Answers to Post-Fire Questions

Following the October 2017 Wildfires

Most Asked Questions at the Sonoma Master Gardeners Help Desk

The 40-plus questions received at the Sonoma Master Gardeners help desk can be grouped into five areas. They are:

Is produce affected by smoke or ash safe to eat?

When in doubt, throw it out. It is best to be cautious of consuming smoke-exposed produce.

There is a difference between smoke from building fires and vegetation fires. Smoke from homes is possibly contaminated with pyrolysis products from plastics, paint, and other building materials. Produce contaminated with this kind of smoke is at risk.

Leafy vegetables can absorb smoke contamination and may not be washable.

Fruit such as citrus and pomegranates can be washed; first with a dish soap solution to remove oily/waxy deposits, and then soaked 15 minutes in a bleach solution (1 tbs. bleach per gallon water), then rinsed with water and dried.

Smoke taint can affect the taste of wine made from contaminated grapes. Grapes can be washed on the vine with a diluted dish soap spray, then rinsed in water and allowed to dry before harvest. Washing picked grapes can result in grape juice loss and possible soap contamination. There are some wine-making techniques to reduce smoke taint such as fining (a process of clarifying or removing undesirable components from wine) with Bentonite clay, but smoke complexes in the wine may re-release the taint with time.

Reference: Researching Post-Wildfire Produce Safety, UCCE Sonoma.
https://ucanr.edu/blogs/ blogcore/postdetail.cfm? postnum=25509
Does ash contaminate food garden soil and can it be tested?

Soil microorganisms may reduce soil contamination with time and repair soil from smoke or ash. But, following very hot urban firestorms, surface layers of soil may experience near to total sterilization of soil. This phenomenon has been the subject of considerable scientific study; for more information see https://forest.moscowfsl. wsu.edu/smp/solo/documents/ GTRs/INT_280/Hungerford_INT- 280.php.

Before working with possibly contaminated soil, protect yourself by wearing a close-fitting respirator mask that is rated N-95 or P-100 to block particles from ash or smoke from being inhaled, as well as other protective gear. First, remove any ash from food garden beds; it is usually on the surface. Dispose of ash in a municipal waste container. Next, spread two to four inches of compost over the bed. Water in if soil is dry. If no rain is expected, you can use a metal tine to rake the compost lightly into the top few inches of soil. During winter and early spring mulch the bed or plant a non-food cover crop. If you suspect soil contamination from structural fires, remove the contaminated soil and replace it with fresh planting mix or compost.

For a full description of health and safety issues and precautions please read Managing Your Property After the Wildfires

Potentially contaminated soil or food products grown from this soil can be tested for contaminants. A list of approved labs is shown at: http://ccmg.ucanr.edu/files/51308.pdf.

When should you remove fire-damaged trees and can you get assistance in replanting?

Fire-damaged trees on private property should be assessed to determine if they will recover or need to be removed due to structural integrity issues. Large trees of value to the homeowner should be assessed by a certified arborist. Fire-damaged trees that may pose a danger to structures, roads, or pedestrian paths should be removed. A guide to replanting can be found by downloading the pdf file available at Recovering from Wildfire: A Guide for California's Forest Landowners. For landowner assistance go to Cal Fire article: http://readyforwildfire.org/Landowner-Assistance-O/. Or, contact Cal Fire Northern Region at: 707 967-1400, or Forest Assistance Specialist in Sonoma County: Meghan Reeves, 707 888-7331.
Is there a list of fire resistant plants?

Developing a fire resistant landscape first depends on a defensible space layout where trees and shrubs are spaced apart to prevent a continuous fire pathway. Plant layout must also be designed to prevent a fire ladder from spreading fire to the home. Lower tree branches should be trimmed a minimum of six feet up, and tall shrubs should not be planted under trees.

Plant List
Fire resistant plants are low growing, have high moisture, and have stems and leaves that are not resinous, oily, or waxy. Deciduous trees are more fire resistant than evergreens. A list of “fire wise” plants for Sonoma can be found at http://firesafesonoma.org. Download the Homeowner’s Guide.

Plants to avoid because they are fire-prone include ornamental grasses and berry plants, which can be highly flammable. Invasive plants such as broom, ivy, pampas grass, as well as trees of heaven (Ailanthus altissima), eucalyptus, and Acacia should be avoided, along with natives that spread quickly and are fire-prone, such as Douglas Fir and Monterey pine.

Reference: Living with Fire in Sonoma County / A Guide for the Homeowner
How is the water quality affected after a wildfire?

Wildfires can compromise water quality during active burning and for months afterwards. Ash can settle in open ponds or reservoirs. After a fire, burned areas are prone to erosion, increasing sediment and possible contamination. Steps should be taken to protect pond water from erosion runoff using wattles, sandbags, or berms.

Depending on whether the water will be used for agriculture or drinking, it should be run through the relevant quality test. This testing can be performed at the UC Davis Analytical Laboratory (530 752-0147). Laboratories certified by the Sonoma County Department of Health Services are listed at: http://sonomacounty.ca.gov/Health/Environmental-Health/Water-Quality/Water-Testing/

Reference: Addressing the Impacts of Wildfire on Water Resources.

Chapter 1 of our fire series can be found here.

Dennis Przybycien / Sonoma County Master Gardener