What a third year of La Niña means for gardens

NOAA recently announced that La Niña is favored to continue through summer and fall this year and could last through next spring. This forecast is bound to strike fear in gardeners in the western United States, since La Niña is associated with drought in the western parts of the country which sorely needs more rain. Los Angeles has announced some stringent watering restrictions due to impending water shortages, and that means gardeners will have to be especially careful there to use the water they have wisely.

Los Angeles Air Force Base uses xeriscaping to conserve water. Source: AF_SMC., Commons Wikimedia.

What is La Niña?

Many people have heard the terms La Niña and El Niño but for those who don’t, let me take a few minutes to describe them. You can also read more in my blog post from last fall when this winter’s La Niña was just getting going. El Niño and La Niña are two opposite phases of an oscillation in the atmosphere and ocean in the Eastern Pacific, with neutral conditions in between the two phases as the oscillation swings back and forth like a seesaw. When that region’s sea surface temperature is warmer than usual near the equator, rising air above the warm water creates thunderstorms which act like a rock in a river diverting the flow of air along the southern US, especially in winter when El Niño and La Niña are usually strongest.

Source: NOAA.

In El Niño winters, the Southeast is usually wetter and cooler than usual due to the presence of the subtropical jet stream overhead. It pushes storms with their associated rain and cloudy conditions through the region, recharging soil moisture for the next growing season. In La Niña winters, the jet stream is shifted to the north over the Ohio River Valley, leaving the Southeast warm, dry, and sunny. That means conditions for severe weather are more favorable in the Southeast than in other phases; we have certainly seen plenty of that this year so far. The lack of a strong jet stream also means that tropical activity in the Atlantic Ocean is more frequent and stronger than in El Niño years. In northern parts of the country La Niña winters are usually cold and snowy with a late start to spring, as we have seen this year. The Pacific Northwest is often wet, which also matches what has occurred in their coastal areas this year.

The ENSO Index shows El Niño periods as positive values (in red for warm Eastern Pacific ocean temperatures) and La Niña periods as negative values (in blue for cold ocean temperatures). Index values between +0.5 and -0.5 are considered neutral and are highlighted with gray.

How often does a third year of La Niña occur?

The atmosphere usually swings back and forth between El Niño and La Niña roughly every 3-5 years. Right now we are ending a second consecutive winter of La Niña; with its predicted continuation, that would make it three years in a row. This is not unprecedented, but it is certainly unusual, since 1950 we have only had two “triple-dip” La Niñas. Since there are so few direct comparisons it can be hard to determine exactly what to expect this growing season and on into fall and winter. Our best bet is to assume that typical La Niña conditions will occur. The 3-month composites of the expected anomalies (differences from average; MAM means March-April-May, etc.) show the seasonal variability of El Niño and La Niña for temperature and precipitation across the US. La Niña and El Niño’s effects stretch far beyond the US and affect global weather patterns.

What does this mean for the growing season across the United States?

Typically effects from a La Niña are weakest in the summer because sea surface temperature anomalies are not strong and is often switching from La Niña through neutral conditions to an El Niño the next year. However this year the La Niña is still going strong, so this seems less likely. That means the pattern of warm and dry southern states are likely to continue, which is trouble for the already drought-ridden Southwest including California (where severe water restrictions are now in place). With the high temperatures, low rainfall, and low humidity, that means water stress on gardens will be higher than normal, and drought and wildfires could dominate that part of the country for the next few months.

In the Southeast, the active spring severe weather season will likely give way to an active tropical season in summer and fall. Rainfall in the Southeast in summer is dominated by tropical systems and small-scale convective rain events that provide only hit-or-miss rain. If you are in the path of a tropical storm, you can experience several inches of rain while areas a few counties away can see none, resulting in a feast or famine of rain. In the Pacific Northwest wet conditions in coastal areas will give way to drier conditions in the summer but may return again in the fall, while inland areas may continue to see very dry conditions that will lead to increasing drought and water shortages. The Northeast could see wetter than normal conditions so a drought there this year seems unlikely. The central part of the United States could be the hardest hit by drought conditions and the drought that is already present across a large part of the central and western US is likely to get worse over the next few months with little rain expected. That will affect not only gardeners but the farmers of the main grain-growing area of the US, at a time when Ukraine, normally a big grain producer, is not likely to be able to produce a regular crop this year because of the ongoing war.

Source: Walter Siegmund. http://commons.wikimedia.org/wiki/File:Eschscholzia_californica_7717.JPG

Managing your garden in La Niña

Gardeners in the Southwestern US will have the most difficult conditions to manage this year due to the water restrictions and ongoing drought there. Proper use of irrigation and conserving soil moisture through mulch and appropriate choice of plants are good ways to keep water use lower. This may also be true of gardeners in the central US, where the drought could also be severe this summer. In the Southeast, the summer rain you get will depend on tropical activity and where the storms go so you could see either wet or dry conditions. Managing your garden for both dry periods and potentially heavy rains is a challenge that you may need to deal with this year. In the Northeast, the climate may be easier to contend with this year but even short-term dryness can be a problem for plants that need regular infusions of water. In the Pacific Northwest, predictions for a warmer and drier than usual summer mean you should pay careful attention to water-conserving measures, especially in inland areas where drought is already a problem. If you are outside the US, then make sure you understand how La Niña is likely to affect your region and manage your garden accordingly.

The plants have eyes! Another foray into B(ad) S(cience).

A week or so ago one of my “friends” sent me a link to a new journal article that claims plants can “see.” (The use of quotes here indicates that plant vision is suspect, as is the friend status of the person who sent the article.) Of course, dissecting the claims in this article became an all-consuming task for the next several hours. And rather than writing off those hours as never to be reclaimed, I decided a blog post would at least set those thoughts down to save other skeptics the time.

The article can be found here; it reports on the ability of leaves to mimic other leaves. While the concept of leaf mimicry is not new and has been seen in agricultural weeds for decades, this article goes a step further in claiming that plants can actually see the leaves they are to meant to mimic.

But let’s back up a bit to explore leaf mimicry, which is a thing. Leaf mimicry serves to protect plants against herbivory and other types of removal (like weeding). This phenomenon was reported decades ago where agricultural weeds were shown to change their morphology to more closely resemble the desired crop. The benefit is obvious: if a weed looks like a crop plant, it is unlikely to be removed through hand weeding. Likewise, if a weed resembles a poisonous plant, herbivores that are visual learners will avoid these weeds. When some plants of a species are disproportionately allowed to survive (i.e., not eaten or removed), they reproduce better. Higher reproductive capacity means more offspring: this is the process of natural selection. We can even see this in dandelions in our lawns and gardens.

One astounding leaf mimic is Boquila trifoliolata (a tropical woody vine). This vine can be found on several host trees, where it mimics the leaves of each host and thus avoids herbivory (this short article by Gianoli and Carrasco-Urra is worth reading).

Boquila trifoliolata [courtesy of Wikipedia]

The article I’m currently dissecting doesn’t report on field observations of mimicry; instead, it looks at an indoor situation where B. trifoliolata is grown in the presence of artificial leaves. The authors claim that the leaves on the living vines began to take on the shape of plastic leaves on artificial vines located on a shelf above them. Despite Gianoli and Carrasco-Urra’s earlier speculations that horizontal gene transfer or volatile chemical signals might trigger the mimetic response, these authors propose that plants can see the artificial leaves and adjust their leaf morphology accordingly. They base this hypothesis on papers written over a century ago that suggest plants have ocelli (“little eyes”) as a way of sensing light. Of course, a century ago we were decades away from discovering pigments such as phytochrome and cryptochrome, both of which inform plants about light conditions in their environment.

Figure
Image from White and Yamashita, 2022

There are a lot of problems with this paper; it would take me a separate blog post to critique the Materials and Methods section alone. But the biggest red flag for me was the following paragraph:

This reflects significant author bias: the experiment didn’t work in the winter, so they did it in the spring and summer to see if they got results they liked better. And apparently they did.

SIDEBAR: Other potential red flags that careful readers might note include
*A lead author with no apparent connection to an academic institution
*A journal (Plant Signaling and Behavior) that focuses on the questionable field of “plant neuroscience”
*An experiment performed under vague and uncontrolled conditions
*Typos, grammatical errors, and awkward writing throughout

I’d like to propose a couple of different reasons that these leaves may have changed shape in the summer and not the winter:

  1. Summer months are hotter and brighter than winter months. The experimental leaves were exposed to increasing heat and water loss compared to the shaded control leaves. Newly expanding leaf morphology changes in response to changing environmental conditions.
  2. Under increasingly hot temperatures, plastic releases volatile chemicals, many of which are toxic. Leaf morphology has been demonstrated to change in response to air pollutants.
Leaves can orient themselves vertically to reduce exposure to high light intensities. Morphology can change, too.

This is a deeply flawed article based on a poorly designed experiment and reflects significant author bias in the interpretation of the results.

And just for more cowbell, here is Christopher Walken’s take on plant ocelli.

People and Plants

This is the springtime installment of our random, look-behind-the-scenes of the plant world blog post. In this episode we’ll take a look at William Forsyth, a gud Scottish horticulturist.

William Forsyth 1737-1804

William Forsyth was born in 1737 in Old Meldrum, Aberdeenshire in northeast Scotland. In 1763 he moved to London to work at Syon Park House for the Earl of Northumberland. After that gig he transferred to the Chelsea Physic Garden and trained as a gardener under Phillip Miller. He eventually took over the head gardener position in 1771 and held that post for several years. Forsyth was quite a “plant nerd” who enjoyed exchanging plants with other botanical gardens. He greatly increased the diversity of horticultural collections throughout Britain and Europe with his avid plant trading.

  • In 1779 he was appointed superintendent of the royal gardens at Kensington and St. James’s Palace and held this position until his death.
  • He was one of the original members of the Royal Horticultural Society which held its first meeting on March 7, 1804.
  • Forsyth died on July 25, 1804.

Always a gardener willing to try new things, Forsyth created one of the first known rock gardens in gardening history in 1774 while curator of the Chelsea Physic Garden. He collected over 40 tons of assorted rock from near the Tower of London, included flint and chalk from nearby downlands (an open area of chalk hills) and threw in some pieces of Icelandic lava. Unfortunately the garden didn’t produce as hoped and was considered a failure. Such is gardening.

A pile of rocks does not a rock garden make.

Forsyth published several works on horticulture and was regarded as an expert on fruit tree management and flowering plants. One of his books, Treatise on the Culture and Management of Fruit Trees (1802), was a great success and ran into several editions. You can read it here. His other book, Observations on the Diseases, Defects, and Injuries of Fruit and Forest Trees, was also popular.

Forsyth had a bit of the salesman in his personality…

In 1798 he created a ‘plaister’ which he claimed would heal defects and wounds in trees even “where nothing remained but the bark.” This secret “Composition” as he called it, had a long list of sometimes changing ingredients which included dung, ashes, lime, soapsuds, sand, and urine. Forsyth claimed his Composition could render the timber of poor and derelict oak trees “fit for the Navy as though they had never been injured.”  The Royal Forests were in poor condition at the time and the nation needed sound timber for shipbuilding so as to continue the war with Napoleon Bonaparte.

Forsyth’s directions for making his Composition, in case you’d like to give it a try.


Naturally the Admiralty was very interested in the concoction (my word) and so the Government was persuaded to pay him a large sum of money. The British Parliament gave him a grant of £1,500 ( approximately $260,868.41 in current US dollars) to continue developing his mixture with the understanding the secret formula would eventually be shared with the government.
In the meantime word had gotten out about the Composition and Forsyth decided to take advantage of the situation. He published a best-selling treatise on his ‘plaister’ and the formula was also published in The London Gazette, all for a fee of course. It was too good to last.
A number of prominent British gardeners and botanists experimented with his treatment and quickly revealed (early Garden Professors, show us the science!) that it was quite useless. It didn’t pass the CRAP test. Plus the government took issue with his publishing the formula for the public while having yet to deliver said to the government which had paid a hefty sum for it.
Forsyth was exposed as a fraud. 
But fortunately he died soon after this and his reputation was saved via his publications and lifelong liaising with gardens and gardeners.

I’m sure by now you must have sussed out the plant, right?
If you thought Forsythia, you’re correct!

Khanh Ngo Photography/Getty Images

Forsythia, a genus of spring blooming plants in the olive family Oleaceae and mostly native to Asia and named after William Forsyth.
I can hear you asking, so how is the name Forsythia pronounced? (Yes you are, I can hear you)
In the UK the name is pronounced “For-sigh-thee-a” reflecting the correct pronunciation of Forsyth. In the USA the name is often pronounced “For-sith-ee-a”. Take your pick.


The moral of this story, dear readers, is people have been selling useless garden potions and notions for centuries. So no matter how knowledgable the advice giver seems to be or how may accolades they’ve won, always sift their “Composition” through a sieve of science to screen out the b.s.
(And remember to never apply any sort of manure, literal or figurative, unless advised to by a soil or CRAP test.)

More reading to help you with sifting:
https://www.researchgate.net/publication/315662987_Scientific_literacy_for_the_citizen_scientist_WSU_Extension_Manual_EM100E

Mycorrhizae! Myco what??

You may have heard about these fungi or perhaps not. But if you look carefully on bags of potting mix and on some fertilizers you will see that they are marketed as “essential” to your garden plants.  Claims on mycorrhizal products suggest dramatic growth increases.  These claims like many “snake oil” products can be extreme and are based on science that supposedly bolsters their efficacy.  Mycorrhize are responsible for tremendous growth increased when compared to plants denied access to the fungi.  This has been known for many decades.

Mycorrhizal plant (right) vs non-inoculated plant (left). With permission from Linderman, 2005.

The disconnect between mycorrhizal claims and garden efficacy is that there are usually mycorrhizae present in most gardens. So adding more won’t necessarily improve the growth of plants. There are also some other concerns. Mycorrhizal products are not all the same. Research on product efficacy suggests that about half the retail products available contain no viable inoculum. Spores of mycorrhizae have poor germination viability and do not last long on the shelf although some products contain hyphae as well as spores and these may last longer. So even though products are out there they might not not infect plants.

While mycorrhizal products may or may not hold value for gardeners, mycorrhizal fungi are essential for almost all plants. A few, such as brassicas, do not form mycorrhizal partnerships but all trees, other woody plants and most annuals do become infected by and benefit from these fungi. Plants and mycorrhizal fungi are symbiotic and each receive reciprocal benefits when each partner is well established.

There are two broad categories of mycorrhizal fungi the VA (formerly VAM) or vesicular-arbuscular mycorrhizae and the ectomycorrhizae, (EM). VA mycorrhizae are fungi in the class Zygomycetes related to the common bread mold fungus. They inhabit 80% of the worlds plants. They can not be seen without staining and careful microscopy. Ectomycorrhizae are the other form and they are exclusively from the Basidiomycete or mushroom forming class of fungi. Many of the mushrooms that grow in forests are actually supported by tree roots they affiliate with. Ectomycorrhizae change the shape of roots giving them a stubby appearance. This is because ectomycorrhizae form a mantle around the root of hyphae called the Hartig Net.

Ectomycorrhizae can be seen in soil threading in and around roots often covering them in white mycelium.

So why the big deal? What are the benefits that plants share with mycorrhizae and how do the fungi benefit from their plant hosts? Early studies showed that mycorrhizae make minerals, especially phosphorus, more available to their plant partners. Studies show that mycorrhizae increase the efficiency which plants use many fertilizer elements, even nitrogen. Fungi become “sinks” for plant carbohydrate or sugar. Mycorrhizal hyphae replace root hairs in most infected plants and vastly increase the surface area of roots. This gives roots the ability to withdraw water from very dry soils since mycorrhize can access water held at higher pressures on soil particles than roots can. Thus mycorrhizae infected plants especially with EM, have greater drought tolerance.

Mycorrhizae are an integral part of the carbon cycle on earth and are the reason why there is roughly 2X the amount of carbon stored in soil than in all the plants growing above the soil. This is because up to 20% of plant photosynthate is excreted into soil as a stable polymer called glomalin. Glomalin is responsible for binding soil particles and creating micro-aggregates and soil with water soluble aggregates does all kinds of good stuff. It increases soil moisture holding capacity while improving porosity and drainage. All of this helps reduce root rot hazard.

Mycorrhizae also affiliate with microbes. The hyphae of mycorrhizae cultivate bacteria which produce antibiotics that protect the host plant from pathogens. Linderman coined the term mycorrhizosphere to describe the microbial community that affiliates with these fungi. Plants are also protected by the Hartig net of EM mycorrhizae because it provides a shield or barrier so that pathogens have a difficult time invading the plant root. So, mycorrhizae greatly benefit plants by defending their roots from pathogens.

Amanita muscari is an EM fungus that grows on tree roots

How do we keep the mycorrhizae growing with our garden plants? Most gardens are well inoculated with mycorrhizae at least the AM kinds. To get more access to EM it is necessary to also provide the organic carbon that they affiliate with. While EM absorb sugar from plant roots, their hyphae also grow into woody mulches helping to solubulize the nutrients contained in mulch and bring them back to their tree hosts. The litter and woody debris that fall in forests (litterfall) are essential for these organisms. We can simulate litterfall in gardens by applying fresh arborist chips and nourish the EM fungi as well as our woody garden plants at the same time.

A chip drop of fresh arborist chippings. Coarse woody mulch supplies additional carbon (energy) to soil fungi that benefit our landscape plants. [For a free, peer-reviewed publication on using arborist wood chips, please click here]

References

Corkidi, L., Allen, E.B., Merhaut, D., Allen, M.F., Downer, J., Bohn, J. and Evans, M. 2004. Assessing the infectivity of commercial mycorrhizal inoculants in plant nursery conditions. J. Environmental Horticulture 22:149-154

Corkidi, L. Allen, E.B., Merhaut, D., Allen, M.F., Downer, J., Bohn, J and Evans, M. 2005. Effectiveness of four commercial mycorrhizal inoculants on the growth of Liquidambar styraciflua in plant nursery conditions

Linderman, R.G. 2005. Bio-based strategies for the management of soilborne pathogens. Presented at the Landscape Disease Symposium, University of California, Santa Paula.

Linderman RG. 1988. Mycorrhizal interactions with the rhizosphere microflora: The mycorrhizosphere effect. Phytopathology 78:366-371.

Measuring the weather in your garden

I started writing for The Garden Professors a little over a year ago. My very first posting was on “The weather where you are.” In that article, I described some simple ways to measure the microclimates around your yard using some simple hand instruments. But many of you are already well past that and have your own weather stations. For those of you who don’t, here are some considerations for adding a weather station to your garden and a shameless plug for CoCoRaHS (Community Collaborative Rain Hail and Snow Network), a citizen science network of rainfall (and snowfall!) observers around the United States and Canada as well as a few additional stations in Mexico and the Bahamas. I am the current state CoCoRaHS coordinator for Georgia and we are in the last week of the March Madness competition to sign up new observers that they have every year. Even though this year’s competition ends on March 31 you can sign up and contribute to the precipitation record for your state any time. They have links to purchase their required rain gauge on their website on the bottom right side. They also have a very useful guide for Master Gardeners. If you are not in the United States or neighboring countries, you may be able to find rainfall observing networks in your country that you can join as well.

CoCoRaHS rain gauge. Source: NASA.

Equipment that is used to measure the weather at a location can vary from a very simple thermometer and rain gauge that you can buy at a hardware store to a sophisticated piece of equipment holding multiple sensors that costs thousands of dollars. The research-grade Campbell Scientific stations that we use in the University of Georgia Weather Network cost about $12,000 each, which is well out of reach of most homeowners, but there are plenty of options for weather enthusiasts that are much more reasonable in price.

University of Georgia weather station in Blue Ridge, GA, at Mercier Orchards. Photo: Eddie Edenfield.

A basic weather station may just measure a few variables like temperature and pressure but most people like to add additional sensors like humidity, precipitation, and wind speed and direction. If you are even more ambitious, you might add solar radiation, soil temperature and moisture, and more specialized sensors like leaf wetness. Weather Underground has a useful list of personal weather stations with some details about what sensors each one has, although you will have to click through the links to get pricing. Weather Underground also provides information on how to hook up some of these stations to the web so that you can share your weather information with others and contribute to their own citizen science network.

The single most important factor in getting useful information from your weather station is putting it in a good location. The weather station should be sited where there is good air flow so that you get a representative temperature and humidity for the area. The temperature sensor should also be shaded so that it does not warm up due to direct sunlight. Many stations include an enclosure to shield the thermometer from the sun’s energy. The enclosures are usually white to reflect sunlight and have louvers to let air flow through the enclosure. Some use fans to increase the ventilation of the temperature sensor, especially when winds are light.

Rainfall measurements also require good siting. Precipitation gauges should be placed where they will not feel the effects of any nearby trees or buildings. Usually you need a cone of 45 degrees wide above the top of your rain gauge that does not have any blockage from trees or buildings. Even that may not be enough in all conditions. My own rain gauge is located to the west of my house because that is the only open spot in my tree-filled yard and I notice that in storm systems with wind from the east, the rainfall is lower than other nearby stations because the building is blocking the wind and keeps some of the rain from falling into the gauge. Obviously, you don’t want any moisture from trees, wires, eaves, or fenceposts dripping into the gauge, so look around before you settle on a spot. Dr. Peggy LeMone from the National Center for Atmospheric Research in Colorado described her struggles with making accurate rainfall measurements and why siting is important after a big rain event in 2013.

Rain gauges at Eskdalemuir, Scotland, at the British Geological Survey Magnetic Observatory. The gauges are in pits to cut down on wind effects on the top of the rain gauges.

Rain gauges come in a variety of types. The simplest is a can or tube with vertical walls that you can use to catch rain and measure it at regular intervals (usually once a day at the same time each day for consistency). The CoCoRaHS gauge is a 4-inch diameter plastic tube with a funnel and an inner and outer cylinder that can be easily read to 0.01 inches. It holds up to 11 inches in all, and in some big rain events, it might need to be emptied several times in a day! Many personal weather stations use a tipping bucket rain gauge that has an opening with a funnel that drips the water into a bucket that has two sides on a pivot point. The National Weather Service uses weighing rain gauges to calculate the depth of precipitation based on the weight of the water inside the gauge. The Weather Makers has a good description of how these three types of gauges work as well as illustrations about what they look like. Other newer types of rain gauges include optical gauges that use a photoelectric eye to count water droplets as they pass through a funnel past a light source and haptic gauges that use the sound of raindrops hitting a surface to estimate how much rain has fallen based on the raindrop impacts.

Wind sensors should also be placed in an open area with no blockages from trees or buildings nearby. Putting them on top of a roof might seem like a good idea, but the wind flow over the roof can divert the air and speed it up, so that is generally not a good place to put them, although they are certainly very decorative. Some wind sensors have separate instruments for measuring the speed and direction of the wind while others use a combined sensor that can do both at once.

Wind vane on the top of King’s Cross Station in London, England.

If you love the weather and want to know more about what is happening in your yard or garden, adding a weather station can provide you with entertainment as well as information that can be helpful to track the climate conditions in your garden such as when frost occurs and how much rain you got so you can water appropriately. It also provides a great place to compare conditions with the other gardeners in your area—you might be surprised at how measurements change from one neighborhood to the next!