, a deer could also be viewed as a sort of “transporter host” for ticks, because they will likely carry the pests into your yard when they come in to graze on your garden in the middle of the night.
Of course, one way to discourage deer from coming into your yard is by building a tall fence. But if that is not in your budget, consider landscaping using plants that do not attract deer, including: