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.
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.
It’s amazing how many things in life seem complex when we try to figure them out for ourselves but then we end up smacking ourselves on the forehead when someone shows us how simple it really is. The infield fly rule comes to mind. Some colleagues of mine here at Michigan State may be on their way to such a solution for the problem of white grubs in lawns. Drs. Dave Smitley (Entomology), Kurt Steinke, and Trey Rogers (Crop and Soil Science) are investigating the effect of mower height on turf damage from grubs.
European chafer grub. Photo: David Smitley
The premise is simple: White grubs damage turf when they consume about 75% of the turf roots present. Raising the mowing height of most standard mowers from 2” to the highest setting (usually 3 ½”) also results in more root growth; often by more than double. Since there’s a limit to how much root mass grubs can consume, increasing the amount of roots ensures the damage threshold is never reached. The working hypothesis has been confirmed by greenhouse tests and now the researchers are taking to the field.
Chafer grub damage. Photo: David Smitley
This may turn out to be another example of how raising mower height and not trying to make your lawn look like a golf course fairway can reduce inputs and keep your turf healthier.