Welcome to the first People and Plants GP blog post. These posts, which will be on a random basis, will take a behind the scenes look at the namesake people behind many plant names. This first one will be about Andrew Jackson Downing.
Andrew Jackson Downing was born October 30/31, 1815 in Newburgh, New York to Samuel Downing and Eunice (née Bridge) Downing. His father was originally a wheelwright but later became a nurseryman. After he finished his schooling Andrew worked in his father’s nursery and was soon bitten by “the plant bug”. I’m sure many of us can identify with that “affliction”. Over time he became more interested in landscape gardening, architecture and the relationship between them. He began writing articles about botany and landscaping but soon realized he needed to know more about both topics and so began a course of self-education. By the 1830’s he was producing pieces for newspapers and hort journals and in 1841 his first book, *A Treatise on the Theory and Practice of Landscape Gardening, Adapted to North America, met with great success. It was the first book of its kind published in the United States.
Downing continued to write on the importance of linking landscaping and architecture and was well thought of in the industry. What really put him on the public gardening radar was a book he and his brother Charles wrote. The 1845 book, The Fruits and Fruit Trees of America, was the most complete one of its kind to date and led to Downing’s becoming the editor of a new periodical, the The Horticulturist and Journal of Rural Art and Rural Taste. The journal came to be his strongest influence on society and operated under the premises of horticulture, botany, entomology, pomology, rural architecture, landscape gardening, and ideas dedicated to public welfare, specifically public parks and what we now call “open space”. As an example he argued for a New York City park, which in time became Central Park, in this journal. It was also in this publication that Downing repeatedly pushed for state agricultural schools. He held the position of editor until his death in 1852.
Downing was greatly influenced by the British “picturesque” landscape theories of the era. By the time he published the second edition of his Treatise he was a firm believer in the advantages of the picturesque landscape movement. He embraced the use of local landscape features especially “the raw materials of wood, water, and surface” and, when possible, the blending in with the local terrain instead of creating an artificial, out-of-place one. He became the mid 19th century champion of natural style landscapes and helped steer American gardeners away from the more formal, geometric lines that had dominated the 18th and early 19th centuries.
Mt. Auburn Cemetery is in the Picturesque style – photo courtesy of Friends of Mt. Auburn
As an editor, Downing repeatedly addressed the importance of urban and suburban public gardens and parks. He felt such spaces would aid in the fostering of moral and civic virtues in the American public. In the October 1848 Horticulturist editorial “A Talk about Public Parks and Gardens,” Downing wrote that public parks would play an important role “in elevating the national character.” He also believed interacting with nature had a healing effect on mankind, wanted all people to be able to experience nature and felt city parks were vital in helping maintain a healthy community. Downing had a wide audience through his books and editorials in the Horticulturist but his influence went beyond the readership of his publications. Private and public gardens and city parks that proliferated through out the USA during the mid 1800’s owed their existence to his ideas.
Downing did much more than this blog post will discuss so let’s move on to the plant.
Downingia concolor
The genus **Downingia is named after Andrew Jackson Downing. It contains 13 annual plants which are native to the western USA and Chile. Commonly known as calico flowers, they are noted for forming large displays of small colorful blooms around seasonal or ephemeral pools of water. Interestingly each pool will usually only host one or two species of Downingia even in areas where multiple species exist. It’s a member of the bellflower family and the plants are 3-10″ tall. Flower size varies but each flower has five corolla lobes or petals. The two upper petals are smaller than the three lower ones. Coloration is mainly blue/purple/pink with a little white, yellow, and black. Downingia must cross-pollinate. To prevent accidental self-pollination, the flowers mature in stages, they go from male to female. This change is time coordinated across each patch of flowers. How this is done is still unknown. The species is pollinated by native solitary bees.
Downingia pulchella Photo by John Doyen Downingia bacigalupii Photo by Gary A. Monroe
Linda’s post last week about “drought-resistant” plants made
me think about drought and how different types of drought affect gardeners in
different ways. In her article,
she defined drought as “an unusual lack of rainfall”. This is one of four
different kinds of drought that climatologists talk about, and I thought it
might be interesting for you to hear about how the four (or maybe five) types
of drought differ and how they affect gardeners in diverse ways. A great source
of drought information across the U.S. is https://www.drought.gov/.
The first type of drought, the one Linda described last
week, is what climatologists consider a meteorological drought. A
meteorological drought is related to how much rain you get compared to usual
conditions at your location. I like to think of it as “too many days of nice
weather in a row”, since in these dry conditions, the sun is shining and it is
a great time to garden, play golf, or do construction. Of course, if you don’t
get rain for a long time, you start to see impacts on plants, water bodies, and
wells, but meteorological drought is usually not identified in terms of
impacts, just on the amount of precipitation measured over weeks, months or
years. Meteorological droughts look different depending on where you are. It is
possible to have drought even in a desert if rain does not fall over an
unusually long time. Droughts in the Pacific Northwest might look quite
different since the frequency and amount of rain looks a lot different there. In
the Southeast, drought can be hard to identify by looks since even when rain
does not fall for a long time, things tend to stay relatively green because in
our worst droughts we still get 35 inches of rain a year. Most gardeners can
cope with meteorological drought by watering their plants at appropriate
intervals and reducing impacts of the dry conditions by mulching to help keep
moisture in the soil.
Iowa County Drought 2012, source: WxMom , Commons Wikimedia.
Agricultural drought
I spend a lot of time talking about agricultural drought
to the farmers and extension agents I work with, because agricultural drought
is always on their mind. Agricultural drought is defined by a negative water
balance that can be related to both lack of rainfall and/or high temperatures
that increase evaporative water stress on growing plants. It occurs mainly in
the growing season because that is when the crops are actively growing and
impacts are most noticeable. A 3-week dry spell may not be a problem for most
gardeners that water their plots, but if you are a dryland farmer without
irrigation, you can lose an entire crop of corn for the year if the dry spell
occurs when the corn is pollinating and the silk dries out before the pollen
can stick to it. Often agricultural drought can occur even when there are no
other impacts to us because it is subtle; most people don’t see the impacts
until months later during harvest. If you have limited access to water for
irrigation or very sandy soil in your garden, then you are more likely to be
affected by agricultural drought since it will be harder to maintain plant
health when the soil is dry.
Agricultural droughts are often related to flash droughts.
Flash droughts are characterized by very rapid development or intensification
over a short time period, and crops are often the first things affected because
of their need for frequent watering. Flash droughts are often characterized by
a lengthy dry spell coupled with very high temperatures, something that is common
when you have a persistent area of high pressure right over your location.
Ladybower Reservoir during the drought of 1989, source: Lynne Kirton, Commons Wikimedia.
Hydrological drought
Where agricultural drought is related to a shortage of water
over time periods as short as a week to a month, hydrological drought is
related to a shortage of water over months or years. Climatologists measure
hydrological drought as precipitation deficits over periods that range from
three months to multiple years. You can see hydrological drought in dropping
stream, lake, and reservoir levels and in dropping groundwater levels if the
deficit lasts long enough. A hydrological drought can occur even if no
agricultural drought is observed when you get rain at frequent intervals but it
is less than normal over a long time period, as long as the rainfall is enough
to sustain the crops (or if it is winter, when there are not many crops
growing).
Hydrological drought tends to affect gardeners’ access to water for irrigation because the long-term water deficits lead communities to enact water conservation measures to protect drinking water supplies. Most local and state governments have tiered conservation measures that get more strict as the water supplies get lower and lower. They may start by merely providing educational materials on water conservation and then progress to even-odd watering by dates or watering during overnight hours only (since there is less loss of water due to evaporation in cooler night-time temperatures). In the worst droughts, they may cut off the use of water for establishing new lawns and gardens (often with an exception for gardens that are used for food production). If a drought lasts for many years or even decades, then it is considered a megadrought, such as the one that is occurring now in the Southwest U.S. Megadroughts are related to long-period shifts in global atmospheric patterns and can lead to the abandonment of cities because of the loss of water to keep their citizens alive over time.
Socio-economic drought is a little different than the
other kinds of drought mentioned above. It is drought caused by a lack of water
due to overuse, hoarding, or war. An example of a socio-economic drought might
be one caused by one country damming a major river in their country to create a
reservoir, keeping the river water from flowing downstream to other countries
that depend on the water for agriculture or water supply. In the United States,
disagreements between who is allowed to use available water often end up in
court as cases like the Georgia-Florida “water war” that was recently adjudicated
in the U.S. Supreme Court. Locally, disagreements about who is allowed to use
the water sometimes result in tiered water pricing, where the more water you
use, the higher the price. This affects gardeners who have plots that use a lot
of irrigation because of the use of water features, plants with significant
water needs, or lack of mulching or other methods of protecting soil moisture.
Recently, a fifth type of drought called ecological drought has been identified, since a lack of rainfall can affect natural ecosystems in ways that are distinct from gardens, farms, or watersheds. I won’t address it further here, but if you are interested in how natural ecosystems are affected by dry conditions, you will no doubt read about ecological drought in publications in the future.
Drought is a naturally occurring part of the climate across the world, and gardeners must understand the nature of drought in their area to recognize how it affects the weather and climate where they live. Linda’s article last week gives some good guidelines for how to make your garden work in your climate.
Nothing drives me crazier than simplistic solutions to
complex problems. Given our changing climate, there has been an explosion of
“drought tolerant” and “firewise” plant lists in the gardening world. Most of
these lists are devoid of science and all of them are removed from reality. The
fact is that taxonomy plays a minimal role in determining whether a plant will
tolerate environmental extremes.
Lack of irrigation and mulch guarantees a drought-stressed landscape regardless of the selected species.
Let’s start with the most obvious problems with these lists.
The goal isn’t to have plants that require less additional water – it’s to have
a landscape that requires less additional water. Similarly, the relative
flammability of plants is less important than whether the landscape surrounding
those plants is protected from fire. Plants don’t exist in vacuum and unless
you are strictly a container gardener a single plant’s impact on water use or
fire resilience is negligible. So a gardener’s questions should be “How can I
make my landscape more drought tolerant? How can I reduce the likelihood of
wildfire damage?” And these are questions that can be addressed with knowledge
gleaned from applied plant and soil sciences.
Drought Tolerance
Arborvitae can tolerate droughty summers, but they don’t tolerate improper planting and management.
First of all, let’s think about what “drought” really means:
it’s an unusual lack of rainfall. It doesn’t mean no irrigation, and it doesn’t
mean dry soil. Drought is a climatological term, not one associated with soil
water management. Fine roots and their root hairs require water to function. Without
sufficient soil water plants will go dormant or die, particularly during
establishment. Plants that are drought tolerant can tolerate seasonal lack of
rainfall, but they can’t tolerate chronically dry soil conditions.
Even “drought tolerant” species like Sempervivum will die if there’s not enough soil water.
So we need to look at the landscape factors that allow
plants to survive droughts. This includes
Root systems that are well established. This means no barriers between the roots and the landscape soil system. Barriers include soil amendments and any materials left on roots during transplant (like soilless media, clay, and burlap). Obviously proper planting is key.
Adequate water movement into and within the soil environment. Anything within the soil environment that creates a textural barrier, like soil amendments, prevents water movement. Anything on top of the soil environment that creates a physical barrier, like sheet mulches or compacted layers, prevents water movement into the soil. Sheet mulches include plastics, fabrics, cardboard, and newspaper.
Adequate irrigation to support all plants in the landscape. The easiest way to determine whether there is enough soil water is to focus on one or two well-established indicator plants that you notice are the first to show wilt in the summer. That’s when the irrigation should be turned on. For our landscape in Seattle, it was a south-facing hydrangea.
Properly mulched soil. Mulch is crucial for soil and plant health, especially in terms of soil water retention and temperature moderation. The best choice for a tree- and shrub-dominated landscape is arborist wood chips. The best choice for arid landscapes is stone mulch – but if this landscape is dominated by trees and shrubs, you need the wood chip mulch. Trees and shrubs, by and large, are not the dominant plant form in arid environments. If you are going to grow plants out of place, you need to include the mulch that matches.
The broad, thin leaves of hydrangeas lose water rapidly and make a good indicator plant for water stress.
These four environmental conditions are key to maintaining a
drought-resistant landscape. In terms of appropriate plants, just realize that
plants with small, thick leaves lose less water than those with broad, thin
leaves. If you want a landscape that conserves water, by all means choose
plants whose evaporative water loss is the least.
Firewise Landscapes
Jack pine (Pinus banksiana) produces cones that require fire to open and release their seeds.
I’m not crazy about the term “firewise” as it’s not really a science-based concept. There are natural landscapes that routinely experience fires, and plants native to these landscapes have evolved mechanisms to survive moderate fires. Trees with thick bark, for example, can survive fires that are low to the ground and quick to move through. Other plants may perish in a fire, but leave behind fire-resistant seeds that are able to germinate after the next rainfall. This is not what’s meant by a firewise landscape. Instead, the premise appears to be selecting plants that are low flammability. (Jim Downer tackled this one a few years back but the message just isn’t sinking in.)
Failing trees of any species are more flammable than living trees of any species.
Once again, the focus of this approach is mistakenly
directed to plant selection rather than landscape resilience. The best way to
reduce the risk of fire is to have a landscape filled with healthy, hydrated
plants and a soil protected by the least flammable mulch. The two mulches
recommended for drought tolerant landscapes also happen to be the least
flammable: stones and arborist wood chips.
Bark mulch is hydrophobic and flammable in the landscape.
Arborist wood chips are hydrophilic and nonflammable in the landscape.
All wood-based mulches are not created equal.
Despite published evidence that arborist wood chips are not very flammable when compared to all other organic mulches, many governmental groups specifically recommend against them. This is a problem. Stone mulches are great choices IF the plants in question are native to arid zones. Trees and shrubs that are not from arid zones generally require the presence of woody debris to enhance mycorrhizal and root health. Without the proper mulch, these woody plants are less healthy and likely less hydrated than their counterparts under arborist chip mulches. That makes them more, not less, susceptible to fire damage.
A stone mulch in a southwestern desert landscape.
Most of the confusion around arborist chip mulches is probably the result of regulatory agencies confusing bark mulches with wood chip mulches. Bark mulches ARE flammable as they contain waxes and are not great choices for root and soil health. They should be avoided. Agencies associated with fire control methods need to be better informed about the significant differences between these two types of mulches and how they affect plant resilience.
The wildland-urban interface faces the risk of extreme fire danger. [Photo byAnthony Citrano]
And finally, it is important to understand that major
wildfires are going to burn anything that’s organic. If you live in such an
environment, the best thing you can have in your landscape is no plant material
of any sort. A buffer of stone mulch is the only logical option.
The holiday season creeps earlier and earlier each year, at least here in the US. Decorations, trinkets, and more start filling store shelves before summer is even over. But some holiday traditions can’t be rushed, like live holiday plants. Many of these picky plants have to be bought and cared for closer to the holidays, else they likely won’t look so festive once the holiday finally arrives. Since the origins of many of the holiday traditions are pagan and druid in nature, it stands to reason that plants are a major theme for the holidays. I’ve written before about the origins of using the plant parasite mistletoe as a holiday decoration and invitation for lip locking. And also about how what most people call a Christmas cactus is actually a Thanksgiving cactus and they are actually two different things (and there’s also a Spring/Easter cactus as well. We have amaryllis, paperwhites, cyclamen, Norfolk Island pines, pine-shaped rosemary plants, and more that make up our usual holiday decor. But none are so vibrant and indicative of the holiday as the poinsettia. So let’s talk a little about the history and lore of this plant and also about how day length affects its colorful holiday display. Just in case you want to try saving one from year to year.
Poinsettias take center stage as a 25 ft tall tree at Lauritzen Gardens in Omaha, NE each holiday season.
What is a poinsettia, anyway? It doesn’t really look like other plants.
This plant is a standout in the mostly weed-filled and much-maligned spurge family Euphorbiaceae. This family includes lots of different plants that take on a variety of forms. It does include many weeds, but also many houseplants that have much more of a cactus form than poinsettia. Relatives you might find as houseplants include a cactus-like plant with leaves on its margins (mainly just called Euphorbia), a plant called crown of thorns and a sticklike plant called pencil cactus. It is a weird family. Most of them do have a sap that can cause dermatitis in the skin or a stomach ache if ingested. But poinsettia has earned an incorrect reputation as being poisonous and a plant to steer clear of if you have kids or pets. Sure, ingestion might cause a tummy ache and associated symptoms, but the amount of poinsettia one would have to eat to actually have life-threatening symptoms is astronomical.
These ugly bits in the center are the actual flowers of the poinsettia.
While we enjoy poinsettias for their bright colors, it would be incorrect to say that poinsettias have large, colorful blooms. The colors that we see are called bracts — brightly colored leaves. These bracts change color much the same way leaves change color in the fall: They lose their green chlorophyll to expose the color beneath. This happens when the flowers, those ugly little yellowish lumps in the middle of the bract, mature.
While the classic red poinsettia (pronounced poin-SEH-tee-uh, not poin-SEH-tuh, by the way) lends itself to the classic colors of Christmas, it might be hard to figure out how this weed from Mexico found its way to the top of the list of traditional holiday plants. After all, it is a much more recent addition to the holiday decoration arsenal than the evergreens borrowed from ancient pagan rituals. And while we most often think of red poinsettias, there are hundreds and thousands of different cultivars and colors – and we’ve even taken to spraying them with dye and glitter (shudder).
Poinsettias these days come in all shapes and sizes and colors.
Poinsettias are famous for having a difficult blooming process. The plants are considered short day plants, thought the more accurate description would be a long night plant. This means that in order to set blooms, the plant needs a few weeks where it receives at least 12, and preferably 16, hours of uninterrupted darkness each night. This creates physiological and chemical cues that allow for development of floral structures, which in turn result in development of the colorful bracts. Even a few seconds of light in the middle of the night can stop, interrupt, or delay the process. This often makes saving poinsettias from year to year difficult, and can even make it difficult for commercial growers to provide darkness in our ever (artificially) brighter night sky.
How did a weed get associated with Christmas?
The poinsettia (Euphorbia pulcherrima) is a native plant (and can grow as a fairly large shrub or tree) in Mexico. The original name used for the plant, prior to Americanization, was cuetlaxochitl. I’ve seen them in several places around the world, including one as big as a tree in Kigali, Rwanda (other Euphorbia, like the pencil cactus also grow there). A local Mexican legend from the 14th century explains that a young girl on her way to Christmas Eve mass was upset that she had no gift for the baby Jesus and picked a handful of weeds on her way to church. As she placed the humble bundle of weeds on the altar, they erupted into brilliant red, and all those around exclaimed that it was a Christmas miracle.
Aside from the miracle legend associated with the flower, there are other connections between the plant and the holidays. The traditional red of the poinsettia is cited by many as a representation of a blood sacrifice and the shape of the flower as the Star of Bethlehem. Before poinsettias became a worldwide symbol of the holidays, Franciscan friars included the vivid plants in Christmas celebrations in the 17th century. In Mexico, the plant is also known as Flor de Nochebuena, or Holy Night (Christmas Eve) Flower.
From ditchweed to international holiday superstar
The poinsettia really didn’t come into its current fame until it was introduced to the United States in 1825, at the hands of a politician. It just so happened that the first U.S. minister to Mexico (this was before we had ambassadors) was an amateur botanist. He brought the plant back to his private hothouses in South Carolina, and then shared it with friends (including renowned botanist John Bartram) who introduced the plant to the nursery trade. It filled an empty spot in the nursery calendar, so nurseries were quick to embrace the plant.
This is the guy who brought you the poinsettia, and so much more.
The plant quickly was renamed Poinsettia (it was originally sold under its botanical name) in honor of the man who brought it to the country — Joel Roberts Poinsett. His contribution to the plant’s history and the nursery business in the U.S. was honored by Congress, which has declared Dec. 12 National Poinsettia Day. A date which, oddly, commemorates the date of Minister Poinsett’s death.
Aside from his botanical triumph and service as minister to Mexico, Poinsett was also an “agent” to Chile and Argentina, a state representative, a member of the U.S. House of Representatives and secretary of war. Most people would be surprised to learn that the man who brought you the poinsettia also oversaw the removal of Cherokees from North Carolina to Indian Territory in 1838 and the military during the second Seminole War. But he was also involved in the Columbian Institute for the Promotion of Arts and Sciences and a co-founder of the National Institute for the Promotion of the Sciences and Useful Arts.
This national institute, composed of politicians, promoted the use of the Smithson bequest to form a national museum. While they were defeated in their efforts, the institute went on to become part of the result of the Smithson bequest — the Smithsonian Institution.
The poinsettia didn’t become common holiday fair for the general masses until Paul Ecke Sr., a German immigrant living in California started growing them on a large scale. Ecke and family were also responsible for breeding poinsettias, turning them in to a weedy plant in to the more robust, bushy form we see today. While the Ecke family has moved a lot of production overseas, they are still responsible for 70% of the poinsettias sold in the US and nearly half of all poinsettias sold worldwide.
Paul Ecke Sr, the Poinsettia King (1895-1991)
So, how can I save my poinsettia and get it to rebloom next year?
But if you do want to save your poinsettia from year to year, here’s how to do it:
Keep your poinsettia in a bright but cool spot to keep it colorful longer. When the leaves start to yellow, or you are done with it for the season, slowly reduce watering until it loses all leaves (and colorful bracts, which will be last to go) and goes dormant.
Store the plant in a cool (50-60 F), dry, and dark area. Keep the soil on the dry side, but water just enough to keep the stems from drying out.
After the danger of frost has passed, or in April or May (if you don’t have frost), remove the plant from storage and repot. Use a good quality and light soil mix – poinsettias do not do well with heavy soils. And it turns out that since poinsettias are typically sold as disposable plants, the soil they come in is crap (even high end houseplants these days come in cheap, crappy soil). Practice root washing to remove all the old soil and pot up to a larger size if the plant seems root bound.
Place the plant outside if possible after the danger of frost has passed, or grow in a bright, sunny window. Keep humid, well watered, and fertilized throughout the growing season.
As the danger of frost approaches, move the plant indoors in a bright, sunny window (if it isn’t kept indoors). Ideal temperatures are 75F during the day and 60-65F during the night.
In late September or early October, move the plant to an area that receives no light at night, even from outdoor street lights. The easiest way to provide exact light and dark needs would be in a dark room with lights on a timer. Provide no fewer than 12, and preferably 14-16 hours of uninterrupted darkness and 8-12 hours of light per day. Alternately, you can move the plant to a dark room or closet for its dark period.
After flowers begin to form and bracts start to change color, move to a preferred place in the home for the holidays. Continue to keep the plant well watered, and regularly fertilized through the holiday season.
This month I continue the series on pruning with a look at pruning established landscape trees. These are trees in the prime of life, growing well, starting to shade the garden beneath them and expanding their canopies. Various reasons can prompt the call for tree care professionals.
What reasons would we have to prune a healthy vigorous mid-aged tree? For those we have to examine what may have happened in the past. The fact that a tree is growing well does not always mean it was “selected” well. After a few years time, that cute little nursery tree is flexing its branches and spreading out and, more worryingly, upward. One of the prime reasons for pruning is to reduce the size or expansion of a tree canopy. There may be impending interference with power transmission or other utility lines. The tree may be blocking a view, it may just be frightening in its shear mass or size and pose a psychological threat to its owner. Size reduction is a frequent object of tree pruning operations.
The tree is too large for my comfort
If you find that you want to reduce size of a tree you should ask yourself is it possible and is it sustainable? Ultimately, do I have the right tree for this spot? Size reduction pruning is a battle with tree genetics. The tree wants to achieve a designated height and the tree owner wants to limit that height. Terminal or leaders can be pruned back to a lateral branch to reduce the length of stems and branches. This kind of “thinning” is effective as long as the branch that a leader is trimmed to is large enough to resume the hormonal role for that portion of the tree. Arborists have a 1/3 rule that suggests the branch you trim back to should be at least 1/3 the diameter of the stem it is attached to. That is, you don’t trim back to a twig otherwise it is a heading cut and re-sprouting will be abundant and require more pruning. The problem with the 1/3 rule is that trees don’t respond consistently to pruning on this basis. Some will re-sprout at the cut, others will not. In any event if you embark on size reduction pruning you will likely be maintaining that strategy over the life of the tree and this may not be sustainable. Removal and replanting with a smaller tree species that can be cultivated with little or no pruning would be a more sustainable approach.
Deadwood, I see Deadwood
Deadwood, especially large stems provides habitat for woodpeckers and other cavity nesting birds.
Deadwood is not the end of a tree or necessarily a reason to call the tree trimmer. Deadwood can serve as habitat for cavity nesting birds and is an important part of tree ecology. But dead branches that hang down and have broken from the canopy pose hazards and should be carefully removed. A dead leader can be pruned back and retained especially if woodpeckers have excavated nests that other cavity nesting birds, such as owls, will subsequently use. Of course if the deadwood is part of the active pathology of an ongoing tree disease, its removal may be warranted to prevent disease progress. This diagnosis would involve consultation with your state extension specialist or agent and or qualified arborist with training in tree diseases.
I have a tree with uncorrected branch faults
Codominant stems are likely to fail. The bulge and crack indicate the presence of included bark.Codominant stems often develop included bark (dark area) and later fail as the stems push each other apart.
Perhaps after careful study you realize your tree has co-dominant stems or too many branches coming from one place on the main stem. Both are important branch faults that precede branch failures. Co-dominant stems look like a “slingshot for giants”, two big stems both the same size. Often they are accompanied by included bark that separates the stems. The problem is often that when the stems are large, pruning one will leave a big wound that can let in decay and decrease the life of the tree. If a codominant is 6 inches or larger, it may be best to not remove it. Or remove the entire tree thus fixing the issue. If you want to keep the tree you should choose one stem to thin and prune rather aggressively (not topped) and leave the other stem unpruned. Over time the thinned out stem will grow slower and the unpruned one faster and the codominance will decline. This strategy will require year over year pruning to achieve your goal of shifting the codominants.
All branches from one point. Note large branch that failed at the attachment. This tree is too large to sustain. It could have crown reduction to prevent more failures and reducing the end weights of other branches. But, given the situation, it would be best to completely remove it. The same tree as above. Note large branches from the same point on the main stem. Instead of crown reduction, “Lion’s tailing” pruning was conducted as the canopy was cleaned on the inside. This will force more weight to the ends of branches and stress at their attachments, hastening failures.
If the problem is multiple branches coming from one point the correction is far more difficult. Removing branches from a cluster again provides decay entry and potentially can weaken the attachments of the other branches. Large trees (especially if a branch has already failed) with multiple attachments at the same point are likely to have a failure. The only correction for some cases is tree removal. If there is no or low risk to people or property the tree can remain as such and or pole braces installed to prevent failure. Again, failure likelihood depends greatly on the species. Elms, Oaks, Acacia, Carob, etc, all are at risk of rapid failure.
What if my tree is storm or wind damaged and needs repair?
Storm damaged trees require pruning to repair broken branches and may require several years of pruning cycles to recover a stable crown architecture.
The occurrence of severe weather events is on the rise. Intense winds, increased rain, high temperatures are all commonplace now. Trees that withstood the elements in the past can now be damaged in these storms. In every case a professional opinion on the salvage of storm damaged trees is important. Expectations for restoring an acceptable crown that is safe for the site and those that use it is highly variable. A qualified consulting arborist can guide you in working with storm damaged trees or providing an opinion on removal vs restoration. It is best to contract an arborist who has no interest in a trimming/removal operation since they do not stand to gain from an easy and profitable removal job.
I realize my tree was harmed by previous tree trimming and I want to make it better
This pruning job did little to correct branch faults (too many branches from one point), left stubs and injuries on the main stem. It will take additional pruning over a period of years to correct this damage. Because the tree is young it can still be trained effectively.
Much like the other scenarios, growth patterns and targeted branch work can fix or resolve past insults to trees from inferior pruning . However, don’t expect to resolve all the issues in a single pruning. Often it takes years of careful work to restore the canopy of an abused tree.
I just want to have my tree thinned
Thinning trees is no longer considered a legitimate pruning objective. The recent trend of thinning Canary Island Pines in Southern California is unnecessary and destructive.
If your goal is to get more light into the garden and the tree is a variety that responds well to thinning, this is great. If you don’t have a reason then this is not a legitimate pruning need. Trees don’t need to be thinned and thinning is actually detrimental to some oak species, depriving them of the inner canopy of leaves that they rely upon. Thinning slows the overall growth of trees and reduced stored carbohydrates. Extreme thinning on a regular basis can predispose trees to some fungal pathogens.
At the end of the day….
Mid size, mid life trees require no pruning. People may have reasons to prune when the tree is too large for the site, has been damaged or needs further training to develop its architecture. Trees don’t require pruning if they grow according to their genetic program. Pruning the maturing tree really seeks to undo damage or correct issues that arise in its culture. Branch faults and tree branching structure may not be apparent to every gardener so seeking a professional opinion is always worth the money if you want to be sure of your tree’s pruning needs.
I got a Facebook message early this week from a friend in Sacramento CA that said after over 200 days with no rain, she got 4.83 inches in a 24-hour period from the latest extreme rainfall that occurred over northern California. Others have reported up to a foot of rain in three days. If you follow the news, you may have heard the term “atmospheric river” used to describe the torrential rains and flooding that have occurred this week in San Francisco and other parts of Northern California. In this post, I want to explain what atmospheric rivers are and how they affect rain climatology in the Western U.S. as well as other parts of the United States and the world.
The term “atmospheric river” first appeared in the modern scientific literature in the early 1990s. Since it was first used, there has been a lot of discussion about what the term actually means. Commonly, it is seen as a band of very moist air flowing into a coastal area, bringing the potential for a lot of rain to the region that is at the downwind end of the flow. In some respects, it is like being on the receiving end of a firehose streaming high-intensity water right towards you! After a lot of discussion by meteorologists (described in this Bulletin of the American Meteorological Society article) the official definition in the Glossary of Meteorology became:
Atmospheric river – A long, narrow, and transient corridor of strong horizontal water vapor transport that is typically associated with a low-level jet stream ahead of the cold front of an extratropical cyclone. The water vapor in atmospheric rivers is supplied by tropical and/or extratropical moisture sources. Atmospheric rivers frequently lead to heavy precipitation where they are forced upward—for example, by mountains or by ascent in the warm conveyor belt. Horizontal water vapor transport in the mid-latitudes occurs primarily in atmospheric rivers and is focused in the lower troposphere. Atmospheric rivers are the largest “rivers” of fresh water on Earth, transporting on average more than double the flow of the Amazon River.
Source: NASA Earth Observatory
Why do atmospheric
rivers produce so much rain?
The strong flow of moisture into a region provides an excellent source of water vapor for the development of heavy rain, especially if it is moving into an area with flow up mountain slopes that can help storms develop vertically. That enhances the rain-producing process. The West Coast of the United States provides a perfect location for the occurrence of atmospheric rivers since there is a broad expanse of ocean to provide the water vapor, dynamic storms that concentrate the flow into bands that can stretch all the way from the Hawaiian Islands to California (which explains an alternate name, “Pineapple Express”), and mountains near the coast to provide lifting for the moist air once it comes onshore. Cliff Mass of the University of Washington often discusses them in his blog on the weather of the Pacific Northwest.
Do atmospheric rivers
occur in other places?
The short answer is Yes! While historically they are discussed most often when talking about weather on the West Coast, atmospheric rivers (ARs) can and do occur in other places as well. Anywhere that has a good source of moisture plus dynamic storms with strong airflow can experience ARs. In the Southeastern U.S., we get them when strong flow from the Gulf of Mexico or the Atlantic Ocean feeds into our region, usually ahead of a strong low pressure center that provides the necessary dynamics to create a narrow band of moisture feeding into the region. According to research by University of Georgia researchers, they occur most often in the cold months of November through March but can occur in any month of the year. In the Southeast, we get about 40 events per year that are classified as ARs. I was surprised to read that there are slightly more events on the East Coast than along the Gulf of Mexico, but anywhere along the Southeast coast can be affected. No trend towards more or fewer events was seen in the 1979-2014 period.
NOAA’s Physical
Sciences Laboratory’s page describing ARs says that on average, about 30-50% of annual precipitation in the west
coast states occurs in just a few AR events, thus contributing to water supply.
ARs move with the weather and are present somewhere on the Earth at any given
time. This site
has some great resources for tracking and forecasting ARs around the world.
Of course, atmospheric rivers are not the only source of heavy rain events, but they are one of the primary sources for the West Coast. In other areas, tropical systems like slow-moving hurricanes or stalled fronts can also drop a lot of rain. You can also get very heavy rains from small local systems of thunderstorms if conditions are right, especially if the storms “train” or move one after another over the same area like cars on a freight train. We saw this in the Nashville area a few weeks ago, where the heavy rains resulted in significant flooding over a few counties.
Rain garden in the Allen Centennial Gardens on the campus of the University of Wisconsin-Madison. Source: James Steakley, Commons Wikimedia.
How do atmospheric
rivers and other heavy rain events affect gardeners?
If you are a gardener in the Western United States, you are already well aware of the long dry season over the summer followed by bouts of rain that can occur over the winter months. The timing of the switchover from dry to wet conditions depends on how far north you are on the coast, with the summer dry spell coming earliest in southern California and moving northward with the position of the jet stream as the summer progresses. Dealing with the effects of an AR is like any other attempt to protect your garden against heavy rainfall, and can mean proactive action to make sure that water-sensitive plants and trees are not located in low-lying areas where rain collects. This 2013 article from the Garden Professors blog on-site assessment is still good advice for planning ahead for soggy conditions by walking through your property in the rain. Designing for erosion control, such as rain gardens, can also help divert water in high-intensity rainfall.
In spite of the heavy rain that fell in this last atmospheric river event, the rainfall barely made a dent in the long-term drought that is present across a lot of the Western U.S. Drought will continue to be a part of the hydrologic cycle that affects gardeners, farmers, and water managers across that region and across the world.
I’ve promoted root washing of containerized and B&B trees and shrubs for a few decades now. The experimental science is slowly coming along – it can take several years to determine if the practice is more successful in terms of plant survival than leaving the rootball intact. But we know how soils function in terms of water, air and root movement, and we understand woody plant physiology. So it’s pretty easy to predict what will happen when trees, whose roots are held captive in layers of stuff, are then planted, intact, into the landscape.
Maple newly purchased from nursery.
Early in spring 2021 I purchased a couple of Japanese maples to frame our garage. As always, I root washed these specimens. Here’s a play by play of what we did, and what we found.
Container removed, exposing fine roots. Some of the media has fallen away and is at the bottom of the wheelbarrow.Since we can’t see the root flare, we mark the point at which the trunk and soil meet.As we remove the container media, we find burlap and twine. And under that, a clay root ball. There is a root crown somewhere…Some beating on the clay rootball helps create some cracks where water can then help with the process.Into a nice soaky bath to loosen up that clay. The longer it sits, the more clay will slough off.We speed the process along with a directional spray of water.Jim gets his fingers into the wet clay to pry it away from the roots. Still no root crown, but you can see the Sharpie line on the trunk a couple inches above the clay.Eureka! A root flare several inches below the original media level.
After more cleaning and untangling, we have a root system ready for planting. Well, almost.
We have roots, but we still have some problems.It’s got some pretty crappy roots (from not being potted up properly at the nursery), and the remanent of a stake next to the trunk (about 4 o’clock). But there is a nice structural root to the left, with healthy fibrous branches.“Knee roots” have to go (I call them “knee roots” because they are at 90 degree angles). They have poor structure and will only continue that downward growth pattern, rather than growing outwards. The easiest thing to do is sever them when they turn downward at 90 degrees – don’t worry about removing them if they are too tightly entwined. New root growth at the cut will be directed outwards.We neglected to get “beauty shots” of our maples through the summer, but you can see one of them to the left of the New Zealand flax plant in the pot. Both maples established their root systems quickly and grew vigorously throughout the summer.Now in late October, the maples are turning color. Note the distance between the trees and the garage – this ensures that we will have little branch/building conflict as the trees grow in height and spread.Here’s one of our beauties getting ready to shut down for the winter. They thrived throughout the summer, even when we reached record high temperatures. We look forward to their continued success in years to come.
If you are still wondering why this is a cautionary tale, consider what would have happened if the rootball was planted intact:
The root flare would have been buried below grade.
There would be multiple layers of stuff between the roots and the native soil (i.e., clay, burlap, and media).
The twine circled around the trunk would girdle it eventually.
The poor structural roots would not create a stable support system.
Now, one can argue all they like that there isn’t a robust body of scientific literature to recommend this practice – and there isn’t, yet. But leaving rootballs intact creates textural discontinuities between the roots and the native soil, and poorly structured woody roots are not going to correct themselves. So why not embrace a practice that removes both the soil and root problems?
Say the word “hydroponics” or the even more mysterious sounding “controlled environment agriculture” and the image that most people conjure in their minds is of large greenhouses or artificially lit rooms filled with complex hoses and tubes using all manner of technological gizmos to pump water and nutrients to plants. True, modern ag technology does allow for some pretty amazing and technical production of food but hydroponics can be super simple and so easy that just about any home gardener can do it.
Why grow hydroponically at home?
Growing vegetables can be pretty easy and straightforward
for outdoor production – seeds, soil, water, and wait (sure, there’s a few
other steps in there), so why complicate things by growing hydroponically? Aside from the challenge and the novelty that
delights many gardeners, intensive growing with hydroponics can allow gardeners
with the smallest of spaces to grow impressive amounts of produce in a short
amount of time. Most of these systems
also do well for winter production indoors with the use of grow lights or some
good-sized south facing windows.
Hydroponic or similar-type production systems are the “craze” right now for folks wanting to grow some of their own produce at home, usually in smaller indoor spaces, but these systems can run into the hundreds or thousands of dollars making production less than economical. Plus, most of these systems require the use of pre-made plant/seed plugs that add to the expense.
Why is hydroponic production important?
On a larger scale, hydroponic and controlled environment agriculture has a few benefits that will help in feeding a growing population on a warming planet. Hydroponic production can be pretty intensive, meaning that it can grow a large amount of food in a relatively small amount of space. This makes it ideal for production in urban areas, which is important as most countries become more urbanized. It also cuts down on transportation needs to get food to consumers. This not only reduces fuel consumption but also, as we can see, makes it easier to get food to large populations when distribution becomes an issue. And as the term “controlled environment agriculture” implies crops can be grown using hydroponics in greenhouses or indoor farms no matter what the season or climate making it ideal for year-round production in areas where it is too cold or too hot part of the year to do so. This also means that hydroponics and controlled environment agriculture can be important mitigation strategies for climate change. When the temperatures or precipitation are no longer favorable for growing outdoor crops in certain areas, controlled environment ag can provide a stable source of produce with indoor production.
And as ironic as it sounds, growing hydroponically
drastically reduces the amount of water used for production. Closed systems, which either recirculate
water or grow in enclosed containers, use much less water than field production
systems relying on irrigation.
A simple system example
Earlier this year I build some super simple enclosed hydroponic systems for demonstration at our Extension office and at the county fair. My goal was to show how easy hydroponic production can be – no need for pumps, tubes, or expensive equipment. The system was so simple that I built it with my non-horticultural interns as an onboarding/team building exercise.
The system we built utilizes the Kratky method of hydroponic production – a simple system where the plant is suspended on top of a container full of nutrient solution. In a typical recirculating hydroponic system where water is moved around air is introduced into the water that then provides oxygen to the roots to avoid hypoxic conditions that damage roots. Some static systems rely on introducing air (like using aquarium air stones) to introduce oxygen but the Kratky method is even simpler than that. Instead of introducing air into the solution, the level of the solution is reduced (usually through use and evaporation) as the roots grow keeping a section of roots exposed to open air. The setup is super simple and low maintenance – no moving parts, no electricity (unless I need to use lights for indoors). Just plants, a medium to hold them, a container and a nutrient solution.
I’ve seen the systems made with all kinds of containers but we chose 25 gallon storage totes because they are inexpensive and pretty easy to come by. Having a lid that is relatively easy to cut/drill also makes these kinds of containers ideal to make multi-plant “beds” but I’ve also seen lidded buckets used as a single-plant system.
To hold the plants we used plastic net pots that you can find at garden centers that sell pond or aquarium plants (or order) that are also now common at hydroponic supply stores, if you’re lucky enough to have one in town. You can also use plastic orchid pots or standard nursery pots, perhaps adding extra holes for roots to grow out. We used 6 inch and 2 inch pots to plant a variety of sizes.
Net pots in the system, with holes made slightly smaller for them to fit and not fall in.
Next we cut holes in the lid slightly smaller than the diameter of the pots so that they sit on top and don’t fall through. You can do this by tracing and cutting with a sharp object, or use a drywall hole saw that you use with a drill to cut a perfectly round hole. We used one with adjustable sizes, rather than buying individual sizes.
And now, to plant!
The pots were then filled with an inert, soil-less medium to support the plants. We used a puffed clay stone called LECA, but you can use rockwool or hemp fiber blocks made for hydroponic starts, large particle perlite, or even something like a poly fiber filling (like used in sewing) – just something that won’t break down to hold the plants in place.
Some of the plants I had started in fiber cubes so those easily went into the LECA, but we did end up buying a few transplants. Since these were started in some sort of potting soil we had to wash as much of the soil off as we could. We placed larger plants like peppers and kale in the large pots and smaller plants like herbs in the small pots.
As for plant selection, leafy greens and herbs like basil and parsley are easiest and can use smaller containers and pots. Plants like tomatoes and peppers will need bigger containers and pots and will also require more light and heat if you are growing them indoors.
A solution for easy nutrient solutions
And last but not least – the nutrient solution. Since we are growing without soil we have to provide basically all macro and micro nutrients. We are used to supplying nutrients like nitrogen and phosphorous, but not so used to supplying things like manganese and molybdenum. This one is probably the scariest to those new to hydroponics, but there are some easy options out there for small scale production that are “off the shelf” solutions. Rather than worry about mixing up nutrients by hand, these pre-made mixes make it easy for home growers to try hydroponics. They come in two or three part sets of either liquid or solid fertilizers, because some of the chemicals used will react and precipitate out into a sludge if kept together in concentrated form. Just mix according to package directions and you’re good to go. If you are growing anything like tomatoes or peppers that require flowering and fruiting, you’ll want to make sure the formula is for flowering plants. Regular water-soluble fertilizers might do in a pinch, but for long term growth you’ll want to invest in something with all micronutrients.
Storage tote hydroponic system, sitting in the office courtyard.
If you’re planning on refining your technique, you might want to invest in a pH meter or TDS (total dissolved solids) meter to fine tune the solution based on the minerals dissolved in your water. And if you have really hard water you can usually get an additional nutrient product to account for the pH and calcium levels to balance things out.
So now we just filled the totes with the solution all the way up until the bottom few inches of the pots were covered. We kept watch on the solution and added water as needed, keeping in mind that as the roots grow out of the pot the nutrient solution level needed to be low enough to expose around 2/3 of the roots to air.
The nutrient solution is only a few inches deep in the bottom of the tote at this time, allowing roots to be exposed to air for oxygen uptake.
As the plants grow, you’ll just want to keep an eye for signs of nutrient deficiency and add nutrients to the water as needed. The solution should be completely dumped and replaced every 6-8 weeks, as the plants rapidly deplete some nutrients, allowing some to build up to toxic levels. You can typically just pour the solution out on the garden or lawn, as it only contains plant nutrients. However, you’ll want to make sure not to keep dumping in the same spot to avoid build up of salts in the area. Spraying the area with a bit of water from the hose can help wash it off of plants and start diluting it into the soil, rain and weather should do the rest of the job. But if you are in an area with little precipitation, you may also want to take care since there won’t be a lot of water to dilute the nutrient build up over time. And just remember, if you harvest and completely remove crops, pull apart and clean the system with some good soapy water and a sanitizer (bleach works well). You should do this every few months if you have a long-lived crop in the system.
In a nutshell…..
A simple system like this one can be a great way to explore a new growing technique, even for beginner gardeners. After these were set up, we basically left them in our courtyard all summer with little to no maintenance, except adding water earlier in the season and changing out the nutrient solution once. If you need a bit more info, or want to try something a little more complex, there are some great resources out there for small systems that I’ll share below.
As the climate warms the value of trees for cooling the environment around buildings, especially in cities, drives tree planting programs. Planting trees is just the first step in growing a tree in a sustainable landscape. Successful plantings require evaluation and guidance of the new tree’s current and future branch architecture. In almost every case, nursery grown trees will require some structural pruning so that a shade tree can develop strong and effective branch attachments that will support the canopy for the coming decades without failure. In this blog I cover maintenance of the newly planted tree including how to structurally prune young trees so that they develop strong and sustainable canopies.
As mentioned in earlier pruning blogs, trees do not require pruning. This is predicated on the assumption that trees are allowed to grow in the way they are genetically programmed to grow without damage. Unfortunately many container nurseries prune trees with a heading cut to the central leader in order to create branches that can further be pruned to make a “lollipop” canopy that mimics the form of a large tree. Consumers have become accustomed to this “in-pot” miniature version of a shade tree and nurseries are accustomed to producing them. Low branches are removed to enhance the tree lollipop shape. Nurseries often stake trees tightly to provide a way to keep them from being blown over in wind events and since all the temporary branches are removed from the low trunk they are top heavy and require rigid staking usually with a stake taped to the trunk. Tightly staked trees grow taller than unstaked trees and their trunks may lack caliper or taper (increase in trunk diameter lower on the stem). This requires that when these trees are planted out that they continue to be staked, otherwise they would fall over. This creates another burden in getting the newly planted landscape tree to survive—helping trees stand on their own.
This newly planted coast live oak complete with gator bag for water retains the nursery stake which should have been removed and has two other stakes because it does not have enough taper to stand on its own. There are no temporary branches low down and it has been “lolipopped” during nursery production. Branch faults such as “all branches from the same point” will certainly develop if it is not structurally pruned.Crape myrtle is notorious for lacking taper when tightly staked during nursery production. this tree retains the nursery tape and stake and has the classic lolipop shape that will require structural pruning to correct.
Nursery pruning creates two kinds of branch faults that if left in the tree canopy will lead to failure later. These result from heading the main leader of the young tree. When buds grow from the pruned tree, they often produce too many branches from the same place or two branches or new leaders that are the same size. We call these faults: too many branches from one point and codominant stems respectively. If the nursery tree retains these branches and they are allowed to mature in the landscape tree, one or more branches may break loose. Almost all structural pruning seeks to correct these faults at some point in the life of a nursery-grown landscape tree. The approaches are different depending on how long the branch fault is left in the tree after planting. Branch faults of newly planted trees are best corrected in the first year–they are easy to correct in the first few years and problematic after that. This is because when poorly attached branches grow well and attain greater size over time, they will pose a problem upon removal as pruning will leave behind a substantial wound which provides an entry point for wood decay. Structural pruning is best done in the nursery or if in the landscape, in the first year after planting.
This young oak retains the nursery stake even after several years post planting. The lolipop shape is indicative of inherent branch faults that have not been corrected
There are several goals of early pruning (1-3 years post planting): -Retain temporary branches on the stem to assist trunk growth (but keep them pruned) -Remove competing leaders (remove a co-dominant stem) – Thin clusters of branches (fix the all branches from one point fault) -Leave the first permanent branch unpruned -Subordinate all other branches to “temporary” status by heading them back – Leave unpruned branches along the stem that will take a permanent place in the crown of the tree. -Leave enough space between permanent branches to support their sustained growth over the life of a tree -Permanent branches should be spaced vertically and helically around the main or central leader
Most trees will do all of this without any pruning if they are unpruned from the seedling stage. They will shade out their temporary branches and permanent large branches will form strong attachments and uniform spacings. Heading cuts on young trees destroy their form and this should be avoided. In the next blog I will cover pruning young to mature trees.
Do you wish you had a crystal ball that could tell you what the climate will be next year when you plan your garden? So do many other gardeners (and climatologists). But while there is no magic answer, we do know that in many parts of the United States and other countries, year-to-year climate variability is strongly dominated by what is going on in the eastern tropical Pacific Ocean. This is through a phenomenon called “El Niño Southern Oscillation” or ENSO for short.
Witch Hazel Covered By Snow In The Garden. Hampshire UK. Source: Si Griffiths, Commons Wikimedia
What is ENSO and how does it affect climate?
ENSO has
three phases—a cold phase with unusually cold water in the equatorial Eastern
Pacific Ocean (EPO) called “La Niña”, a warm phase with unusually warm water in
the EPO, and the neutral phase that occurs between the two extreme phases. The
ocean see-saws back and forth between the two opposite phases on a semi-regular
pattern that usually lasts between two and five years from one El Niño to the
next. Sometimes you can have two La Niña years (or even three) back-to-back (the
end of 2021 is expected to be a second La Niña in a row), but you almost never
have two consecutive years of El Niño.
In many parts of the world, the phase of the ENSO is highly correlated with the climate. Scientists can use that relationship to predict what the climate might be like in the coming months. That is helpful for gardeners who need to know what to expect both next season and next year for planning purposes. Not all parts of the world have a climate that is well correlated with ENSO, however, and so folks in those areas will have to depend on other methods to look ahead to next growing season. Winter has the best correlation between ENSO phase and climate, while summer is much less predictable. And every El Niño and La Niña is distinct, leading to variations from the statistical pattern we expect.
How does the temperature of the tropical Pacific Ocean affect climate in other parts of the world?
You might think that unusually warm or cold water in the equatorial Pacific Ocean would not have much impact in other parts of the world because of the distances involved, but it does. Since the atmosphere flows like a river, putting unusually warm water (El Niño) into the EPO acts like putting a rock into a stream. The flow of water (or air) shifts around the rock, changing the pattern of atmospheric winds that blow weather systems around. When we are in a warm El Niño phase, the storm track shifts south and covers the southern US, leaving the northern US warmer and drier than usual. When I lived in Wisconsin, we noted that lake ice cover in El Niño winters did not last as long as other years, which made ice fishermen like my dad unhappy. La Niña shifts the storm track in the opposite direction. Because of that, La Niña winters are colder and wetter than average in the northern US since the storm track shifts north into the Ohio River Valley and sometimes even farther. This leads to cold, damp winters in the northern US. Similar correlations, called teleconnections, are seen statistically in climate records at many places on earth.
If we know what the phase of ENSO is likely to be, that tells us what climate conditions are expected in areas where there is a teleconnection between the EPO and that region. While every El Niño and La Niña is unique, statistically they do provide guidance on what to expect in that region, and most years they are correct, although once in a while a wildcard like a Sudden Stratospheric Warming will occur and give us an occasional busted forecast, as it did in February 2021.
What do we expect this year?
Right now, we are in neutral conditions following last winter’s La
Niña, but we are headed back towards another La Niña in the next couple of
months (almost an 80% chance in the November through January period). That phase
should last for most of the winter but is expected to return to neutral by spring. After that, it is too far out to make a
believable prediction. The Global
ENSO Temperature and Precipitation Linear Regressions website provides
global correlations between the ENSO phase and what kind of temperature and
precipitation anomalies to expect. In it, each three-month period shows the
relationship between the temperature anomaly of the EPO and other parts of the
world (regression) and how strong that relationship is (correlation).
In the map below for December-February (DJF) temperature, it shows that if the EPO is unusually warm (+) in an El Niño, then the northern part of the US will also be unusually warm (+) while the southern states are cooler than normal (-). The storm track over the southern US in an El Niño year brings rain and clouds to that region, keeping conditions wet and cool due to lack of sunshine. A La Niña year is just the opposite. The strong correlation in both southern and northern states shows that it happens most of the time, but in areas with little correlation, you can’t use ENSO reliably to predict seasonal conditions. If you have a hard time interpreting these maps, the website has a tab that explains it in more detail.
The bottom line
For this coming winter, I expect warmer and drier conditions than usual in the southern tier of US states as the storm track shifts north. That means more overwintering of insect pests and diseases; an early start to the growing season is also likely. The northern US is expected to see colder and wetter conditions than usual, which means a later start to the 2022 growing season but less chance of drought next year, although fungal diseases could be bad if the damp conditions continue into spring and summer. Western Europe could see warmer conditions than usual but the correlation is weak so that is not a strong forecast. Australia is likely to be colder than normal, with a fairly high probability because the correlations are high, at least near the coasts. This should last until spring, when the La Niña ends, and we swing back into neutral conditions when other climate factors become more important. In the Southeast, the summer after a La Niña ends is also a hot and dry summer due to the lack of recharging rain over the winter, so I think we have the potential for drought in the Southeast next summer.
