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Scorched Earth – Soil Rx
September 1, 2022 – Tery Susman, UC Master Gardener of Mariposa County – Wildfires can create immediate and potentially long-term soil erosion. However, there are a number of ways to mitigate this 
post-fire concern.
Adapted from the California Native Plant Society Fire Recovery Guide: https://www.cnps.org/give/priority-initiatives/fire-recovery.
- Leave the mess; keep it under cover. Much needed soil protection is provided by what the fire left behind. Ash, debris, fallen heat damaged leaves as well as the charred remains of plants can protect the land from wind and water erosion.
If a fire has burned so severely that no material is left on the ground, patches of soil form a crust and become hydroponic (water repellent), increasing runoff. This might necessitate applying chips, mulch from dead debris or straw.
Spreading mulch is the most effective erosion control treatment because it provides what the fire and heavy equipment removed – ground cover! This ground cover allows water to infiltrate the soil instead of running off and eroding it.
Prune or remove only high hazard fire-damaged trees near buildings and roads. Keep felled trees and pruning on-site. These trees can be a source of mulch.
- Minimize soil compaction. Keep foot traffic and equipment off burned landscape. Activity on slopes increases erosion weakening soil’s bonds, dislodging soil particles, and trampling newly sprouted plants. Activity on flat ground can compact the soil and lower its water absorption rates, which increases runoff.
- Successful Strategies:
Spread: a mulch application. Straw mulch has high efficacy in reducing rainwater runoff, soil erosion, and downstream sedimentation. Use loose barley or wheat straw because it is longer lasting. Rice straw is less expensive. Use when the straw doesn’t need to last as long. Use straw mulch in “free form”, no more than 2-3 inches deep. Mulch in 6-10 foot strips along contour, spaced at 50-100 foot intervals, depending on the steepness of the slope.
Use wood mulch from local materials, including burned trees, shredded debris, or thinned, unburned trees ,wattles, mulch, rocks, and branches can slow down and disperse the runoff, limiting erosion and sediment.
Use straw wattles to shorten slope length. They are designed for short slopes or slopes flatter than 3:1 and low surface flows. For more information on the proper wattle installation go to: https://ucanr.edu/sites/postfire/files/247999.pdf.
Sink: Place rocks, gravel, or crushed rock in areas of high traffic.
Share: Work with neighbors to create a plan to slow runoff. In disturbed areas of moderate to high fire intensity, a neighborhood plan can be critical in preventing sediment and fire debris from washing into sensitive creek habitats and contributing to flooding.
- Seek advice: There are many professionals available to assist with on-site fire damage. If you are concerned that your property may be at risk from flooding or debris flow, reach out to these organizations:
Natural Resources Conservation Services – www.nrcs.usda.gov/wps/portal/nrcs/site/ca/home, call (209) 966-3431
CAL Fire – www.fire.ca.gov (209) 966-3622
Recovering from a wildfire can be a daunting process. Be patient with yourself and with nature. Do what you can, ask for help, and know that our community is STRONG!
Next: Give Trees a Chance – Ecosystem Resilience
Photo Credit: Maxwell Rygiol, from 2017 Detwiler Fire
Photo Credit: Maxwell Rygiol, from 2017 Detwiler Fire
For assistance, contact our Helpline at (209) 966-7078 or at mgmariposa@ucdavis.edu. We are currently unable to take samples or meet with you in person but welcome pictures.
The U.C. Master Gardener Helpline is staffed; Tuesdays from 9:00 A.M. – 12:00 P.M. and Thursdays from 2:00 P.M. – 5:00 P.M.
Clients may bring samples to the Agricultural Extension Office located at the Mariposa Fairgrounds, but the Master Gardener office is not open to the public. We will not be doing home visits this year due to UCANR restrictions.
Serving Mariposa County, including Greeley Hill, Coulterville, and Don Pedro
Please contact the helpline, or leave a message by phone at: (209) 966-7078
By email (send photos and questions for researched answers) to: mgmariposa@ucdavis.edu
For further gardening information and event announcements, please visit: UCMG website: https://cemariposa.ucanr.edu/Master_Gardener
Follow us on Facebook at: https://www.facebook.com/mariposamastergardeners
Master Gardener Office Location:
UC Cooperative Extension Office,
5009 Fairgrounds Road
Mariposa, CA 95338
Phone: (209) 966-2417
Email: mgmariposa@ucdavis.edu
Website: http://cemariposa.ucanr.edu/Master_Gardener
Visit the YouTube channel at UCCE Mariposa.