A lawn expert is warning against fertilising your grass during a heatwave, stating that it will do far more damage than good. And while we all want to enlist the best August lawn care tips to restore our grass to its former glory. That is wrong; fertilising your lawn now can stress your grass even more, making it take even longer to recover. Latest Videos From Ideal Home Watch full video here:Why can't your fertilise a lawn during a heatwave? While fertilising your lawn might sound like a good idea right now, it’s really not.