title: Pandas: increment datetime
body: <p>I need to do some actions with <code>date</code> in df column</p>
  
  <pre><code>buys['date_min'] = (buys['date'] - MonthDelta(1))
  buys['date_min'] = (buys['date'] + timedelta(days=5))
  </code></pre>
  
  <p>But it return </p>
  
  <blockquote>
    <p>TypeError: incompatible type [object] for a datetime/timedelta operation</p>
  </blockquote>
  
  <p>How can I do it to column?</p>