The Garden Professors™ – Page 50 – Advancing the science of gardening and other stuff since 2009

Hello Charlotte!

I’m sure you haven’t been wondering where I’ve been for the past five months or so, but just in case you have, I’ve been reshuffling my life and relocating. Where am I now? The family and I have moved to Charlotte, North Carolina where I now work at Central Piedmont Community College. Why? Because we wanted to be closer to family, we wanted a warmer climate, and I wanted to spend more time teaching. That said, I had a great time at the University of Minnesota and have only good things to say about my time there.

The great thing about my new job is that I have the opportunity to teach a diverse student population a broad spectrum of classes. This coming semester I’ll be teaching five classes including Specialty Crops (we’ll be concentrating on hydroponic systems for growing veggies – it’s a great way to learn about what plants need to grow), Plant Propagation (My favorite! Everything from cuttings and seeds to budding and grafting), Greenhouse Management, Applied Plant Science and Plant Materials I. And Hey, if you live near Charlotte, I’d love to see you in one of my classes! CPCC is one of the most affordable schools in the country and the classes are open access – in other words anyone can sign up! Since I don’t have the chance to do as much research as I did in Minnesota, I’ve compensated by having my students conduct experiments in the classes – and we’ve had a lot of fun. We’ve done everything from extracting essential oils using cold fat and steam extractions to rooting cuttings using 2,4 D and spiking the atmosphere with carbon dioxide using soda bottles. I’ll be posting about all of these projects in the coming weeks. Meanwhile, it looks like vinegar based BBQ with fried okra for dinner!

My favorite on-line conifer resources

Posted by Bert Cregg

I just wrapped up putting together a species profile on grand fir (Abies grandis) for Great Lakes Christmas Tree Journal, which is the professional trade publication of the Michigan Christmas Tree Association. I do a lot of articles and presentations on conifers and while I draw on my personal experience and background as much as possible, invariably I’ll need to consult some references. Here are some resources that may come in handy if you need to develop a presentation or article or just want to know more about conifers.

Silvics of North America
Silvics is a forestry term that refers to the “study of the life history and characteristics of forest trees especially as they occur in stands and with particular reference to environmental influences.” Back in the day, just about every forester worth their salt had a weathered and dog-eared copy of Silvics of North America on the bookshelf. Today it is available on-line. Silvics contains lots of basic information about trees species; where they grow, how fast they grow, common best problems, and their genetics. Silvics also includes range maps from Dr. Elbert Little, which are a handy reference when you need to know whether or not a species in native in particular location.

Gymnosperm database
Chris Earle’s website is a botanical tour de force. It covers all gymnosperms, not just conifers but, of course, conifers make up the biggest portion of the site. The Gymnosperm database includes species descriptions for essentially every conifer in the world. Many species descriptions also include images. Earle discusses taxonomy of conifers, which for many species, is taking more plot twists these days than an episode of ‘Law and Order’. There are often interesting tidbits under enthnobotany for many species. Bottom line, you can look up just about any conifer species you know on the database and learn something you didn’t know.

American Conifer Society Database
The previous two resources deal primarily with conifers in their native environment. The ACS is dedicated to the Horticultural aspects of conifers. The ACS database includes hundreds of species and thousands of cultivars. For Picea abies alone the database includes over 200 cultivars. For each cultivar the site presents information on hardiness zone, growth rate, form, color and other characteristics. Many descriptions also include photos.

Autumn joy…

No, not Sedum…Cardoon! (Cynara cardunculus). Just a TGIF photo. I love autumn’s many shades of brown – kind of underrated with the fixation on blazing foliage.
Now’s the time to collect and save seeds for next year. Though it seems these are trying to escape…

How NOT to do an experiment

Over on Facebook I follow some groups who find provocative topics, and today’s “science fair” post was so over the top that I had to share it here.

Here’s the original post. Now the accompanying text about microwaves is whacky enough on its own (and well worth reading), but my primary interest is with the experiment. This exemplifies why there are basic rules for doing science.

This starts out okay – identical pots, the same type of media (I assume), similar sized plants – but then things go downhill:

1) Replicates are important. There is one treatment and one control, meaning that it’s impossible to run any kind of statistical analysis. Ideally between 10-20 replicates of the control and the experimental treatment are used in this kind of experiment. That’s 20-40 plants total.

2) Variable control is important. Plants in a windowsill are subject to light and temperature gradients. That makes analysis more complicated unless one has an extremely long windowsill so that all plants are treated uniformly. And then our researcher prunes the tops of the plants – yet another variable.

3) Consistency between treatments is important. It appears that the pot on the left is wetter than the one on the right – the media is darker. If it’s not draining well – for whatever reason – then you’ll have a hypoxic root environment. Plants don’t like that.

4) Objectivity is important. It’s difficult (impossible, really) for any researcher to be completely objective. Ideally, the pots would have been watered by another person and then labelled in such a way that the person recording the data would have no clue which was which.

I think it’s really important to get kids excited about science. But it’s just as important giving them guidelines about doing science in a way that advances their own understanding about how the world works. Otherwise, it’s just more fodder for the aluminum hat crowd.

For Mulch

Posted by Bert Cregg

Just a quick note up front that today’s post is a little data heavy, so if you’re still adjusting to this weekend’s time change; be advised.

A few weeks back Jim Urban wrote a post entitled ‘Against mulch’ on the Deep Root blog. The principle reasons he cited for his position were: 1) Mulch floats and can clog drains and releases “lots of phosphorus” as it breaks down, and 2) work by Gilman et al. that suggest that mulch does not reduce evapo-transpiration. We discussed the Gilman et al. paper ad nauseum here already so I’ll stick to the other points.

Most organic mulches float, it’s true. However, if mulch is repeatedly washing from a bed into a drain this suggests a problem with the design as much as anything. Second, I’m not sure what constitutes “lots of phosphorus”. Branch and stem tissue of hardwood trees is about 0.1% P. If we use just the bark as mulch, the P concentration is about 0.2 to 0.3%. Is that ‘lots of phosphorus”? I don’t know. I suppose if you put enough it down and allow it wash into a drain it could be.

So let’s stick to what we do know about landscape mulch. Linda has written the most comprehensive review of mulch out there and it demonstrates the benefits of mulch. Nevertheless I’d like to add some recent observations of my own to the discussion. These come from follow-up measurement on some studies that we have already published on shrubs and conifers. But I think our new data are important because they demonstrate the long-term benefits of much on tree and shrub growth.

2006 Conifer study. In 2006 we installed a trial to compare several different weed control strategies for newly planted conifers. Weed control, either by hand, Vis-pore mulch mats or 3” of coarse wood chips, dramatically increased tree survival.

After 8 growing seasons, trees that had the wood chip mulch or mulch mats had significantly greater caliper than trees that were not mulched.

2004 shrub study. In another trial we compared the effect of various mulch types (wood chips, pine bark, hardwood bark) on growth of common landscape shrubs (golden globe arborvitae, Runyan yew, ‘Tardiva’ hydrangea, cranberrybush viburnum, and arrowwood viburnum). We re-measured heights of the shrubs study a couple of weeks ago (nine growing seasons after installation). To keep things simple here I’ve lumped the mulches together and simply compared mulched vs. un-mulched.

After nine years mulching increased height growth for all shrubs except the arborvitae.

Even more interesting is that the growth benefit of mulch extends beyond the establishment phase. If we start at age 4 and look at the relative growth rate for the past five years (i.e., growth increment for past 5 years / height at 4 years) we see that mulch continues to provide a growth advantage for all shrubs except the arbs.

As I said at the outset, a little data heavy today but I think this is an import point. There is a lot of discussion these days about proper planting techniques but I think after-planting care often gets overlooked and mulching is an important part of that. That’s why I’m for much.

We’re baaaaaaack…scary plants and all!

Just a quick post to try out the new system. Very exciting
Here’s a Halloween-week treat: Solanum pyracanthum – porcupine tomato. Not hardy, very poke-y. Deer don’t mess with it. Native to Madagascar and available through Annie’s Annuals or by seed from several sources. Photo taken in my friend Elissa’s fabulous garden, right before frost last week.

Don’t worry…we’re still here!

I can’t even tell you how many months it’s been since I posted on the blog. It’s been a perfect storm for the four of us, with writing books (Linda), new jobs (Jeff), doing the Garden Professors gig in Toronto (Holly, Bert and Linda) and writing grant proposals (all of us). I am going to try my best to post once a week, even if it’s short and silly.

Something new to let you know…the blog will be moving to a new format in the near future. It will be a WordPress blog, which means it’s easier for us to post and easier for you to search. In theory, all of the old posts will migrate as well, along with the pictures and comments. We are all looking forward to a more user-friendly format.

In the meantime, take a look at the new portal to our WSU Gardening Webpage!

You can find the page by clicking here. We’re in the process of adding more material all the time, but you can be sure that whatever you find on this new page is relevant, peer-reviewed science for use by home gardeners.

Let us know what you think!

R U nuts?

One of the things that comes along with having an extension appointment at a major university is I get lots of calls and e-mails from homeowners on a never-ending list of sometimes bizarre tree topics. Technically, my extension responsibilities are related dealing with professionals; such as arborists and nursery and Christmas tree growers, but the ‘consumer horticulture’ calls still find me. Last week I received a voice-mail message from an excited gentleman speaking at a decibel level somewhere between rock concert and jet plane take-off. From the disjointed and rambling message I could tell the gentleman was elderly and maybe disoriented or had just had a few. After identifying himself he indicated that he wanted to learn where he could find a “pine-nut tree”. Although he didn’t give it, I knew the man’s location from his area code. A legitimate response to such calls is to redirect them to the individual’s local extension office, but I hate getting the runaround as much as the next person, so I usually respond when it’s something I can help with and in this case I could.

I dialed the number and the gentleman picked up right away. He sounded just as he did in the voice mail; gregarious, slightly rambling, and VERY LOUD. His story, however, made me glad I called back. His father had emigrated from Lebanon many years ago and he remembered how his dad had always reminisced about eating pine nuts in the Old Country. For years he had wanted to plant a “pine nut tree” in memory of his dad. The problem was every time he went to a nursery and asked for a “pine nut tree”, nobody knew what he was talking about.

Pine nuts. Photo: Paul Goyette – Wikimedia commons

Pinus pinea cone. Photo: Luis Fernandez Garcia – Wikimedia commons

I explained to him that the pine nuts his father cherished were from stone pine (Pinus pinea) trees, which are the pine nuts (pignoles) favored for making pesto. In the US, the pine nuts that are sold commercially usually come from pinyon pine (Pinus edulis), which is native the southwestern US. Unfortunately, neither of those trees will grow in the Upper Midwest, where he lives. I pointed out that there are many other pine trees that produce edible nuts – the main reason those two species are widely used is because they produce very large nuts making them relatively easy to harvest. In fact, there are about 20 species of pine that produce seeds large enough that harvesting the nuts is worthwhile. Two pine species that produce edible nuts and grow well in our area are Korean pine (Pinus koraiensis) and Swiss stone pine (Pinus cembra). I include both in my recommendations for alternative conifers for Michigan. I gave the gentleman some information on nurseries in his area that I knew carried those trees and he was excited to have some direction on his quest to renew his father’s memory.

Korean pine (Pinus koraiensis) at the University of Minnesota Landscape Arboretum

Swiss stone pine (Pinus cembra) at Hidden Lake Gardens in southeaster Michigan.

Sidenote: The heartbreak of ‘Pine mouth’.

Have you ever experienced a bitter or metallic taste that persisted for days, even weeks, after eating pine nuts? Then you’ve likely experienced Pine Nut Syndrome or ‘Pine mouth’. The cause of the disorder is not completely known, but research by an industrious graduate student in the Netherlands suggests that nuts from certain pines; particularly an Asian pine, Pinus armandii, are most likely to cause the issue. So, if you are a pine nut fancier, learn what you can about your source. Pine nuts supplies can be cyclical since pine nut crops are often subject to biennial bearing. Soaring prices during poor supply years provide incentive for inferior nuts to work their way into the market.

Let’s get (soil) physical…

We’ve had quite a bit of discussion this past week on the FaceBook page regarding Kelly Norris’s article in Fine Gardening on dealing with clay soils. While Kelly’s article mainly addressed selecting plants for heavy soils, there was a side-bar on cultural approaches to dealing with clays; including the standard advice to avoid adding sand to clays. This advice has been around for years. The first time I recall hearing it was from Dr. Carl Whitcomb when I took his Arboriculture class nearly 30 years ago (Fall 1984 to be exact). The rationale that is usually given is that adding sand to clay is the essentially recipe for concrete. Technically, of course, this is not entirely true since making concrete also requires cement. Nevertheless, trying to amend a clay soil with sand can lead to more problems than it solves. The fundamental issue is not that clay + sand = concrete. After all, there are plenty of highly productive soils in nature that have various ratios of sand and clay and they don’t form concrete. The bigger issue is that tilling a clay soil (which you’d have to do to incorporate added sand) leads to a loss of soil structure.

So, what is soil structure? Soil structure is a physical property of soil that describes its relatively ability to form aggregates. Unlike soil texture, which can be quantified as percent sand, silt, and clay; structure is a qualitative soil physical property. Common examples of soil structure are granular, platy or blocky.

While we usually think of clay as a negative thing (“Geez Jim, my wife just told me you have clay, I am so sorry…”); a well-structured clay soil can have excellent properties for plant growth. Well-formed clay aggregates (referred to as ‘peds’) in a granular soil can function very much like larger soil particles in terms of water movement and drainage. Soil structure is one of those things you have to experience to understand. About the best description I can come with is that peds in a well-structured granular soil often have the consistency and texture of Grape Nuts cereal.

There are also soils out there that are sometimes referred to a ‘structureless’ soils. These include single-grained soils and massive soils. Single-grained soils are essentially pure sand. In West Michigan these occur near Lake Michigan and are often called ‘blow sands’. We have several seedling nursery operations in these areas. Since there is no clay these soils have almost no nutrient-holding capacity – growers have to manage their fertility almost as it were a soilless system like a hydroponic or aeroponic system. The advantage of growing in these soils is it makes lifting bare-root seedlings easy. Massive soils, on the other hand, are very dense soils where particles do not show any evidence of aggregation. Repeated tillage can result in loss of structure and a soil (or portions of the soil) may show attributes of a massive soil including crusting or formation of hardpan. The example below shows how structure (indicated by % aggregation) is lost through repeated cultivation.

Effect of soil tillage on soil structure. Source (Greacen 1958, Australian J. Ag. Res. 9:129-137).

What can be done to improve or preserve structure? This is a case where less is often better. Natural processes such as freeze-thaw cycles and the action of earthworms and other invertebrates work to loosen soil and create aggregates. The tips in the Norris article (avoid overworking soil and adding organic matter) are essentially the same advice I would give.

A Tree Story

Given my line of work, it’s probably no surprise I’m a sap for tree stories (no pun intended). Last week I was in Nova Scotia for the biennial International Christmas Tree Research and Extension conference. The conference and associated tours provided an opportunity to learn about Christmas tree production in Nova Scotia, one of the leading Christmas tree producing regions of North America. During the conference I also learned about the annual tradition of Nova Scotia’s Tree for Boston.

Each year Nova Scotia, through its Department of Natural Resources, presents a 40’-50’ Christmas tree (balsam fir, white spruce or red spruce) to the city of Boston. The gesture is an annual reminder of Nova Scotia’s gratitude for Boston’s and Massachusetts’ immediate aid and generosity in response to the Great Halifax Explosion of 1917. For those of you, like me, that were not familiar with the story, the Great Halifax Explosion occurred in Halifax Harbor on the morning of December 6, 1917. The French Freighter Mont Blanc, packed with explosives bound for the Allies’ war efforts, collided with another ship and caught fire. The explosion that followed, reported to be the largest man-made explosion of the pre-nuclear era, leveled a large portion of Halifax and neighboring Dartmouth, killing nearly 2,000 people and injuring 9,000 more. Within hours of the massive explosion, the governor of Massachusetts sent two trainloads of relief supplies to the devastated city. As a token of their appreciation, the citizens of Halifax provided Boston with a Christmas tree for Christmas 1917.

The tradition of providing a Tree for Boston was revived 1971 and has become an annual event ever since. While the cynical may deride this as a crass and commercial promotion for tourism and Christmas tree exports, the gratitude and affection of Nova Scotians for Boston seems heartfelt nearly a century after the disaster. And, if nothing else, Nova Scotia’s Tree for Boston serves as a history lesson, at least for those of us in the U.S., on this over-looked chapter of World War I.