Cool Research – Page 5 – The Garden Professors™

Out of the lead frying pan and into the phosphate fire

A recent NYT post reports that adding fish meal to lead-contaminated soils will cause the lead to bind to phosphate found in fish bones. As the article explains, this chemical reaction results in the formation of pyromorphite, “a crystalline mineral that will not harm anyone even if consumed.”

Given my concerns about excessive phosphate loading in urban soils, I contacted Dr. Rich Koenig, an urban soil scientist and chair of WSU’s Crop and Soil Science department. I wondered, at least, if the article should have directed people to have a soil test done first to determine how much phosphate was already in the soil before adding more.

Dr. Koenig was likewise concerned that the application rate of fish meal was probably far higher than what plants would require, thus increasing the risk of phosphorus leaching and runoff. He also referred my question to Dr. Jim Harsh, a soil chemist in his department familiar with the process described in the article.

And as Dr. Harsh pointed out, it’s important to make lead less susceptible to uptake by people and other animals exposed to contaminated soils. However, he’s unconvinced that phosphate is the best choice; in fact, research by Dr. Sally Brown (cited in the NYT article) and others (including Dr. Harsh) have found that compost containing iron is also able to bind and immobilize lead. The advantage of high iron compost is that iron will not leach into nearby waterways, nor cause the same kinds of plant toxicity problems, as phosphate can.

Thanks to both Dr. Koenig and Dr. Harsh for their quick and informative responses on this topic.

Helium Makes Kudzu Float Away

As promised — some happy news: There’s this kid in Valdosta, GA (close to Tifton where I spent a few years as a graduate assistant), who has been experimenting with ways to kill kudzu. Here’s the video.

To see this kid work on something like this at such a young age is fantastic and gives me hope for the future. I wish the kid were here so he could come to the University of Minnesota – I think he has a lot to offer and he makes me slightly more optimistic about where horticulture ends up.

For those of you who choose not to view the video, what this kid does is to inject helium into the soil around the root system of a kudzu plant. After the injection the plant apparently dies. The exact reason why isn’t known, but one person who was interviewed said he suspected that the helium smothers the plants roots thus killing it.

I’m a little bit suspicious about that explanation, and I’m also a little bit skeptical about how much more economically feasible it would be to use the helium instead of more standard herbicides. I’m also very interested in any other gasses that he might have tried to kill the kudzu – I wonder, for example, if he tried propane? It might work, but I’d say it was too dangerous to try.

I’m suspicious about the helium smothering the root system of kudzu because kudzu has such an extensive root system and because the helium should dissipate pretty quickly, especially in sandy soils like they have in Southern Georgia. It’s also very unlikely that the helium itself is acting as a poison because helium is an inert gas. It just doesn’t react with anything. What I think is more likely is that, by finding the site where the kudzu’s stem enters the ground, this kid has found a “weak spot” on the kudzu which is susceptible to damage. Then I think that the helium acts a refrigerant when it is released and actually freezes the stem of the kudzu. However it works though, it’s a neat trick!

Harvesting an Experiment

This has been an exciting week for me. On Monday we started cleaning off 72 rootballs of various tree species that had been planted 5 years ago for a study. These trees had been planted in containers and become potbound at the nursery from which we received them. We treated them in one of three ways. Either we did nothing (in other words we just dropped the pot bound tree in a hole), we used the standard methods that Universities recommend for slicing potbound roots (Four deep slits down the sides and a deeply cut X across the bottom), or we cut off all of the circling roots by cutting the pot bound root system into a box shape.

A root ball cut into a box shape

The plan was to harvest after 4 years to see what happened – we decided to wait 5 – and boy did we see some interesting stuff. At this point our results are preliminary – we need to run statistics before we can say anything conclusively – but this is what my eyes tell me.

Trees that had their roots cut into boxes suffered reduced growth the first few years, BUT, their root systems look as good as any root systems that I’ve seen – almost no circling.
We planted our trees with the surface of the soil at the same level as the surface of the media in the containers – which is too deep in most cases. For trees with circling roots this created a severe problem as the circling roots often surrounded the stem – potentially causing suffocation of the tree later in life.
Root systems that were cut using the 4 slit method didn’t look much different from those that weren’t cut at all.
The number of large roots emanating from all of the treatments appeared to be about the same (we’ll need to run the stats before I commit to this one). This is particularly interesting because many people expect large roots that are circling to continue circling — but that isn’t what usually happens (unless the hole where the tree is planted has hard sides which can force the roots to circle just like the container did).

This root system was from a control — no root pruning at all, but still plenty of large roots.

No matter what the results/statistics end up saying there will be more questions. For example, all else being equal, how damaging are circling roots to the health of a tree if the tree is planted properly (no stem tissue under the surface of the soil) and the circling roots are under the surface of the soil? If the answer is that circling roots under the surface of the soil aren’t very damaging (after all, there’s no stem tissue for them to crush) then why are we bothering to try to root-prune pot bound plants at all – what we should really be concentrating on is planting at the proper depth.

All the above is hypothetical though – I just enjoy thinking about this stuff as the data starts to roll in. As we get more definitive answers and start to run the statistics I’ll let you know more.

Are Pretty Flowers Useful?

Yesterday I had the opportunity to listen to Marla Spivak, a very highly regarded bee scientist, talk about how bees defend themselves from disease. Very interesting stuff. I took a lot of information away from the talk, two bits of which I want to share with you.

The first is a vocabulary word — propolis – go ahead, google it (I don’t think too much inappropriate stuff will pop up) – it’s an antimicrobial “ointment” which bees create from stuff like the resins on tree buds.

The second is that the number of bee colonies is the US has been going down in the US since 1945 for a number of reasons. One of the most important of which is the fact that we like to kill flowers, such as dandelions and clover, which bees like, and then we plant crappy flowers – at least as far as the bees are concerned. The whole crappy flower thing isn’t something that I’d spent much time thinking about, so it was kind of an ah-ha moment for me.

Here’s how it works. People tend to like double flowers. Double flowers usually occur because the male parts of the flowers – the parts which normally contain pollen – instead develop into petals. It’s a mutation – very pretty – but it inhibits the flower from reproducing itself through seed and it certainly isn’t great for bees who rely on pollen for food. So when we plant our gardens we are removing plants that bees may love because we consider them weeds. Then we replace these flowers with what amounts to plastic fruit. My opinion – this is probably more significant to the lives of both honey bees and native bees than whether we plant natives or exotics.

So let your yard go wild! The bees will thank you.

Plant containers – does size really matter?

A few days ago I got a question from Cynthia about “potting up.” For those of you for whom this is an unknown phrase (and no, it’s not a euphemism for a certain herbal activity), it refers to the practice of moving plants into ever larger containers. She was wondering if there was any “real science” behind the practice – in other words, why not just start out with a larger container?

Hah! I needed no further encouragement and spent several days collecting and reading decades’ worth of research. And there is a LOT of research on this topic. As you might guess, it’s geared towards production nurseries and greenhouses. But the good part is that it’s been done on just about any kind of plant material you could want. Vegetables. Annuals. Perennials. Grasses. Shrubs. Native plants. Ornamental, fruit and forestry trees. Seeds, seedlings, cuttings, big plants, little plants. Ahhhhh…data!

Almost without exception, you get better growth on plants grown in larger containers, whether you’re measuring height, number of leaves, leaf area, stem diameter, shoot and root dry and fresh weights, whole plant dry and fresh weight,…you get the idea. This isn’t surprising, because with a larger root zone you can support more roots, which in turn support more above-ground growth.

The only parameters which tended to diverge for some species were flower and fruit production. Restricted roots can stimulate sexual reproduction in plants, possibly because poor growing conditions spur the plant to reproduce before it dies. Other drawbacks include increased probability of circling root systems, and higher ambient soil temperature, compared to plants in larger containers.

Smaller containers might be considered desirable when one is trying to limit above-ground growth – the “bonsai” effect. And they require less water than larger containers – which brings us to the bottom line, as far as production nurseries are concerned.

Larger containers take more space. And water. In at least one study, water costs were shown to be “prohibitive for larger container sizes.” Furthermore, smaller containers are preferred by production nurseries to “optimize production space.” Another economics-based study found that “the smaller of these was the more economical.”

But most of you probably aren’t interested in the economics of plant production – you want to know what’s best for your own container plants, whether they are houseplants or pots of herbs or punches of annual color on your patio. The science is clear: it’s best to pot up plants in small containers quickly into their final destination, rather than making several (pointless) intermediate transplants.

Off-label Use of a Chicken*

[Extremely] Preliminary research results from the University of Maryland indicate
chickens may be of interest in the fight against Halyomorpha halys, the brown
marmorated stink bug.

There are good stink bugs and bad stink bugs. The brown marmorated stink bug is a bad one. A relatively new introduced pest, it is piercing, sucking, and generally ruining vegetable and fruit crops (as well as some ornamentals) across a good part of the U.S. There are apparently few natural predators for this imported species and they reproduce like mad, thus the potential for this to become a very serious economic issue. USDA funding has appeared, and scientists are working against the clock on every angle of the problem.

Dr. Stanton Gill, Extension Specialist in IPM for Nurseries and Greenhouses at the UM Central Maryland Research and Education Center, is among them. He is not only a great entomologist, but a total hoot, just like several other bug people I know. He’s doing plenty of conventional research as well as loads of critical Extension service spread out over several states. As an orchard and nursery owner, he also has a personal stake in the issue.

I had the pleasure of hearing about Dr. Gill’s latest work at a recent nursery association meeting. He related the severity of the problem as well as several stink bug-related research projects he’s involved with, but the one that really caught my attention was his work with chickens.

On a tip from a gardener/hen owner, Dr. Gill decided to explore further. In a nutshell: the stink bomb hidden in the thorax of Halyomopha species is a terrific defense mechanism against bird and reptile predators. But chickens seem to be immune (and unconcerned about their breath). Actually, not a big surprise – I’ve caught my hens eating some pretty amazing/disgusting things. His preliminary study consisted of a few borrowed hens in a couple of nice little fresh-air pens, free to scratch about. A request to some battle-weary local gardeners yielded tupperware containers full of brown marmorated stink bugs. Through some feeding trials, he found… a hen’s capacity for stink bugs knows no bounds.

The hens had access to their regular feed, but gobbled up all the stink bugs offered. I can’t recall the exact quantity, but it was A LOT.

Stink – it’s what’s for dinner.
Action photo courtesy of Dr. Stanton Gill, University of Maryland.

The hens would only go for the stink bugs if they were active. Dr. G. put some in the freezer (stink bugs, that is), rendering them immobile, and the girls turned their beaks up. Once thawed and moving (!!!), they became dinner.

Finally, he worked with a food scientist to answer what should now be a burning question – did the eggs taste funny? Blind taste tests found that participants preferred the eggs produced by the stink bug-eating hens versus controls. I believe further studies may be in the works, as well as some publications relating his findings.

* Ha, ha, I kid!!! This post is neither an endorsement nor recommendation of the research described within. There is no MSDS available. No REI. No PPE guidelines. No EPA approval. No acronyms at all, actually. You’re on your own.

Sudden Death Syndrome in Soy — Biggest Threat to the Entire Food Chain?

This past week we received an interesting e-mail about something called “sudden death syndrome” which we were asked to blog about. Here’s the article we were sent. We don’t always take requests, but we thought that this was an interesting one, so we decided to write a little post about it. Sudden death syndrome is basically a fungal disease which affects the roots of soybeans. Recently there has been some press out there about how Round-up ready soybeans are particularly susceptible to this disease and that the spraying of roundup itself can lead to favorable environments for it.

This is a particularly attractive disease for a number of groups because it provides fuel to their fire. The anti-biotech group likes it because it makes Round-up ready crops look bad, the anti-pesticide group likes it because it makes pesticides look bad, the anti-Big Ag group likes it because it makes Monsanto look even more evil than usual. So, in short, lots of happily indignant people.

So is it true? Is using Round-up and Round-up Ready Soybeans a sure way to condemn ourselves to a soyless future? On a side note this is something I really care about – I am a chronic soy sauce user. If something is good without soy sauce it then it is going to be even better with it. Well, I spend most of Monday and Tuesday looking through scientific articles and here, in a nutshell, is what I came up with:

Sudden death Syndrome is certainly real, and it can devastate a field. It was around before Round-up and it will be here after Round-up is gone. The biggest factor in whether it will be a bad year for SDS is the weather. So what about the Round-up connection? This is something that has been looked at by researchers, and here’s what they find. In terms of the fungus responding well to Round-up – some studies show that it does – most that it doesn’t. Round-up Ready varieties of soybean may be resistant or non-resistant to SDS and, of course, the non-resistant varieties won’t fare as well as the resistant varieties if SDS is present (it seems possible that this is where the whole hullabaloo started — a field full of Round-up Ready soy but which wasn’t resistant to SDS contracted the disease while nearby non-Round-up Ready soy which did happen to be resistant to SDS did fine.)

Now there are some studies, mostly in test-tubes and greenhouses, which show that Round-up could make SDS worse, but in the field, where it actually matters, there just aren’t that many studies which show a correlation between using Round-up Ready soybeans and SDS — and more studies that show that there isn’t a correlation. What it all comes down to is that there is a possible relationship between Roundup and SDS, but, despite a lot of research (both government and industry dollars flow easily to agronomic crops), this link isn’t crystal clear and may not exist at all.

Should we use biochars in our gardens?

In the last few years, I’ve had a number of people ask me about biochar: what is it and what does it do? Should they add it to their garden? Should they make their own biochar? So while the subject deserves a longer review, I thought it would be useful to discuss it briefly on the blog.

In the strictest sense, “biochar” refers to charcoal that’s made as a byproduct of biofuel production. Various crop residues, livestock manures, and just about any other organic material you can imagine has been studied for this purpose. Biofuel production not only helps diversify our energy resources, but the biochar itself also boasts several benefits, not the least of which is that it serves as a long-term, stable repository of carbon. Since the carbon in biochar decomposes so much slower than the parent organic material, it is often considered to be a “carbon negative” material.

Even more exciting is that biochar offers some distinct, tested benefits to agriculture. It is a porous, charged material that has been used to remediate soils by binding contaminants such as pesticides and heavy metals. It offers a physical environment to mycorrhizae, which often benefit from biochar amendment. It binds nutrients such as nitrogen, preventing runoff or leaching, and releases these nutrients to crops, most of which are shown to benefit from biochar additions. The scientific literature is robust in examples, worldwide, of how various biochars benefit agricultural soils and crops.

But before you rush away to buy (or make) your own biochar, there are some significant caveats. First, there is a sophisticated process used to make biochars, whose characteristics will vary tremendously depending on how they are produced. Differences in temperature, for instance, will produce very different biochars from the same parent material. (And you would be hard pressed to do this at home: temperatures can range from 100-700C.)

Second, there is little, if any, research on the use of biochars in nonagricultural situations other than soil remediation. This means no information on how it affects trees, shrubs, home gardens and landscapes, and other urban greenspaces. As readers of this blog should know by now, there are many agricultural production practices that do not translate well to the home garden or landscape.

Third, biochars are generally very alkaline, often with a pH close to that of lime. While this might be fine for some soils and plants, naturally acidic soils and their respective acid-loving plants are not going to react kindly to a more alkaline soil environment.

Finally, I hate to see people (and they are out there) who are now taking their pruning debris, arborist wood chips, and other organic material, burning it, and burying it. Ideally, both bio-oils and biochar are made from excess crop residues and other debris generated in agriculture. Arborist wood chips and other plant debris generated in a home landscape need to go right back onto the soil as part of a compost/mulch layer. To burn this valuable resource strikes me as the classic “penny wise, pound foolish” mentality.

Planting trouble: multiple trees in one hole

[I enjoyed Jeff’s Valentine story so much that I thought I’d stick to the theme of togetherness…for better or worse.]

A week or so ago a reader asked about the practice of planting three or four fruit trees in the same hole. Having not heard of this before, I checked on the web and found many “how to” pages geared to home gardeners who either want a longer harvest of a particular fruit (early to late) or a mixture of different species. Doesn’t it sound just great, especially for smaller urban yards?

One of these sites has these written instructions: “Plant each grouping of 3 or 4 trees in one hole at least 12 to 15 inches apart.”

Now, I’m sorry, but this is just asking for trouble down the road. Readers of this blog know that root systems extend far past the drip line, and that roots from different trees are going to compete with one another. You’ll end up with three unhappy trees, all jostling for space and resources, just like kids in the back seat during those long car rides.

But wait! you might say. There’s research on high density tree planting, and it’s been shown to increase fruit yield on a per acre basis!

Yes, in fact there is a lot of planting density research on many different species of fruit trees. What’s considered by researchers to be “high density” varies, but it rarely exceeds 2698 trees/acre (6666/ha for our international readers). Optimal and sustainable levels of high density planting are also variable, as they depend on not only species but rootstock and the crown architecture; 1214/acre (3000/ha) might be a mid-range number. This can be converted to a per-tree requirement of 36 sq. ft. or a 6’x6’ planting area.

How does this compare to the 12-15” recommendation given earlier? If we’re generous and use the 15” recommendation, this translates to 6.25 sq. ft. per tree or 6970 trees/acre. The 12” recommendation would lead to a whopping equivalent of 10,890 trees/acre. (And no, it doesn’t matter if you’re using dwarfing rootstock or not; most of the higher densities in the literature are for dwarfing rootstocks.)

You don’t have to be a math whiz to see that these densities are totally out of line with reality. Sure, you can probably keep overcrowded trees alive with lots of water and fertilizer, but they’ll be under enough chronic stress so that pests and disease might take hold, and fruit production will likely be poor. And it’s about as far from a sustainable practice as you can get.

Insects and Fertilization

Linda got a few comments and questions on her post a couple of weeks ago on fertilization and insect resistance. This is an issue I’ve been peripherally involved with over the years so I wanted to share a few thoughts. First, the relationship between plant nutrition and insect resistance is extremely complex. We often have difficulty predicting how a plant is going to respond to fertilization, let alone predict how an insect is going to respond to how the plant responded. I haven’t kept up but Koricheva (2002) reported over a dozen different theories have been proposed to explain insect response to plant nutrition. One of the factors that makes it difficult to generalize about plant/insect interactions is that various insects feed on different plant parts in different ways; some are leaf feeders, some suck sap, some bore into wood, some feed on seeds or cones. How an insect feeds can affect its response. To stick with an illustration I’m more familiar with, we can look at insect response to plant drought stress. Bark beetles are widely known to key in and attack pines and other conifers under drought stress but pine tip moths prefer succulent buds and new growth and are more likely to attack well watered trees. It’s not unreasonable to think there are similar differences with nutrition.

Nevertheless, as noted above, there have been attempts to come up with general theories on the effect of plant nutrition on insect resistance. One of the most widely cited is the Growth-differential balance theory proposed by Dan Herms and Bill Mattson (“The dilemma of plants: to grow or defend.” Q. Rev. Biol. 67: 283-335). A quick check on Google Scholar indicated this paper has been cited by over 1,400 other papers, which is an astounding number and speaks to its influence. The basic premise of the theory, as suggested by the title of the paper, is that plants make a trade-off between allocating carbohydrates for growth or allocating carbohydrates for secondary defense compounds. Dan Herms subsequently applied the theory in synthesizing the literature on woody ornamentals in his 2002 paper, “Effects of Fertilization on Insect Resistance of Woody Ornamental Plants: Reassessing an Entrenched Paradigm.” (Environmental Entomology 31(6):923-933.). I have heard some arborists and others use this paper to argue that we shouldn’t fertilize landscape trees at all. The problem is they oversimplifying the theory – which is understandable, this is pretty heady stuff. They get the ‘trade-off’ idea; if plants grow fast they produce lots of yummy stuff for bugs. But what is often overlooked – even though Herms makes a point to say it – is that when nutrition or other plant resources are low; there is no trade-off.

This figure from Herms and Mattson illustrates the idea. If nutrients are deficient and we fertilize a plant the plant may increase growth and secondary compounds; it’s not always an either/or situation. The bottom-line remains the same; nutrient deficient plants can benefit from fertilization or correcting the factors (e.g., alkaline pH) that made them deficient in the first place.

Koricheva, J. 2002. The Carbon-Nutrient Balance Hypothesis Is Dead; Long Live the Carbon-Nutrient Balance Hypothesis? Oikos 98 (3): 537-539