With drought predicted for the west, southwest, and south through June 2015 (National Weather Service March 2015), many conscientious vegetable gardeners will try to conserve water by using soaker-hoses, those bumpy black hoses that weep water onto the soil through tiny pores.
Soaker hoses are made from fine-crumb rubber, usually recycled from vehicle tires. Research strongly establishes that tire particles leach heavy metals, carcinogens, and mutagenics, among other toxins. Yet soaker hoses have not been studied for potentially increasing the toxicity of edible plants. Are they really safe to use safe on our edible plants?
Soil in the City
Urban soils already contain high levels of heavy metals (Murray et al. 2011) from years of household runoffs—chemicals from pesticides, cars, painting, cleaning, and more. Adding soaker hoses made of crumb tires might exacerbate the problem.
Whether plants take up enough heavy metals to be toxic, however, is a complex equation, depending on a slew of interrelated factors, including:
• Soil pH (Costello 2003) and texture (Singh and Kumar 2006; Murray et al. 2011)
• Temperature (Murray et al. 2011; Lim and Walker 2009)
• The size of the rubber particles (Gaultieri et al. 2004)
• Chemical composition of irrigation water (Singh and Kumar 2006)
Furthermore, the plant species and even the cultivar can affect a plant’s uptake of zinc and other heavy metals (Murray et al. 2009 and 2011).
Growing Healthy Food
If you’re looking for the key to ensuring that your vegetable patch grows healthy food, however, I’m sorry to disappoint you. Too many factors are involved to predict the toxicity of what we grow in our gardens.
A good way to get more information is to contact your local extension agent for a list of laboratories that test soils not only for nutrient composition but for heavy metals. Although this information won’t guarantee you’ll be able to grow heavy-metal-free produce, it’s a step in the right direction while we wait for more research to be done.
Cindy Riskin is a Master of Environmental Horticulture and freelance journalist raising edible plants, an unkempt ornamental garden, and elderly mutts in Seattle, Washington.
NOTE: This article is excerpted from a longer one soon to appear in Cindy Riskin’s upcoming blog, tentatively named Muddy Fingers Northwest. Please contact Cindy Riskin at email@example.com for an advance copy or the blog’s web address.
1. Costello, Laurence Raleigh. 2003. Abiotic disorders of landscape plants: A diagnostic guide. Oakland, Calif.: University of California, Agriculture and Natural Resources. P. 117.
2. Gualtieri M., M. Andrioletti, C. Vismara, M. Milani, and M. Camatini. 2005. Toxicity of tire debris leachates. Environment International 31 (5): 723–30.
3. Lim, Ly, and Randi Walker. 2009. An assessment of chemical leaching releases to air and temperature at crumb-rubber infilled synthetic turf fields. Albany, N.Y.: New York State Department of Environmental Conservation. http://www.dec.ny.gov/docs/materials_minerals_pdf/crumbrubfr.pdf.
4. Murray, H., T.A. Pinchin, and S.M. Macfie. 2011. Compost application affects metal uptake in plants grown in urban garden soils and potential human health risk. Journal of Soils and Sediments 11 (5):815–829.
5. Murray, Hollydawn, Karen Thompson, and Sheila M. Macfie. 2009. Site- and species-specific patterns of metal bioavailability in edible plants. Botany 87:702–711.
6. National Weather Service Climate Prediction Center. March 19, 2015. U.S. Seasonal Drought Outlook. NOAA/National Weather Service National Centers for Environmental Prediction. http://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_summary.html.
7. Singh, S., and M. Kumar. 2006. Heavy metal load of soil, water and vegetables in peri-urban Delhi. Environmental Monitoring and Assessment 120 (1-3):1–3.
William H. McCaleb, Blog Contributor
Program Assistant for Agriculture and Natural Resources, Halifax County, VA. and Master Gardener
For gardeners in the eastern U.S., last year was a better than normal gardening season. Better than normal yield, better than normal precipitation, and in our case in Virginia cooler than normal which yielded excellent spring cool season crops as well as early summer crops.
But all good things must come to an end; that being the result of several heavy frosts. With that said, I am looking forward to next year’s challenges and what I want to grow for our family. Oh, for the taste of one more summer ripened tomato, but for now, that is a dream and it is time to reflect on what grew well in the garden as well as what didn’t do so well. Hopefully you have kept a garden journal to help you in this task. I find that writing down details of what is planted, the orientation, spacing, fertilization/liming rates and frequency, weekly rainfall amounts, production amounts, etc. is helpful as you start planning for the next season.
Like me, you should start thinking about what you want to grow in 2015. Take time to reflect on your 2014 garden production, care, and location. Also, evaluate what went right and what went wrong with the plants and varieties you planted and harvested. This will start you off in the right frame of mind in preparing for the next growing season. Good planning and preparation for next year gives you the tools to have an even better gardening season. A successful vegetable gardener is a happy well fed gardener!
I know, you too are already missing those fresh tomatoes, potatoes, peppers, squash, okra, and other great home grown vegetables we treated ourselves to this year, but the next season is ‘just around the corner’ so to speak. After all the days are getting a little longer. Spring can’t be far away!
If you just happen to live in an area that hasn’t had frost yet, take your prompt from your plants: when annuals and seasonal vegetables turn brown and begin to die back, it is time to clean up your garden.
Clean up the Garden Your best action is to remove any spent or failing plant materials. Experienced gardeners know that many of the bacteria, fungi, and other disease-causing organisms that caused those diseases. Pathogens that are sources of those diseased plants this past season can survive over the winter in dead leaves, stems, roots, and dropped fruits that get left in the garden. Much like a piece of bread that is kept too long and looks like it has penicillin growing on it, garden debris also will carry the pathogens that can come alive with those same problems when the temperatures begin to rise in the spring. Prevention of diseases and insect infestation now, will keep you from a repeat of problems in next year’s garden.
A good leaf rake, given enough ‘elbow grease’, works well in getting the bulk of dead plant material out of your garden. If you experienced early or late blight or other tomato related diseases this past growing season, you want to make sure you reduce, to the best of your ability, the risk of repeating that problem again next year. Yes, there are many new varieties of vegetables available today that are ‘resistant’ to some of these diseases, but ‘resistant’ does not mean they are immune to them. You don’t want to take the chance of returning pathogens, so do a good job, cleaning and ‘sanitizing’ your garden now. Make sure, when removing the plant debris, that you totally destroy that debris so that no pathogens are left behind.
To Compost or Not! Can you compost this dead plant material and use it next spring? Information that you find from Extension offices across the U.S. will recommend that you do not. The reason being is that most people do passive composting i.e. put it in a pile, and then using what compost develops, put the compost back in the garden for the next season. It is best to burn the plant material; this will destroy the pathogens and weed seeds as well and return some carbon back into the ground when you spread it out. Please check local/state laws prior to burning. Many states and/or localities have burn bans especially this time of the year. Another method, if your local law allows it you can bag the material and send it to the landfill. Each year there are more localities that ban yard waste from their landfills. If you are not sure, check with your locality to learn more about your local waste and recycling laws.
If you do decide to go with active composting; composting at a temperature 140°F, or higher, will destroy many of the disease organisms as well as many weed seeds. You will need a temperature probe to monitor compost temperatures. It’s really not hard to source a compost thermometer either through the internet or local retail outlets such as garden centers or nursery supply stores. If in doubt about your compost pile reaching these high temperatures, it is best to side with caution and discard the material by properly bagging it or by burning based on your local ordinances.
Preventing Overwintering Pathogens Some of our most notorious insects of the garden such as Mexican bean beetle, squash vine borers, European corn borer, cabbage loopers, can also overwinter in garden debris. Larvae will use debris as a safe harbor. Flea beetles and spider mites, as well, can find food and winter shelter in spent plant material and weeds.
After you have finished cleaning up the debris from your garden, it is time to turn over the soil to both aerate and break up any remaining debris into smaller pieces that will be turned under. A good rototiller will help make this job easier. Once buried, any plant material left will decompose more rapidly.
For some pests and pathogens, turning over the soil after removing spent plant materials is recommended as the main line of defense against overpopulation next year. Consider this information from “Home and Horticultural Pests: Squash Bugs and Squash Vine Borers,” from Kansas State University,
“A vigorous autumn… rototilling can physically destroy cocoons and larvae (of the squash vine borer). Brought to the surface, cocoons and larvae are more susceptible to predation by birds and exposed to cold winter elements, leading to their demise. Deep plowing physically destroys cocoons and larvae burying them deep beneath the soil surface so pupated moths become entombed underground.”
Steps to a Healthier Garden If you haven’t done a soil test in three years or more, it is time to retest and determine the needs of your garden soils based on what you will be growing in the next season. Soil test kits and instructions are available from your local Extension Office. Also, in planning next year’s garden, rotation of your crops is a must do item. This simple action will help keep disease issues down. If your soil test(s) recommend liming, you can go ahead and put down lime this time of year, allowing it to start adjusting the pH. If the ground is frozen already, wait until spring. As you add lime, you can also help build soil structure by incorporating compost or shredded leaves. These soil additives will also add beneficial micro-nutrients and beneficial organisms. If you want to further build the soil, you may want to consider putting in a cover crop that will not only hold soil, but when tilled in early spring, will further build a healthier garden soil. A legume such as white or red clover would be something to consider. Check with your local Extension Office for best cover crop recommendations for your area.
We’ve had quite a bit of discussion this past week on the FaceBook page regarding Kelly Norris’s article in Fine Gardening on dealing with clay soils. While Kelly’s article mainly addressed selecting plants for heavy soils, there was a side-bar on cultural approaches to dealing with clays; including the standard advice to avoid adding sand to clays. This advice has been around for years. The first time I recall hearing it was from Dr. Carl Whitcomb when I took his Arboriculture class nearly 30 years ago (Fall 1984 to be exact). The rationale that is usually given is that adding sand to clay is the essentially recipe for concrete. Technically, of course, this is not entirely true since making concrete also requires cement. Nevertheless, trying to amend a clay soil with sand can lead to more problems than it solves. The fundamental issue is not that clay + sand = concrete. After all, there are plenty of highly productive soils in nature that have various ratios of sand and clay and they don’t form concrete. The bigger issue is that tilling a clay soil (which you’d have to do to incorporate added sand) leads to a loss of soil structure.
So, what is soil structure? Soil structure is a physical property of soil that describes its relatively ability to form aggregates. Unlike soil texture, which can be quantified as percent sand, silt, and clay; structure is a qualitative soil physical property. Common examples of soil structure are granular, platy or blocky.
While we usually think of clay as a negative thing (“Geez Jim, my wife just told me you have clay, I am so sorry…”); a well-structured clay soil can have excellent properties for plant growth. Well-formed clay aggregates (referred to as ‘peds’) in a granular soil can function very much like larger soil particles in terms of water movement and drainage. Soil structure is one of those things you have to experience to understand. About the best description I can come with is that peds in a well-structured granular soil often have the consistency and texture of Grape Nuts cereal.
There are also soils out there that are sometimes referred to a ‘structureless’ soils. These include single-grained soils and massive soils. Single-grained soils are essentially pure sand. In West Michigan these occur near Lake Michigan and are often called ‘blow sands’. We have several seedling nursery operations in these areas. Since there is no clay these soils have almost no nutrient-holding capacity – growers have to manage their fertility almost as it were a soilless system like a hydroponic or aeroponic system. The advantage of growing in these soils is it makes lifting bare-root seedlings easy. Massive soils, on the other hand, are very dense soils where particles do not show any evidence of aggregation. Repeated tillage can result in loss of structure and a soil (or portions of the soil) may show attributes of a massive soil including crusting or formation of hardpan. The example below shows how structure (indicated by % aggregation) is lost through repeated cultivation.
Effect of soil tillage on soil structure. Source (Greacen 1958, Australian J. Ag. Res. 9:129-137).
What can be done to improve or preserve structure? This is a case where less is often better. Natural processes such as freeze-thaw cycles and the action of earthworms and other invertebrates work to loosen soil and create aggregates. The tips in the Norris article (avoid overworking soil and adding organic matter) are essentially the same advice I would give.
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.
April is turning out to be a soggy month for most of Michigan and our surrounding states. While most homeowners are inclined to hunker down indoors and keep an eye on their sump pumps on these dark, dreary days; our current run of wet weather is a good opportunity to take a stroll around your property and make some notes. In particular, note any areas where water is accumulating.
Poor drainage is one of the most common sites factors that limit landscape tree and shrub survival and growth. Sites that retain water for more than a day or too after rains stop are especially problematic. The challenge with wet areas is we usually wait to plant trees and shrubs until things are high and dry and it’s easy to forget where the wet spots are.
There are two primary strategies for establishing healthy trees and shrubs in flood-prone spots. First, determine if the problem can be corrected. In some cases homeowners may be able to re-direct water flow from downspouts or other sources to keep water form accumulating in one spot. Again, these kinds of problems are easiest to spot if you go out when it’s raining. Re-grading the area or installing drain tiles are other options but these are usually require skills and equipment beyond the average do-it-yourselfer.
If correcting the drainage issue is not an option, the second strategy is to plant trees or shrubs that are tolerant of flooding. Plants vary widely in their tolerance of soil flooding and, not surprisingly, trees and shrubs that grow naturally along riverbanks and other low areas are usually the most tolerant.
This low spot in my yard was a good site for a Baldcypress
There are numerous resources on flood tolerant trees and shrubs on the web. Two of the better resources are from the Morton Arboretum and from Cornell University. Please note the Cornell guide is a large (>6 MB) .pdf file.
These Michigan holly (Ilex verticullata) I planted a couple of years ago a doing fine even though they are periodically flooded each spring.
Wet areas on your property do not have to be a ‘dead zone’, but establishing trees and shrubs in low laying areas takes some planning. The first step in the process is assessing your site and identifying the problem areas. The best way to do this is to put on a raincoat and take a walk in the rain.
I spent the last two weeks in Spain, combining business with pleasure. It’s interesting when something that starts out as part of the pleasure ends up being business instead.
Charlotte translated this sign for me – it’s historical information. Note the brightly colored mine tailings in the background.
My daughter is teaching English in Mazarrón, a small town in the province of Murcia. The climate there is very similar to southern California, though drier and not as warm: it’s pretty much a scrubland ecosystem. Since we both enjoy hiking, we decided to take advantage of exploring the abandoned mine sites. Unlike such sites in the United States, there are no restrictions to hikers and in fact there’s signage explaining the history of the mines. This is a popular hike after a rainstorm because of the unnaturally red pools that form in the landscape.
The abandoned mine works; these buildings are over 100 years old, though this area was mined since Roman times.
It took some Internet research to find out that lead, silver and zinc were the minerals of interest extracted from these mines. For those of you who aren’t aware of how ore processing works, it includes adding various chemicals to crushed rock to solubilize and isolate the desired minerals. The leftover tailings are nearly always highly acidic and full of environmentally available heavy metals. The various metal oxides and sulfides that formed at Mazarrón are vividly red, orange, and yellow, and there is a pervasive sulfur smell throughout the site. If this isn’t hell on earth, I don’t know what is.
Mountains of mine tailings
So it was really quite a shock to both of us that not only could we walk into this mine site, but that there were no warnings regarding exposure to whatever toxic chemicals might be in the soil and water. We took pains not to touch anything – but others were not so cautious. Some hikers ahead of us watched their dog cavort through the largest of the pools, and later took photos of each other on the mine tailing spoils.
Visitors and dog and red pool of ????
Yes, the dog went in the water
And then a photo op on the side of Spoils Summit
This hideously beautiful landscape was unearthly, primarily because there was absolutely nothing alive in it. No plants, no insects, no birds. Along the edges of the mine tailings there were spring flowering shrubs, bees, and birds, just as one would find elsewhere in the region. (But not in the spoils. What an apt name…)
A blood-red seep into the pond
Crystals forming as water dries in the pools
Just off the side of the tailings, life continues
How do the mines of Mazarrón fit into gardening? Unlike this mine site, where the evidence of heavy metal contamination was clearly visible, it’s not so obvious in our garden soils. The residues of arsenic-containing pesticides, leaded gas, zinc from car tire wear, and other possible contaminants are unseen and unknown unless we have soil tests done to confirm their presence or absence. Yes, it can be expensive to have these tests done, but if we are handling our soils, breathing the dust, and eating the plants that grow there, wouldn’t it be smart to find out what’s there first?
Longtime reader Ray Eckhart sent me a NYT story on urban chicken eggs and lead contamination. As I’ve mentioned before on this blog, urban gardeners should have their soils tested for lead, arsenic, and other commonly found heavy metals before they plant edibles. Chickens that are allowed to peck and scratch in metal-contaminated soils will pass that unwanted load on to you via their eggs.
So test your soils! It costs a bit of money, but then you know exactly what’s lurking in there. If your soils have significantly high levels of lead or other contaminants, you can still raise chickens as long as they don’t roam your garden.