In the world of arboriculture, or at least the arborist, a variety of factors impart effects on the trees we care for each and every day. One of the most impactful, or at least most commonly referred to is weather. The adage goes like this: “Can’t figure out what’s wrong with a customer’s tree? Well, you can always blame the weather.”
A few terms are helpful to consider: Weather is what we experience day to day and week to week. A forecast is what we expect, or are told to expect. Climate is an accumulation of weather events over a long period of time.
In a sense, weather can be a good answer for the unknown or the hard to determine, as it is such a major influence. There’s nothing like it terms of impact. After all, it’s multi-component factor with winds, flood, hail, heat, drought, sun, rain, snow and ice. It’s an all-season and ever-present factor. There is no rest from the weather; it’s dramatic – extremes seemingly are commonplace these days — and, it’s a mimic because weather related maladies are often difficult to diagnose because they closely resemble insect or disease related injury causes.
Good and Bad Weather Conditions
Weather is often defined in black and white terms of good or bad, at least from the human perspective — but what’s good weather for a tree? Perhaps it’s best to describe it in two ways, in the establishment phase and the maturity phase, or even year one and year two and beyond.
Initially, even if a tree is touted to withstand soggy or dry soils such as a baldcypress or a chinkapin oak, most trees tend to be favored by moist, not soggy or dry soils, moderate temperatures and moderate winds. Sure, eventually drought tolerant species will be able to survive well on limited water, but at first, moist soils, favor the development of roots and shoots. Likewise, exposure to gentle to moderate winds encourage a tree to respond by developing a strong structural root system and bole to resist wind throw. After establishment, good weather conditions are those where most days are in the desired range for the species in terms of moisture, wind and sun.
Conversely to the above, bad weather conditions are those that present a tree with significant time outside of the desired range for a given species.
An important caveat to the good and the bad is the ugly, which is the time lag or the length of time that it takes for symptoms of injury that are due to weather to express themselves. For herbaceous plants such as tulips, turfgrass or hostas, there is a short time involved with the visibility of a cause and effect of weather ie. it’s hot and dry for 4 weeks, without supplemental irrigation, Kentucky bluegrass is going to wilt in the heat and appear highly stressed. With established woody plants, the symptoms often show up several months later or even the next year in response to the same heat and drought. Most customers simply cannot fathom this difference in responses to weather; therefore it’s wise to try to explain or at least warn them in advance of what could come to pass.
Here are some of the more commonly observed/encountered maladies due to weather:
Drought injury and leaf scorch — Caused by extended periods without adequate rainfall or supplemental irrigation. Prevent it by providing even moisture, mulching to retain moisture once received, monitoring often with a soil probe/screwdriver to gauge moisture content.
Winter desiccation — Caused by strong, consistent winds that dry out leaves; worst on broadleaf evergreen species such as holly and arborvitae. Prevent it by irrigating to moisten soil and enter the winter with roots fully hydrated, apply an anti-desiccant product 3-4 times as per label instructions, install wind screens in high value situations.
Sunscald — Caused by solar rays that warm the surface of thin barked trees in winter, causing it to be warm and cold in a series of diurnal cycles. Prevent it by installing white wrapping or PVC drain tile to reflect solar rays in late fall, remove in late winter.
Hail Damage — Caused by ice chunks striking the bark with sufficient force to break the surface and allow desiccation and entry of pathogens. Correct it by pruning out badly affected branches.
Wind Encouraged Herbicide Drift — Caused by movement of broadleaf herbicides from adjacent areas. Prevent and correct it by discussing potential for damage with nearby property owners. Provide for future needs of tree but avoid overwatering and overfertilizing.
Frost Injury – caused by cold temperatures received after buds have broken dormancy. Prevent or correct it by avoid species that are prone to frost injury. Prune out badly affected branches.
Wet Soils – caused by overabundant moisture from flood, irrigation system leaks and zealous turfgrass irrigators. Prevent or correct it by measuring rainfall and irrigation amounts received and adjusting accordingly.