Walnut warfare

Recently, a question about using black walnut chips for mulch was posted on our Garden Professors Facebook group page. As gardeners know, black walnut has a reputation as a chemical warfare species that will kill anything growing underneath it – a phenomenon called allelopathy. So it’s logical to wonder about the lethality of walnut chip mulches.

To get a good feel for the science behind black walnut’s allelopathic abilities, I was fortunate to find a relatively recent review on the topic (Willis, R.J. 2000. Juglans spp., juglone and allelopathy. Allelopathy Journal 7(1):1-55.). This well-written review includes a fascinating section on the historical background of walnut allelopathy, which was first mentioned in 36 BC by the Roman author Varro. But the science of allelopathy really started less than 100 years ago, when a Virginia researcher noticed the injury caused to tomato plants growing near black walnut (Juglans nigra) in his home garden. Subsequent experiments by him and others suggested that the orangish hydroquinone juglone leaching primarily from leaf litter and hulls.

SONY DSCSource: Wikipedia.

The research results on walnut, juglone, and allelopathy have been nothing if not inconsistent. For every report of toxicity in an exposed species, another report found no effect. In fact, much of the supposed allelopathy might instead be due to walnut’s highly competitive root systems, which could suck up available water and nutrients over a vast expanse of soil.

Black walnut tree Source: Flickr user davidburn

There are a number of other factors that help account for ambiguous results:

1) Juglone is not the only secondary metabolite produced by walnut species. They are loaded with a number of untested phenolics, flavonoids, alkaloids, terpenes and other quinones which could have allelopathic activity.
2) Juglone concentrations vary greatly among walnut species. They also have seasonal variability in the same individual.
3) Light conditions, rainfall, soil chemistry, and many other abiotic factors can influence juglone levels.
4) Organic matter and clay particles in soils can bind juglone, reducing its movement within the soil.
5) Microbial activity breaks down juglone.

Carefully controlled laboratory experiments can demonstrate juglone allelopathy to a number of plant species, especially at the seedling stage. However, there is little evidence from landscape level research to suggest that allelopathy is the reason that plants are damaged by being in proximity to walnut trees. In fact, the author of the review study concludes that even though Juglans species provides the best known and most widely accepted example of allelopathy, there is “still is no unambiguous demonstration of its effect” as “no one has as yet demonstrated that juglone is actually taken up by plant roots.”

walnut tree Source: Wikipedia

Where does this lead us in our discussion of walnut mulch toxicity? Fresh hulls and leaves appear to be the primary source of allelopathy, but not the wood. And even these sources may be quickly neutralized by soil conditions. Therefore, a walnut chip wood mulch should pose no danger at all to landscape plantings.

Cross-pollination making you cross?

No, your cucumbers have not hybridized with your melons.

I’ve been fielding different versions of the same question a LOT lately.
Three different people have sent pictures of “cucumelons” telling me they planted cucumbers next to their melons, and now the cucumbers look strange, so they’re concerned that they have cross pollinated with the melons. One person planted what was supposed to be a red raspberry next to their yellow raspberry, but the new plant is producing yellow fruit, so they think that it must be cross pollinating with their yellow plant, causing the fruits to turn yellow. Not to mention similar queries about tomatoes, peppers, and watermelons. It seems like every time a piece of produce turns out looking differently than what people expect, they blame pollen from the plant next to it.

I’m sure the highly educated readers of The Garden Professors know this already, but to clarify, there is a very simple reason why you don’t need to worry about one plant pollinating another plant and changing the quality of your produce UNLESS you are planning on saving seeds to grow for the next year.

When a flower is pollinated and starts developing into a fruit full of seeds, it is only the seeds themselves that combine the genetics of the two parents to develop into something new. Everything else – the flesh of a tomato, or cucumber or melon or raspberry – is produced solely by the mother plant, and the daddy of those seeds inside doesn’t matter a bit. Think about when a woman is pregnant… the identity of the father of the child inside her doesn’t change the character of the skin of her belly.

If you want to save seeds of your plant for next year, it is another matter, and you should be sure to isolate or (better yet) hand pollinate different varieties of the same species from each other to make sure they don’t hybridize unintentionally. You still don’t need to worry about your cucumbers and melons, however – they won’t hybridize by chance in your garden. If a plant doesn’t produce the right colored fruit or flower, most likely it was just mislabeled at the nursery. Grow a strange looking cucumber, chances are it was left on the plant too long. Cucumbers are harvested and eaten when young and immature, leave them too long and they get… strange looking. No need to blame it on the melons next to them.

There IS one exception to this, one common plant in the garden where the source of pollen makes a huge difference in what you harvest: Corn. Corn is the exception because what we’re eating is the seed itself, not the fruit produced by the mother plant surrounding the seed. That’s why if your sweet corn gets a dose of pollen from the field corn the farmer is grown next door, it comes out starchy and not sweet.

It also makes breeding colorful corn for fall decorations REALLY fun… Because when you see a multicolored ears of corn like this from my garden last year:

multicolored corn
You can carefully pick out just the seeds showing the colors you like best, say the palest blues and pinks, sow them together the next year, and get something looking like this:

pink and blue corn
Or plant all the darkest kernels together and get this:

black corn

Spring = really?

You've got to be kidding...
Bebe the Wonder Dog says “You’ve got to be kidding…”

I’m sorry I’ve been so quiet, but I am not feeling SPRING. Here in the Blue Ridge of Virginia (Zone 6), March is averaging 10 F below average. Snow and ice is piled up on the north side of buildings. My Herbaceous Landscape Plants class is not impressed by the inch-tall Mertensia and the fact that the only thing we can call a cool-season annual (pansies/violas) is brown mush. All the delightful Zone 7 things I’ve been pushing on people for several years here – er, whoops. This is as far north as I’ve ever lived (please don’t mock me Bert). I’m tired of bales of laundry. Flannel sheets, corduroy, fleece…I am NOT good with winter. I admit I am at my best with only one layer on. And if one more person says “at least we’ll have fewer ticks”…
*snap*

Re-using containers? A cautionary tale.

I attempted to clean up our little home greenhouse over the holiday break. There’s no good place to recycle pots around here, and I hate throwing them away…so I suffer from container build-up. Figured I’d sort through the haphazard pile in the corner of the greenhouse, wash and re-stack the useable ones, and finally ditch the busted ones.

As I started separating the first stack, I noted a tiny flash of red. It is well-known and oft-reported among my gardening and grower buddies that the Southern Black Widow (Latrodectus mactans) really enjoys a nice stack of grubby pots. But I hadn’t seen one in quite a while, and not at our current location.

Boy, did I hit the jackpot.

blackwidow1

I’m not afraid of spiders. At all. Quite fond of them, actually – they are immensely useful and fascinating critters. And only a very few pose any kind of danger.
In the case of the Black Widow, a bite injects a neurotoxic venom (latrotoxin). The bites and ensuing symptoms are allegedly quite painful, though rarely fatal. In this instance, I chose not to sacrifice my comfort for our collective edification, i.e. “How Bad Can it Hurt?” (see Blister Beetle post).

So, I squished her. But felt pretty bad about it.
As I worked through the stacks, I found another.

spidy2

Shook her to the floor and did some more tap-dancing. Perhaps it was time to stop taking pictures and put some gloves on.

By the time I got through the entire pile, I’d found and mushed thirteen of them, sized small through pretty darn large. The landscape fabric on the greenhouse floor was peppered with little beige, black, and red blobs (you don’t need to see that photo).

There were none in the stacks of shiny new nursery pots I’d ordered for our blueberry transplants. But if there was some growing media or plant debris still stuck inside, there was a high probability of finding a spider.

Moral of this story? Think twice about leaving a bunch of dirty plant containers piled up. A simple hosing out before I’d stacked them would have probably prevented such a large infestation.

There’s also a significant chance that I will forget all about the need for caution the next time I’m potting up stuff. Which may lead to an even more educational and entertaining blog post, where I describe “Adventures In Lactrodectism.” Because I’m sure I missed a couple, or they’re hiding in the gravel. As the old saying goes,

“Seeing a spider isn’t a problem. It’s a problem when it disappears.”

Sheep-eating flowers?!

I was planning to follow up on Jeff’s phosphorus post with a bit more “phun with phosphorous.” However, I was completely derailed by Ray Eckhart’s message and link left for me on our GP facebook page with this headline:

RHS ‘sheep-eating’ plant about to bloom in Surrey

“The Royal Horticultural Society (RHS) at Wisley said the Puya
chilensis
, a native of Chile, would bloom in the next few days and last
about a week.

In the Andes it uses its sharp spines to snare and trap sheep and other animals, which slowly starve to death.”

“The animals then decay at the base of the plant, acting as a fertiliser.”

[Dear BBC News: “Snare” and “Eat” are not really interchangeable]

How…have I not heard of this before.

I’ve posted previously on my Puya fixation. I asked readers to bet on how long it would take for me to kill my wee Puya bertoniana, mail-ordered from Annie’s Annuals.  I am happy to report that it made through the winter (greenhouse) and is now sunning itself on our deck.

Now this really ups the ante – it captures sheep!  Maybe P. bertoniana isn’t as robust as P. chilensis though. Perhaps…a vole or rabbit?

Container planting: intuition vs. reality

I’m just starting to think about getting my containers planted for the summer and happened to get an email on the topic from a blog reader. John was frustrated with a local columnist’s advice on using gravel in the bottom of the containers for drainage. When challenged, the columnist refuted John’s accurate comments with “logical thinking.” (You can find the posting and comments here.)

Here’s part of the post: “I like to cover the hole with a layer of gravel to improve drainage. Plants need to have their roots exposed to air in the soil to survive and thrive. If the container has no holes for drainage, it will fill with water and drown the plants very quickly. It is better to keep your plants on the drier side than to keep them constantly moist or wet. The big danger in using pots is drowning plants.” Later, he goes on to explain “The potting soil plugs up the drain hole and the water is trapped behind the plug. The layer of gravel creates an area for the water to drain through to escape. The creation of drainage commonly involves a layer of gravel.” This reasoning is part of what he calls “Logical thinking 101.”

As my husband pointed out, this isn’t logical thinking: it’s intuitive. It’s what we think is going to happen in the absence of any evidence. And in this case, it’s wildly inaccurate.

Jeff and I have both discussed the phenomenon of perched water tables in containers as well as the landscape in previous posts and on our Facebook page. The fact is, when water moving through a soil reaches a horizontal or vertical interface between different soil types, it stops moving. Here’s a photo from a very old research paper on the topic:

A layer of silt loam sits above a layer of sand, and water from an Erlenmeyer flask drips in. Intuition says that when the water reaches the sand, it will move more quickly through the sand because the pore spaces are larger than those in the silt loam. But intuition is wrong, as this series of photographs clearly demonstrate. Water is finally forced into the sand layer by gravitational pressure, after, of course, saturating the silt loam.

Intuition has its uses (I am quite proud of my own intuitive powers), but it doesn’t trump reality.

Buying locally-grown plants

Of course we want to buy locally-grown plants! There are a gazillion sound reasons to do so.  In a paper that may be from near here, or not, I perused the gardening column over Sunday coffee, written by (a human) (name withheld to protect the very, very nice and usually accurate author). But in this particular article, the writer ventured deep into huh? territory.

And that territory is my area of expertise: nursery and greenhouse production and marketing. My favorite talk to give to gardening groups is “From Grower to Garden Center.” As the Garden Professor Least Likely To Get Riled Up, it pains me a bit to even bring this up when someone’s willing to crank out a column week after week. Heck, I haven’t been able to write anything lately, accurate or otherwise. The bulk of the article was correct and positive, plus promoted a great local grower (of which we have very, very few), BUT there were a few statements made that I thought might make good points for clarification (teaching moments) and maybe generate some discussion.

“Just like locally grown food, a locally grown plant is going to be much easier on the environment. Transportation and fuel costs are lower, and carbon footprint emissions are decreased. Plus, without a need for the special packaging to ensure a safe journey across the country, less packaging ends up in a landfill.”

I’ve unloaded plenty of trucks – the only things that use any “special packaging” are poinsettias and sometimes florist mums – sleeves and or boxes. “Cross-country” is rarely the case, even for big box stores – they work with regional growers (albeit large ones) for annuals and perennials.  However, the writer’s point is well taken in that even here in the “far east,” some independent garden centers and big box stores get shrubs and trees from the west coast (Monrovia must give them a heck of deal).  One of our two local garden centers carries Japanese maples from Monrovia; this retailer is located less than 10 minutes from a nursery that specializes in Japanese Maples.  Go figure.

“Beyond the environmental impact, when you buy a locally grown plant you usually are buying a healthier plant. It will already be accustomed to our native soils and growing conditions.”

“Usually” is a good qualifier here. Regarding health, I’ve seen amazing quality from far, far away, and real crap from a couple local growers. Local does not automatically equate to pest and pathogen free, well-rooted, non-stretched, or any other criteria for quality.  The second sentence, however, has haunted me for a week. Nursery and greenhouse plants are grown in soilless media – peat or peat alternatives; pine bark; fir bark; etc.  How can that particular plant be accustomed to “our native soil”?  To put a finer point on it, what, exactly, IS our “native soil”? Our own 19 acres has yellow clay, red clay, forest duff, sandy loam, loamy sand (I made that one up), and everything in-between.

Regarding growing conditions, your spring-purchased plant has most likely been in a controlled environment of some degree, whether a greenhouse or coldframe. If I went shopping at any retail greenhouse or garden center (which I probably will do this weekend), I would probably purchase some plants right out of the greenhouse. Of which they are accustomed.

“And, with less travel time, the plant is less likely to be stressed by excessive handling and is less likely to be over watered or over fertilized.”

On the truck, off the truck. Place on retail bench. This is how a plant would be handled whether it was grown by a local wholesale nursery 10 miles away or 1000. How excessive is that? And why would travel time cause over-watering or over-fertilizing? If anything, the inverse is true.

“New gardeners can be assured that they are buying a variety that grows well in our climate, as local growers supply what grows here. The plant will be put out for sale when it’s actually time to plant, not when a buyer across the country wants to sell it to you.”

Grows well? What grows here?  I’m not even sure where to begin with that bit of information.  Isn’t that part up to the gardener, new or otherwise?

And wherever you may live, I guarantee there were plenty of tender annuals, tomato transplants, and other jump-the-gun goodies available for sale from your local grower or garden center 45 days before your last frost date. What IS true – a good grower/retailer or garden center staffer won’t let you leave without a gentle (or not-so-gentle) reminder to keep ’em in until after last frost.  To which I always nod, agree, and then commence with trying to produce the earliest tomato in the tri-county area. Because I’m an expert.
*snort*

 

Scientists Put the Dog in Dogwood

(special guest post by/with permission of good friend Mr. John Friel, marketing manager for Emerald Coast Growers – Holly Scoggins)

How do you recognize a dogwood? By its bark.

That old joke might not be a joke anymore, if the innovative folks at Metamorphic Agriculture Developers (MAD) get USDA approval for a new line of ornamental and functional shrubs that blur the line between the animal and vegetable kingdoms.

MAD scientists claim to have successfully introduced genes from Canis familiaris into a cultivar of Cornus canadensis. In other words, they’ve crossed a creeping groundcover dogwood with … a dog. Specifically, a dachshund.

“Imagine a guard dog that you never have to feed, license, or walk,” enthused Dr. Horace Sass. “Imagine a shrub that not only beautifies your home but guards it when you’re away,” adds his colleague, Dr. Ariel Sturgeon. The two bring a unique perspective to their work: Dr. Sturgeon is a mermaid, while Dr. Sass is a centaur.

After considerable trial and error, the team believes its Canis /Cornus combination is the best of both kingdoms. The first hurdle was finding the right plant.

“We tried Physocarpus first,” said Dr. Sturgeon, “but every one that grew to maturity would bark nine times when approached. Our focus group said that was too many.”

Crosses involving Cornus alba succumbed to a fungal disorder that afflicts that species. Said Sturgeon, “The blight was worse than their bark.”

Once they’d settled on Cornus canadensis, the next step was to find the right canine breed. “The pit bull shrubs were tough and sturdy, but their bite was worse than their bark,” said Sass, gingerly rubbing his right foreleg.

While they hope for widespread acceptance of their remarkable new hybrids, the team admits there are challenges, In winter, the plant/pet eventually goes dormant, but not before trying stubbornly to get into the house.

“The whining may be a turn-off for some homeowners,” Dr. Sturgeon admits. “In those cases, we recommend large containers, overwintered in the garage.”

The End (hopefully) of Molasses Malarkey

I’ve been discussing the purported insecticidal properties of molasses in my last couple of posts. I’m hoping this will be the final nail in the coffin (or stopper in the bottle):

Here’s the end of the original blog piece linked above:

“Microbial bloom and Fire Ants
“These two things seem unrelated. Microbes and specifically bacteria consume simple sugars (which is why your momma made you brush your teeth). When soil born microbes are exposed to simple sugars, their numbers can double in just 30 minutes. As microbes go through their life cycle, they add organic matter and micro nutrients to the soil, improving the soil and making nutrients more available to your plants. Regularly applying molasses to your soil and plants greatly improves the quality of the soil over time. Soils with high microbial activity are easier to dig in and stay moist longer.”

I’m actually going to leave this paragraph alone, since it’s relatively accurate (except for the sentence about applying molasses to your plants, which I dealt with in my first post). Let’s move on:

“So, about the Fire Ants…since it seems that the big universities can’t make money studying the effects of molasses on Fire Ants…they don’t do any research on the subject. But, it has been proven that molasses makes Fire Ants pack up their mound and migrate to your neighbor’s yard. It may be that the bloom of microbes, irritates the little stinkers. It could be that they are running from a specific microbe. It could be that they just hate sugar (they eat mostly protein which is why you can turn a greasy over baked pan upside down over a Fire Ant mound and they will clean it for you). What ever the reason, applying molasses to your yard makes them leave.”

This entire paragraph is nonsense, beginning with equating grease with protein (it’s a fat) and ending with the supposed lack of research on fire ants. There’s a LOT of research on fire ants; pest studies are very well funded. Out of the 1500+ articles I pulled up on fire ants in the Agricola database, only one includes molasses. And that’s in a 1986 study comparing different kinds of baits (“Comparison of baits for monitoring foraging activity of the red imported fire ant (Hymenoptera: Formicidae)”), where molasses was found to be more attractive to fire ants than peanut oil. How this translates to “molasses makes Fire Ants pack up their mound and migrate to your neighbor’s yard” I’m not quite sure.

“If you’re crunched for time and money, molasses is the answer to a lot of your gardening problems. The benefits are undeniable, your yard will smell great and you get to feel good about letting your kids and pets play in the yard. Whether you choose dry molasses (applied to soy chaff) or the liquid (which is cheaper to use), molasses is the single best thing you can do for your soil and plants.”

The typical snake-oil pitch! (For a completely unrelated but accurate and amusing example of an old-time snake-oil pitch, check this link. You’ll see the similarities).

“It was brought to my attention that I forgot to add this info. (It is hard to remember everything when you are trying to rule the world!) During moquito weather mix:

  • 3 tbsp molasses
  • 1 tbsp Liquid Garlic (a deterent and has some fungicidal properties)
  • 1 tbsp liquid organic fertilizer of your choice (seaweed, fish emulsion, etc) into 1 gallon of water

Spray with abandon, every week if necessary but it may last up to 2 weeks if we don’t get much rain. This also works like a charm on lace bugs on azaleas and lantana.”

Spray with abandon???? This has to be one of the most reckless pieces of advice I’ve ever read. Whether it’s a fertilizer or (more importantly) a pesticide, it should *never* be applied lavishly. (Though this is such a dilute solution that it probably isn’t much different than water.)

This topic has made me crave the molasses popcorn balls my grandmother used to make. Anyone have a recipe for those?

The Return of Molasses Malarkey

Last time I posted I began discussing this link about horticultural molasses. Let’s continue with the dissection:

“When molasses is sprayed directly on plants, it is absorbed straight into the plant. Once absorbed, the sugar content of the plant goes up. If you need proof, go pour a Coke on a spot in your lawn, in a week you will see exactly what I mean. Simple sugars are how plants store energy for rainy days and winter hibernation. So, why is this important to you as a gardener? Aside from basically giving your plants a power boost, you are stopping bugs. “What?” you ask. Yes, it stops bugs. Insects are very simple creatures. They can only feed within a narrow window of sugar content. When the sugar content of plants is raised, insects can’t feed on them. They take one bite and move on.

“The second way molasses controls insects, is by being directly ingested by the insect. What most people don’t know is that only Sugar Ants and bees can process the simplest sugars. Insects have no way of expelling the gas that builds up from fermenting sugar and the vegetation in their gut (draw your own mental pictures please). Plus, they have exoskeletons and can’t get bloated. Their delicate internal organs are crushed from the inside out. All a bug needs to do, is walk through or try to feed on a molasses covered plant. Insects are constantly cleaning themselves. They will try to lick the molasses off their feet and swallow it. If they take a bite of a molasses coated plant, they will swallow it.”

Some specific observations and comments:

1) “If you need proof, go pour a Coke on a spot in your lawn, in a week you will see exactly what I mean.” I just don’t think I can do this comment justice, so I’ll leave it to your imagination as to what you might see and how it relates to a 1% molasses solution sprayed onto leaves.

2) “Simple sugars are how plants store energy for rainy days and winter hibernation.” Actually, no. Simple sugars are difficult to store as they contain a lot of water and they can be quite reactive. Plants transform simple sugars (monosaccharides and disaccharides) into polysaccharides for storage.

3) “Insects are very simple creatures. They can only feed within a narrow window of sugar content. When the sugar content of plants is raised, insects can’t feed on them. They take one bite and move on.” Obviously the author has never seen Men In Black.

Give me sugar…in water

4) “What most people don’t know is that only Sugar Ants and bees can process the simplest sugars.” Please explain this to the cockroach I once saw in a sugar bowl.

5) “Insects have no way of expelling the gas that builds up from fermenting sugar and the vegetation in their gut. Their delicate internal organs are crushed from the inside out.” Did you know that termites are significant producers of methane gas – a byproduct of fermentation? And they release it the old-fashioned way.

From NASA’s website on methane production

More next week!