The Science Behind Southern Grasses,
When my husband and I moved to northeast Florida in 2004, we inherited a St. Augustine lawn that had been weed & feed'ed, fertilized, irrigated, sprayed with pesticides and herbicides--all the typical actions people in Florida have been advised to take in order to maintain their lawns. We stopped all the chemicals and have irrigated only when needed. The irrigation system pumps water from a nutrient-rich lake, so each time we run the irrigation system, we essentially feed the lawn. We don't mow the lawn when it's dormant--from November to March. Under our no-chemicals care, there are still quite a few areas where the St. Augustine is doing well, but there are others where different grasses, clovers, and many other plants have moved in. It looks quite presentable as a lawn despite our not spending all that money on chemicals. This type of lawn, where we mow whatever is there, is called a "freedom lawn."
When researching my book, "Sustainable Gardening for Florida," I found lots of information on how to maintain turf so that it is green all the time. Most of the sources provided the same advice: fertilize several times per year, over-seed with annual rye in the winter, apply pre-emergence herbicide, and poison all the bugs. I was looking for information on more sustainable lawn care, but this advice varied widely. I finally decided to take the consensus approach and also relied on practices that worked for me in the Mid-Atlantic States. My advice on fertilizing was to do so only once a year, if needed, and to do so after the hurricane season is over in November. I was wrong. As one highly educated reader pointed out; I had not taken into account the science--that southern grasses use a more efficient photosynthesis process.
Photosynthesis is the process that green plants use to turn carbon dioxide and water into sugar and oxygen with the energy from sunlight.
Respiration is the reverse process whereby plants and animals use sugars from food and oxygen from the atmosphere to gain energy for living. The byproducts of respiration, carbon dioxide and water, are usually released into the atmosphere.
Heat will shut down photosynthesis in most plants when they close the pores (stomata) on their leaves to protect against dehydration. Carbon dioxide is not available from the air when the stomata are closed. When these plants respire, carbon dioxide and water are released into the atmosphere through the open stomata. But when the stomata are closed, respiration is also slowed. Because this method of photosynthesis creates sugars with multiples of three carbon atoms, this is called the "C3 pathway" for photosynthesis. This type of photosynthesis can take place in relatively weak light and cool weather, but not in the heat of a summer day.
In contrast, many
plants that thrive in hot weather have a different, more efficient
process for photosynthesis than plants that use the standard C3
photosynthetic process. These hot-weather plants include southern
grasses used for lawns such as Bahia grass, Bermuda grass, Centipede
grass, Seashore Paspalum, St. Augustine grass, and Zoysia grass.
Other plants in the grass family, such as corn,
cord grass, muhly
grass (See photo to the left.), sugar cane, goose grass, switch
grass, and crab grass; plus some non-grasses including spurge and
purslane also use this variant process.
Ginny Stibolt would like to hear from readers who have suggestions and questions. After all, there are more than a few transplanted gardeners here in northeast Florida trying to figure out what works and what doesn't in planting zone 8/9. She's written a book, "Sustainable Gardening for Florida," published by University Press of Florida.