Hasta la vista, La Niña!

Last April 30, 2022, I wrote a post about what a third year of La Niña meant for gardens. La Niña, you might remember, is an atmosphere/ocean phenomenon driven by unusually cold water in the Eastern Pacific Ocean (EPO) that shifts the jet streams that steer storm systems around the world. In La Niña winters in North America, it is often linked statistically to colder and wetter than normal conditions in northern parts of the United States and north into Canada and warmer and drier conditions in the southern tier of states in the US. Just a couple of weeks ago, NOAA announced that the long La Niña has finally ended and that we are now in a neutral period. In last year’s post, I described the difference between La Niña and the opposite climate phase, El Niño, and how they affect climate conditions around the world. So now you might be wondering how this switch to neutral conditions and then potentially to an El Niño later in the year will affect your gardens in the coming growing season.

Elfen-Krokus (Crocus tommasinianus), AnRo0002, Commons Wikimedia

How good was last year’s forecast?

A discussion of how accurate the forecast for last winter was can be found in NOAA’s ENSO blog. As you can read, the temperature forecast was much better than the precipitation forecast (as it usually is). That is not surprising because many causes of rain and snow occur on very small spatial scales from a variety of physical processes that are not always well-captured in our current climate models. You can hear a more detailed discussion of historical ENSO patterns by David Zierden, the Florida State Climatologist, in this 15-minute video for the March 2023 Southeast Climate Monthly Webinar starting at minute 28:35).

Two U.S. maps comparing predicted and observed 2022-23 winter temperature

As a result of the cold and snowy conditions in northern parts of the country, spring there has been delayed, and my friends in the Upper Midwest have only started to see daffodils and other early spring flowers, while in the Southeast, our azaleas and dogwoods are already in decline about a month earlier than usual (you can track this at the National Phenology Network website we’ve discussed before).

What happens next?

Now that La Niña has ended, we are in neutral conditions. That means it is difficult to predict the climate during the next few months because without La Niña (or El Niño) to give us statistical guidance on what climate to expect, almost anything can happen. The variations in climate in neutral seasons are caused by local variations, other interactions in climate on regional or global scales, and other factors that are not always well understood. In addition, we are in spring, which historically gives us the least trustworthy predictions for the coming seasons due to what is called the “spring predictability barrier.” That means that while we think we are likely to swing into an El Niño in the next few months, the atmosphere might have other ideas and could keep us in neutral conditions for quite a while before we switch to an El Niño.

This year, we are already getting signs in the Eastern Pacific Ocean that a switch to El Niño will come quickly. The water near the coast is already quite warm and the warm pool is starting to stretch out to the west. In other words, El Niño-like conditions are already present in the EPO, but have not lasted long enough yet for an official El Niño to be declared. That usually takes several months of monitoring to make sure this is not just a short-term change.

https://iri.columbia.edu/wp-content/uploads/2023/03/figure1.png

What do neutral and El Niño conditions mean for the Northern Hemisphere growing season?

Usually, ENSO conditions do not strongly affect the NH summer climate. That is because both La Niña and El Niño are strongest in the winter months and tend to weaken or disappear in the summer. Local conditions including soil moisture variations such as drought, ocean temperature variations, and local weather systems have a much bigger impact on growing season weather than ENSO does in most areas.

However, the ENSO state does have one strong influence. That is in the tropical activity in the Atlantic and Eastern Pacific Oceans. When neutral conditions or La Niña conditions occur, the jet stream aloft is weak and it is easier for tropical waves to develop into tropical storms and hurricanes, so neutral and La Niña seasons tend to be more active and have more named storms. When an El Niño occurs, the jet stream is unusually strong and that keeps tropical waves growing vertically into strong storms, so the number of tropical storms and hurricanes in the Atlantic is usually lower in years when an El Niño is occurring. Of course, it only takes one storm (Hurricane Andrew in 1982 was in an El Niño year) to cause tremendous damage if it hits somewhere vulnerable. In contrast, the storm activity in the EPO increases in El Niño years due to the pool of warm water there.

a graphic showing el nino weather pattern over nation

This year, the likely storm activity may be more tied than usual to the ENSO state. If we see a quick switch to El Niño after just a few months of neutral conditions, the Atlantic may be most active early in  the season, while storms later in the season will be suppressed. By comparison, in the western US where some moisture enters the country through EPO storm activity, you may see an increase in thunderstorms that are fed by the water vapor entering the country from the storms in the EPO.

What does this mean for your gardens?

If you live in an area that normally gets rain from Atlantic tropical activity, even if it is not from actual tropical cyclones or hurricanes, you can probably expect drier conditions this year, or at least more variable rainfall from less organized systems as more precipitation will be produced from local influences. El Niño does tend to delay the onset of the Southwest Monsoon, so that could be something to watch next year, although it may not have much impact this year. In Texas, the switch to neutral conditions means rain in April through June is more likely, which would be great for avoiding drought. If you live in an area that does not receive much moisture from the tropics, it will be hard to make a good forecast because the statistics just don’t give much guidance. We do know that globally, El Niño years tend to be very warm, so it is likely that 2023 may be one of the warmest, if not THE warmest, since global records began in 1880 due to the long-term rise in temperature from greenhouse warming. Warmer weather will mean a longer growing season, more hot days and nights, more humid conditions (unless a drought occurs), and more diseases and pests that thrive on the warmer conditions.

What do we expect next winter?

If you like to plan far ahead, you can see seasonal forecasts from NOAA’s Climate Prediction Center at Climate Prediction Center – Seasonal Outlook (noaa.gov). If you are not from the United States, your own country’s weather service may provide similar outlooks for your region. Here in the US, we are likely to see wetter and cooler conditions in the southern US as the jet stream steers storm systems over us (days will be cooler because of the clouds, but nights won’t necessarily be colder than usual since clouds trap nighttime heat). In northern states, warmer and drier conditions will be more likely, and that could mean an earlier start to the growing season next year. Now that something to look forward to if you are a gardener!

Tulipa “El Niño” 2015, Retired electrician, Commons Wikimedia.

My “Dirty Dozen” garden products

Image courtesy of Rotten Tomatoes

“Dirty Dozen” is one of those short, alliterative phrases that’s easy to remember and fun to use. In today’s post, I’m applying it to garden products whose production or use can be damaging to the health of ecosystems, environments, and even humans. How many of these products are in your garden shed, or appear in ingredient lists of other products? Each short description below has one or more links to additional information. After you count them up, see how you rank on the Charlotte Scott Meme-O-MeterTM

Product manufacture damages ecosystems

A protected peat bog in British Columbia

Peat moss. Peat moss bogs are slow-growing ecosystems that store vast amounts of carbon. Removing peat moss destroys these ecosystems (which can take centuries to regrow) and releases C02 into the atmosphere. Do a little experimentation with sustainably sourced or locally available crop residues and see if you can find a more environmentally friendly substitute.

Kelp forest at low tide. Image courtesy of NOAA Photo Library

Kelp. Kelp, or macroalgae, are the basis of intertidal and subtidal food webs. Removal of these plants creates underwater deserts where little life can be found. Restoration can be done, but it’s a slow and expensive process. Ask yourself why you think you need kelp and compare this to the facts.

There are lots of sources of manure on the internet…

Bat guano. Seems like a reasonable use of a waste product, right? Nope – and Dr. Jeff Gillman explained why in a post more than a decade ago. If you want a sustainably produced, manure-based fertilizer, you can find many options at garden centers.

Products whose use damages garden and landscape soils

Rubber mulch. Look closely and you can see bits of metal from steel-belted tires.

Rubber mulch.  Recycling used tires is a good idea; grinding them up and putting them on top of your living soil, not so much. There are much better mulch choices out there.

Landscape fabric with healthy crop of weeds

Landscape fabric. Landscape fabric does not control weeds, nor is it permeable once installed. It’s a sheet mulch that restricts water and air movement between the soil and the atmosphere. Weeds will quite happily colonize the surface while the roots of desirable plant struggle for water and oxygen below the barrier.

Black Death in a sad landscape

Plastic mulch. There is nothing worse (see chart in this link) you can put on a living soil unless your intention is to kill everything under it. You may see it used in agricultural production, but that doesn’t make it a good choice for your gardens and landscapes. Again, there it a much better alternative to this and all other sheet mulches.

Lots of claims about Epsom salt…but does your soil need magnesium?

Epsom salt. Would you be so excited about buying this stuff if it was correctly labeled as magnesium sulfate? That’s all it is – an inorganic chemical. Despite its soothing name, Epsom salt is not a cure all for anything except a magnesium deficiency in the soil. Overuse can create nutrient imbalances in soils.

Products whose use damages plants and plant-associated microbes

Always check that NPK value before you buy anything

Phosphate fertilizer. The most overused nutrient in home gardens and landscapes, and one that can cause iron deficiency in plants. The only time you should add anything containing phosphate – including compost or other rich organic material – is if you have a soil test indicating a deficiency.

DIY garden remedies. Self-proclaimed gardening experts come up with all kinds of home-made potions as safer alternatives to conventional fertilizers or pesticides. There are good reasons that both fertilizers and pesticides are regulated at state and/or national levels: it’s the only way you can know exactly what the active ingredients and when, where, and how to apply these chemicals. To follow some “chemical-free” recipe from the internet is playing Russian roulette in terms of collateral damage to soils and non-target organisms.

Another fine Black Death product

Wound dressings. Unfortunately, many gardeners don’t understand that plants and people respond differently to injury. While antibiotic dressing and bandages are good for healing our nicks and cuts, trees have a completely different response. Slathering black goo or paint over tree wounds is the last thing trees need to seal damage naturally.

Product whose use can be harmful to human health

Read the label before purchasing a hydrogel

PAM hydrogels. PAM (polyacrylamide) hydrogels have limited usefulness in home gardens and landscape – worse, they have to potential to injure people and pets. (There is also a list of references used in the linked article.) After these same materials are used in labs for gel electrophoresis (used for DNA analysis, for example), their disposal is generally regulated. No such regulations exist for using them in the landscape. Hydrogels based on starch or other natural polymers are fine – but avoid anything that contains “acrylamide” or “acrylate” on the label. Better yet, use a well-chosen mulch to absorb and release water to the soil.

Time to take the quiz!

You score zero: Well, well!
You score 1-3: Maybe you’ve been a part of this community for a while or maybe you’re just acutely aware of sustainable products and practices. Either way, the Garden Professors thank you!
You score 4-6: So maybe you recently broke up with your local garden center and are reevaluating some of the products they recommend. Stay strong!
You score 7-9: Oh, bless your heart. Let’s talk.
You score 10-12: So you take the phrase “scorched Earth” pretty seriously, huh?

All jokes aside, sustainability and gardening require constant adjustment and learning. You came here, you read through this list, and you are thinking critically about your practices.

Don’t be a garden gambler: You’ve got to know when to sow ’em, know when to plant ’em

For many gardeners around the US (and the northern hemisphere) the weather is warming up for spring planting season and many are itching to get out in the garden. But when is the right time to plant those veggies and flowers and not gamble on their success? Just like Kenny Roger’s character in The Gambler, knowing when to do something is important (this is where I’ll end the cheesy comparison – you’ve just got to come up with a catchy title sometimes).

I’ve spoken previously on this blog about understanding frost dates, which is important for planting warm-season crops like tomatoes, peppers, and cucumbers that won’t survive a frost. (You can read that article here.) But another temperature factor we must consider, especially for cool season plants that we plant BEFORE last frost is the soil temperature.

Soil temperature is especially important for direct sowing seeds in the garden, but it can also affect the success of transplants planted in the garden. For transplants, having an appropriate soil temperature supports root growth and development and helps plants get established faster.

Many warm season plants, especially plants like peppers, won’t establish easily or thrive unless soil temperatures are sufficient for root growth.

Why soil temperature matters for seeds

For direct sowing of seeds, soil temperature has a major effect on the speed of germination, which also affect the success rate of germination. Each different seed has a different optimum temperature for germination. If the soil temperature is below, or above, that level then germination can be slowed down. Slow germination can decrease germination rates through a few different avenues:

  1. Germinating seeds are vulnerable to infection or decomposition by fungi and bacteria in this soil. When starting seeds indoors, this can be limited by using a sterile seed starting mix. But when direct sowing outdoors, there are any number of fungi and bacteria in the soil that will decompose a struggling seed/seedling. Some seeds sold for large-scale production will have a coating of fungicide on them that will provide a few weeks worth of protection. You won’t likely find this on home garden seeds, but it might appear if you buy seeds from a farm supply store or a catalogue that caters to farm-scale producers.
  2. Seeds have a finite amount of stored energy. Once germination begins, the respiration rate of the embryo in the seed radically increases. If germination is slow, the embryo can expend the stored energy before the seed leaves emerge and start producing energy to support the developing seedling. (This also occurs if you plant the seed too deeply).

Below is a graphic I made for Nebraska featuring the best soil temperature range for major vegetable crops (notice how it also lines up with last frost dates). Just ignore the info on frost dates for Nebraska, unless you live in Nebraska.

Most of the resources you’ll find on soil temperature and germination are for vegetable crops. If you are trying to start seeds of ornamentals, you’ll likely have to find the information yourself. The seed packet will give you some indications of when to sow (before/after frost, or maybe in the fall for overwintering to break dormancy) and you can search online for guidance for specific plants. For info on starting seeds indoors, check out this previous article I wrote on the subject.

How to measure soil temperature

Of course, the tried-and-true old fashioned way is to use a thermometer. You can find a soil thermometer at many garden centers and retailers. You’ll want a soil thermometer because the ones for your kitchen likely don’t have the right temperature range – we’re measuring well below the temperature of a roasted chicken here. Instert the thermometer two to three inches into the soil and wait several minutes for the temperature arm to adjust before reading. Also keep in mind that temperatures fluctuate with the weather and throughout the day depending on temperature and the amount of direct sunlight hitting the soil surface – so you want to measure a few times to make sure the temperature is staying within the right range.

Now, the new technological way is to find a soil temperature monitoring station online. Soil temperature monitoring is a common feature of many weather stations these days and data is more available than ever. Many university extension services or ag research centers compile soil temperature maps for use by farmers and this data is also often accessible through NOAAA or weather.gov. In Nebraska, we have an extension program called CropWatch that provides average daily and weekly soil temperatures year round. We also have a weather station with soil temperature probes at our extension office (perks of having a meteorologist as a master gardener volunteer) and we (and our master gardeners) use it when providing information to clients. It can be hard to find a resource that provides soil temperatures nation-wide to share in the patchwork of private and public stations (and the National Weather Service site can be notoriously hard to navigate). There are a few online resources from the ag industry that provide a country-wide system, like this one.

And now its time for me to walk away, time for me to run

Unlike The Gambler you don’t want to wait until after the plantings done to count your money, er, check the temperature. Remember that knowing the soil temperature, whichever method you use, will help your plants succeed in the garden. If you do, your garden could pay out bountiful winnings all through the season.

By knowing the soil temperature, your seeds will turn into a sure bet. Source: Wikimedia Commons

No Mow May: Is it a good idea?

I know what you’re thinking: “No Mow May? But it’s March!” Although spring currently seems like a distant wonder for us here in Montana, many of our warmer states are seeing the signs of spring that get you thinking about, among other things, your lawns (and if you’re a bee enthusiast like myself, you’re also thinking about the early season pollinators that are beginning to emerge in these landscapes).

What is ‘No Mow May’?

No Mow May (or April, or March- depending on where you are) is a movement that was originally made popular through an organization based out of the United Kingdom called Plantlife. The intention behind the campaign is to eliminate mowing your lawn for the month of May, with the goal of creating habitat and floral resources for early-season pollinators. This initiative has since become more and more popular in the United States in addition to other countries, where we see the classic image of a turf lawn speckled with bright yellow dandelions along with signage that says ‘No Mow May’.

No Mow May sign (from beecityusa.org)

Lawns are a staple of American landscaping and one can hardly imagine urban and suburban areas without the iconic image of the green turfgrass yard associated with many homes. We have about 40 million acres of lawn, which accounts for 2% of all the land in the continental US, making lawns the number 1 irrigated crop in the country! The ideal vision of a good lawn has long been a weed-free, monocultural, uniform green space and people spend a lot of time, effort, and money to maintain them in this way. The image of overgrown, non-uniform, unconventional, and weedy lawns have been historically considered to be unattractive, unkempt, and poorly managed. Although more and more people seem to be changing their opinions and preferences for these conventional turfgrass lawns (and we likely need to rethink some of these expectations anyways), most people still have those underlying perceptions.

The idea behind No Mow May is that flowering lawn weeds, if left unmown, would provide food sources for early season pollinators such as newly emerging native bees (with the added benefit of less work in terms of lawn maintenance). The primary targets of this initiative are generally more urban and suburban areas where food sources and habitat for pollinators can be harder to find and spaces where weedy lawns are less tolerated.

Although the intention behind this campaign is a good one, providing food for pollinators, there are some aspects of this initiative that seem to miss the mark.

So let’s get into some of the science!

Is ‘No Mow May’ good for pollinators?

The answer to this question is: yes and no.

Studies have shown that certain common flowering lawn ‘weeds’ can be an important food source for pollinators, especially in urban and suburban areas where other floral resources can be scarce. A paper from the University of Kentucky found 50 species of pollinators, including 37 species of bees, foraging on white clover and dandelion in lawns (Larson et al., 2014). Although white clover is a nutritious source of nectar and pollen for bees, dandelions on the other hand are not very nutritious (with low protein content in their pollen). That being said, bees and other pollinators will still forage on dandelions especially if other floral resources are unavailable at that time. In the ideal world we would have a plethora of floral resources for pollinators which would incorporate an abundance of diverse flowering plants from early spring all the way through the growing season and into the fall. Unfortunately, most urban and suburban spaces do not meet the specifications of this ideal pollinator-friendly world. Dandelions, on the other hand, are pretty universal in these urban areas (and you have likely seen them in many lawns in your neighborhood). Although they are not a great resource, abundant dandelions can fill the gaps of food sources for bees (especially when the alternative is no food). Other lawn ‘weeds’ and bee lawn plants (as you have seen in last year’s blog post) can also support a diversity of pollinator species and can be a great way to offset the lack of pollinator-friendly resources in a turf-only lawn.

An American bumble bee ( Bombus pensylvanicus ) feeding on white clover (Photo: B. Merle Shepard, Clemson University, Bugwood.org )

Research from a pilot project of No Mow May in Appleton Wisconsin evaluated the bee species richness and abundance in properties that participated in the initiative and found a higher species richness and abundance when compared with areas that had been mowed, but this paper was retracted shortly thereafter, so it is difficult to judge the validity of those results.

That being said, if left unmown: your turfgrass will soon outgrow any other flowering lawn weeds which can make them difficult to find for pollinators, and that is if these flowering lawn weeds aren’t smothered by the tall grass altogether. A study conducted in Massachusetts which evaluated the impact of mowing frequency on bee abundance and diversity showed that lawns which were mowed once every 3 weeks had 2.5 times more flowering plants, though lawns which were mowed every 2 weeks had the highest bee abundance, likely due to easier access and visibility of these floral resources in shorter grass (Lerman et al., 2018).

Is ‘No Mow May’ less work?

The answer to this question, as you probably could guess, is also: yes and no (but mostly no).

I am a self-proclaimed ‘lazy gardener’ and am always looking for ways to reduce the amount of effort I need to put into my gardening endeavors. No Mow May claims to be less work for you in the month of May. Although that is true (because the intention is not to mow for a month), it can often result in more long-term effort in trying to reign in your turfgrass in the after-effects. Not to mention the negative impact that this style of management (or lack thereof) can have on your turf itself.

Photo: Iowa State University Extension

In many places, lawns can grow a foot or more during the month of May. An un-mown lawn can set you back on your lawn maintenance and result in more work for you in the long run . Then when you are trying to get your lawn back on track afterwards- remembering the rule that you should only remove 1/3 of your turf in any given mowing, it could take weeks to get back to a good functional height (which varies depending on the type of grass, but for most of our lawns, it ranges between 2.5-4 inches). Furthermore, most mowers don’t have the capacity to handle a lawn with a 12 inch height. This will result in removing too much of the grass leading to unintended consequences like stress and decline of your lawn, which can also make it more susceptible to pest and disease issues. This will also lead to a large amount of grass clippings which, if left on the lawn, could smother sections of it and result in an unpleasant and patchy lawn.

Unhealthy lawns can also struggle to compete with and leave spaces open for other undesirable invasive plants, including noxious weeds. These can then spread to other areas and have significant ecosystem impacts (and make it even more difficult to get your lawn under control). Following weed management needs could also require the use of herbicides that can have unintended consequences on pollinators and other beneficial insects.

Furthermore, as noted in an article on No Mow May by Iowa State Extension’s Consumer Horticulture Specialist, Aaron Steil: lawns are not actually a natural space, as most lawns are constructed out of non-native grasses, usually for functional purposes, and require quite a bit of maintenance including water and nutrients. Leaving your lawn unmown will not make your lawn a more natural landscape, and it would not be a responsible way to manage these non-native landscape plants.

What you can do instead of No Mow May: Low Mow May!

Based on what we’ve learned so far: lawn weeds can sometimes be an important food source for bees (especially in urbanized areas, where the diversity and availability of floral resources are fewer) and mowing less frequently results in more of these flowering lawn weeds for bees. We also know that slightly higher (though not too high) mowing heights for many lawn turf species make for healthier root systems and make turf more resilient to stress, pests, and disease issues.

If you have flowering lawn weeds and pollinator conservation is your intention, your best bet would be to aim for a sweet spot between the extremes of mowing way too frequently and not mowing at all. Mowing every other week could be a way that you can reduce the amount of time spent mowing and also support urban and suburban pollinators by letting your lawn weeds flower (in addition to maintaining your lawn at the recommended heights for healthy turfgrass).

Even better yet, you can reduce the amount of space in your landscape that is dedicated to a traditional turfgrass lawn and incorporate a flowering groundcover and/or a pollinator garden that hosts an abundant array of diverse floral resources that provide food for bees all season long!

Now that’s something to be buzzing with excitement about!

Less lawn (speckled with clover), more pollinator plants, and habitat! Photo taken at the home of a colleague and scientist on the Wild Bees of Montana project (Dr. Casey Delphia).

Resources

Iowa State University Extension, Aaron Steil: Tips for participating in No Mow May
https://hortnews.extension.iastate.edu/tips-participating-no-mow-may

Larson et al. (2014): Pollinator assemblages on dandelions and white clover in urban and suburban lawns
https://link.springer.com/article/10.1007/s10841-014-9694-9

Lerman et al. (2018): To mow or to mow less: Lawn mowing frequency affects bee abundance and diversity in suburban yards
https://www.sciencedirect.com/science/article/pii/S0006320717306201?via%3Dihub

Washington State University Extension: Lawn Care Basics
https://s3.wp.wsu.edu/uploads/sites/2076/2018/03/C067-Lawn-Care-Basics-16.pdf