Shrubs

Bottom line

Shrubs can carry low intensity ground fires into trees or expose nearby windows, siding, and vents to embers, radiant heat, and/or direct flame contact. Remove shrubs within five feet of structures and create separation between shrubs and trees located 5-30 feet from structures.

Overview

Shrubs can carry low intensity ground fires into trees or expose nearby windows, siding, and vents to embers, radiant heat, and/or direct flame contact.

All shrubs are combustible regardless whether they are irrigated, and shrubs that produce fragrant volatile organic compounds like rosemary, lavender, junipers, oleander, and cypresses are particularly hazardous because the oils they produce are highly combustible. They also tend to generate more debris and/or retain dead needles or bark within their structure. When exposed to heat and embers, this material can quickly ignite.

Definition

There is no botanical definition of a shrub. Many plant species contain the genes that enable them to grow in a way that we would describe as a shrub or a tree.

Wildfire Prepared Home defines a shrub as any herbaceous plant or woody plant whose combined stems are less than four inches in diameter when measured at 4.5 feet above the upward slope (also known in forestry as diameter at breast height or DBH).

Attributes

Dead/Dying

Any dead or dying plants and shrubs need to be removed from the property. Dormant plants are not dead or dying.

Shrub height

Height of the shrub. This determines the potential flame lengths if the shrub were to ignite and determine which other features of a structure or property would potentially be exposed to direct flame.

Horizontal canopy spread

The maximum distance from the outermost portions of an individual shrub or a group of shrubs.

Canopy separation distance

The minimum distance from the outermost portion of an individual shrub's or group of shrubs' canopy to the next nearest shrub's, group of shrubs', or tree's canopy.

Zone Zero (0 - 5 feet from structures)

Shrubs should be removed within five feet of structures and are increasingly required to be removed by standards like Wildfire Prepared Home and a forthcoming Zone Zero regulation being developed by the California Board of Forestry.

Zone 1 (5-30 feet from structures or to the property line)

Wildfire Prepared Home

As we move into Zone 1 (5-30 feet from structures), different standards require different management of landscaping. The Wildfire Prepared Home program allows for groups of shrubs no greater than 10 feet in canopy spread from tip to tip and with 10 feet of separation between shrub (and shrub group) canopies.

California

PRC 4290 and 4291 apply to the State Responsibility Area and certain portions of Local Responsibility Areas and requires that individual shrubs and groups of shrubs be separated by at least two times the height of the tallest shrub.

Zone 2 (30-100 feet from structures or the property line)

Wildfire Prepared Home

Does not have any requirements for vegetation beyond 30 feet from structures or the property line.