So you think you want a home greenhouse, do you?

Given the growth in home gardening, the fervor around houseplants, and the interest in hydroponics and other growing methods, it makes sense that the interest in home greenhouses is also building.  Sure, home greenhouses have been a “thing” for a long, long while – from well-to-do folks with conservatories on their estates to the more common and basic home greenhouse in the last few decades.  But shifting interests, and more/cheaper options have made home greenhouses more accessible to the masses.  The number of calls that I (and other extension folks) get about greenhouses and other controlled climate production methods is increasing.  And even retailers like Walmart and Wayfair have greenhouse options on their websites (I know, because my social media and email is filled with ads about them).  So let’s explore some of the benefits and pitfalls as well as some of the things to keep in mind if you are considering (or already have) a home greenhouse.

Honestly, it is planted like a jungle. You can’t even walk through my greenhouse.

Now, the timing of my thoughts on this couldn’t come at a better time (or really, I just write these blogs on topics that are current in my life).  I just bought a new house and one of the benefits of this new house, aside from less peeling paint, fewer creaky floors, and (hopefully) fewer plumbing problems is that it came with a greenhouse!  A real, honest-to-goodness greenhouse.  Not a fancy one – its just a heated high tunnel, but it’s a real greenhouse.  Apparently, the previous homeowner was enough of a plant geek to not only have a greenhouse, but plant it like a conservatory as well.  So it is full of palm trees, citrus trees, and tropical plants all planted in the ground.  Aside from everything being planted so close you have to bushwhack like you’re in the jungle it is quite lovely. So my big winter project will be controlling those plants and making room for stuff I want to grow.  But I digress…

A few considerations for home greenhouses

There are a lot of things we could discuss about managing a greenhouse, so I won’t go in depth on a lot of things (maybe more articles to come?).  But there are definitely several things you should consider before buying or installing a home greenhouse.  Here’s just a few of them:

Purposes and uses

First up is to think about how you’re going to use the greenhouse.  Will it be for tropical plants (houseplants), for starting seeds, growing produce, or something else?  Having the purpose of your greenhouse in mind can help you choose things like size, materials, and more.  For example, if you’re just planning on starting seeds in the spring for your home garden you might get away with a small greenhouse that’s just a few feet by a few feet.  If you are going to grow fruits and vegetables, keep large tropical plants, or grow on a larger scale you’ll need something bigger.  Keep in mind that the bigger the greenhouse, the more it will cost both in terms of materials or installation and in terms of climate control.

Climate Control & Associated Costs

Whether you live in a cold climate or hot climate, you’ll need to have some sort of climate control in your greenhouse.  In cold climates, heat is the major factor.  In warm climates and during hot spells, cooling and air flow can be major issues.  While we think most plants like heat, there’s definitely a temperature sweet spot for plant growth and it can definitely be too hot.  You’ll want to be able to control your temps to keep your plants growing best.  Many of the kits available from box stores/etc. don’t include a heat source or fans, so you’ll have to either find alternatives or install your own.  Amazingly, the greenhouse I inherited is heated with a space heater.  This is a cheap, no-frills option but can also be risky.  Shorts and fire hazards are risks, of course.  But so is failure of the unit and also power outages. I’m not putting my fancy/expensive plants in the greenhouse because I could imagine a power failure during a Nebraska snowstorm with below zero temps killing everything in the greenhouse.  I keep an eye on the temperatures in the greenhouse with a smart sensor (left by the previous owner) that sends temperature information and alerts to my phone, but that can only do so much when you don’t have a method to keep the temperatures up. 

That space heater is the sole means of heating the greenhouse

Of course, the other hazard will come when I see the electric bill for keeping the greenhouse warm.  Even on cold days the temperatures usually warm up on their own with even a little bit of sun, but keeping the plants warm at night is the problem.  I have the heater set to keep the greenhouse just warm enough so that the plants aren’t damaged killed (between 45 and 50), so I’m not paying to keep it super warm all winter long. 

Of course, using fans to cool or control air flow will be another expense for most greenhouses, as will water.  Greenhouses are typically pretty high humidity, but if you have a lot of air flow you’ll need to water more often.  Amazingly, my greenhouse doesn’t have vents or fans, but it is small enough that it doesn’t really need them.  If it were a big greenhouse, it would require some airflow to keep it much cooler in the summer.  Right now, an open door (covered with netting) suffices.

One way that some folks are reducing energy costs in cold areas is by building geothermal greenhouses.  These are becoming oddly common in Nebraska.  These are a much bigger undertaking than just popping up a kit from a box store in the back yard.  You have to dig down deep enough for the ground to aid in temperature control, have to install an underground system to intake and deliver air (to help with temperature control), and usually build a solid block or concrete wall to absorb solar heat amongst other considerations.

Location, location, location

A place to put your greenhouse is also an important consideration.  Whether you are an apartment dweller popping a small greenhouse structure on a balcony (it is possible) or someone installing a walk-in greenhouse on a larger property location is important.  Some greenhouse structures are lean-to or attach to the house, meaning that you get the added benefit of the heat holding properties of your house siding.  I’ve even seen some greenhouses used as sun rooms – which basically is a modern day solarium. If you attach the greenhouse to your house, you’ll also want to have a safer heat source than just a space heater.

This kit greenhouse is much cuter than mine…but it probably costs a whole lot more.

Orientation of a greenhouse can be important for those that are either elongated (like mine) or those that are on the side of a house in terms of sun exposure and temperature control. Square or roughly square freestanding greenhouses don’t have to be as planned out.  For greenhouses on the side of the house, you’ll want to place it on the side of the house, or closest to the side of the house, that faces the sun.  For the northern hemisphere this would be the south facing wall.  For the southern hemisphere this would be on the north wall. However, in warmer climates where over heating may be an issue you might want to place it elsewhere, like on an east facing wall to get morning sun but protect it from the hot afternoon sun.  This is, of course, dependent on light levels available to plants, as you’ll want to maximize light exposure in winter. 

For elongated greenhouses, a common orientation is to have the greenhouse oriented north to south so that the sun passes over and both sides receive the same amount of light.  An east-west orientation will mean that one side will receive more light. In windy areas like Nebraska, orientation is also important to preserve the structure.  My greenhouse has a curved or hooped top (sometimes called Quonset style), which allows wind to blow over the structure.  If the flat end of my greenhouse was facing into the wind (west), a strong gust of wind could damage the structure.  So location and structure play a part in the ability of a greenhouse to weather the storm. 

In conclusion?

We’ve covered purpose, climate control, and location in setting up a home greenhouse.  There’s plenty more to talk about when building and managing a home greenhouse, so if interest is high enough perhaps I’ll talk more about the topic in future installments.  What say you?  Is there enough interest to keep talking about home greenhouses and following the adventures of my home greenhouse jungle? 

Landscape Fabric Strikes Again–Oh the Horror!

I have a very interesting research project on the effects of urban pressure on Coast Live Oak (CLO). CLO is a California native oak and I am interested in seeing if urban cultural conditions prevent the development of mycorrhizal fungi on their roots.  My study is blocked, that means that all the treatments occur in a block and the blocks are repeated for replication.  Blocking allows the statistics to account for variability in field locations.  Its a good thing too, since one of the blocks has never done well.  One tree died, two are severely chlorotic etc.  This was not just the effect of the urban pressure treatments, but way more severe than any other trees growing in other blocks.  It turns out there was a reason…  I had unwittingly planted my sapling oaks in an area of our research farm where  buried landscape fabric was installed.

Landscape fabric in my test plots prevented rooting of coast live oak in the undersoil

So most trees that were covered by the landscape fabric were chlorotic. One died and one grew normally. The one growing normally had extended roots over the top of the fabric and then grown into soil beyond the fabric. Note in the picture above a lack of roots despite adequate moisture.

One of the oaks in the fabric affected block. Even coarse arborists chips can’t help this tree when landscape fabric is in the way. The yellow coloration of the leaves is chlorosis. Likely because the roots do not have enough oxygen to acidify their rhizosphere.

How does landscape fabric hurt trees? Let me describe the mechanisms… First and foremost soil coverings reduce the ability of soil to diffuse gases, both into and out of soil. As we know from other blogs on this subject in the archive Dr. Linda Chalker Scott and colleagues conducted research on gas diffusion rates under different kinds of landscape or soil coverings. It is important to understand that gases go both ways. For roots to remain healthy, they must convert sugar to energy through the process of respiration. During chemical respiration oxygen is combined with glucose and converted into energy (for cell growth) and carbon dioxide is produced. Carbon dioxide must diffuse out of soil and oxygen diffuse into soil for this reaction to occur.

Image from Shahzad et al., 2019. The chart indicates how fabrics and plastic are impermeable to carbon dioxide.

Many of our blogs have touted the benefits of coarse, fresh, arborist chips for woody plants. One of the supreme benefits is the increase in rooting under these mulches. Unlike landscape fabrics, wood chip mulches eventually modify soil actually promoting gas exchange into deeper levels. Also, landscape fabrics prevent soil arthropods and other organisms from transporting organic matter to lower levels. Think of plastics and fabrics as a suffocating blanket over root systems, they deprive roots of moisture and gas exchange and prevent soil modification and organic matter movement.

While thick, coarse organic mulches actually enhance establishment and rooting of landscape plants without limiting gas exchange they can not overcome the impact of landscape fabrics. A common practice is to lay down fabrics and then apply mulch over the fabric. This often results in a “tatty” look years later when the mulch decomposes and the fabric shows through. Landscape fabrics and weed barriers are landscape pollutants. We should be limiting the use of petroleum products in landscapes because they do not break down easily and they have a bad impact on all forms of life.

As mulches break down “tatty” landscape fabric shows through giving a trash-like look to any landscape they are used in

References

Cahill, A., L. Chalker-Scott and K. Ewing. 2005. Wood-chip mulch improves plant survival and establishment at no-maintenance restoration site (Washington). Ecological Restoration 23:212-213. https://www.researchgate.net/publication/303445066_Wood-chip_mulch_improves_plant_survival_and_establishment_at_no-maintenance_restoration_site

Chalker-Scott, L. and A. Downer. 2022. Garden Myth-Busting for Extension Educators: The Science Behind the Use of Arborist Wood Chips as Landscape Mulches. Journal of the NACAA 15(2). https://www.nacaa.com/file.ashx?id=6c7d4542-7481-4f0a-9508-d8263a437348

Shahzad, K., A.I.Bary, D.P. Collins, L. Chalker-Scott, M. Abid, H.Y. Sintim and M. Flury. 2019. Carbon dioxide and oxygen exchange at the soil-atmosphere boundary as affected by various mulch materials. Soil & Tillage Research 194. https://doi.org/10.1016/j.still.2019.104335

Let it snow, let it snow, let it snow?

If you follow current weather news, you have likely read the astounding story of the recent lake effect snowfall in Buffalo, New York, and other areas downwind of the Great Lakes, where over 6 feet of snow fell in just a day or two in some locations. My mom, who still lives in Grand Rapids, Michigan where I grew up, reported that in her city some areas got up to 30 inches during the same time frame. So this month I want to discuss lake effect snows and how heavy snows can affect your trees and gardens.

Source: photochem_PA, Commons Wikimedia

What is lake effect snow?

Lake effect snow is snow that is caused or enhanced by differences in the temperature of warm water in the lakes and the cold Arctic air that blows over it. Calling it “lake effect” is a bit of a misnomer, since cold, dry air blowing over a warmer ocean can cause the same effect. In the United States, it most often occurs downwind of the Great Lakes, especially in fall when the lakes are still warm and the air blowing in from the north is much colder and drier than the lake surface. It can even sometimes occur downwind of smaller lakes or reservoirs if the conditions are just right.

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As the cold dry air crosses the warm water, copious amounts of water vapor evaporate into the air mass and once that warmer, moister air blows onshore again clouds drop huge amounts of snow in the areas downwind of the lakes. The snow usually falls in heavy bands that drop snow in areas that are highly dependent on the direction of the wind. Often the bands are just a few miles wide but if you drive through one your visibility can drop to near zero in just a short distance. When I lived in Valparaiso, IN, near the south end of Lake Michigan, winds blew straight from the north for much of the month of December 2000 dropping 32.0 inches of snow when Decembers there usually get just a few inches, thanks to the lake effect snow that occurred. (I moved to Georgia the next month, although it was not because of the snow—mostly.) As winter progresses and the lakes get colder with more ice cover, lake effect snow is reduced because of the decrease in available water vapor so fall and early winter are the prime times of year for the heaviest lake effect snow.

In this case, weather forecasters were well aware of the potential for record-breaking snow because of their knowledge of the lake temperatures plus the computer-generated forecasts of wind direction and persistence over time. Winter storm warnings and maps of predicted snowfall were produced well ahead of time. Even so, the amount of snow that was produced from this historic event is still amazing.

Source: Carolyn Thompson / AP Photo

Why did Buffalo experience such extreme snowfall amounts?

Buffalo is known for its incredible snowfalls due to its position downwind of Lake Erie, a long and shallow lake that is usually warm well into fall. The long distance of the wind blowing over the lake (called the “fetch”) allows the air to pick up tremendous amounts of water that becomes snow as it hits the land NE of the lake; the exact location of heaviest snow depends on the direction of the wind over the lake (see my poorly drawn map annotated on a screen capture of the Earth Nullschool streamline map for the day of the heaviest snowfall below). In this month’s case, the lake had temperatures well above the long-term average, and the wind across the lake was very consistent over a few days, allowing the snow to pile up dramatically. In some locations snow was falling at the rate of several inches an hour and the extended period of snowfall allowed it to build up to over six feet in some locations in just a day or two, while other areas not along the direct path of the wind received much less. The area of heaviest snowfall shifted as the winds changed direction over time.

The result of this weather event was the nearly complete shutdown of Buffalo and other areas affected by the heavy snow. Even a city that experiences as much annual snow as Buffalo does can be stopped in its tracks for a while by the sheer volume of snow that has to be removed. The weight of the snow also caused problems for a number of building roofs and caused some power outages as well. Even the professional football game between the Buffalo Bills and the Detroit Lions had to be moved from Buffalo to Detroit because of the impossibility of clearing out the open-air stadium and the roads around it for fans to get there safely (or at all).

Does climate change affect lake effect snow?

A warming climate does have some impact on the conditions that make lake effect snowfalls most likely. The lakes are generally staying warmer later into the fall, so when cold continental air does develop over Canada and move across the lakes there is more potential for large amounts of water vapor to be evaporated, increasing the chance of heavy snow. It is likely that there may be some reduction in the production of the coldest, driest air in polar regions, but it will still occur often enough for lake effect snow to continue to be a climate factor downwind of the lakes. It is more difficult to say how or if the weather patterns that determine the direction of wind flow will change as the climate gets warmer.

A tree with pink flowers

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Source: Dan Taylor-Watt, Commons Wikimedia

How does heavy snow affect trees and gardens?

Lake effect snow is often very wet and heavy which makes damage to trees and power lines more likely. An average snowfall may have about one inch of water equivalent in ten inches of snow, but in a lake effect snow it is often more like six inches of snow to one inch of water equivalent which means it is very dense stuff to shovel. Wet snow may weigh up to four times as much as newly fallen regular snow per square foot. No wonder most heart attacks from clearing snow occur when this very wet and heavy snow has fallen.

The weight of this much snow can easily collapse the roofs of buildings. It can also do a lot of damage to tree limbs and shrubs, especially when the wet snow sticks and freezes to either needles or leaves adding to the weight on the limbs. Trees and bush varieties that are brittle or have poor branching structure are especially vulnerable to damage from heavy snow. Snow on the ground can help insulate the plants from very cold weather, but the moisture that is left after the snow melts can cause saturated soils that can negatively impact roots. Salt added to help melt the snow from paved surfaces can also harm plants and the deep snow cover in some lake effect storms can also provide cover for voles and other critters that like to nibble on bark.

For me, lake effect snow in my Michigan winter when I was growing up was the ultimate fluffy Christmas snow, with big fat flakes drifting down like a picture postcard. But when the flakes come down fast and heavy the holiday snow becomes a problem that can affect travelers, home owners, and gardeners too. I hope that as you travel over the holidays this winter, the snow that you see, whether you stay or go, is a delight and not an obstacle to spending time with your friends and family.

“This one secret hack will save you time and money!”

I’m resorting to clickbait tactics to get your attention. Here’s another – “Warning! Graphic photos follow!”

Uncorrected roots in containers or landscapes will create chronic water stress problems for trees.

If you have failing trees on your own property or on property you manage, you need to do one simple thing before you assume that pests or disease are responsible: you need to determine whether the root system is healthy and functional.

Now, I know you can’t see underground, but you can draw some informed conclusions based on whether you can see the root flare. To find the root flare, pull away any mulch or groundcover that’s obstructing your view. Once you can see soil, you should be able to see the root flare. If your tree looks like a utility pole (meaning you can’t see the flare), then it’s been planted incorrectly. This single mistake will have myriad consequences:

No flare = no chance

  1. It’s buried too deeply – the flare needs to be at the surface.
  2. If it’s buried too deeply, it’s likely the tree was planted without removing the materials surrounding the roots. Bare–rooting woody plants before planting is crucial to their survival.
  3. Roots that are buried too deeply will not have sufficient oxygen to establish a fine root system for water and nutrient uptake, much less develop any structural roots.
  4. Moreover, without removing the materials around the root, the roots are less likely to establish into the surrounding native soil. Neither are you able to remove poor structural roots. Check out this post for more information.
  5. A structurally flawed root system, stressed for oxygen and encased in layers of clay (or potting media) and various combinations of burlap, twine, and wire baskets, is not going to establish quickly or well. Increasingly, it’s not able to supply sufficient water to the growing crown.
  6. Oxygen-stressed roots will die, compounding the reduced water uptake problem.
  7. As the crown experiences chronic water stress, it will experience dieback while opportunistic pests and disease take advantage of a tree unable to chemically defend itself.
  8. Opportunistic pests and diseases are not the cause of tree failure – they are simply indicators of an environmental problem. Proper diagnosis is discussed here and here.

Bare-rooting plants allows you to correct defective structural roots before planting.

You should be able to confirm lack of root establishment by performing the wiggle test (that’s the secret hack). This will allow you to see whether the soil around the roots moves. If it does, that means the roots are not established. If the tree has been in the ground for more than 6 months, it’s probably not going to establish. The sooner you can dig up and correctly replant a relatively newly planted tree the better your chances that will recover and establish.

The wiggle test!

Po-TAY-to, po-TAH-to: Let’s call the whole yam thing off!

As most folks in the US prepare for a Thanksgiving meal, or at least eat more Thanksgiving-inspired fall meals, potatoes and sweet potatoes often play a major supporting role in these most delicious victuals.  Whether mashed, smashed, baked, candied, or turned into casseroles or pies, these starchy vegetables are stockpiled in grocery stores and markets in the fall for shoppers to turn into those tasty treats. 

But sometimes there is confusion lurking in those grocery aisles and even in the minds of unwary shoppers….enter the “yam”.  Wander down the canned vegetable aisle and you’ll see canned yams.  Are they the same thing as sweet potatoes?  And are they related to the standard potato that you usually mash, bake, or fry?  I yam going to set the set the record straight. 

First things first, sweet potatoes and yams are two totally different species so they are not the same thing.  They’re even in different plant families so they aren’t even closely related.  And neither of them are related to the regular old potato.  So those “canned yams” at the grocery store are mis-named.  They are sweet potatoes.  Yams are rarely consumed or sold in the US, except usually though markets that sell specifically African/Caribbean foods. 

A sweet potato in bloom….look familiar?

Sweet potatoes are soft when cooked, thin/soft skinned, usually pretty sweet, and usually orange.  Though there are some white-fleshed, less sweet varieties available.  Native to tropical regions of the Americas sweet potatoes, or Ipomoea batatas, are members of the Convolvulaceae, or bindweed, family and are closely related to morning glories many of which are in the same genus Ipomoea.  These sweet veggies are part of the root structure, so they are modified storage roots that store starches and sugars produced by the plant. 

Yams, on the other hand, are white with a hard skin like tree bark, and are usually pretty dry when cooked.  There are three main species of yams in the Dioscorea genus, which has its own family Discoreacea.  Also tropical in nature, three different species were domesticated independently in Africa (D. rotundata), Asia (D. alata), and the Americas (D. trifida).   Yams are monocots, meaning they are more closely related to lilies and onions than they are to sweet potatoes.  Also, unlike sweet potatoes, the edible portion of a yam is a tuber, which is structure arising from modified stem tissue. 

Piles of yams…that look nothing like sweet potatoes

And just to round out the tater trifecta – the humble potato.  Sometimes called a white potato or an Irish potato (which are both bad descriptors for them because they come in many different colors, and while they are a staple in Ireland they originate from the Americas), these versatile spuds, Solaunum tuberosum, are members of the Solanaceae family and are closely related to tomatoes, Solanum lycopersicum.  Their morphology has similarities to those of the yam, though, as they are tubers arising from the stem vs being a root like sweet potatoes. 

So where does all the confusion come from? 

There are various theories on how yams and sweet potatoes got caught up in this mash-up, and I don’t pretend to be an expert here.  But the most common theory that I’ve seen is that enslaved African people held in the US south called the local sweet potatoes by the names they used for yams, as the sweet potatoes reminded them of the yam that was part of the staple diet in many African countries.  The word yam is derived from nyam, nyami, or nyambi, meaning “to taste” or “to eat” in certain African language dialects.  Adding to the story, apparently Louisiana sweet potato growers in the 1930s used “yams” as a marketing name for a new orange-fleshed sweet potato cultivar and the name stuck. 

One thing I find interesting is that yam was used to describe orange sweet potatoes when the white fleshed ones (which are less common now) would probably more resemble an actual yam, both in appearance and flavor.  In fact, in my travels in Rwanda I ate many white fleshed sweet potatoes, as they are now a major staple crop in many African countries.  It is also interesting to note that the refugee farmers in our urban farm programs prefer to grow the starchier, less sweet varieties of sweet potatoes, which often complicates things as they can be hard (and expensive) to find. 

Whether you cook sweet potatoes or “white” potatoes for your Thanksgiving feast, now you’ll know a little bit about how each of those crops are different…and you’ll at least know that sweet potatoes aren’t yams. 

Big Blog on the Block

There’s a new1 blog on the social media block—The Big Blog of Gardening (BBoG). Already it’s a heavy hitter in the gardening social media world. The question is: How may foul balls are hit?

My wife came to me recently saying “Hey! Did you know that your friend Linda Chalker-Scott changed her institution?”
“What?” I said.
“Yeah, she moved to University of Washington. It says right here on this MSNBC article.”
“It’s from the Big Blog of Gardening? What’s that?”
Turns out that the BBoG is hooked into national media and gets consistent play on the home pages of those who go to MSNBC. This is because the BBoG is “now part of the Microsoft Start Program” that places content on the MSN homepage whenever a user logs in.

The originator of the BBoG is not a scientist and in the “About” section of his web page states that he started gardening as a child (like many other of us that had school gardening programs around the country). I also started gardening as a child, volunteered at Descanso Gardens in La Canada, but in my own case I followed up my childhood experiences with a dual major in Botany and Horticulture, an MS in plant pathology, a PhD in plant pathology, and a 30-year career with Cooperative Extension advising and researching in landscape horticulture. These are the typical qualifications for the blog writers at the Garden Professors web pages. Unlike writers for the BBoG, we are the folks who actually conduct research on horticulture and gardening subjects that other people quote and cite.

For us scientists, one of the pitfalls of the BBoG is it’s not a science-based blog. In a blog on pruning, the title proposes to inform how to prune any landscape plant. When you read that article, it just directs you to a link to Amazon.com to purchase a publication of the American Horticultural Society (which is not a science-based organization even though it sounds very much like the American Society for Horticultural Science – the oldest horticultural science society in the US). Rather than cite current research or address the blog title’s topic, the article leads to a product you have to buy to get your information. BBoG posts are full of of links to products available online or to “paid for links” for non-scientific and misleading garden books or other resources.

Broad strokes are used in titles of the blog. For example: “Staking a tree is almost never the right thing to do”. In some ideal world where nurseries grow trees w/o stakes and landscapes don’t require protection from damaging elements this may be true, but this is not the world we live in. Trees grown in nurseries are often staked to facilitate production and shipping. Staking can be used as a protection process on trees that may suffer impact from moving vehicles (these stakes have no attachment to the tree but serve as protective bollards). Titles in some other posts are merely attention getting or serve to promote products – not to reflect accurate horticultural science.

The BBoG often cites Dr. Linda Chalker-Scott, quotes her published work, provides links to her white papers, but doesn’t actually email or otherwise contact the original author. The problem is that often there are peer-reviewed sources by the same author containing this newer information (e.g., WSU Extension publications). BBoG often seems to miss the actual scientific or peer reviewed work but focuses on popular sources such as Fine Gardening or, even worse, Consumer Reports. Consumer Reports is not a legitimate resource for science-based information. (link to Jeff Gilman’s blog post)

Beware the comments at the end of articles on the BBoG as there can be pseudo-scientific information there (using gypsum to create drainage in soils) that goes unrefuted by the article authors. It is important that site administrators approve comments before they are listed, or at least address the misconceptions in a response.

When BBoG stories hit the mainstream media (like MSN) the blog owner does not always mention the original sources of their stories, or the scientists who developed the information: they take credit and reap the rewards of increased eyeballs on their posts and clicks on their advertising links. Wouldn’t it be nice if members of the media could dig a little deeper and find the science-based gardening sites and give them some well-deserved publicity?

Frosts and freezes: As cold as ice…

Here in the Southeast we were surprised last week by a much earlier than usual freeze, putting an end to many gardens full of tender plants, although the cold was not deep enough to kill more cold-hardy species. In many parts of the region the frost came earlier than the 10% probability of frost indicating that early freezing conditions like this will come in fewer than one in ten years. Of course many of you in more northern interior parts of the United States have already seen your first frost this year, but here we never seem to be ready for it. In fact in parts of southwest Georgia last year’s first fall frost did not turn out to be until well into January, which caused a lot of problems for gardeners and farmers who had to deal with pests and diseases that easily overwintered the mild conditions.

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Median date of first 32 F fall frost, from https://www.weather.gov/iwx/fallfrostinfo.

Frost versus freeze

One of the questions I often get this time of year is what is the difference between frost and freeze? The National Weather Service (NWS) puts out both frost and freeze warnings but has different criteria for each. For a frost warning, the predicted temperature may not even get down to 32 F (0 C), but may hover in the mid 30’s. For a freeze warning the predicted temperature is expected to get down to 32 F or below and for a hard or killing freeze it usually gets down to 28 F or lower. Once the area has gotten down to 28 F or lower, the NWS usually stops issuing additional freeze warnings since at that point all but the most cold-hardy plants have completed their growing season and are either dead or dormant.

A close up of a spider web

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Hoar frost on Indian rice grass. Source: NPS Photo by Neal Herbert at Arches National Park via Commons Wikimedia.

How does frost form if the temperature does not get down to freezing?

To understand frost formation and when warnings are issued it helps to know both how frost forms and how temperatures vary near the ground. Frost crystals form on surfaces that get down to freezing and have something on the surface that is conducive to seeding crystal formation. This can happen even when the air temperature is above freezing in conditions of light wind and clear skies that allow surfaces to cool to freezing temperatures by emitting heat radiation out to space at night when there is no incoming solar radiation. Conditions for this can occur with temperatures anywhere in the 30s with a reasonable amount of water vapor in the air and as long as the surface (a metal car body, an asphalt roof, or a blade of grass) can cool to the freezing point. At that point, anywhere on that surface that has an appropriate scratch, particle, or other imperfection can serve as a place for ice crystals to form and start to grow. These are called nucleation sites and allow the initial formation of an ice crystal upon which more ice can grow into delicate but visible frost.

Frost will not form if the humidity is too low because there is not enough moisture to produce visible crystals. Often frost does not damage the plants a lot because most of the frozen water is confined to the surface of the plant and does not affect the interior cell walls, although there may certainly be some damage where the ice forms. Large formations of ice crystals can sometimes form on trees or fences if the conditions are right; this is called hoar frost.

Hoar frost on ”Burgbühl” (also Hexenbühl) near Obernheim (Swabian Jura). Source: Olga Ernst, Commons Wikimedia.

Frost forecasts are also provided with the understanding that the NWS is forecasting temperature values for their thermometer heights of about 2 meters or 6 feet high, since that is how they verify the accuracy of their forecasts. In light winds and clear skies the temperature at the ground level is often colder than the temperature at the thermometer height due to cold air sinking so the ground in your garden may be colder than the forecast would predict. Frost is also more likely to form on elevated surfaces that don’t have contact with the ground, since soil temperature keeps the ground surface warmer in Fall than later in the year due to residual heat from the summer warmth. Blueberry farmers that I work with tell me that you can sometimes see quite a difference in frost damage to their bushes from top to bottom due to the different temperatures that the plant may experience at different heights above the ground. Bridges often have signs that they freeze first for the same reason.

A close up of a flower

Description automatically generated with medium confidence
Saucer magnolia with freeze damage. Source: Famartin, Commons Wikimedia.

Freeze damage to garden plants

The NWS issues freeze forecasts when the temperature is expected to get down to or below 32 F. The damage that the freeze does to plants depends on how long the temperature drops below freezing and how susceptible the plant is to cold temperatures. If the temperature barely gets down to 32 F for a short period damage is likely to be minimal since the water inside the plant cells did not have sufficient time to freeze. But if it lasts longer the water in the cells freezes and, as you undoubtedly know, ice expands and breaks the cell walls causing irreversible damage to plant leaves and stems that leads to their death. John Porter provided a useful table of how different garden vegetables respond to cold temperatures in his 2020 blog on spring frosts, which underlines why some vegetables like spinach and cauliflower do better as late-season vegetables than tomatoes and melons.

The discerning reader who looks at John’s article will also note some differences between the first frost map he published in his blog and the map above, because they cover different time periods. John used the map for 1980-81 to 2009-2010, since that was the current one at the time of his post. The map here uses the 1990-91 to 2019-2020 period since the normal temperatures have been updated since John’s blog was published. Average frost dates change over time as you can see especially in some areas like eastern Oregon and northern New York State and generally, as the earth gets warmer, the first frost of fall is occurring later in the year than it did in the past (although there are a few exceptions such as parts of northern Georgia).

Frosted Kale. Source: Tracy from North Brookfield, Massachusetts, USA, Commons Wikimedia

With winter on the way, we are sure to see many more examples of frosts and freezes in the coming weeks for almost everyone other than those who live in tropical areas. For those of us who enjoy chilly weather, the magic of frosts and freezes is something we look forward to as it paints our dying gardens in icy white.

Understanding how weird weather affects our plants

Nutrient deficiency? Or something else?

I’d intended to write the column earlier in the year, but it’s as relevant now as it was in the spring. This post will familiarize you with how unseasonable weather can affect your plants. Though I’ll be focusing on my own location in Tacoma, the phenomena are global. You just have to pay attention to what happened last week, last month, last year in your own location.

Our two potted Japanese maples

Our spring started out wet and cool, which is nothing new. But it was REALLY wet and REALLY cool compared to normal. This meant that our trees and shrubs had plenty of water to fill their expanding leaves and blossoms – but the lower than normal temperatures affected leaf growth. These dwarf Japanese maples had lots of leaves, but they were tiny! And they stayed that way, because once the leaves begin to lay down cuticle, they don’t expand any longer, even when it gets warmer. These maples put on a second flush of growth in the summer. Look at the difference in leaf size, determined solely by ambient temperature.

We had an abundance of flowers on our fruit trees – so dense that I put off pruning some of our heritage apple trees so we could get an even bigger crop (our black Angus love apples). But summer rolled around and…virtually no apples on ANY of the trees. What happened?

Normally, our apple blossoms are opening when there is lots of insect activity

Well, that cool spring ensured that most of our pollinators were late to emerge from overwintering. I had wondered about them in the spring, as I could only see a few pollinating flies and no bees. But sure enough, we had almost zero pollination. No apples this year. Next year if the weather is similar I’m going to try using my battery-powered leaf blower to pollinate these trees. I’ll take pictures.

This chart only goes through August 28. We had no rain until October 20th.

Fast forward to summer – for us, a record-breaking drought (again). Our temperatures weren’t as high as last year, but we still had very hot weather and no rain. For our landscape it’s not a problem, as we have well water for irrigation. But those gardeners who have little or no supplemental irrigation may very well find that their woody plants and perennials don’t perform very well next year: perhaps fewer flowers or branch dieback will appear. This is due to root dieback that happened all summer in unirrigated conditions. The damage is only seen in the following spring, when there aren’t enough roots to supply water to emerging buds.

Crown dieback from water-stressed roots.

Being able to predict the impact of specific weather events on your landscape plants is key to avoiding misdiagnosis and subsequent misuse pesticides or fertilizer in a futile attempt to rescue them.

Oh, and if you are wondering about the photo at the top, you’ll have to look at a post from 2009 to see what’s going on.

Tulips for the desert?

Spring bulb planting time is on across North America!  Many types of bulbs do well in desert and xeric gardens: hyacinths, ranunculus, iris, narcissus, crocus, alliums can all be happy. One bulb that’s often left off the list are tulips. Why is that?

The tall flashy hybrid or Darwinian tulips that fill the catalog photos are usually considered an annual in most desert gardens. They require more chilling than the our desert winters can usually provide and can be a little fussy about soil and water.
But tulips can be very happy in xeriscapes. In fact they can get so happy they’ll set seed and naturalize in the right conditions. And which tulips are those you ask? (Yes you did, I heard you.)
They’re species tulips and are non-hybridized. They’re more of “wild” type of plant. What’s so special about them?
They’re tough, amazingly tough.

Tulips are originally from mountainous areas of the Mediterranean, Middle East and Asia. Some are also native to Southern Europe, North Africa, and several Mediterranean islands. They’re frequently found clinging to barren mountain ledges, rocky areas exposed to wind and cold, and drought ridden slopes.

Map by Tulips in the Wild
For an interactive format with species information go here:
https://www.tulipsinthewild.com/map_table/tulip_origin_map.html

Species tulips are shorter and smaller than hybrids but what they lack in stature they more than make up for in resilience and showy display. They’re an early bloomer in the desert southwest which is wonderful for the pollinators that are often active on warm winter and early spring days.

Their foliage is usually more varied than hybrids; some have broad, curled edged leaves, some are tall and narrow. The color varies too, from a bluish tint to shades of green. Some varieties even have multiple blooms per stem.

Many species are attractive whether the blooms are closed or opened. They often have very different coloration inside and out.

Closed…
…and open

Some have contrasting pollen color which adds great visual interest.

These have a deep purple pollen.

Species tulips are usually perennial in warm winter climates. They increase via bulb offsets while many will set seed. They aren’t fussy about soil as long as it’s well drained. But like all plants they do require water during bloom and while the leaves are green but still, not as much as other bulbs. They’re perfect for xeriscaped or low water landscapes since they require less overall water than other bulbs. Plus, they prefer to be dry during their dormant season, which is summer to fall.

These tough little beauties can occasionally be found in garden centers but for the best selection shop online, search for “species tulips.” Do some homework first, and become familiar with the the available varieties.

Plant these tulips from fall to early winter. Provide full sun and good drainage, rocky or lean sandy soils are ideal and most closely approximate their native conditions.

Don’t overplant with species that require a lot of summer water. Mix these bulbs with other plants that prefer hot dry conditions. Tuck them into those corners that get spring – early summer sunshine, spots that don’t get much summer water, or put in containers that you can enjoy and then ignore during the summer. Pot them in cactus mix combined with a small amount of regular potting soil and top with an organic mulch. Remember, drainage is a must and overly rich or high organic matter conditions aren’t to their liking.

If you live in a dry or desert region and have never tried species tulips, why not give them chance. You might just discover a new favorite.

Predicting hurricane tracks and what they leave behind

In my last blog post in late August, the Atlantic tropical season was just beginning to wake from a long nap, with several areas of interest appearing on the National Hurricane Center’s (NHC) map. Since that time, the season has become incredibly active, with Hurricanes Fiona and Ian causing tremendous damage in North America. Other parts of the world have also seen damaging storms, including Hurricane Kay in the Eastern Pacific, post-typhoon Merbok in Alaska, and Typhoons Hinnamnor in South Korea, Nanmadol in Japan, and Noru in the Philippines. So, with apologies to those who live far from hurricane parts of the world, I want to talk one more time about tropical systems.

Heavy rain. Source: Faldrian, Commons Wikimedia

Where do we stand with the tropical season now?

As I am writing this on Thursday morning, September 29, I hear the sound of Ian’s wind in the tulip poplar trees outside my house in Athens, GA. Ian is still in central Florida, just about to come off the coast into the Atlantic Ocean, so that gives you an idea of how far the influence of a tropical storm can spread, especially with a strong high-pressure center to our north that is increasing the pressure gradient driving the winds. Ian made landfall yesterday afternoon near Fort Myers, Florida, as an almost-category 5 storm, with winds of 150 mph (some reports say 155 mph). The videos I saw yesterday showed the power of the storm, with tremendous wind gusts and a storm surge that surpassed 10 feet in some places. I know the damage is horrific, and some of those areas will never recover completely from the storm, as buildings have been washed away and even shorelines may have changed due to the force of the wind and water. Since Ian is expected to curve back toward the East Coast on Friday and may strengthen again, its effects are not over yet. Fortunately, a weaker storm has lower impacts, but folks along the Georgia and South Carolina coasts will be feeling those impacts in the next few days before Ian moves out of the area and dissipates.

Hurricane Ian, September 27, 2002.

Hurricane Fiona lashed Puerto Rico and the Dominican Republic with rain of up to two feet in some places around September 18-19 before moving rapidly to the north and slamming into Nova Scotia as a post-tropical cyclone on September 24. It caused tremendous damage in both places from storm surge, wind, and rains. The floods in Puerto Rico destroyed a lot of local farms and gardens in the southern half of the islands where the rain was heaviest and in doing so, eliminated an important source of locally produced food as well as disabling a fragile power grid that had not yet recovered from Hurricane Maria in 2017. The storms in other parts of the world have had similarly bad effects on the lands over which they moved, with loss of trees and buildings and high storm surges wiping out coastal infrastructure. Not all hurricane impacts are bad, however, since the rain from Hurricane Kay in southern California helped reduce drought conditions there in a time when not much rain usually falls in that part of the world.

Predicting the tracks of hurricanes

One of the questions that have arisen with Hurricane Ian has been the prediction of where the hurricane would go. Predicting the track of a hurricane is an art that includes the use of multiple computer models that simulate conditions over the life of the storm. That includes sea surface temperature, vertical atmospheric structure, and the surrounding wind field which will push the storm around. On the news you will often see maps that show all the individual model results on one map, which ends up looking like a mass of spaghetti noodles, hence the term “spaghetti models”.

Ensemble of Hurricane Ian forecasts from the GEFS model issued on September 26, 2022. Source: WeatherNerds.org

Forecasters look at all the individual model tracks together to see how consistent they are with each other and where the differences lie. Then the human forecasters use their knowledge of how well those models behave under different weather conditions to create a “forecast cone” that shows the region where the center of the storm is likely to go.

No one model is right all the time because they weigh different weather factors differently. In the case of Ian, the models run by European weather services did better, but that is not always the case. Generally, they say that 2/3rd of the time, the central low pressure will stay within the predicted cone, although the storm itself is usually much larger than the cone and hazards like high wind, heavy rain, tornadoes, and storm surge can and do occur far outside the cone. If there is a lot of spread in the models, then the forecast cone is wider, indicating that they are less certain about where the storm will go.

The models are run every six hours or so, and each time the cone is updated to include model results that include new weather data observed since the last forecast was issued. As this happens, people that are in or near the cone must respond to the forecast by deciding whether to evacuate or stay in place and where to go if they do leave, since they don’t want to evacuate to a location that could be hit by the storm if the cone shifts. When the forecast is especially tricky, as it was with Ian, the movement of the cone over time can become overwhelming to people who just want to find a place they will be safe. The forecasts of where the storm is likely to travel are improving over time, but the tracks will never be 100% accurate because the atmosphere is a complicated place that we can’t simulate perfectly using even the best computers, so confusion is likely to continue to occur in future storms.

Downed trees and powerlines in Bartow, FL, following Hurricane Ian. Source: State Farm, Commons Wikimedia.

Dealing with flooded gardens

Since this is a blog about gardening, I want to end up mentioning what impacts these storms have on gardens. Coastal areas where there is a storm surge will see inches to feet of seawater flow over their land. The water contains salt but can also contain toxic chemicals from boats and tanks that are damaged by floating debris or strong waves. The salt and chemicals can kill garden plants but also may get deposited in the soil as the water sinks in, leaving toxic residue behind. The physical motion of the water on and off the land can also scour the topsoil and change the soil structure or deposit sand on top. Saturated soils can drown the plants by keeping oxygen from reaching the roots of plants. And of course, the howling winds can snap the plants, bushes, and trees above the ground, leading to damage that can be taken advantage of by pests and diseases. In areas where there is heavy rain and freshwater flooding, salt is not usually a problem, but all the other problems with too much water can occur there, too. For those who live where storm damage is heaviest, helping their gardens to recover will be a long process even if their houses survive the storm.

Hurricane Ian clouds at sunset. Source: Jason Mallard.

The Atlantic tropical season is not over yet for us in the Southeast, but I know that in other parts of the United States and the world, the seasons march on, so in the next months I will move on to talk about fall frosts and the upcoming winter. Thanks for bearing with me as I explore tropical storm systems. Please keep all of those affected by our storms this year in your thoughts and prayers as they work to recover from damage and disaster.