The Garden Professors™

Shooting Fish in a Barrel

Someone recently posted a scientific article on our Facebook page which purportedly demonstrates that Roundup can be damaging to earthworms at concentrations that would typically be used in a field situation. Wow. Scary. I mean really, if we’re damaging earthworms when we apply Roundup, then that lends fuel to the emotional fires that rage against this pesticide. But is that really what this article shows?

It’s unfortunate, but most of you will not be able to see the article that I’m writing about because you won’t have access to the journal in which it was published. Here’s the abstract though.

http://link.springer.com/article/10.1007/s11270-014-2207-3

Basically what the authors did was to place worms in small pots, expose the pots to different concentrations of a commercial formulation of Roundup, and measure how the worms fared over time (about a month and a half). Unsurprisingly, the worms not exposed to Roundup performed better than the worms exposed to the Roundup.

After reading the above paragraph you might think that this is an open and shut case. Roundup is bad for worms, potentially leading to “local extinction” of these animals in agricultural fields (that’s the authors’ wording).

It’s not that simple. The authors are stretching well beyond the data, and the research has some issues, most of which could be cleared up by better, more thorough reporting.

First, let’s take a look at some of the problems that this paper has in terms of reporting its materials and methods. You may think this is picky, but it’s not. It’s fundamental to figuring out how valid the reported results are. From the materials and methods as they were written it is impossible to figure out exactly what was done in terms of watering the pots (we know soil moisture was kept at 80%, but we don’t know how. Watering? With what?). We don’t know what the ground plant materials were that were added to the pots (Lima beans?). We know that pots were placed into 1m X 1m X 0.60 m containers, but we don’t know how many pots were placed into each container or whether pots were randomized by treatment within each container. Sure, we could make assumptions – but in a well written scientific paper we shouldn’t have to. Would knowing these things affect how the worms performed in the Roundup treatment versus the no Roundup treatment? In a word, yes. The watering regime in particular might very well alter the results of this study.

That’s enough of that. Now let’s take a look at my BIG PROBLEM with this study. Six worms were placed into small (28cm X 14cm), half-filled pots and treated, or not treated, with Roundup.

Let me offer an extreme analogy to explain why this is such a problem. Let’s say that you want to see whether shooting bullets into the ocean will kill all of the fish that live there. To test the theory you grab a 50 pound fish and you stick it in a 5 gallon bucket. The tail is hanging out, the fins are flapping, water is getting all over the place. Then you shoot the bucket. Dead fish. You do this 50 more times. Each time, dead fish. You conclude that shooting bullets into the ocean is indeed a threat to fish and may lead to local extinction. Right?

Wrong.

From this study you can conclude that bullets can kill fish. That’s an easy conclusion to make. You cannot conclude that shooting bullets into the ocean will kill all the fish there. Now, if we hired a swat team to fire bullets into the ocean and all the fish were killed, well then we could make that conclusion. Would that actually happen though? No way of knowing unless we try it. I suspect the ocean would retain its fish – but I’m just hypothesizing. (Quick FYI – high velocity bullets lose so much of their speed when they hit water that they wouldn’t be lethal to fish after traveling about 3-4 feet).

There are any number of studies out there that FORCE target organisms to be exposed to whatever chemical is being tested (that is basically what is being done here). These studies CAN show that the chemicals tested MAY affect the target organism. They CANNOT show that the target organism IS AFFECTED IN A GIVEN ENVIRONMENT. You need to test the chemical in that environment to figure that out.

To give an example of how you might test the effects of Roundup against worms in an agricultural environment: Take an acre of agricultural field, divide it into six sections. Treat three with Roundup and control weeds in the other three sections with hand weeding. Sample the sections every two or three weeks after Roundup application to see how the worms are doing.

Now, my final problems with this paper. Much of it is related to other, already published studies. This, in and of itself, is no problem. It is good that there are many studies on this topic. The problem is that most of these studies weren’t mentioned in this article. When I read a scientific article I count on its authors to put their study into context for me so that I can see where it belongs in the already existing collection of related literature. Without referencing these older papers the authors do us a disservice. I’m not going to list out all of the studies, but if you go to scholar.google.com and type in earthworm and glyphosate you’ll see what I mean.

I believe that any experiment from which data can be extracted should be published. I think that the authors of this article had every right to publish it. However, as a scientist, I think that there are enough problems with the reporting of this article, particularly the materials and methods, that, as it is currently presented, I can’t extract much of value. I certainly can’t reach the sweeping conclusions that its authors do.

The Walking Dead: Christmas tree edition

Zombies are big deal these days. Seems like you can hardly turn on the TV these days without seeing someone (or someTHING) coming back from the dead. Turns out Christmas trees are no exception. Every so often during the Holidays I will get a call or an e-mail that starts off, “My Christmas tree is starting to GROW!” And indeed they are. Under certain circumstances, conifers that are cut and brought indoors can break bud and begin to grow; sometimes putting on considerable new growth.

It's alive! Concolor fir Chrsitmas tree pushing new growth. Photo: Doug Thalman — It’s alive! Concolor fir Chrsitmas tree pushing new growth. Photo: Doug Thalman

So what gives? Like the proverbial chicken running around with its head cut off, Christmas trees are dead they just don’t know it yet. After they are cut, conifers can continue physiological functions – photosynthesis, transpiration, respiration – for weeks. In some cases they can break bud and begin to grow like it’s springtime when a homeowner brings them indoors. There are a couple of key factors that come into play. First, the tree must be exposed to enough cold weather to meet its chilling requirement. This varies among species, but most conifers need to accumulate at least 6 weeks of chilling below 40 deg. F to overcome dormancy. So early cold weather where the tree is grown and harvested is step one. Second, the “Zombie tree syndrome” is most likely to occur in species that are adapted to high elevations or northern latitudes. The usual suspects are concolor fir (Abies concolor) and corkbark fir (Abies lasiocarpa var. arizonica). These trees have evolved in areas with a short growing season, so there is a selective advantage to breaking bud rapidly when weather warms in the spring – or if brought into a toasty 70 degree living room.

Walking dead - new growth on concolor fir Christmas tree. Photo: Doug Thalman — Walking dead – new growth on concolor fir Christmas tree. Photo: Doug Thalman

So what do you do if your tree turns into a Zombie and comes back from the dead? Don’t panic. It’s a natural phenomenon; just be sure to check and refill the water in the stand regularly so the new growth doesn’t desiccate. And lock your bedroom door at night – just in case…

If trees have met their chilling requirement the they can begin to growth when brought indoors. Photo: Doug Thalman

Organic insecticides that will get you high

Plants are crazy chemical factories, synthesizing a whole host of compounds that we use for flavoring and dye and medicine and… getting high. And why are they making all these chemicals? They’re certainly aren’t doing it for our sake… no, quite often they’re trying to kill something – usually insects — and it just so happens that sometimes our brains and bodies react differently enough that instead of killing us, they make us high. Well, and sometimes they kill us too.

Nicotine, the addictive force behind cigarettes, is a potent natural insecticide. if you’ve heard of neonicotinoids, the pesticides that some are concerned with in relation to honey bee health, they’re synthetic insectides based on the chemistry of nicotine, and like it, they effectively kill insects. No word on if anyone has tried smoking them yet.

Opium poppies are full of a thick latex loaded with chemicals like morphine and codeine, to name a few, which are obviously used as pain killers, and of course opium is taken directly or processed into more potent forms like heroin. The research on these chemicals indicates multiple possible functions, acting to prevent damage by herbivores (like insects), and possibly also acting to prevent pathogen damage and maybe even a more structural function in strengthening cell walls in response to damage (see: http://pubs.acs.org/doi/abs/10.1021/np020583l) I didn’t find any research looking directly at opium’s ability to kill insect pests. Probably because that type of research is usually aimed at a practical solution to pest problems, and even if heroin proves to be a potent insecticide, I doubt anyone would issue and extension bulletin recommending you use it to control your whitefly…

But that lack of practical application didn’t stop a researcher from publishing a paper titled Cocaine as a Naturally Occurring Pesticide in which they found that cocaine was highly effective in killing tomato hornworm! Organic growers, take note! Maybe THAT’S why organic tomatoes are so expensive at the farmers market…

In any case, it is fascinating to note all the interesting, sometimes useful, often dangerous chemicals that have evolved thanks to the on-going chemical arms race between plants and the things that try to eat them. We’re the accidental beneficiaries – and sometimes victims – of that very, very old battle.

Some Thoughts on Extension

For those of you who are out of the academic loop, Extension is that part of academia tasked with delivering research based information to those who can use it. You’ll hear other definitions, but I think that this basic one is the most useful for the following discussion. Extension, as a general rule, is tightly tied to agricultural sciences though it may include everything from child care to math or even computer science.

For fifteen years I was a part of Extension at the University level. During that time (1998-2013) my formal Extension title was Nursery Management Specialist and my job was to deliver information to the nursery industry. I was OK at this job, but discovered that my real passion was delivering horticultural information to the public. In 2008 my job was formally changed. I retained the title Nursery Management Specialist, but my duties expanded to include delivering information to the public. Besides my extension title, I also had an academic rank which was, from 1998-2004, Assistant Professor, and which became Associate Professor after I achieved tenure in 2004. For personnel in the applied sciences it is typical to have a percentage associated with their Extension appointment which indicates (roughly) how much of their effort should be put into extension. My Extension appointment was 60% throughout my University career.

I’m giving the above information so that anyone reading this will have a sense of what my experience with Extension is and the perspective from which I speak. I welcome disagreement, I know that my views aren’t the only ones out there. That said, here are the points that I want to make:

1. I believe that Extension is important.
2. I believe that Extension is dying.
3. I believe that Extension cannot be saved unless personnel in administrative roles make some fundamental changes to the way things are currently done.

Let’s start with #1. Extension is important because it provides a link between us and the people who do research that impacts us. Simple as that. Though I have known of exceptions, Extension personnel are usually non-biased individuals who deliver research based information to whoever they can. If you aren’t getting your information from someone in Extension then you’re probably getting it from someone who stands to profit from whatever information they provide. This alone makes Extension important.

#2. Extension is suffering a slow and agonizing death. Certainly there are some people out there who choose to ignore what’s going on, or to see it through rose colored glasses, but that doesn’t change what’s happening. I’ve had numerous people show me particular things that Extension has done which are wonderful, but these things are exceptions and not rules. There are a number of reasons why Extension is failing, many of them are economic, but I think the problem sits much deeper than that and that even a major influx of money would fail to turn things around unless Extension administration changes their tune.

There are actually two types of Extension work. The first is commercial, and the second is consumer. Commercial Extension has a strong presence. Extension personnel who work with farmers who grow crops like soy, corn, cattle, etc. have a long history of working with the industry and that relationship is strong and promises to stay strong, though industry reps from pesticide and fertilizer companies are making great headway in reducing the dependence that farmers have on Extension personnel. In horticultural crops (nursery, greenhouse, etc.) I see essentially the same thing. Extension personnel are respected, but day to day information needs, such as how to control a particular pest, come from pesticide and fertilizer companies who put a lot of time and effort into building relationships with their customers. Once upon a time much of the information that pesticide and fertilizer companies doled out did come indirectly from Extension, but nowadays most of these companies have their own experts (Who may have been trained by Extension people). Though I see an eroding dependence on Extension in the world of commercial extension, the place where I have a much greater concern is consumer Extension. Extension personnel who work in consumer Extension deal with the public. Over the years consumer Extension has come to mean Master Gardeners and 4H. Both of these are fine institutions, but if you think that Extension is providing research based information to everyone who needs it by educating these two groups then you’re sadly mistaken. They are competing poorly with companies like Scott’s or businesses like Home Depot. And when the consumer thinks of a horticulture guru they’re more likely to think of Paul Tukey or P. Allen Smith than their extension agent or specialist. The long and short of it is that Extension has better information than any other source, but they’re not very good at disseminating it.

I see two fundamental problems with extension. The first is that extension has failed to keep up with current communication trends. Right now you are reading a blog with some information on it. There’s a garden professors facebook page too. But when the average individual is looking for information on how to care for plants where do they go? That’s right, a search engine – probably google. And when you type in a query about something like “when to seed your lawn”, or “how to fertilize”, what pops up? Mostly information from Lowes or Scott’s or Home Depot, or youtube, or Popular Mechanics or This Old House. Extension articles may or may not be present in searches. When they are I select them, but how many consumers are this discriminating? Sure, it’s possible that Extension originally provided the information that other companies are now spreading around, but you’d never know it by reading the articles. In fact, some of the recommendations are so terrible that I can’t imagine them coming from Extension. Over the last few years something called eXtension has popped up that supposedly provides extension with an online presence. I know that some people are using it. Indeed, this blog is currently housed in eXtension. Seen eXtension pop up in your google searches much? The problem of largely missing trends in information dissemination dovetails nicely with the next problem, that of reward for accomplishment.

The second fundamental problem that I see with Extension is that the experts who we rely on to gather and distribute research based information aren’t given credit for what they do. By experts I mean the University Faculty who are supposed to gather content and distribute it. This problem has many facets, perhaps the most important of which is that University faculty are judged primarily on two things: the number of papers they write and the grants they bring in. I can’t say that the other stuff, like teaching and presentations, are ignored, but they certainly don’t hold the same weight as papers and money. When new faculty are brought in they quickly learn that they need to write papers and bring in money to achieve tenure. So here’s the issue, to get tenure (and keep my job) I need to write papers and get money, but to accomplish my job I need to communicate with people – so should I spend my time and creative energy trying to develop new ways to communicate with people and avenues for disseminating information, or on producing papers and getting money when I know I can just do a few Master Gardener talks giving me enough credit for doing Extension work that nobody will complain. The answer is obvious, and demonstrates another problem with the system, new faculty hires who have Extension appointments are brought on for their ability to write papers and get grants rather than their ability to communicate. For Extension Faculty the number of people reached with useful information and the novel techniques used to disseminate this information are largely ignored. I suppose that if you published a paper about disseminating information you’d get credit, but come on, if I’m stopping to publish a paper about it – it takes a heck of a long time to write a paper – then I’m going to lose any momentum I have over my competition who doesn’t have to publish a paper – like a pesticide or fertilizer company. For most of the world the proof is in the pudding. In academia the proof is in the paper. This is a problem when you’re competing with for-profit companies.

#3. In my opinion Extension can only be saved if academic administrators value Extension work at a level that is at least close to how they value research. Extension people who are competing with for-profit companies to deliver information are hamstrung from the get go not only because they don’t have the financial resources that for-profit companies do, but also because they don’t receive tangible appreciation for their work (such as raises, tenure, and promotion). An “attaboy!” just doesn’t cut it. As anyone in the business world knows, to accomplish a goal you hire good, qualified people and reward them for their successes. If Extension is to succeed that’s really all that needs to be done.

So, you may disagree with me on some of my points above. Good! Let me know about it. I’d be very pleased to have my mind changed.

Harvesting, Curing and Storing Sweet Potatoes (A Visiting Professor feature)

Submitted by Ray Eckhart

Introduction
Sweet potatoes (Ipomoea batatas) are warm-season plants in the morning glory family (Convulvulaceae). The part we eat is the fleshy storage root of the plant, which is a little different than the regular Irish, or white, potato (Solanum tuberosum), a plant in the family Solanaceae. In that case, the part we eat is a fleshy underground stem of the plant, called a tuber.

Although sweet potato roots continue to grow until frost kills the vines, an extremely hard frost can cause damage to the ones near the surface. Chilling injury also results when soil temperatures drop to 50°F or lower, and this can result in internal decay in storage. The greatest danger from delayed digging is the risk of cold, wet soil encouraging decay. So the best time to dig is around the time of first frost in your area, or shortly thereafter. The vines can be clipped approximately 5 days before digging to improve skin-set or reduce the incidence of skinning the roots during harvest. To avoid exceptionally large sweet potatoes, a few hills should be dug in advance of the anticipated harvest date to determine the size of the sweet potato roots.

Freshly dug sweet potato ‘Puerto Rico’

You can cook newly dug sweet potatoes right away, but their flavor, color and storage quality is greatly improved by curing at warm temperatures immediately after harvest. It is during the curing process that starch is converted to sugar.

Cure sweet potatoes by holding them for about 10 days at 80-85°F and high relative humidity (85-90 percent). Commercial producers have temperature and humidity controlled housing to guarantee good results, but for the home grower, they can be cured near a furnace or heat source to provide the necessary warmth. If the temperature near your furnace is between 65-75°F, the curing period should last 2-3 weeks. To maintain the required high humidity (85-90 percent relative humidity), stack storage crates or boxes and cover them with paper or heavy cloth.

Sweet potatoes curing

Once the sweet potatoes are cured, move them to a dark location where a temperature of about 55-60°F can be maintained, like an unheated basement, or root cellar. Sweet potatoes are subject to chilling injury, so don’t refrigerate them. Outdoor pits are not recommended for storage because the dampness encourages decay. Good results can be obtained by wrapping cured sweet potatoes in newspaper and storing them in a cool closet. Sweet potatoes can also be stored in sand.

Ornamental Sweet Potatoes
Have you ever wondered what, if any, is the difference between the ornamental sweet potato vines grown as a season-long ground cover, or, as “spillers” in container arrangements, and the vegetable we grow as food? The answer is – not much. They are just different cultivars of the same plant species, Ipomoea batatas. The ones we grow for food are selected and bred to produce large, uniform, good tasting roots, high in nutrients for eating, whereas the ones we grow ornamentally are selected for the striking shapes and colors of their leaves. Plant breeders introduce new variations every year. If you dig up the earth around your ornamental vines, you’ll find the same fleshy roots (different colors, perhaps) as the familiar ones we grow, or buy, for food. So, can you eat them? Well, technically, yes – but there’s no guarantee how they’ll taste. Most ornamental varieties are pretty bland. However, if you dig, cure, and store them as above, it’s possible they can stay viable until spring, when you can try to continue their growth for another season.

Propagating new plants (called slips) the following spring

References:
http://waynesword.palomar.edu/ww0804.htm
http://urbanext.illinois.edu/bulbs/bulbbasics.cfm
http://content.ces.ncsu.edu/ornamental-sweetpotatoes-for-the-home-landscape.pdf

Ray Eckhart is a former Penn State Extension Educator and avid home vegetable grower, with a weakness, bordering on obsession, for home grown tomatoes.

You CAN grow it, but is it worth it?

As winter sets in here in Michigan, I’m seeing gardeners deploying winter protection. Like this, which I saw on a visit to Hidden Lake Gardens with some friends recently:

Well. Isn’t that attractive? Come around to the far side, and you see this:

Pinus contorta ‘Chief Joseph’ which is a stunningly beautiful conifer, green in the summer, this brilliant shade of gold in the winter. Sadly, those gold needles are also incredibly prone to turning a less brilliant shade of brown if exposed to too much winter sun and wind. Hence the ever-so-attractive sun-and-wind shade they’ve installed here.

Call me old-fashioned, but the point of a garden is to be pretty, and though you CAN wrap delicate shrubs in burlap or upend styrofoam cones over tender roses or even (yes, I’ve seen it) put little roofs over your hardy succulents to keep excess rain off of them, but is it really worth it? For me, if I have to put something ugly on my plants to keep them healthy, it isn’t worth it. In my garden, I’d lean towards something else I also saw on that visit:

Chamaecyparis obtusa ‘Crippsii’ No, it isn’t quite as stunning as the pine… but it will grow and not turn brown, with no fuss.

What about you? Are there plants you are willing to make your garden ugly to keep happy?

When trees can’t predict weird weather

Our normally mild corner of the country got hit early and hard with cold weather a few weeks ago. For several days straight, our home thermometer read anywhere from 22-25F. Now, Seattle routinely gets temperatures this low sometime during the winter. But this cold spell came very early – much earlier than our regionally adapted trees and shrubs were used to. The effect on our plants was significant.

Rhodies react to cold but tolerate the freezing temperatures

Trees and shrubs start getting ready for dormancy in the summer. They key in on the progressively shorter days and make biochemical preparations that are unnoticeable. When the first frosty evenings arrive, leaf color changes begin immediately. Chlorophyll, proteins and sugars are scavenged and stored in trunks and roots – we see leaves change from green to red, orange, yellow, and eventually brown. Slowly an abscission layer is laid down at the base of the leaf petiole, and when the layer is complete the leaf dies and falls.

But this year the trees weren’t ready. It got cold really fast, and green leaves died on the trees. And they are still there. Eventually these old leaves will fall, though some of them may stay on until spring.

Both the hydrangea in the foreground and the styrax in the back have retained their leaves after the cold snap.

What does this mean in terms of tree health? Well, it won’t kill them, but it does set them back in terms of food storage. A lot of the nutrients that were still in the leaves when they froze are lost to the tree. So there may not be as many reserves for winter root growth, or for spring leaf flush. Overall, we could expect to see less than normal growth in established trees and shrubs.

Infographic with a BIG grain of salt

Infographics can be great: They’re bright colorful ways to make sometimes complex concepts visual and easy to understand. Sadly, “easy to understand” does not necessarily equal “accurate” and they can also be extremely misleading.

Take this beautifully made image from National Geographic. It is an older image — first posted back in 2011, but it makes the rounds on social media from time to time, and popped up in my facebook newsfeed a couple days ago.

Look at it! Oh no! We’re loosing all of our vegetable genetic diversity!

Or not. First, it is comparing apples to oranges. This image looks a commercially available varieties in 1903 and compares it to the number of varieties in one specific center for preserving genetic diversity. What happens if we compare the same metric? If you look at the number of varieties in the National Seed Storage Laboratory, that was founded in 1958… so in 1903, at the top of the graph, the number for all these vegetables would be… zero. If you look at the present day, the current umbrella organization for all the US government funded efforts to preserve genetic diversity of crop plants is GRIN, (Germplasm Resources Information Network) and if I do a quick search through that database using the keyword “tomato” I get… 9281 results. That is a pretty overwhelming improvement over 79 in 1983.

And what about commercially available varieties? To use tomato as an example again, in 1903, they found 408 varieties offered commercially. I just added up the varieties listed by just ONE seed company, Baker Creek Seeds, currently lists 287 different varieties of tomatoes. That is just ONE company. I have no doubt that if I added up all the varieties that are offered for sale in the giant pile of seed catalogs I get every spring it would be FAR more than the 408 on offer in 1903.

So… are we losing genetic diversity in our crop plants? Probably. There are lots of traditional varieties and land races that were never available commercially that have do doubt been lost, but to be honest, I think we’ve done a pretty good job at preserving the diversity. And certainly the USDA’s system of gene banks is an incredibly well run, impressive thing that deserves high praise indeed, for not merely preserving vast amounts of important genetic diversity but also working hard to characterize it and make it available to researchers and breeders so it can actually be put to work in the development of new and improved selections to try and feed the world.

So despite how colorful and easy to understand this infographic is, you don’t need to freak out about a massive loss of genetic diversity in our vegetable crops. Save that freaking out for all the wild species that have gone extinct or are about to go extinct thanks to habitat destruction and climate change world wide…

You think YOU had a bad day…!?!

I'm itchy all over. — I’m itchy all over.

Just downloading some photos from the end of the summer, and found this. Rarely can I work up sympathy for a tomato hornworm (Manduca quinquemaculata). Though the moth is quite lovely, the caterpillars really did a number on my tomatoes (and two spindly eggplants) this year, and I recall joyously taking this photo in August.

However, I’ve had a rough Monday, and can kind of relate to being covered in Braconid wasp pupae. The larvae have chewed their way through the caterpillar, to spin their grisly cocoons of death (would have made a great post a couple of weeks ago) and dangle there in the breeze until emerging. I know it is nature’s way, but, dang.

Get a handle on your microclimates

Practically the first thing a budding gardener (at least in the US) learns is their USDA winter hardiness zone. Based on average winter low temperatures, hardiness zones have many flaws but are still a very useful tool in figuring out what plants can and cannot survive your particular winters.

Right after learning about winter hardiness zones, we generally hear about microclimates – the idea that small precise locations within our garden may be, sometimes significantly, warmer or colder (or wetter or drier) than the surrounding climatic norms. The most pronounced producer of microclimates in most people’s gardens is their house – the sunny southern and western walls in particular can be markedly warmer than the rest of your yard. If you have hills, you also get frost pockets in low lying areas and warm south-facing hill sides.

But just how much warmer ARE your microclimates? I used to live in a drafty, poorly insulated nearly 100 year old house which had VERY warm microclimates all around it because all the heat my furnace put out was rapidly leaking out into the outside world. Great for growing plants that normally wouldn’t take my winters, but oh, the heating bills! A modern, well insulated house leaks a lot less heat out into the garden. Over time in a garden, you can learn by trial and error just how far you can push growing tender plants in warm microclimates by planting things and watching them die or survive. But there is an easier and faster way to figure out your microclimates. Collect some actual data, getting firm numbers of how warm and cold different parts of your yard are.

I’m heading into the first winter in a new garden, and getting ready to deploy a handful of cheap mechanical min-max thermometers. I’m placing one out in the open, the others against the south wall of a shed and other places I think should prove to be warm microclimates. Out they go, and after particularly cold weather – or just in the spring – I can check the different minimum temperatures they’ve recorded. A few degrees differences isn’t worth worrying about, but get to 10 degree differences, and you are talking a whole winter hardiness zone warmer.

In addition to comparing different locations in my garden, I also like to compare the actual temperatures I’m recording with those from local official weather stations (to do that, just go to www.weather.gov, enter your zip code, and then click “3 day history” on the right side of the screen). The zone map is created based on readings from weather stations like these, and if your particular yard is consistently showing temps warmer or colder than the local official readings (provided, of course, your thermometers are accurate), you should adjust your winter hardiness zone accordingly.

Finally, a min-max thermometer is a great way to test various winter protection methods. Tender plants can be insulated with a thick layer of leaves or (my favorite) cut conifer branches or even styrofoam boxes. How well do these protections work in your garden? Tuck a thermometer in with the plant before you cover it and then, come spring, check the minimum temperature it recorded against what you saw in the open air. Again, a difference of 10 degrees Fahrenheit corresponds to a whole winter hardiness zone warmer, giving you real actionable information about what you might be able to over-winter with the help of different sorts of insulation.

It is worth reiterating that minimum winter temperature is only one of a myriad of factors that go into winter hardiness, moisture, duration of cold, health of plants, and even summer heat matter as well, but winter lows are important, and it can be easily and precisely measured. So why not get some numbers on it so you can have a better idea of just what tender plants you can get away with in your various microclimates? A few thermometers is a lot cheaper than putting out a bunch of rare perennials and having them freeze out on you.