CUMBERLAND COUNTY'S WEATHER AND OUR PLANTS

We have had a cycle of extreme and unpredictable weather the last ten years, and some plants are showing the accumulated stress. Plants don't know when winter or spring comes (nor do we). A few examples:

Cold Weather

Damage to Plants: Winter damage can be divided into 3 categories: desiccation, freezing, and breakage.

• Freezing: Damage most often occurs in the fall when new growth has not hardened off or in spring when a late frost occurs after new growth has started. Mid-winter damage occurs when daytime sun warms up bark of trunk; if a severe freeze occurs that night, the bark may split. Wrap young trees with cloth or paper to reduce chance of bark splitting.
• Desiccation from winds: Winter winds cause "winter burn." Winds increase the rate of transpiration, causing the plant to dry out, particularly if the ground is frozen and the plant can not take up more water. If weather has been dry, water deeply on warm days in midwinter to keep plants well hydrated.
• Breakage: Usually caused by a combination of ice, snow, or wind, or by improper removal of ice and snow. Frozen, laden limbs are very brittle and snap easily if bent the wrong way. Remove snow by gently sweeping branches upward to lift off snow without further stressing the limbs.

Frost damage will be less if it is cloudy or if there is some wind. Cold air settles and causes more damage in low-lying areas. It often takes several weeks, sometimes months, after the cold weather to see the damage. Azaleas may not show damage until the first hot spell. Hold off pruning until damage is clear, then cut back to healthy wood. To check other woody plants, use fingernail to scrape back a tiny bit of the bark. If you see green, the plant is alive. Since pruning temporarily decreases hardiness, delay it until all danger of frost is past.

A brick wall on east or south side is usually the first spot to warm up in spring. Plants on south side are subject to rapid thaw after a freeze. The plant vascular system is closed down, then gets abrupt demand to function. Dessication (abnormal drying): heat, wind cause water loss which leads to winter burn.

Cold weather effects on insect populations: Gardeners look out on their frozen winter gardens and console themselves with the idea that at least the cold will decrease the insect populations next year. It ain't necessarily so! The picture is complicated; some insects may freeze but others may flourish as a result of a cold winter. Certain caterpillars overwinter well below ground level, whereas their predators overwinter above ground. If their parasites are killed, caterpillars will be more abundant the following year. Japanese beetles overwinter below the frost line and neither suffer nor prosper as a consequence of freezing weather. A significant decrease in the number of blue-winged wasps would result in an increase of the green June beetle population. Don't count your bugs before they hatch.

Protecting plants: The purpose of covering a plant is to trap the radiant heat that is in the soil. Therefore covers will be more effective if they go all the way to the ground.

• Covers should not touch plants (often impossible); use stakes to hold covers off plants.
• Burlap, bed sheets, blankets, agrifabric are best materials to use.
• DO NOT USE plastic sheets or metal buckets. Plastic buckets should not touch foliage.
• For special plants: make a wire cage and fill it with leaves.

Next morning: Watch the weather. You want to protect plants from wind and sun but leaving covers on in a fast warm-up situation can harm them. A plastic sheet can quickly steam the plants. Be realistic: sometimes you simply cannot protect all plants. Usually the foliage gets hurt but the plants survive.

Melting Ice in Winter: Salt and rock salt are not recommended; runoff can damage plants. Sand, kitty litter or ashes are a better choice, or one of the following: calcium nitrate, calcium chloride, or urea fertilizer. These are less harmful to plants than salts and do not stay in soil for any length of time.

Fruit Trees: Most fruit crops have a chilling requirement, meaning a specified number of hours below 45 degrees, which varies with the species and variety, but the crop cannot bloom until its individual requirement has been met. Once met, as soon as there is warmth, buds will swell. The extent of possible cold weather damage depends on the stage of bud formation when the cold hits. Some freezing is not entirely bad as most fruits profit from some thinning. Some fruit trees have latent buds which swell and blossom if other buds have been frozen.

Wet Weather

Very wet spring: Spring-planted fescue will not develop a good root system with many desirable feeder roots; all the moisture fools the grass into thinking it is not necessary to do so. If weather is warm as well as wet, fungal diseases on woody plants will be earlier and more severe (cedar-apple rust, black spot, spot anthracnose on dogwood). Entomosporium leaf spot of photinia prefers cool, moist conditions.

Hot, Dry Weather

Q 10 Rule: For each 10 degree increase in temperature, the speed of metabolic processes doubles in plants. This rule explains in part why some cool-weather plants do not thrive in Cumberland County. Our days are hot but, more important, so are our nights. Cool nights allow plants to build up a supply of energy for growth. Hot days and hot nights are the plant equivalent of working a 24-hour day, with no rest period. Neither plants nor people do well in these conditions. Cool weather plants have a shorter life span in Cumberland County. They may also show increased susceptibility to diseases in our humidity and root rot problems from our often wet soils in summer. (In the mountains, for every 300 ft. of elevation, the climate is equivalent to latitude farther north.) Some environments on Mt. Mitchell are comparable to those of New Hampshire.

Rain: After a hot dry period in summer, rains tend to be hard downpours that run off without soaking into the baked soil. Clay soils absorb water at about 1/4 " per hour. Despite a 3" rainfall, the roots of your plants may still be in need of water. Use the on-and-off system so that water has a chance to soak in and reach the root zone: water for 15 minutes, turn off to let water soak in, water again for 15 minutes, turn off, etc.

Drought stress: Stress occurs when water loss through evaporation and transpiration exceeds the amount available to the plant in soil or the amount the plant is able to take up via normal physiological processes. (Plants have to sit out there and take it--they can't move to an air-conditioned spot.) Treat plants like people: during extreme heat stress you take it easy, don't overfeed yourself, work less, and drink lots of water. The temperature on the soil surface in the sun can be higher than the air temperature, cooking seeds or seedlings.

Fertilizer: Never fertilize unless you have adequate water and are diligent about using it. Fertilizers can make things worse by desiccating plants. They are salts and act like salt = they draw water to them, away from plants. Nitrogen applications can induce growth which outstrips the roots' capacity to support the foliage. Few plants do much growing in extreme heat; forcing them to grow increases stress.

Wind: Plants lose water 2-3 times as fast in those soft warm breezes.