Proper way to use getter/setter in form

I am able to use a model.getter in my volt form like so: {{ model.getMyDate() }} but what is the proper way to do this with the tags and forms?

In my form I create a text input like so:

       $startDate = new Text('startDate', array(
            'placeholder' => 'Start Date',
            'id' => 'start_date',
            'class' => 'form-control'
        ));

        $this->add($startDate);

Then in my volt view I am rendering it:

{{ form.render("startDate") }}

Since this is no longer attached directly to a public property of my model but needs to attached to the getter, what is the best way to do that?