Here’s an interesting phenomenon you can see in any group of plants – it’s what we call the edge effect:
Today’s question: why are the trees in the foreground so much shorter than those just a few feet farther from the edge? Answer on Monday!
Building a Better Container
As most of you know, roots circling around a container isn’t considered a good thing. And so people try various things to control circling roots. One of the more creative horticultural minds out there, Carl Whitcomb, a guy why basically got sick of academia and went into private industry (and, as far as I can tell, loathes peer review and the whole process of publication), decided to see what he could do about making containers that don’t encourage circling roots. He came up with a number of designs, but my favorite is the RootTrapper. The container is made of a flexible cloth which roots get lodged in, preventing them from circling. Not that I’ve never seen a circling root in a RootTrapper, it’s just that these circling roots are extremely rare.
A row of elms in RootTrappers
A cut open RootTrapper
This is one of those innovative products that really works and it surprises me that so few people use this growing system. Yes, it’s a bit more expensive than standard containers, and yes, it does take a little more effort to take the tree out of this container than a smooth sided one. But man, I’ve never seen a better root system come out of a container than those which you get out of these.
Permaculture – more concerns
One of the gardening topics I’ve researched extensively is the use of landscape mulches. (You can read a literature review I did a few years ago here.) So I was more than a little frustrated to see one of the worst mulching techniques – sheet mulching – extolled in the book Gaia’s Garden (pp. 85-90).
Sheet mulches, like newspaper and cardboard, can be used successfully as a temporary weed control measure (i.e. a few weeks before planting a vegetable garden). Long term, they are not a sustainable choice and often cause more damage to the system than the presence of weeds.
The two-dimensional structure of sheet mulches functions as a barrier to not only weeds but to the movement of air and water as well. While this may initially increase soil water retention since evaporation is reduced, over the long term they will create soils that are unnaturally dry. This condition is worsened on low-maintenance sites,where neglected sheet mulches easily dry out, causing rainfall or irrigation water to sheet away rather than percolate through.
In contrast, wet, poorly drained soils will become even more so as layers of moist paper or cardboard restrict evaporation and aeration. Moreover, this condition encourages root growth on top of the sheet mulch, which can injure desirable plants when and if the sheet mulch is removed.
There are other disadvantages as well. Exposed newspaper and cardboard mulches are easily dislodged by the wind, animals and pedestrians and often provide food for termites and shelter for rodents such as voles. Combined with a somewhat marginal ability to control weeds compared to other organic mulches, sheet mulches are arguably one of the least attractive or effective choices for a sustainable landscape.
Sheet mulching proponents will argue that newspaper and cardboard are only part of the mulch structure – that organic materials such as compost and wood chips need to be added as well. To which I respond – then why bother with the sheet mulch? Why not just use deep layers of coarse organic materials? That’s exactly what forest duff layers consist of. It’s been repeatedly demonstrated that thick layers of coarse organic materials are the best and most natural choices for mulching. (See, for instance, my Ecological Restoration article on using a foot of arborist wood chips to suppress blackberry and enhance native plantings. )
The appeal of sheet mulching is its formulaic structure and logical approach – it’s like making lasagna (the name of yet another nonscientific approach to mulching). Unfortunately, sheet mulching is neither natural nor particularly effective.
Last-Frost-Date Roulette
We all play the game – at least the more impetuous among us do. You sneak a few tender things out into the garden, or on to the patio. When the temperature drops and there’s a frost warning, no problem…just cover them up or bring them in.
Unless you forget.
This WAS a rare and neato Pereskia aculeata ‘Variegata’. Paul W., please send me another…
Before dawn on Monday morning, (May 9) the temperature on our little mountainside dropped below freezing for four hours, going as low as 29.5 F according to our weather station. I had tucked everything back into the greenhouse or up under the eaves…except for the contents of a built-in planter on a far outpost of our deck.
Dahlia Mystic Desire, edged in frost at 7:00 a.m., May 10.
NOAA has a handy set of maps that illustrate last dates of “Spring freeze occurrence”. The maps present data averaged between 1951 and 1980.
Walking around the garden last evening with a nice hot cup of martini, I surveyed the damage. Big, juicy-stemmed bleeding hearts that seem so fragile and succulent? Not a speck of injury – but they’ve been up since March. Newly emerged (and really expensive) Asian Jack-in-the-pulpits looked like wet rats. Annuals and tropicals exposed out in the open didn’t stand a chance. Early-to-leaf-out trees can take a beating, too. Japanese maples are notoriously precocious, flinging their fabulous foliage out as much as 45 days prior to last frost here. They’re in pretty good shape now, having acclimated a bit. But for our previous hard frost,15 days ago, we had eight little maples individually draped in white row cover (looked like Halloween).
Dahlia Mystic Desire, kaput at 7:00 p.m., May 10.
So why the damage on some and not others? Plants differ in the amount of sugars, proteins, and other compounds that affect the osmotic potential in cells. The lower the content of these compounds, the more likely freeze damage will occur. Young and unacclimated tissue tends to have a higher ratio of water. Like an overfilled water bottle stuck in the freezer, something’s got give as the liquid crystallizes and expands (vast oversimplification, sorry). Cells burst, or are crushed from the freezing of intracellular water, and fluid goes everywhere – hence the limp, dark, water-soaked appearance.
Fog or dew on the plant can delay injury; as external moisture freezes, in gives off heat (an exothermic reaction; one of the amendments to the Laws of Thermodynamics), until all the water is frozen. This is why citrus groves are continually sprayed with water during a freeze event. So it also depends on the duration of the cold; if temperatures just briefly drops below freezing, damage is minimal. Four hours for non-acclimated tissue? See the grim photos for results. Will I wait until May 15 to plant stuff out next year? Absolutely, positively, not. We’re due a no-late-frost spring!
Green mystery disk identified!
Initially I was disappointed that no one answered the question…then Paul W. emailed to say that the post wasn’t accepting comments. We’re not sure why that happened, but Paul and perhaps many of you knew this was part of the flower of Sarracenia flava – the yellow pitcher plant:
I think this is a stunning flower whose floral structure promotes cross-pollination. Insects crawl in between the long yellow petals and the green "umbrella" to enter the flower and reach the pollen:
Before they reach the anthers, however, their backs rub up against the stigma, which are five tiny points at the "spokes" of the umbrella. Pollen already on their backs will be transferred to the stigma before new pollen is gathered, so that the chances of selfing are reduced:
So thanks, Paul, for being so persistant that you emailed me to supply the answer and alert me to the comment fail!
Every survivor has a story
It’s been suggested, not unfairly, that the Garden Professors are sometimes a little ‘Tree-Centric’. As a forester and tree physiologist by training, I’m probably the guiltiest among my co-conspirators on that count. But occasionally I do notice things less than 10’ tall and lacking a single, woody trunk.
When weather permits I like to take my lunch down to the MSU annual trial gardens behind my office here at the Plant and Soil Science Building. Every summer the annual gardens are awash with the color of impatiens, geraniums, petunias, and other annuals. This time of year, however, it’s bulbs that steal the show. This spring there was a display of bright pink tulips that was especially striking. Wandering by the beds recently I noticed a tag in one corner; ‘Susan Komen mix’. For those that aren’t aware, Susan Komen lost a long, brave battle with breast cancer in 1980. The foundation founded by her sister, Susan G. Komen for the Cure, is the leading advocacy and fundraising group for breast cancer awareness and research in the US. Komen for the Cure also provides services and advocates for our country’s two and half million breast cancer survivors.
In many ways, tulips are a fitting symbol for breast cancer survivors and the brilliant pink show made me think of a cancer survivor I know, my college girlfriend, Lisa. I remember learning about her cancer nearly two years ago. We had followed our own paths after our undergrad days and contact was sporadic as we each set out on careers and started families. I missed her at our 30th high school reunion but found her number in the reunion directory and rang her up. The words hit like a punch in the stomach, “I underwent breast cancer surgery and treatment this past winter.” I was stunned but in the next instant knew her trademark grace and humor were still intact. “Yeah, when the reunion notice came out I had just lost both my boobs and all my hair. Ya know, I just wasn’t up for all the ‘Hi, how are ya’s?’” Today, Lisa remains cancer-free though after-effects of radiation treatments linger. Through the wonder of Facebook we now keep up on each other’s awesome and talented kids. She’s looking forward to two year’s cancer-free in July and then the all-important 5-year mark beyond that.
So, what does all this have to with landscape horticulture? My friend and colleague Art Cameron concluded a talk at our Master Gardener College last Saturday with a quote: “To plant a garden is to believe in tomorrow.” So much of what we in do horticulture is an expression of our faith in the future. When we plant tulips in the fall we know they must endure dark, cold days each winter in order to bloom the next spring. Breast cancer survivors and their families have to endure more than their share of darkness to see brighter days. We’ve become a society obsessed with instant gratification and the old cliché ‘stop and smell the roses’ seems trite and shopworn to a lot of folks. But gardens connect us to the earth and to each other and provide the perfect place to take time and reflect on things that really matter.
According to the American Cancer Society nearly one in eight women in the US will develop invasive breast cancer in their lifetime. To learn more, read breast cancer survivor stories, and to support breast cancer research go to www.komen.org
Friday’s “disk of mystery”
What is this "green disk of mystery?" It’s about 2" in diameter:
Answer on Monday – have a great weekend!
The Approach Graft
Seeing as this blog is called “The Garden Professors” it has been far too long since we’ve given you a lecture on a useful practice for your garden, so this week I thought I’d give you a little how-to demonstration on something called approach grafting. Approach grafting is a technique that you could use to graft a tomato to a tomato (good if you want to use a disease resistant root with a non-disease resistant top — common in heirloom tomatoes), a tomato stem to a potato root (just a fun project), or an eggplant root to a tomato shoot (good for wet locations).
So here we go. First, you need two plants that are about the same size, and you need to plant them in the same container as demonstrated below with a potato and tomato. You will also need to strip off lower leaves as they may get in the way of the graft.
Above we have a young potato and tomato plant to be grafted.
In the above picture the potato and tomato plant have been planted in the same container and their lower leaves have been stripped off.
After the two plants are in the same container a small slice is made on each plant at the same height. This slice will be, ideally, just a little bit deeper than the cambium into the center of the stem (you’ll be able to see the plants pith — in the center of the cut — it’s tough to see in the image here).
In the above picture the stem of both the tomato and potato are cut so that they can be joined together.
After making the required cuts on both plants the cuts are pushed together and wrapped. We used parafilm to wrap this graft, but saranwrap, or even an elastic band would also work.
In the above picture the cuts are being joined.
Here the cuts are wrapped.
The next step is to wait until the graft “takes”. This could take 3-5 weeks. After a good strong union is formed the top of the potato and the bottom of the tomato plants are cut off. Wait a few days to make sure everything’s working properly and plant the result in your garden.
Permaculture – the discussion continues
We’ve started a robust discussion on the topic of permaculture, especially as applied to home gardens. Let’s continue looking at some of the advice provided in Gaia’s Garden targeted towards home gardeners.
The book contains several lists of plants suggested for specific functions. For brevity’s sake, I’ll just mention two:
“Host plants for Beneficial Insects” (pp. 157-159)
This list is prefaced in the text with “many of these florae are very attractive and can (and should!) be included even in the most formal garden bed.” With this strong endorsement, the author then presents an unsourced list of plants, several of which are identified as noxious weeds in many states in the country. They include Washington noxious weeds false indigo (Amorpha fruticosa), fennel (Foeniculum vulgare), Queen Anne’s lace (Daucus carota), toadflax (Linaria vulgaris), cinquefoil (Potentilla recta), sulfur groundsel (Senecio vulgare), and tansy (Tanacetum vulgare).
“Dynamic Nutrient Accumulators” (pp. 131-134)
We are told “certain species draw specific nutrients from deep in the soil and concentrate them in their leaves” and given an extensive table of these plants and exactly which nutrients they accumulate. The references for this table are not scientific, and in at least two cases are mystical in nature (Cocannouer’s Weeds: Guardians of the Soil and Pfeiffer’s Weeds and What They Tell). As in the previous table, many of these plants are designated noxious weeds in Washington or other states and include nodding thistle (Carduus nutans), Canada thistle (Cirsium arvense), fennel (Foeniculum vulgare), toadflax (Linaria vulgaris), creeping thistle (Sonchus arvense), and tansy (Tanacetum vulgare).
As readers of this blog know by now, we GPs are not “plant purists.” But it is highly irresponsible to encourage people to plant listed noxious weeds in their gardens. Even the author seems to understand this, and states (on page 15) that “it is foolish to deliberately introduce a species known to be locally opportunistic.” It’s mystifying, then, that he does exactly that in these two tables.
The inclusion of the table of “dynamic nutrient accumulators” demonstrates that this book tends to wander far afield of the philosophical roots of permaculture. It is an excellent example of pseudoscience, as it creates a scientific-sounding phrase (“dynamic nutrient accumulator”) and misleads non-experts into believing a scientific claim (nutrient accumulation of specific minerals) without providing actual supporting data.
Visiting Professor guest post: Native wildflowers
Recently I have been fascinated by the native wildflower field I planted last fall. Although I seeded it with the same mixture of seeds (mixed with sand to spread them evenly), you can see that we have clumps of different flowers throughout the area.
Figure 1. Descanso Gardens, California
The area where the wildflowers were planted had several 1-2 foot raised mounds; some were in the shape of keyholes. These were built with silty sand from a nearby seasonal stream that had some erosion problems in a rainy year.
Small differences between the temperature, moisture, light and soil on the different parts of each mound have favored different species of wildflowers. In one of the keyholes, I even found some miner’s lettuce (Claytonia perfoliata), a species I had not seeded that favors wetter areas. If I sampled for insects, I bet I might find a similar patchy distribution as well.
As an ecologist/biologist, I am really fascinated by the way that species diversity can be affected by topography, climate, moisture, and soils. As a gardener, I like that I could create conditions that favor different plants just by moving soil around. Plus I think that the waves of color are lovely as well.
Rachel Young is the head of the California Garden at Descanso Gardens, just outside Los Angeles. She has an MS degree in Ecology and Evolutionary biology from UCLA and lectures on various garden and horticulture related topics.