Seasonal Needle Drop in Evergreens
Over the course of the last 3 weeks, we have seen a rather dramatic increase in photos of natural needle drop in conifers. While this is typically a regular AND natural process, the AMOUNT of needle drop is creating quite a stir in a lot of regions across the country. It seems that 2022 is up to another one of its nasty surprises.
There can be multiple factors that can determine the amount of needle drop that occurs. Some of the “lesser” factors are soil pH, soil porosity and structure. However, when determining IF what YOU are dealing with is natural needle drop, focus on the “Big Three”
2) Location – where are the off-color needles located on the tree
3) Soil moisture – as it relates to available resources
So, let’s look at these 3 factors to give us a clearer picture of what defines natural needle drop.
NOTE: Only interior needles affected on the White Pine
NORMAL needle drop on Arborvitae
SPECIES / LOCATION
Despite being called evergreens, conifers (pine, spruce, yew, cedar, etc.) will also drop their needles (leaves) in the fall. Just like in deciduous trees, the leaves of conifers will change colors and begin to drop in response to shorter days and cooler temperatures as winter approaches. While this may be alarming, this is normal for this time of year.
Conifers will produce new needles every year. Therefore, there are always new and old needles on a tree at one time. How long these older needles stay on a tree will depend on the species. Eastern white pines will usually keep their needles for 2-3 years.
Other pines, like Austrian and Scots, pines usually keep their needles for three years, and red pines for four years. Spruces typically keep their needles longer than pines do, generally for 5-7 years.
Only the oldest needles are dropped during fall (aka natural, seasonal, and inner) needle drop. Since new needles are added every year, these older needles are on the inside of the tree canopy. Just like in deciduous trees, the older needles will begin to turn colors, like yellow, brown, or reddish tan, when it is their turn to be dropped from the tree. Fall needle drop occurs uniformly throughout the tree from top to bottom. If entire branches or needles at the tips of branches begin to die or the pattern is not uniform in the tree, it is not fall needle drop. Something else is happening to the tree and will warrant a closer inspection.
This year fall needle drop is probably most noticeable in arborvitaes. Since these trees only hold their needles for 2 years, there is less new growth at the tips to cover up the older, yellowing foliage. Additionally, cultivars like ‘Emerald Green’ have a more open structure, making it easy to see fall needle drop.
SOIL MOISTURE – As it relates to available resources
Trees are like batteries. They are storage vessels that need to uptake and store quantities of not only minerals but water as well. A 30″ DBH Beech/Maple/Oak can uptake and move 30-40 gallons of water a day.
This year in many places throughout the country water was at a premium, as rainfall was WELL below normal. ALSO, and often forgotten, but just as important was wind speeds in most areas of the U.S. were well ABOVE normal. This combined with low humidity created a perfect storm for a weather event known evapotranspiration to be at an all-time high. In Michigan in mid-June this phenomenon was recorded at 412% of normal. What this means is that even if the plants were watered adequately, they were losing moisture 4+ times faster than they should. So, what does that mean now? Trees DO have some ability to compensate for water loss by “making it up” later in the season. However, NOW plants have shifted their “emphasis” to STORAGE, above USAGE. Therefore, they can not send adequate moisture to their needles/leaves now, as downward activity has taken precedent over upward movement. So, they are shedding higher than normal amounts of needles as a way of balancing demand. This IS IN THEIR DNA. This is a normal occurrence, and in truth tells you the tree is operating as it should. Re-allocating resources, as demand outpaces available reserves.
What can we do?
Kelp is an excellent stress reducer; I would also recommend the additive Ristora. This will offset some of the “loss” these trees have suffered, as well as increasing resistance to frost damage and, believe-it-or-not disease. Kelp contains numerous hormones like auxins, cytokinins, and gibberellins as well as betaines. These are critical for GROWTH, but also important for DEFENSE.
Remember, this is NOT a life-threatening situation. With a little care, you will have healthy trees for years to come.