- Author: Jeannette E. Warnert
A summer of smoke and ash in many parts of California has raised questions about the safety of produce growing on farms and in the garden, eggs laid by chickens who peck around in ash-laden areas, and remediation needed to safely and effectively grow food in the future.
UC Agriculture and Natural Resources brought together experts who have researched the effects of previous fires' fallout and studied soil contaminants to share their insight in a two-hour webinar now available on YouTube.
“The No. 1 health concern during a fire is smoke inhalation, and it's been well documented that wildfire smoke can negatively impact both the heart and the lungs,” said Claire O'Brien, a pharmacology and toxicology doctoral student at UC Davis. “However, the chemicals found in the smoke don't just stay in the air. They can deposit onto plants and into soil and water.”
Although every fire is unique, some generalizations can be drawn from research conducted following previous fires. UC Cooperative Extension food systems advisor Julia Van Soelen Kim detailed a study conducted following the October 2017 wildfires in Sonoma County and across the North Bay.
With the help of UC Master Gardener and community volunteers, the researchers collected over 200 samples of homegrown collard greens, lettuces, kale and chard that were exposed to wildfire smoke and ash. A subset of the samples were analyzed by a private laboratory.
“There was very low concern about chemicals on produce,” Van Soelen Kim said. “No samples had detectable levels of lead, arsenic, mercury or chromium. And that's a huge sigh of relief.” However, analytical results vary by site, site history and by fire event, and few have pre-fire baseline data to compare with.
Van Soelen Kim said basic food-safety practices should be followed when preparing to eat food grown in a home garden, regardless of ash or smoke contamination.
“You should always wash your hands before and after harvesting, and wash your produce in running water to mitigate any kind of potential risk,” she said.
Are backyard chicken eggs safe to eat?
Another study outlined at the webinar used a similar process to determine whether there might be contaminants in the eggs laid by backyard poultry that live and feed in areas exposed to wildfire ash and smoke.
Scientists know from previous research that chickens exposed to lead in their environment can produce eggs with high lead content and that heavy metal content of ash from urban wildfires is higher than from rural wildfire.
“We combined those two pieces of research with what we know that chickens do all day: they peck at the ground for hours on end,” said Todd Kelman, a veterinarian in the School of Veterinary Medicine at UC Davis. “That makes for a pretty good hypothesis that urban wildfire could pose a risk for the production of eggs and poultry that contain heavy metals.”
Kelman and his team put out a call for eggs from backyard poultry and received samples from 344 premises in fire-affected and non-fire-affected areas of California.
Surprisingly, egg samples that contained higher lead levels came from parts of the state that were not directly impacted by ash and smoke.
“Did our data support our hypothesis that proximity to urban wildfire is a driving source for lead in eggs of backyard poultry? The answer is not so much,” Kelman said. “So, is it safe to eat eggs from your backyard poultry? We can't give you a definitive answer to that question. But we do suggest you assess your risk and reduce the risk of contamination.”
Practices that reduce the risk include keeping chickens off the ground, using a chicken feeder that prevents spillage onto the ground and making calcium readily available, for example in the form of oyster shells, because calcium can prevent the absorption of lead. Making sure that chickens are provided uncontaminated water is also an important part of risk reduction.
For confirmation on the safety backyard chickens and their eggs, lab tests for eggs are available for $60 from the California Animal Health and Food Safety Laboratory at UC Davis, or chickens may be submitted to CAHFS for necropsy.
Are soils safe for growing food after a fire?
Fire effects on soil is another consideration in burned areas, said UC Cooperative Extension urban agriculture advisor Rob Bennaton.
“Fires heat topsoil layers. They reduce the amount of living micro-organisms at the site of the burn, and also affect organic matter and nutrients. Ash deposits over time may make soils more alkaline,” he said. “As a result of these combined factors, there are temporary changes in nutrient levels and the capacity for soils to exchange nutrients for optimal plant growth and nutrition.”
With proper land care and management, soils can be remediated over time.
“It won't happen overnight. Soils were developed over millions of years,” he said.
Some ways to improve safety when gardening in fire-affected areas including keeping the soil covered with wood chips or other landscape mulch to reduce airborne soil dust. Use drip irrigation to prevent up splash onto the undersides of growing vegetables. Promote good drainage, especially at the bottom of slopes to prevent the concentration of contaminants.
Lab tests are often needed to determine the soils' post-fire characteristics. “Don't guess, but test,” Bennaton said.
The UC Master Gardener Program can provide technical assistance to help home gardeners find resources for home soil testing, he said.
Additional resources and information shared during the webinar include:
Post-fire soil resources and soil testing information
- UCCE publication on Soils in Urban Agriculture with soil testing & sampling information
- The UC ANR Healthy Soils Website, which has many resources worth reviewing.
- Tips for Interpreting Soil Analysis
- UC Master Gardener of Sonoma County 2018 workshop video “Effects of fire on soil”
Post-fire food safety
- Research on produce safety and backyard chicken egg safety after the 2017 wildfires in California is available on this web page. To view a past webinar recording with these research findings, click this link.
- Poultry wildfire resources from the UC Davis School of Veterinary Medicine:
- Best Practices for Produce Safety After Fire
- Understanding Risk: A community guide for assessing the potential health impacts of locally grown produce exposed to urban wildfire smoke
Firewise and sustainable home landscaping design in the defensible space zone
- Visit the UC Master Gardener Program of Sonoma County firewise landscaping web page.
- For a recent firewise & sustainable design and maintenance video by the Resilient Landscapes Coalition.
Impact of smoke & ash on plants
Urban Agriculture Soil Information
Without understanding the actual links between UA and food security or which specific characteristics, models or approaches reduce insecurity, urban policymakers and advocates risk backing policies that could have unintended consequences or negative impacts on vulnerable individuals and communities. We argue that in addition to more robust analyses that measure the actual social, economic, and health impacts of urban agriculture, and how they impact food security, it is important to understand which approaches to policy, governance and civic engagement support UA models that are effective in reducing food insecurity.
In general, we see three trends in current scholarship on UA in relation to community food security: (1) a focus on the production potential of urban lands, (2) individual case studies highlighting various nutritional, health, and other community benefits or outcomes from urban gardening initiatives, and (3) more critical analyses of UA through food justice and equity lenses. To this latter point, robust theoretical analyses have emerged critiquing the risks of UA when approached without an equity lens, potentially reinforcing structural injustices and racism and negatively impacting communities that ideally should benefit the most.
Deeper historical and structural challenges including poverty, racism, and divestment in specific communities and neighborhoods are increasingly being recognized as the root causes of the problem of unequal access to sufficient supplies of safe, nutritious, affordable, and culturally acceptable food facing cities. Designating land for agricultural use in urban areas may conflict with other city planning priorities around affordable housing, community economic development, or smart growth approaches associated with reducing urban sprawl and mitigating climate change, such as transit-oriented development. Because of the persistent legacy of systemic discrimination, it is neither inevitable nor guaranteed that urban agriculture will redress food system inequities; in fact, urban farms can sometimes lead to displacement through eco-gentrification. This is a particularly acute concern in areas experiencing housing pressures and population growth, such as the San Francisco Bay area and New York City.
Analyzing the intersection of food access and food distribution literatures reveals three key factors mediating the effect of UA on food security in the urban food system:
(1) the economic viability of urban farms (to sustain the provisioning of affordable urban produced foods)
(2) the role of city planning and policies in advancing racial equity through UA such as secure land tenure and public investment, and
(3) the importance of civic engagement to advocate for and hold cities and counties accountable to the needs of low-income communities.
We highlight examples from both the scholarly and gray literatures that demonstrate how UA can improve food access, distribution, and justice, in a way that supports both consumers and producers of food in cities. The gray literature in particular reveals many emerging and informal distribution networks for urban produced foods that would benefit from further academic study, such as gleaning networks, distribution apps, and online platforms.
The review concludes with a set of recommendations for researchers, practitioners, and policymakers who seek to create spaces in cities for food justice, equity, access, and sovereignty. Most notably we acknowledge that urban farms are producing a lot more than food; and that equitable planning, public investment and civic engagement are crucial elements in securing the long-term viability of urban farms. More robust analyses documenting the multifaceted benefits and risks of UA such as public health, food security, youth development, food literacy, eco-gentrification and environmental justice can help inform more equitable public policy and planning efforts.
Flowering insectaries also provide food for bees and other pollinators. There are both greater numbers and more kinds of native bees in fields with an insectary consisting of a row of native shrubs planted along the field edge (called a hedgerow). Native bees also stay in fields with these shrubs longer than they do in fields without them. Therefore, not only do insectaries attract natural enemies, but they can also boost crop pollination and help keep bees healthy.
- Flower flies (Syrphidae) and other biological control agents for aphids in vegetable crops. (PDF)
- Good news for hedgerows: no effects on food safety in the field.
- Hedgerow benefits align with food production and sustainability goals.
- Habitat restoration promotes pollinator persistence and colonization in intensively managed agriculture. (PDF)
- Reducing the abundance of leafhoppers and thrips in a northern California organic vineyard through maintenance of full season floral diversity with summer cover crops.
- Author: Stephanie Parreira, UC Statewide IPM Program
To read the full transcript of the audio, click here.
Successful IPM in honey bee colonies involves understanding honey bee pest biology, regularly monitoring for pests, and using a combination of different methods to control their damage. Visit these resources for more information:
Sources for the Value of Honey Bees:
- Author: Reyna Yagi
Reyna Yagi (firstname.lastname@example.org), Northern California Urban Agriculture Program Coordinator, University of California Cooperative Extension - Alameda and Contra Costa Counties
How can we as urban farmers do our part to conserve water? Turns out there are a lot of ways that not only will help to save our beautiful state's water, but also help you build a healthier farm or garden with less work on your hands!
Rainwater Harvesting allows you to capture rainwater from roofs, collect it in a cistern for diversion to your landscape for supplemental irrigation. You should also observe your site's water runoff patterns and see how you can manage and maximize your runoff to deal with large rain events, stormwater runoff and infiltration around your site. Consider a rain garden!
- Dry Farming depends on the water stored in the soil from winter rains that plants can use in the spring as the weather warms. Plants rely on good soil moisture and deep roots to seek out this extra water without needing much supplemental irrigation. Grapes, potatoes, tomatoes, winter squash, fruit trees and grains can be dry-farmed.
- Deep watering wets entire root zones which promotes deeper root growth.
- Always water early in the morning to prevent daytime water loss through evaporation.
- Keep an eye on the weather! A refreshing rain or cool, cloudy day will extend the time between watering.
- Maintenance, maintenance, maintenance. Visually inspect your drip system regularly for breaks, leaks and missing pieces. If you don't, your plants will certainly let you know with plant diseases.
California's agricultural industry is the largest in the nation and abroad, carrying with that a great responsibility to protect and conserve our resources. Urban farmers are highly cognizant of this. They are some of the most innovative and conservation-minded folks out there who understand the fragility of our water supply and their role in being model stewards of our lands and waters.