Fertilization is most effective when done on a regular, consistent schedule. Knowing when fertilization should be stopped is an important part of that regular schedule.
We fertilize plants in order to make sure that essential nutrients are consistently available during the growing season. There is no reason to apply fertilizers when plants are not actively growing, when they are dormant. Our climate is unusual in that we have two dormancy periods annually. Winter dormancy begins with the first frost; our average first frost date is Nov. 15.
Fertilizing just before or during cold weather can force frost-tender new growth. Our winters are short and winter dormancy ends in late January when soil temperatures become warm enough to allow for seed germination.
The second dormancy period occurs in mid-summer, July into August, when our daytime temperatures regularly exceed 95 degrees. When temperatures are above 95 degrees, plants enter a state of semi-dormancy during which growth, bud production and root development slow significantly. Fertilization during the hottest time of the year can force new growth that can be scorched by the heat.
Roses are a good example of perennial plants which have a limited fertilization schedule. They should be fed monthly just seven times a year. The first feeding is given in mid-February when new growth is an inch and a half long. In our climate, they are not fed in July when temperatures are excessively hot. The last feeding of the year is applied in late September or early October at least four to six weeks in advance of the average first frost date to avoid potential freeze damage to tender new growth.
Warm-season grasses, including Bermuda, have an early fall growth spurt in our climate. Many gardeners scalp Bermuda lawns in late September or early October before overseeding with annual rye for winter color, but Bermuda will rapidly fill in bare spots in the lawn where weeds can sprout if given a late September feeding with a high nitrogen lawn food. (Use the same high-nitrogen food to give your fruit and nut trees a last feeding of the year after harvest). Wait until mid-October to scalp a Bermuda lawn or, to save water, tolerate a dormant brown lawn for a few months.
Cool-season grasses including the fescues and perennial rye are fed just four, maybe five, times a year. These grasses also have two dormancy periods, winter and summer, and our summers are really long. Feed cool-season grasses in September and October then not again until late March, when they come out of winter dormancy. Feed again in April and, if temperatures remain cool enough, again in May.