Lawn and Landscape Checklist - August Continue to mow the lawn at the 3-inch level until the first of September. The first part of the month may be the hottest and that is when the lawn may show the most stress. If the cause is just heat and lack of rain, don’t worry about it. See Water, Water – When and Where for more information. The cooler fall days and fall rains will help all your plants perk up. If you do find any areas in the lawn that need reseeding, the latter part of August and into early September is an ideal time. Sow seeds for fall garden crops, such as lettuce, radishes, beans, carrots and spinach. Start harvesting onions for winter keeping after the tops have turned brown.