Spring is off to a warm and fast start here in Michigan. March was unseasonably warm and the past week or so has seen temperature 20 degrees above average or more. Needless to say this is pushing all of our landscape trees and shrubs. Forsythia and saucer magnolia are in full bloom, at least two weeks ahead of schedule. The warm weather also has us scrambling to get some research projects in the ground as well. Today I was working with members of my lab to install a trial to look at the relationship between fertilization in the nursery and subsequent of shade trees in the landscape. For the past two years we’ve grown Acer miyabei (‘State street’ maple) and ‘Harvest gold’ Linden trees in 25 gallon containers as part of a trial on controlled release fertilizer. Interestingly, in the nursery we saw a significant increase in chlorophyll index and foliar nitrogen with fertilization (no surprise) but no difference in caliper or height growth (somewhat of a surprise). This indicates that in the nursery, fertilization induced ‘luxury consumption’ or an uptake of nutrients beyond what the trees need to meet their growth requirement. This observation provided the opportunity for our current, follow-up study. In the forest nurseries there is a growing interest in the practice of ‘nutrient loading’ seedling trees before they are lifted. Forest nursery managers deliberately induce luxury consumption by fertilizing late in the season. At this time seedlings have set a hard bud and won’t grow but can take up additional nutrients. Numerous studies, particularly by Dr, Vic Timmer and his associates at the University of Toronto have shown that nutrient loaded seedlings will outgrow standard seedlings when out-planted on reforestation sites; even though the seedlings are the same size when transplanted. How does this apply to large-caliper shade trees? We don’t know. There are certainly some underlying commonalities that are intriguing. Nutrient loaded forest seedlings have an advantage when planted on tough sites where follow-up culture is minimal – basically the seedling has to get by initially with its own energy reserves and resources. Shade trees planted as street trees often face the same hardship; once planted they may receive little or no after-care beyond an initial watering. Could nutrient loading provide a better internal nutrient reserve and jump start the re-establishment process for street trees like it does for the smaller forest cousins? We should gain some insights this summer and next.
I love living in Seattle…but I’m getting increasingly impatient with the City’s “Building Healthy Soils” propaganda. For years I’ve questioned their recommendation to perpetually amend landscape soil with organic material to no avail. Let’s see what you all think of their “fact sheet” (which you can read here in its entirety).
“The best way to improve the soil is to add plenty of compost or other organic matter throughout the entire planting area before planting. Thoroughly mixing these materials deep into the soil helps provide water, air and nutrients to plant roots.”
Hmm. No mention of how to determine IF your soil needs improving; without a soil test, you have no idea what your baseline organic matter level is.
But perhaps this recommendation is only for vegetable gardens and annual beds? Nope. In the next paragraph, we’re told to “Mix in organic material before planting lawns, perennials, trees and shrubs.” We’re given helpful how-to instructions: “Use a shovel or digging fork to mix amendments into the top 6 to 12 inches of soil. It is important to amend the entire planting bed — not just small holes for each plant. When planting individual trees and shrubs in lawns or existing beds, amend an area at least 3 feet wide, or 3 to 5 times as wide as root balls over 12 inches in diameter. Rototill large areas where digging is impractical.”
Now we’ve got a serious problem. This practice is recommended for existing beds. Not only will extensive digging or rototilling destroy any soil structure you might have, it will also take out the roots of any desirable plants in the vicinity).
But let’s continue to ignore reality and go on to the annual recommendations for adding compost to soils.
“Clay soils: 16 cu. feet (.6 cu. yard) = 2 inch layer of compost for new gardens. Use 1 inch per year in established gardens.”
“Sandy soils: 24 cu. feet (.9 cu. yard) = 3 inch layer of compost for new gardens. Use 1 – 2 inches per year in established gardens.”
Is the compost used as a mulch in these existing gardens? No – the guidelines are prefaced with this instruction: “Gardens: mix compost to 10- to 12-inch depth.” (Can’t say this does much for promoting root growth either.)
This document shows a breathtaking lack of understanding of how landscapes function, especially over the long term. It takes an agricultural practice (annual organic amendment of crop fields) and misapplies it to permanent landscapes. It is devoid of the research which continues to show that improper soil amendment can cause serious problems such as soil subsidence, perched water tables, and nutrient overloads. This last point is especially important to anyone living near aquatic ecosystems, since excess nutrients always end up in the water.
Before you plant this year, find out what your soil needs before amending it. And remember that mulching is the natural (and sustainable) way to add organic matter to the soil.
One of the hallmarks of science is that our view of the world evolves and changes as new evidence comes to light. When I was a grade-schooler following the Apollo missions, for example, I knew all the planets in order from Mercury to Pluto and how many moons each one had; Jupiter was the champ with 12. Today, Jupiter has as many as 63 moons depending on who’s counting. And Pluto, let’s not even go there. Likewise, our view of plant science has changed over the years. As I’ve mentioned before, when I took introductory Botany as an undergrad thirty-some years ago we learned that there were 16 essential plant nutrient elements. Since then we’ve learned that nickel is also essential at least for some plants.
If you took your plant science more than 10 years ago, you also learned that nitrogen is taken up from the soil as either ammonium or nitrate. This view is now being revised due largely to evidence from the ecological literature. Ecologists have found that in northern boreal regions where soil temperatures are cold and mineralization and nitrification rates are low, plants will take up intact amino acids from the soil (Nashholm and Persson, 2001; Kielland et al., 2006). Recent studies have extended these observations to temperate forests (Gallet-Budynek et al., 2009) and horticultural crops. (Ge et al., 2009), indicating that a range of plants may be able to derive a portion of their N requirements directly from organic sources.
So what does this have to do with the Garden Professors and the science of landscape horticulture? First off, this is pretty cool stuff and certainly will cause a lot of re-evaluation of some established paradigms. From an applied perspective, fertilizing with amino acids and related organic source has some potential benefits. In warm, well-aerated soils, nitrate-N predominates. When plants take up nitrate, it must be reduced via nitrate reductase and nitrite reductase before it can be assimilated into amino acids. These steps require metabolic energy. In theory, amino acids could bypass the reduction and assimilation processes and provide a more efficient means of fertilization. At this point, most of the scientific focus is on quantifying how much organic N can be directly taken up from the soil. Evaluating efficiency of uptake and utilization is a couple steps down the road. Amino acid fertilization could potentially provide another benefit over nitrate fertilization by reducing nitrate leaching.
Of course there’s a potential downside as well. A quick Google search of ‘amino acid fertilizer’ reveals sites shilling all manner of concoctions for fertilizing plants; many of dubious value. One of the first sites I hit proclaims that, unlike inorganic fertilizers, their product provides the 70 elements needed for plant growth. Seventy?! Well that’s close to seventeen. Point is be prepared for an ever increasing barrage of claims about organic fertilizers. There is no doubt that compost and similar organic sources can provide essential plant nutrients and effective fertilizer sources. As always, however, be skeptical of spectacular claims and secret, proprietary ingredients and pay close attention to the cost of amino acids compared to conventional fertilizers. There is some science here; clearly many plants have the capacity to take up amino acids directly. Beyond that we’ve still got a lot to learn.
Gallet-Budynek, A., E. Brzostek, V.L. Rodgers, J.M. Talbot, S. Hyzy, and A.C. Finzi. 2009. Intact amino acid uptake by northern hardwood and conifer trees. Oecologia 160:129–138.
Ge, T., S. Song, P. Roberts, D.L. Jones, D. Huang, and K. Iwasaki. 2009. Amino acids as a nitrogen source for tomato seedlings: The use of dual-labeled (13C, 15N) glycine to test for direct uptake by tomato seedlings. Environmental and Experimental Botany. Volume 66: 357-361.
Kielland K, J. McFarland, and K. Olson. 2006. Amino acid uptake in deciduous and coniferous taiga ecosystems. Plant Soil 288:297–307.
T. Näsholm and J. Persson. 2001. Plant acquisition of organic nitrogen in boreal forests, Physiol. Plant 111: 419–426.
First of all, who we are and what we do. All of the Garden Professors are in the business of the science of Horticulture. What’s Horticulture? The standard definition of Horticulture is the art and science of tending a garden. Horticulture is clearly more than science but science is the foundation and underpinning. For anyone that needs convincing that Horticulture is an art as much as a science I suggest the following exercise. Go to a major research university and wander through their Botany or Plant Biology greenhouses. Observe the plants. They look like crap. The people working there are on the cutting edge of plant science; they sequence genes, they elucidate biochemical pathways but they can’t grow a plant to save their lives. Now wander through the Horticulture greenhouse; plants are thriving, flowers are blooming. What’s the difference? The horticulturalists not only have the science, they have the art. There is no denying that art and intuition play a role in growing plants, especially in ornamental horticulture where we deal with hundreds of species and cultivars, each with its own subtleties and nuances. But as educators, especially public funded educators, how do we teach intuition? It’s very difficult. What we teach are principles developed through systematic scientific inquiry. How do we know there are 17 essential elements needed for plant growth? Repeated experiments over the years. And our knowledge continues to evolve based on the scientific method. I’m old enough that I learned 16 essential elements as an undergrad; the need for nickel by some plants had not yet been established. As extension educators our role is to disseminate science-based information. For some of us that phrase is even in our job description. We can try to impart our experience and intuition but it’s a difficult thing.
It can be especially difficult when we deal with alternative systems for which a long-term knowledge base may be lacking. Despite perceptions to the contrary, we are not apologists for the status quo. Overuse and misuse of pesticides and fertilizers are rampant, especially in ornamental horticulture. A lot of our current research and extension programming deals with reducing water and nutrient usage to reduce run-off and to reduce leaching. I spend a lot of time telling growers things they don’t really want to hear. How do we know growers are potentially impacting water resources? Because we and others have done the scientific research. We’ve set out plots, we’ve fertilized, we’ve sampled leachate, we’ve measured run-off. And we’ve conducted extension programs teaching growers that they can back off fertilization and irrigation rates without reducing crop growth.
Where we get concerned is that some assume or take on faith that because a nutrient source is ‘organic’ or ‘natural’ it’s automatically better or safer for the environment. Is the nitrate from Chilean nitrate less likely to cause blue baby syndrome then nitrate from ammonium nitrate? Dr. Corey Reams developed his principles as revealed to him through divine revelation. Unfortunately most of us are not blessed with such experiences. Instead we rely on systematic scientific investigation to develop knowledge that we share with our clients. Personally I do not believe that faith and science are mutually exclusive. Some of the most brilliant scientists I have met in my career have been people of deep and abiding faith. But we need to keep each in its context. Science is knowledge gained through systematic inquiry. Faith is a belief system. The central tenets of most Christian denominations are stated in the Nicene Creed which begins, “We believe in one God…” Note it doesn’t start “We know…” or “We can prove…” In their liturgy Catholics, “proclaim the mystery of faith; Christ has died, Christ is risen, Christ will come again.” Not only can they not prove these things they celebrate the fact that it’s a mystery. Faith does not demand proof. Science does.
It’s days like this that I am so grateful to have this blog at my disposal!
It’s 7 am on Sunday and I’m just finishing the paper, drinking Earl Grey tea, and listening to NPR. Liane Hansen just finished an interview with Martha Stewart, who among other things was discussing healthy eating for the new year. She’s a proponent of organic food (as are many of us), and mentioned two reasons she doesn’t like conventionally grown produce. The first – residual pesticides – is a legitimate concern. But then she stated her second concern that “chemical fertilizers in the soil are taken up and stored in the plant.”
Plants really don’t care (excuse my anthropomorphizing) where their mineral nutrients come from. Nitrogen in ammonium sulfate is the same element as the nitrogen in cottonseed meal. The plant uses it for amino acids, chlorophyll, alkaloids, and many, many other compounds.
Martha’s faulty thinking falls into the “organic is safer than chemical” mindset that way too many people hold (you can read a column I wrote about this in 2001 here). “Chemical” is not intrinsically bad and “organic” is not automatically safe. This is an emotion-based argument and inspires fear rather than thoughtful discussion. When someone parrots this mantra, I can’t take them seriously.
I believe that organic methods in production agriculture, ornamental landscapes, and home gardens are superior to conventional practices and support a healthy soil-microbe-plant-animal system. I also believe that many fertilizers are misused and/or overused – but this includes both conventional and organic varieties.
Gerald Horton, a science historian at Harvard, once stated that “persons living in this modern world who do not know the basic facts that determine their very existence, functioning, and surroundings, are living in a dream world. Such persons are, in a very real sense, not sane.”
This is the quotation that came to mind this morning.
Bet you weren’t expecting this on TUESDAY, eh?
Situation: these photos are from a grad student project. We wanted to create, observe, and record nutrient deficiency symptoms, so we grew the plants hydroponically in a made-from-scratch nutrient solution, containing everything except one particular nutrient. There were 12 separate batches of solution, one missing each essential mineral nutrient (N,P, K, Ca, Mg, S, Fe, Mn, Cu, B, Mo, Zn – couldn’t exclude Cl as it’s too common in salts). As my research interest is herbaceous perennials, some common perennial taxa served as our victims, er, subjects.
Here’s the set up for the Verbena ‘Homestead Purple’ experiment – rooted cuttings were placed in the little buckets and secured by the lids. The nutrient solution was constantly aerated. For most elements, symptoms appeared between two and four weeks after the start of the project. Symptoms, depending on the elemental deficiency, included chlorosis (yellowing) of old or new leaves, leaf curl, speckling, stunted growth, and in one case, some excessive growth.
Below are results from day 42 of the study. We lifted the lids, hanging-basket style, so we could examine the roots. The control (received a complete nutrient solution) is on the left; Rapunzel there, on the right, lacked a nutrient. Quiz question: What element was missing in this particular case? What made you come to this conclusion?
Hint: If you have a rudimentary knowledge of garden fertility, be it veggie or ornamental, you can probably figure this out. I’ll go ahead and rule out the pesky micronutrients.
(L) Control: received complete nutrient solution (R) Deficiency solution
About 3 months after I started my job in Minnesota I hired a technician to help me run the nursery and to manage research plots. His name is Chad and he stands about 6 foot 4, has shoulders that threaten to pop the sides of the skid steer loader whenever he enters it, and he knows his stuff because he needs to (and even if he didn’t know his stuff you’d be scared to tell him that because he looks dangerous with his frightening Fu-Manchu moustache). Currently Chad is responsible for day to day operations in the nursery as well as writing publications. In other words he’s indispensible. When you read a post from me, particularly when it’s regarding nursery or landscape research, you’re usually reading a combination of both of our thoughts.
Over the years Chad and I have seen a lot of nursery stock; some of it good, and some of it bad. Between us we’ve seen poor pruning, unhealthy root systems, pot-bound plants, trees planted in soil that was much too alkaline or acidic for them, trees planted in the wrong zone, trees sold that weren’t close to the size that they were supposed to be, trees that were girdled by critters, root systems completely eaten by voles and even a tree shot with a handgun. I once saw a whole field of Japanese maples topped (basically topping is when you cut horizontally through a trees canopy to give it a flattop – talk about competing leaders and narrow crotch angles!). Seeing that field almost made me cry – A planting worth $20,000 – $30,000 wholesale almost instantly became worth the price of kindling. But we agree that none of that can hold a candle to Sara’s Nursery (Named after the owner’s daughter).
I received a call a few years ago from a nursery in western Wisconsin (which, for those of you who aren’t familiar with this part of the world, is much closer to the Twin Cities than to Madison, WI where the University of Wisconsin is). The caller was very concerned that the plants in the nursery which she had been hired to run were failing. Basically, their leaves were dropping and she couldn’t figure out why. This was even happening to plants that we usually consider “indestructible” like potentilla. I had never heard of such a thing, but it sounded like a soil problem and so I asked her to have some soil tests done and to send me the results. She agreed, but she was distraught and asked me to come and take a look at her operation. I balked at first, but after a few minutes of begging I gave in. I asked Chad if he’d like to join me on a trip to the nursery the next day; he agreed and we were off.
The nursery that we found was a retail operation on a road which was once a major thoroughfare, but had been reduced to a minor highway when the interstate, which ran parallel, had been expanded. Still, it seemed like a pretty good location for a retail nursery in terms of customer traffic. After we parked the car Chad hopped out and began inspecting balled and burlapped evergreens while I joined the manager to look at their container stock. It was a mess. It was the end of summer when we visited, but the leaf drop made it look as though we were in the late fall.
I popped a potentilla out of a container and could find no roots reaching the containers edge. Taking a closer look I quickly discovered one major problem. These were bare root plants planted into containers filled with soil. Soil is almost never a good thing to put into a container because it’s usually too heavy and prevents air from working its way down to the plant’s roots. The gentleman who owned the nursery (not the manager – in most cases she just seemed to do what the owner wanted to do) was a farmer who had decided that it made sense to save money by using this soil which grew his field crops so well. This nursery was buying bare-root plants, popping them into containers filled with field soil, and then selling them at quite a mark-up (by the way, this is considered an unethical practice).
This field soil was obviously a problem, but, while plants usually suffer because of the use of soil in containers, I didn’t think it was likely to cause the carnage that I was seeing. I asked about their fertilizer and watering practices. Both of those seemed reasonable and unlikely to cause a major problem.
Meanwhile, Chad came back to report on the evergreens. Almost all of the evergreens (which showed signs of repeated shearing – good for Christmas trees — not good for the long term health of landscape trees) were missing needles close to the base of the tree and appeared to be suffering somewhat. I thought it might be a water issue, particularly if city water were being used, and asked where it came from. The manager told me that all of their water came from a well on site. In this part of the world we frequently have issues with well water being too alkaline, but it usually doesn’t cause the type of damage that I was seeing here. I filed water away as a possible, but unlikely cause.
I was pretty stumped, as was Chad. Obviously we saw problems, but these just didn’t seem sufficient to cause what we were seeing. The manager offered to show us the potting operation, we followed. The first thing that struck me about the potting shed was that it seemed old, and yet the timbers themselves hardly showed any rot which is kind of unusual. We asked when the shed had been built and the manager indicated that she had reason to believe that the shed had been built in the 1940s or 50s.
We entered the shed and noticed a large pile of what we assumed to be soil. Nothing special. Then our eyes began to adjust to the dim light and we realized that this was no ordinary pile of soil. It was mostly white. We were confused. The first thought that went through my head was “what is this, cocaine?” Then I thought, no, it must be perlite. I looked at Chad. His eyes were big and round. I went over to the pile, poked my finger into it, and then touched it to my tongue.
“What the EXPLICATIVE DELETED is this place?” I asked Chad (OK, I may not have used those exact words, but it was something close). The manager must have overheard.
“Well, it’s a potting shed now, but it was built to store salt for the highway” she responded. “That’s just a pile of leftover salt. We stack our soil against it when it comes in.”
We tested both the soil from the pots and their irrigation water. Both were ridiculously high in salt (and, not coincidentally, sodium levels). In fact, salt levels were high enough in the irrigation water that it would literally burn foliage off of the plants.
Shortly after visiting this nursery Chad became a Buddhist and my beard turned more gray than brown. I can’t swear that it was this nursery that caused these changes, but I can tell you that I haven’t been the same since.
Every year I teach a class called nursery management. In this class students have the opportunity to try all kinds of different growing techniques out in the nursery. They get to use a tree spade and prune and all kinds of other stuff. But something else that I have the students do is to make hydroponic systems for growing plants. No, hydroponics is not a common technique for growing plants in a nursery, but to grow plants hydroponically you need to know what you’re doing, and so this is a convenient way to make the students think about the plants they grow and what these plants need to prosper.
To start this project I give the students a water pump and an air pump (courtesy of our friendly neighborhood drug dealers — no, seriously — when the cops bust pot growing operations they give us the equipment that they’ve confiscated after they’re done using it as evidence. Much of the equipments is new, some is very high end.) Then I divide the students into a few groups, tell them what they’re growing, and give them two weeks to come up with a growing system and a nutrient solution to grow their crop (I do allow them to use our stock hydroponic solution, which will grow the plants, but won’t win anyone any prizes — most groups choose to use this as a base solution and then add to it.). The group whose plants grow the largest after twelve weeks wins a modest bonus to their grade.
So, what do we have for set-ups this year? Some very, very cool ones! First, we have a number of groups who went with a simple, non-circulating system, as seen below. Basically just an air-hose and a container filled with nutrient solution.
Another group decided to use a flood and drain system. They use a timer to trigger the water pump to fill a tray with nutrient solution for five minutes every few hours. This hydrates the containers which hold the extremely well drained ceramic beads in which the plants are held.
And finally, one group decided to use a capillary action system where the base of the container is filled with nutrient solution which is wicked up into a well drained media (a combination of rockwool, vermiculite, and perlite) into which the plants are placed. This group decided to lay their plants on their sides to encourage extra root growth.
I’ll let you know in about 12 weeks which group wins!