By By Steve Strong / area horticulture extension agent
July 2, 2003
Rain, rain, go away. That old nursery rhyme has about as much chance of working as getting rid of the big purple dinosaur on my kids' television station.
East Mississippi would normally be begging for a little relief from drought by Independence Day, but instead the tropical storm season is dropping even more of the wet stuff on already waterlogged landscapes.
The good news is that temperatures are about 10 degrees cooler than usual. That translates into money savings for homeowners this summer by shutting off their irrigation systems for a while.
The bad news is that there is no way to shut down nature's watering system, and that our lawns, gardens and pastures are starting to suffer from too much of a good thing.
Plant roots are happiest when they have equal amounts of air space mixed with water pores in the soil. When rainfall and irrigation continue to keep all of the pore spaces in the soil filled with water, roots cannot absorb enough oxygen and the top parts of the plant begin to show symptoms.
The most common symptom of suffocated roots is yellowing of lower leaves inside the plant canopy. Certain plants are more sensitive to "wet feet," and will display chlorosis quicker (progressive yellowing and leaf drop as the green chlorophyll breaks down) such as azalea and gardenia.
Soil diseases such as Fusarium, Pythium and bacterial wilt are thriving in the current weather conditions. Sadly, not much can be done to combat these soil rots during the growing season. But next summer you could try planting better disease-resistant varieties or possibly a soil-applied fungicide depending on the pathogen.
Other ornamentals may succumb to fungal and bacterial leaf diseases as a result of too much moisture clinging to leaf surfaces. Crape myrtle and dogwood are prime victims of powdery mildew this summer, and hybrid tea roses are rampant with black spot fungus again, fungicides are the only desperate solution.
Vegetable gardens are also beginning to display moisture problems, in the form of fruit rot on okra and squash. Wet rot cannot be effectively controlled with a fungicide, so the best strategy is to remove some of the foliage, and to correctly space the plants to allow for better air circulation.
For root problems where soil drainage is the culprit, water may possibly be diverted away from the site with one or more horizontal drainpipes commonly called French drains.
Drain lines are typically dug between 18 and 24 inches deep (with a 1 percent to 2 percent slope or drop from one end to the other), and filled with about a half-foot of gravel before placing the plastic or clay drain lines in the trench (place the pipe's side drain holes facing down).
In areas where horizontal removal of excess water is not possible, vertical drainpipes can be used to divert small amounts of water.
Posthole diggers can be used to a depth of 2 feet or greater, with a "sleeve" of 4-inch PVC pipe placed inside and holes drilled in the sides for faster water movement (fill the pipe with slag or coarse gravel and cover the top with landscape fabric or other porous material to prevent silting).
Last but not least, try improving the soil drainage before replanting by adding compost or other coarse soil amendments.
About 3 to 4 inches of amendment well tilled into existing soil can help improve most soil types, but avoid adding straight sand to heavy clay unless you are trying to make bricks.
When all else fails, contact your county Extension office, or plan on building an ark.