April and May of 1996 were the wettest on record for Ohio, since records began in 1882. The cool and very wet spring delayed normal plant development by about 10-14 days. Unusually low temperatures and scattered frosts were reported from around the state on May 12 and 13. These frosts damaged some early-planted annuals and new growth on woody plants.
Salt injury symptoms on evergreens were especially evident this spring on plants located near highways. This was attributed to the heavier use of road salt during the winter to melt heavy snowfall.
Several species of plants exhibited abnormal foliage color during the summer, including pale-green foliage, physiological scorch symptoms, and early fall coloration. Limited root development during the wet spring may have contributed to these problems.
Reports of "toxic" mulch damaging plants were numerous this season and related to excessive spring moisture. As mulch ferments under anaerobic conditions, chemicals are produced that can be toxic to plants.
Extension agents, specialists, and a few others in the industry hold a weekly conference call during the growing season. Information on current weather conditions, pest problems, cultural problems, and other topics that relate to ornamental plants are discussed, summarized, and then distributed. This is an effort to keep members of the green industry, Extension personnel, and others apprised of problems occurring in landscapes.
Included here is a compilation of Ohio weather conditions and noteworthy environmentally induced and cultural plant problems in 1996. Observations are drawn from information provided in Ohio State University Extension's Buckeye Yard and Garden Line and from the Ohio Department of Natural Resources Monthly Water Inventory Report.
April rainfall was heavy across the state. At the end of April, the Ohio Agricultural Statistics Service reported that soil moisture was at "surplus" for 90% of the state. This was beneficial for water supplies, but caused moderate flooding and greatly delayed planting activity.
Rain continued in May; in many areas, it rained more than 20 days. Flooding increased in many areas. In the last 10 days of May, northern Ohio began to dry out, though rain continued in southern Ohio.
In the two months of April and May, many locations received one-half to one-third of normal total precipitation for the year. By the end of May, Dayton was +12.4", Cincinnati +11.7", Columbus +7.4", Mansfield +10.7", Akron +4.2", and Cleveland +1.3". Also in this period, temperatures remained cooler than normal, and cloud cover was significant.
Rain continued into June; however, the second half of the month began to dry out. The drying trend continued into July; some parts of the state had no rain during the first two weeks, and lawns began to show signs of stress/dormancy. In mid-July, a few storms crossed Ohio, delivering adequate moisture to re-green browning turf in many locations.
August was dry with only scattered rainfall across most of the state. West-central Ohio reported virtually no rain. Lawns were dormant in many locations, and recommendations to irrigate lawns and new ornamental plantings were given. Many locations reported soil moisture deficits at the end of the month.
During the first week of September, Hurricane Fran delivered rainfall, varying from +5" in the eastern and northern regions of Ohio, to only a quarter inch in west-central Ohio. Scattered storms continued across Ohio through the month. At month's end, Cuyahoga County reported the wettest month ever on record, with over 10" of rainfall; Lorain County reported just over 11" for the month.
Roller coaster weather in April led to a "late" spring. Hail; rain; tornadoes; alternating mild, sunny days; and cold, snowy days were all reported. Ornamentals such as Callery pear, early crabapples, and cherries were blooming side-by-side in the Cincinnati area, an unusual occurrence. The cool, wet spring delayed normal development of many plants and insects by 10-14 days.
On May 12 and 13, temperatures were in the low 30's (deg F) throughout most of the state, with record lows reported in Cincinnati and Columbus. Scattered light frosts were reported. Damage was most severe to early planted annuals and those on display in garden centers. Hostas were damaged in several locations, as well as tender, new growth of some ornamentals. Frosted new growth on Taxus spp., which appeared curled and brown, was commonly seen and commonly misdiagnosed as growth-regulator herbicide injury.
Little winter injury was reported on ornamental plants, with the exception of ornamental grasses. Many grasses were slow to emerge in the spring, particularly fountain grass (Pennise-tum alopecuroides). Many plants had dead centers or limited growth on the perimeter of the clump.
Injury attributed to road salt spray was particularly evident on conifers along the highways and byways of Ohio this spring, and reports continued through May. The salt used to treat icy roads became airborne and affected plants 100 to 150 feet from highways, depending on the force and direction of the winter wind. Salt damage on evergreens tends to appear in late winter and worsens in early spring.
Needles turn progressively brown from the tips towards their base. Damage to deciduous plants was not apparent until bud break, when bud and branch dieback was noticed. Classic symptoms of airborne salt injury appear on one side of the plant, the side facing the salted highway. However, this year, whole-plant injury of trees along highways occurred, perhaps due to heavier use of highway salt combined with winter desiccation.
Injury from airborne salt spray is caused primarily by cell and tissue sensitivity to the chloride ion. Chloride moves in the transpiration stream to leaf tips and margins and may accumulate there in toxic concentrations. Salt injury from salt runoff into soil is more complex. Toxic accumulation of ions in plant tissues may occur, but salts also increase the osmotic potential of the soil solution, which can severely impair the ability of roots to absorb water and nutrients. Roots, in essence, experience drought in high salt soils, even when moisture is available.
Plants reported in the literature to be sensitive to salt injury include azalea and rhododendron, beech, river birch, boxwood, black cherry, cornelian cherry, cotoneaster, crabapple, dogwood, Douglas-fir, white fir, sweet gum, forsythia, hemlock, hickory, American holly, common lilac, red and sugar maple, eastern white pine, flowering plums, flowering quince, Allegheny serviceberry, white spruce, sycamore, tulip tree, and yew.
With the record spring rainfall, limited plant root development occurred. By mid-June, plants such as birch, maple, some viburnums, winged euonymus, and several others were exhibiting light-green foliage. In July, during the dry spell, plants began to show additional symptoms of stress, including physiological leaf scorch and early fall coloration. Plants such as flowering dogwood, oaks, tuliptree, and several species of maples exhibited leaf scorch. River birch, European white birch, burning bush, callery pear, flowering dogwood, and red maple showed early fall coloration.
Reports of chlorotic, scorched, or dying bedding plants attributed to "toxic mulch" occur every year, and excessively wet conditions this year increased the number of reports. Organic mulches can undergo anaerobic (without oxygen) fermentation when stored for extended periods in piles greater than six to eight feet in height. The chemicals produced by fermenting organisms can be quite toxic to plants. Small annual plants were severely damaged or killed outright by toxic fumes or direct contact with the mulch; perennial plants exhibited leaf chlorosis and defoliation. Woody ornamental plants with low-growing branches close to the mulch can also be damaged.
Fortunately, "toxic mulch syndrome" is quite easy to diagnose and prevent. Mulch that has gone anaerobic will have a very strong, acrid, sour odor. In contrast, mulch that is safe to use will have a pleasant, musky smell, like freshly cut wood or compost.
Mulch handlers can prevent the problem by turning mulch piles frequently to prevent anaerobic conditions and by maintaining piles under six to eight feet in height. Mulch stored in plastic bags is not immune to this problem, especially if water gets into the bags. Bagged mulch should be stored on wooden pallets with room for air flow. Anaerobic mulch can be used if leached heavily with water to remove harmful toxins and if aerated for several weeks.