Gardening Ground Truths: Revisiting “Finding Credible Sources”

On By durhammastergardenersIn Uncategorized

This is the time of year gardeners begin to dream about spring and summer and the possibilities for their landscapes, vegetable gardens, and containers. The old adage “fail to plan, plan to fail,” rings true in gardening. In addition to keeping detailed records annually about your garden, doing your homework both upfront and along the way is key. But not all research–especially on the internet–is created equal. As you begin planning your 2023 garden, it seems like an excellent time to revisit Ann Barnes’s 2017 article on conducting quality scientific-based research and best practices for your own experimentation. In keeping with Ann’s suggestion to look for the latest information, we’ve included updated links and resources.

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Spring daffodils with white petals, an orange cup, and ringed with yellow at the base.
photo shows hands typing on a laptop keyboard.
Delosperma, or Ice plant, shown here with small pink flowers with yellow centers, emerging from fleshy green leaves that look like a mat.

(Image credit: M. Heigel; North Carolina State University)

By Ann Barnes, EMGV

When looking for answers to gardening questions, the internet is a fast and convenient place to search. It is important to remember that anyone can post content online, and there is no review process to ensure information on every website is correct. Extension Master Gardeners recommend unbiased, research-based information. There are many websites that claim to provide gardening information. Not all of them can be considered credible.

The “Who, What, Where, When, Why, and How” of Finding Trustworthy Information

Who are the authors, and for whom are they writing? Are they experts in a scientific field related to gardening, affiliated with a university, or trained Master Gardener Volunteers? Do the authors cite sources and/or provide links for further reading, and are those links to research-based sources? Does the author (or the entire website) seem to have an agenda or are they presenting unbiased information? Are the authors even listed, or does the article appear to be shared from some unnamed source? If you can’t determine who wrote the article (individual or organization), how can you know if the author is a credible source?

If a light switch in my house wasn’t working, I would call an electrician. Advice from my pharmacist or from a blogger who posts “home hacks” would not give me as much confidence as advice from an expert. The same should hold true for gardening – consult an expert in agriculture for the most reliable answers to questions about growing plants.

What: There is a science to growing great plants, so look for answers on sites that are research-based. There should be links to studies that support recommendations. When applicable, both organic and chemical options will be discussed in an unbiased manner. Keep in mind that natural doesn’t always mean safer or more effective, and not everything presented as a fact on the internet is true. Always check sources, particularly when you see a “scientific fact” shared as a meme or a link on social media.1

Credible sources don’t promise miracles or promote home remedies over conventional growing practices. Credible sources aren’t trying to make a sale or to criticize an existing product. Credible sources typically won’t promise that “your jaw will drop.”

Where: Check the URL of sites in your search results. Sites that end in .edu or .org (education or organization sites) are more likely to contain unbiased and research-based information. Master Gardener Volunteers are affiliated with Cooperative Extension, whose purpose is to share information obtained from research conducted at land grant universities, such as North Carolina State University (NCSU) and North Carolina Agricultural and Technical State University (NC A&T). Therefore, we recommend searching extension websites. Sometimes answers can be found at any state’s land grant university, but keep in mind your USDA Plant Hardiness Zone when searching for information about specific growing questions. For example, the average last frost date in the Triangle is much earlier than the average last frost date in Wisconsin, so you would need to look closer to home when searching for when to plant your tomatoes.

Here’s ONE WEIRD TRICK for finding all the garden answers you need:

Bookmark this link, and you can search like a Master Gardener: https://search.extension.org/

This will take you to a custom search engine that will only search Cooperative Extension sites. If you’d like to broaden your search beyond land grant universities but still search only for sites associated with academia, use your favorite search engine and follow your search terms with “site:.edu”. For example, when researching how to grow tomatoes in containers, type: Tomatoes in containers site:.edu in your browser’s search bar.

When: Does the article have a publication date? Science is an ongoing process and recommendations sometimes change due to new research, so it is best to use fairly recent sources. If there are links, are they current? Broken links may be a clue that an article is older.

Why: What is the purpose of the site? Is it providing unbiased, research-based information? If it isn’t a university website, is it selling a product? Does the site have bias towards or against a certain way of gardening? A site promoting a product has a goal of making sales, so there will be a bias towards their product. Similarly, articles published by authors with a general mistrust of agricultural chemicals will show a bias towards organic-only solutions. While biased sites may provide information that is correct, they may not be showing you all your options or the data behind these options.

Finally, there are the click bait articles, those amazing home remedies that are supposedly better than commercially available products, full of “facts” that sound miraculous but often aren’t true. The same information, word-for-word, may be posted on multiple websites. Click bait sites are designed to get people to click on them; it’s as simple as that. They don’t have to cite sources, use research methodology, or even be scientifically accurate. There is a lot of bogus science out there, and some of it looks pretty believable if you don’t check for source material.

Debunking some internet myths about gardening:

https://durhammastergardeners.com/tag/baking-soda/

https://durhammastergardeners.com/2013/04/07/pinterest-myth-busters

How: Good science is based on experiments that follow the scientific method, in which a scientist tests his or her hypothesis in a series of experiments. If I wanted to test Grandma’s Homemade Weed Killer to see if it was as effective as a leading Big Agricultural Product, I would need to conduct tests using each product on similar weeds in similar conditions, then compare results to see if there is a statistically significant difference in the two.

If I simply sprayed weeds with the Grandma’s Homemade Weed Killer, found some dead weeds, and announced that this remedy was safer and more effective than the Big Agricultural Product (without comparing the two in well designed experiments), my claim would be invalid, since I didn’t test for safety, nor did I compare the two weed control products. Claims need to be backed up with experiments.

How to design an experiment:

https://explorable.com/conduct-science-experiments/

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Notes

1–Many botanical gardens, cooperative extension offices, and master gardener volunteer programs now have a social media presence on apps like Instagram and Facebook where they present videos and links to solid information. Make sure you are following the organizations’ official accounts. You can follow Durham County Extension Master Gardeners on social media at @durhamncmastergardeners on Instagram and NC State Extension Master Gardener Volunteers, Durham County on Facebook.

Resources and Additional Information

Three great examples of university-based sites with searchable gardening information appropriate for our Plant Hardiness Zone are North Carolina State’s Plant Toolbox, NC Cooperative Extension, and Clemson University’s Home and Information Garden Center. See links to these amazing resources below.

https://plants.ces.ncsu.edu/

https://www.ces.ncsu.edu/categories/lawn-garden/

https://hgic@clemson.edu

Botanical gardens, arboretums, and gardening non-profit organizations such as state native plant societies (.org or .edu sites) can be excellent and trusted resources for gardening information. The American Horticultural Society website, while not a complete listing, has geographic search features for master gardener programs, plant societies, and over 345 North American botanic gardens, including links to their websites. Some great North Carolina-based garden sites that have a plethora of plant information on their sites include the J C Raulston Arboretum, North Carolina Botanical Garden, and the Sarah P. Duke Gardens.

https://ahsgardening.org/gardening-programs/rap/?state=NC

https://jcra.ncsu.edu/index.php

https://ncbg.unc.edu

https://gardens.duke.edu/

Look for Extension Master Gardener training materials online. For example, North Carolina State University and NC Cooperative Extension provide full online access to their entire gardener handbook, the foundation for all Master Gardener Volunteer instruction.

https://extensiongardener.ces.ncsu.edu/extension-gardener-handbook/

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Calling Plant 911: Understanding Cold Injuries and Caring for Plants After Extreme Weather Hits

On By durhammastergardenersIn ask a master gardener, gardening in NC, gardening in pots

by Melinda Heigel, Extension Master GardenerSM Volunteer of Durham County

evergreen fern with partial purple and brown discoloration appearing a week post-extreme cold
Discoloration on an evergreen fern (Crytomium spp.) began to appear a week following the extreme cold in our area. (Image credit: Melinda Heigel)

Regardless of where you live, if you’re in the US, you know what unusually prolonged cold much of the country experienced in late December 2022 as a bombogenesis (“bomb cyclone”) made an unwelcome appearance. Here in Durham, NC, December nighttime temperatures typically range in the low 40s. But during the “freeze out” of December 2022, our nighttime lows plummeted quickly ushered in by strong sustained winds. Beginning on December 24th, temps averaged a mere 14.3 degrees over 3 nights and averaged a frigid 20 degrees over 6 consecutive nights. While this is not arctic by a long shot, it is for our plants, trees, and shrubs, many of which are neither hardy nor acclimatized to these constant low temperatures. With such weather extremes, even zone-appropriate plants can come under great stress.1 Needless to say, many gardeners had some nail-biting nights. While this extreme weather event has passed, you may just be seeing its effects in your landscape. Identifying the damage and understanding how to treat cold injuries will likely come in handy about now. In a later blog post, we’ll address how to protect your plants best when cold temperatures hit, including those late-season frosts that always tend to zap blooming hydrangeas in late April and early May. Right now, though, let’s get down to brass tacks about cold injuries and how to evaluate and tend your plants.

red and brown leaves show evidence of chilling injury on princess flower.
Red leaves evidence chilling injury on this princess flower (Tibouchina urvileana). (Image credit: UCCE Master Gardeners of Sacramento County)

Understanding and Identifying Cold Injuries

There are several types of cold injuries plants can experience. A chilling injury is damage to plant parts like leaves, flowers, or fruit that happens when the temperature is above the the freezing point. This generally occurs between 32 -55 degrees depending on the cold-hardiness of the plant. This kind of injury is often found in tropical or subtropical specimens. This damage often shows up quickly after the exposure. Signs of chilling injuries can appear as leaves that turn red, purple or black in color, leaves that wilt, and flowers that die. This damage may stress plants, lead to some dieback, or slow future development, but it isn’t always fatal.

pansy in pot exhibits freeze injury with droopy, collapsed dark green leaves atop some lighter green leaves.
Freeze injury to a pansy in container (Viola x wittrockiana). Notice that the leaves look both wet and wilted in appearance. Containerized plants are especially susceptible since their roots don’t have underground protection. (Image credit: M. Heigel)

Frost and freeze injuries are more in line with what most of us experienced in the recent deep freeze. When the conditions are like those we experienced in December, we have what is known as an advective freeze.2 Frost and freeze injuries are very similar and tend to affect plants in the same way. With these injuries, water inside the plant cells basically crystallizes with rapid temperature fluctuations. As these ice crystals expand, they cut and burst cell membranes, and fluids leak from the cells leading to plant death. Leaf and stem tissues are most at risk with this type of fast freeze.

The timing for identifying frost and freeze damage to plants can be tricky. Sometimes, as in the case of the photo of the potted pansy, the evidence of injury appears quickly. This photo is after only one night of severe cold. However, in other cases, frost and freeze injuries can take days, weeks, or even months to show up. Immature plants are more susceptible than mature ones. Damage often starts with the softest, actively-growing plant parts–like the basal leaves of the pansy. Some signs of damage may show up after a week or two. For example at my house we have mature yucca plants (Yucca spp.) and after the 6 nights of extreme cold, they appeared to have weathered fairly well. One week later, they began showing signs of distress. And today, nearly one month later, the extent of the injuries is becoming more and more evident as the photos below demonstrate. Overall, damage to flower buds, vegetative buds, stems, and entire plants may remain hidden until active growth begins again many weeks later in the springtime. When it comes to evergreen shoots, the extent of impact is usually evident within 2 weeks.

Formerly evergreen mature yucca leaves exhibit brown discoloration a week post-freeze.
Once evergreen mature yucca begins to show significant die-back, with yellow and brown leaves, at the top of the plant one month post-freeze.

(Left to right) Freeze damage may take time to materialize. This once-evergreen mature yucca began to show discoloration and necrosis about a week after the deep freeze. It continues to evolve nearly one month later as what appears to be significant dieback is now occurring in the apex of the plant. (Image credit: M. Heigel)

Frost and freeze injuries can impact all of the parts of a plant and show up in myriad ways. Leaves can appear wilted, black or otherwise discolored, have a mosaic-like appearance due to damaged or dead cells, and even look wet or waterlogged from the bursting of plant cells. Later signs might be misshaped or curled leaves. In evergreens, coloration changes can occur. Needled evergreens like junipers (Juniperus spp.) may turn uniformly brown to bronze; broadleaf evergreens such as boxwoods (Buxus spp.) and hollies (Ilex spp.) may show leaf burn or scorching at their margins from cold damage. In terms of vegetables, many cool-weather crops like kale, collards, and Brussels sprouts and can handle temperatures below 26 degrees briefly, but damage can materialize in the form of affected foliage and potentially reduced yield.

Boxwood leaves, formerly uniformly light green, exhibit some yellow and brown colored leaf burn around the edges.
Boxwood plant exhibits freeze damage via yellow leaves, particularly at the ends of branches.

Boxwood (Buxus spp.) following December’s freeze exhibiting damage with marginal leaf burn and possible desiccation.3 (Image credit: M. Heigel)

The bark of woody plants and trees can also be impacted by rapidly freezing temperatures. Long cracks that are deep and narrow called frost cracks can occur in trees that experience wide-ranging temperature changes. The crack can expand and contract after the initial injury and callus over in the summer. Frost cracks can reoccur. In other woody plants such as azaleas, rapid temperature changes can cause the bark and/or stems to literally split near the plant’s base. Unfortunately, this can be a tough injury for plants to overcome. Damage to roots, while harder to see, can definitely occur. This is especially true if plants are in containers where their roots aren’t protected below ground. Likewise roots of ball-and-burlap plants are also at higher risk. According to Clemson University’s Home and Information Garden Center, even zone-hardy plants planted above ground in planters with “unprotected roots” can experience lethal root injuries at temperatures beginning at 28 degrees.

Caring for Plants

Pruning –Once you look for and identify signs of frost/freeze damage, exercise restraint. Some plants may appear dead, but they aren’t. While you might not like the looks of your plants, think twice about reaching for the clippers. Dead foliage might protect the plant’s crown and roots from further damage by providing insulation, especially with evergreens and perennials. As mentioned, damage is not always apparent and can take months to surface. Any pruning or cutting back now may mean you would be leaving potentially unhealthy plant tissue behind. Wait until you can fully determine the extent of damage before taking action like cutting out dead wood and plant material. This could mean waiting until the spring. One exception to this would be herbaceous plants (plants that have no woody stems above ground) like the pansy above whose cells have essentially collapsed. Removing this specific kind of dead plant material is recommended as there is little hope for revival.

Fertilizing–While it might seem tempting to help nurse your ailing plants with added nutrition, don’t apply fertilizers following these types of events. Your actions may indeed encourage the plant to put out some new growth, but if we are in the dead of winter or in late fall or early spring when frosts happen, you might be harming your plant further. Tender new growth is especially prone to cold injury. Wait until the any threat of additional frost/freeze has passed before your fertilize.

Watering–Pay close attention to moisture. After an extreme event like a hard freeze where the ground is potentially frozen around the plant, its roots are not able to take up adequate moisture. Likewise, very windy conditions like we experienced with the December cold snap also contribute to plants’ inability to capture and use moisture when under stress. Water your plants at the soil line after harsh cold-weather events to ensure proper hydration. Likewise, make sure the plant receives adequate water if nature doesn’t provide it throughout the upcoming growing season. The cold pressure plants experience in these freeze events means that gardeners need to pay special attention to keeping them healthy in the months that follow.

Mulching–Some experts suggest that keeping the base of plants well mulched is a way to help protect roots of plants, moderate soil temperatures by lessening heat loss, and hold moisture–all things especially critical during extreme freeze events.

If you haven’t surveyed your landscape thoroughly after the December weather–or even if you have, go out and assess what you see today using these descriptions of cold injuries as a guide. Be patient and remember that spring is on the way!

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Notes

1–Knowing your area’s USDA Plant Hardiness Zone is an important tool in plant selection and success year round in outdoor growing. However, it’s not a bulletproof guide. These zones are based on the average minimum temperature your area has historically experienced. In extreme weather, how quickly and low temperatures fall can negatively impact even zone-appropriate plants.

2–An advective freeze is a wind-borne event that happens when an air mass with below-freezing temperatures moves into an area and displaces warmer air. With this type of freeze, windy conditions tend to persist throughout the event. This influences the temperature of the plants and makes conditions right for ice crystals to form within the plants’ tissues.

3–Desiccation can also be a type of cold-related injury to plants, and evergreens, both narrow and broad-leafed varieties alike, are especially susceptible Our December 2022 weather event presented the perfect example of conditions that easily lead to this type of damage. During very windy conditions, and especially when they are exacerbated by frozen ground, plants can lose water faster than they can take it in. This often results in damage that appears like leaf burn on scorch on leaves. This damage pattern can also come from extremely low temperatures. Root injury can also result.

Resources and Additional Information

To determine your USDA Plant Hardiness Zone, plug in your location on USDA’s interactive map.

https://planthardiness.ars.usda.gov/

NC Cooperative Extension offices have several sites with articles featuring cold-related plant injuries and possible methods for protecting plants during extreme weather.

https://lenoir.ces.ncsu.edu/2018/01/plants-and-cold-temperatures/

https://lee.ces.ncsu.edu/2018/04/identify-frost-damage/

https://forsyth.ces.ncsu.edu/2021/04/protect-your-plants-from-frost/

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