A number of readers have inquired as to the status of garden soil or landscaped ground following a fire.

Burnt soil has obviously lost any mulch that had been present, as well as the layer of decomposing organic material or humus just below it. Microbial soil life, from aerobic bacteria to symbiotic mycorrhizae, has also been destroyed. Thus, soil fertility has been lost. In order to correct the deficiencies wrought by fire, copious inputs of compost are a prerequisite for bringing soil back to health.

Another issue concerns ash. If ash covers foliage, it can inhibit photosynthesis, stunting growth, and should immediately be rinsed off with a hose. Ash also elevates soil pH, a problem for us since our soil leans in an alkaline direction, and most plants — vegetables, fruit trees, many ornamentals and even California natives — grow best in a slightly acidic pH. Ash may also contain toxic compounds if it comes from incinerated plastic, asbestos, or other hazardous material. If we are talking about wood ash that derives from trees and other vegetation, it will contain up to 50% calcium, an element that increases pH, although beneficial elements such as phosphorus, magnesium and potassium will also be present, as well as certain micronutrients such as zinc and molybdenum. Ash will also absorb rainfall; if rain is light, the elements in ash will be washed into the earth, where they will eventually be taken up by plant roots, but if the rain is heavy, it can carry ash away along with any minerals dissolved from it before they can be incorporated into the soil.

If you see weeds coming up in your garden or denuded slope, leave them alone until the rainy season ends. Where an intense fire burns the earth, roots are consumed along with above-ground vegetation. Should heavy rain then occur, mudslides result, since there are no roots holding the soil together. For immediate erosion control on bare slopes, biodegradable coconut blankets are an excellent mudslide preventive measure. You can find them at sandbaggy.com and other sites. Hay netting bulk rolls, available through gutzbusta.com, serve a similar purpose.

Patricia McGrath, who gardens in Silver Lake, wrote me with reports on the efficacy of fire-retardant gel in protecting buildings and plants. Barricade II Fire Blocking Gel is such a product. Its usefulness, however, is limited to approaching fires since it offers protection on the surfaces of structures and vegetation for no more than 36 hours. Such a gel proved itself in a fire of record intensity that swept through the Black Hills National Forest near Custer, South Dakota. Houses sprayed with fire retardant gel were untouched, while several dozen houses nearby that went unsprayed burned to the ground.

“Seed banks” are the means by which certain plants regenerate after a fire. Cones of certain pines and cypresses, for example, are serotinous, meaning they act as seed banks awaiting an environmental event — in their case fire — to open. The soil also serves as a seed bank for plants such as the endangered Refugio manzanita. In fact, fire is essential to the germination of its seeds so that if their viability expires and then a fire comes along and incinerates the mature plants, that could spell this species’ extinction in the area where the fire occurred. While mulching bare, fire-scorched soil is generally recommended, it should not be more than 2-3 inches deep where native plants have grown, since their seeds may not sprout when buried under a thick layer of mulch. Some plants, however, including certain manzanitas (Arctostaphylos species), coast live oak (Quercus agrifolia) and toyon (Heteromeles arbutifolia), will often resprout from their crowns (where trunk meets roots) after a fire.

Trees burned in a fire should be treated with special care. As long as the tree appears structurally stable, it is advisable to wait three years before considering its removal. Even though it may appear to be dead, there is a chance it is still alive and will regrow. This is especially true if the bark of the tree is intact, even if only at the base of the trunk. Many oak species have thick bark that protects the inner cambium layer, from which new growth occurs. This growth produces xylem cells to the outside and phloem cells to the inside; xylem conducts water and minerals from the roots up into the tree branches and leaves, while phloem conducts sugar made in leaves in the opposite direction.

It must also be noted that dead trees themselves are valuable when it comes to wildlife preservation. More than 80 species of birds depend on dead trees, known as snags, for their sustenance, especially when it comes to satisfying their appetite for insects. Many mammals and reptiles also rely on snags for hunting and nesting.

Soil disturbance on slopes should be kept to a minimum in order to allow native vegetation to regrow. Disturbed soil can invite invasive plants, including certain invasive California natives. Reseeding of plants native to a burned area is sensible, but avoid planting seeds where the slope is greater than 35%, since they are likely to wash away in the rain.

For a complete discussion of how to restore garden soil and slopes that have been burned in a wildfire, see the “Fire Recovery Guide” published by the California Native Plant Society, available at cnps.org.

Does anyone have experience with restoring a burned area, whether in the wilderness or around your home? If so, you are invited to share your story in an email to joshua@perfectplants.com. Your questions, comments, gardening conundrums and successes are always welcome.