Las Pilitas Nursery

California Native Plants are all we grow!

Blog Contact Us Directions

3232 Las Pilitas Rd
Santa Margarita, CA 93453
Fri. & Sat. from 9am-4pm
8331 Nelson Way
Escondido, CA 92026
Tues. to Sat. from 9am-4pm

Shop For Plants Cart Contents

This website is dedicated to Bert Wilson. His genius continues to inspire us.

Leaf burn times of California native plants (& Several Non-Native Plants)

California Plants and Fire

In a two week period of September of 2005, temperatures were in the 90's and the humidity was about 30%. Individual leaves, or leaf clusters, of similar size, of various plant species, were tested for ignition times until two numbers were  within a few seconds. If after five tries, numbers were still divergent, numbers were either listed as a range or averaged if all over the place. Most plants tested were field grown and had not been watered all summer (exceptions noted in table below). Every effort was made to duplicate  a very dry coastal garden under water rationing.

Garden watered plants should be considerably harder to ignite if watered as little as fifteen minutes once every two weeks, BUT, not always. However, the worst fires I've seen are at the end of a drought cycle when there is no water to even fight the fire, never mind water the plants.

Field tests of experimental crown fires revealed that wooden walls can successfully survive intense flame fronts from as close as approximately  30 feet  away.
Most structures are lost because of firebrands, (debris on fire that is falling from the sky). (Cohen, 1995)

If you live in town and have a twenty foot front yard, ignore this list. This is primarily for those of you in rural residential areas, at the worst with a poor well, thirty minutes from the nearest fire engine and are gone a lot. The designers that are planning an urban interface should find this useful also.

Using a propane torch with a one centimeter length flame (+/- 1mm), the blue tip of flame was placed on to a leaf, if leaves large, or first leaf cluster if leaves small, until the leaves ignited and held a flame longer than five seconds. Some leaves would flash. If they held a flame or carried to other leaves that was counted. Some blacked and never ignited, some never even glowed, and others ignited easily. At first the tests were done on the plants themselves, but that proved too exciting and the slightest breeze altered the results (and had potential for even more excitement). I settled on collecting a few stems of a few plants and testing those in a closed barn within minutes of collection. Results were not what I'd had heard or read, and often not what I expected. Generally, (and boy are there inconsistencies,) the more drought tolerant the plant, the poorer it burns, the smaller the leaf, the poorer it burns, and the wider spaced leaves are very hard to ignite. For the most part, unwatered natives did better than watered non-natives.
Good mulch is an important component of California's gardens/landscapes and ecology. The moisture that mulch retains helps keep the plant material hydrated and a little less flammable. Mulch (shredded redwood bark or shredded cedar bark) does burn, and creeps along with a smoldering fire that can be kicked or raked out. This type of mulch burns with a lot of smoke,and  little flame. A pile of dead leaves, twigs and sticks does not burn in the same way. Think of the comparison of a newspaper laid flat on the ground versus each page wadded up into a pile. The worst situation is when you have flashy fuels like dead grass running up into either taller weeds, dead leaves of garden plants or some of the native plants.

This experiment really points out that weed control and garden hygiene are as important, or more important, than plant choice or irrigation practices.

This is how the flame test was applied. 1 cm. from leaf, time when the leaf will sustain flame without torch. - grid24_6
Flame applied to leaf. Notice it is not bursting into flame.
One of the burnt leaves after the test. - grid24_6
Many of the leaves never even glowed.
If after sixty seconds the plant didn't light, that's amazing. Bushes that burnt after 15-30 seconds are about as flammable as your home.
Some of the Ceanothus should be considered heat shields.

Genus

Species

Variety

Cultivar

live ignition (seconds)

dead leaf ignition (seconds)

notes

Abies

bracteata



>60



Acacia

greggii



>60


one weak flash

Acer

circinatum



15



Acer

macrophyllum



>60



Acer

negundo

californicum


30

1


Achillea

millefolium

californica


5

1

six inch flame height

Achillea

millefolium

rosea

Island Pink

>60

1


Adenostoma

fasciculatum



30


dried seed heads -1 second.

Adiantum

jordanii



>60



Aesculus

californica



>60



Agrostis

pallens



>60


a lot of dead grass, but the green leaves extinguished the dead ones

Alnus

rhombifolia



15



Ambrosia

psilostachya



>60



Anaphalis

margaritacea



>60



Anemopsis

californica



>60


leaves develop water blisters

Aquilegia

eximia



no fuel



Aquilegia

formosa



no fuel



Aquilegia

pubescens



no fuel



Aquilegia

shockleyi



no fuel



Arbutus

menziesii



>60

15


Manzanitas are all over the chart and do not appear to change when watered.

Arctostaphylos



Baby Bear Manzanita Bush

>60



Arctostaphylos



Ian Bush Manzanita

10


watered ones were also 10

Arctostaphylos



John Dourley

45


watered sample

Arctostaphylos



Mama Bear Manzanita

7



Arctostaphylos



Margarita Pearl

30



Arctostaphylos



Pacific Mist

30



Arctostaphylos
crustacea
eastwoodiana

10-20


Arctostaphylos

densiflora


Harmony Manzanita

>60



Arctostaphylos

densiflora


Howard McMinn Manzanita

15


watered sample was 30

Arctostaphylos

densiflora


Sentinel Manzanita

>60



Arctostaphylos

edmundsii


Big Sur Manzanita

20



Arctostaphylos

edmundsii


Carmel Sur Manzanita

30



Arctostaphylos

glandulosa

adamsii


5



Arctostaphylos

glandulosa

glandulosa


10



Arctostaphylos

glandulosa

ssp.crassifolia

Del Mar Manzanita

>60



Arctostaphylos

glandulosa

zacaensis

San Marcos Manzanita

10



Arctostaphylos

glauca



20



Arctostaphylos

glauca


Ramona Manzanita

50



Arctostaphylos

hookeri


Wayside Manzanita

>60


watered sample

Arctostaphylos

hookeri

franciscana

Franciscana Manzanita

7


extreme drought -7 secs. watered- 7 secs., but it sure looks better

Arctostaphylos

hookerii X pajaroensis


Sunset Manzanita

>60



Arctostaphylos

insularis



7



Arctostaphylos

manzanita


Dr. Hurd Manzanita Tree

15



Arctostaphylos

manzanita


Real manzanita

>60


watered sample

Arctostaphylos

manzanita_x_densiflora


Austin Griffiths Manzanita

45


watered plants easier to ignite than dry land ones?

Arctostaphylos

mariposa



>60


even charcoal wouldn't ignite after 90 secs.

Arctostaphylos

morroensis


Park View Manzanita

12



Arctostaphylos

obispoensis


San Luis Obispo Manzanita

15

3


Arctostaphylos

pajaroensis


Paradise Manzanita

7



Arctostaphylos

parryana


Snow Lodge Manzanita

20

1


Arctostaphylos

patula



12



Arctostaphylos

pechoensis



5



Arctostaphylos

pilosula

pilosula

Atascadero Manzanita

5



Arctostaphylos

pungens



30



Arctostaphylos

purissima


Burton Mesa Groundcover

15



Arctostaphylos

refugioensis


Refugio Manzanita

15

1


Arctostaphylos

rudis



7



Arctostaphylos

silvicola


Ghostly Manzanita

12



Arctostaphylos

standfordiana



10



Arctostaphylos

stanfordiana

bakeri

Louis Edmunds Manzanita

15



Arctostaphylos

uva-ursi


Point Reyes Manzanita

>60


watered sample

Arctostaphylos

uva-ursi


Radiant Manzanita

15


watered sample

Arctostaphylos

uva-ursi

suborbiculata

San Bruno

>60


watered sample

Arctostaphylos

viridissima



>60



Arctostaphylos

viscida

ssp. viscida


15


regularly watered sample- 15 secs.

Arctostaphylos

wellsii


Wells Manzanita

20



Argemone

munita






Aristolochia

californica


Sierra Giant Pipe Vine

>60



Artemisia

californica



>60

1

'melted' down to dead/dry leaves then burned after 60 secs.

Artemisia

californica

Canyon Gray

Canyon Grey

>60

1


Artemisia

californicaX

Montara

Montara

>60

1

dead material difficult to extinguish

Artemisia

douglasiana



15



Artemisia

ludoviciana

ludoviciana


>60

10


Artemisia

tridentata



>60


watered sample - >60 secs.

Asclepias

eriocarpa



>60



Asclepias

fascicularis



>60



Asclepias

speciosa



55

3

no flame after 5 secs., had to work to light

Aster

ascendens



>60


one ignited at 45 secs.

Atriplex

canescens



>60



Atriplex

lentiformis

Breweri


>60



Baccharis

douglasii



>60


will not sustain flame

Baccharis

pilularis

consanguinea


25


varied from 12 to >60 secs. on very old plant

Baccharis

pilularis

pilularis

Pigeon Point

>60


used dry, unwatered plant

Baccharis

pilularis

pilularis

Santa Ana

>60



Baccharis

pilularis

pilularis

Twin Peaks




Baccharis

viminea



>60



Brickellia

californica



>60

1

if leaves clustered, can be burnt

Calliandra

eriophylla






Calycanthus

occidentalis



>60

>60

will not stay lit

Camissonia

cheiranthifolia

ssp. suffruticosa


>60



Carex

globosa



>60



Carex

praegracilis



15


summer deciduous

Carex

sartwelliana



>60



Carex

spissa



>60



Carpenteria

californica



>50


one in four tries was able to get leaf to burn

Ceanothus species are relatively hard to burn and respond well to light overhead watering once every two weeks. A dust- off once every two weeks makes them really hard to burn.

Ceanothus



Blue Jeans

>60



Ceanothus



Celestial Blue

>60



Ceanothus



Concha

>60



Ceanothus



Frosty Blue

30


very drought stressed watered sample = >60

Ceanothus



Joyce Coulter

>60



Ceanothus



Julia Phelps

>60



Ceanothus



L.T.Blue

>60


sparse foliage difficult to light

Ceanothus



Mills Glory

45


>60

Ceanothus



Mountain Haze

>60

15


Ceanothus



Ray Hartman

>60



Ceanothus



Remote Blue Ceanothus

>60

2


Ceanothus



Tassajara Blue Ceanothus

45


watered sample

Ceanothus



Wheeler Canyon

>>60



Ceanothus

arboreus



20


watered sample = >60

Ceanothus

arboreus


Owlswood Blue

>60


melted leaves will not ignite

Ceanothus

crassifolius



15



Ceanothus

cuneatus



25



Ceanothus

cuneatus


Sierra mt. lilac

50



Ceanothus

cyaneus



>60



Ceanothus

cyaneus


Sierra Blue Ceanothus

10-30


leaves roll and ignite

Ceanothus

gloriosus


Hearts Desire

>60



Ceanothus

gloriosus

porrectus


>60



Ceanothus

griseus

horizontalis

Yankee Point

>60

50

looked like it would burn

Ceanothus

hearstiorum



>15


with regular watering = >60

Ceanothus

impressus

impressus


50


flame held just 5 secs. on unwatered plant

Ceanothus

impressus

nipomoensis


>60



Ceanothus

maritimus



30



Ceanothus

megacarpusX


Tranquil Margarita

55



Ceanothus

oliganthus

oliganthus


>60



Ceanothus

prostratus



>60



Ceanothus

ramulosus

fascicularis


7



Ceanothus

rigidus


Snowball

>60



Ceanothus

sorediatus


Klamath

>60



Ceanothus

spinosus



>90



Ceanothus

thyrsiflorus


Big Sur California lilac

>60



Ceanothus

thyrsiflorus


Skylark

>60



Ceanothus

thyrsiflorus

repens


>60



Ceanothus

tomentosus



>60


one leaf burnt out of six

Ceanothus

verrucosus



75


kept getting just over 60 secs.

Cephalanthus

occidentalis

californica


40


watered sample = >60

Cercidium

floridum



>60



Cercis

occidentalis



>60



Cercocarpus

alnifolius



>60


did light once in six tries

Cercocarpus

betuloides



50


mostly >60 secs., some ignition

Chamaebatia

foliolosa






Chilopsis

linearis



>60



Chrysothamnus

nauseosus



>60

10


Clematis

ligusticifolia



>60



Comarostaphylis

diversifolia



15


leaves rolled and ignited

Corethrogyne

filaginifolia



>60



Cornus

glabrata



15



Cornus

stolonifera



7



Corylus

cornuta

californica


10


only lights 50% of time, vaporizes then

Crataegus

douglasii



>60



Cupressus

forbesii



>60



Cupressus

nevadensis



15



Dendromecon

rigida



>60

1

prune to ground every 3-5 years

Diplacus

aurantiacus


Sierra monkey flower

>60


watered sample

Diplacus

aurantiacus

australis

Ramona

>60

deciduous, 5

need to tidy!

Diplacus

aurantiacus

lompocensis

Vandenberg Monkey Flower

30


old flower/capsules burn

Diplacus

grandiflorus



3

1

need to tidy!

Diplacus

longiflorus



>60


at water's edge

Diplacus

longiflorus


Conejo monkey flower

3


seed capsules ignite watered and trimmed sample = >60

Diplacus

puniceus


Otay monkey flower

3


dead-heading would fix

Diplacus

rutilus



>60


water sample

Dudleya

pulverulenta




3


Elymus

condensatus



>60



Encelia

californica



>60

1


Encelia

farinosa



>60



Epilobium

angustifolium






Epipactis

gigantea



45



Ericameria

arborescens



>60



Ericameria

ericoides



>60



Erigeron



Wayne Roderick Daisy

>60



Erigeron

glaucus



>60

1


Erigeron

glaucus


Cape Sebastian

>60

1


Eriodictyon

angustifolium (californicum)



40- >60


very variable

Eriodictyon

crassifolium



20



Eriodictyon

tomentosum



20

5


Eriogonum

arborescens



>60


foliage was non-flammable

Eriogonum

fasciculatum

foliolosum


>60

1


Eriogonum

fasciculatum

polifolium


>60


similar to lavender

Eriogonum

giganteum



>60

>60


Eriogonum

grande

rubescens


>60



Eriogonum

parvifolium



>60



Eriogonum

umbellatum



10


dead leaves are a problem

Eriogonum

umbellatum

polyanthum

Shasta Buckwheat

50


turns to charcoal and burns

Eriogonum

wrighti

subscaposum


>60



Eriophyllum

confertiflorum



2


took 3 tries to carry flame

Eriophyllum

staechadifolium

artemisiaefolium


>60



Fallugia

paradoxa



>60



Ferocactus

acanthodes

cholla


3


spines burn good!

Fragaria

californica



>60


nothing left after 20 secs.

Fragaria

chiloensis



>60


occasionally lit, but no live coals

Fraxinus

dipetala



10



Fraxinus

latifolia X velutina



>60



Fremontodendron



Ken Taylor

20

15


Fremontodendron



Pacific Sunset

15



Fremontodendron

californicum



>60



Fremontodendron

californicum

decumbens


>60



Garrya

elliptica

James Roof


15



Garrya

flavescens

pallida


20

3


Garrya

veatchii



15

3


Grindelia

camporum



>60



Haplopappus

squarrosus



>60

1


Haplopappus

venetus

vernoniodes


>60



Heleniun

hoopesii



>60



Heleocharis

parishii



>60



Helianthemum

scoparium



>60



Heteromeles

arbutifolia



50


burn out moisture to burn leaf

Heterotheca

grandiflora






Heuchera

maxima



>60


blew holes in leaves

Holodiscus

discolor



5

1


Horkelia

cuneata



>60



Horkelia

parryi



>60



Isomeris

arborea






Iva

hayesiana



>60

>60


Juglans

hindsii



>60


leaves melt, flash, flame dies

Juncus

patens



>60



Juniperus

californica



>60



Juniperus

communis

montana


>60


burned creeping, smouldering, slowly

Keckiella

antirrhinoides



>60

1


Keckiella

breviflora



>60

1


Keckiella

ternata

septentrionalis


>60

3

tidy, if summer deciduous

Larrea

tridentata



>60


low flammability

Lepechinia

fragrans



>60


smokes a lot

Leptodactylon

californicum



1 sec.



Libocedrus

decurrens



30



Lithocarpus

densiflorus



15



Lobelia

cardinalis



>60



Lobelia

dunnii

serrata


>60


appears non-flammable

Lonicera

hispidula



45

5

watered sample = >60

Lonicera

interrupta



10



Lonicera

subspicata

denudata


15



Lotus

scoparius



>60

3

if untrimmed = 3 seconds

Lupinus

albifrons



60



Lupinus

excubitus



>60


'melts into black mass'

Lyonothamnus

floribundus

ssp. asplenifolius


30



Mahonia

aquifolium


Compacta

>50


burns as leaves dry out

Mahonia

Higginisii



10



Mahonia

nevinii



20-50


leaves burned a second, then went out

Mahonia

pinnata



10



Mahonia

repens



20

3


Malacothamnus

fasciculatus



>60



Malacothamnus

marrubioides



25

1


Malacothamnus

palmeri

involucratus


45


smells like cow chips

Maurandya

antirrhiniflora



>60



Mimulus

cardinalis



>60



Mimulus

guttatus



>60



Monardella

antonina



>60



Monardella

linoides

stricta


>15



Monardella

macrantha



>60



Monardella

villosa



10


flashes, then dies

Monardella

virides



15



Muhlenbergia

rigens



3


slow, like straw broom

Myrica

californica



15-40


watered sample = very inconsistent

Oenothera

caespitosa

marginata





Oenothera

hookeri



>60


no coal embers

Ornithostaphylos

oppositifolia



30



Penstemon



Margarita BOP

<60

2

tidy dead leaves

Penstemon

eatonii



>60



Penstemon

grinnellii



10


very dry plant

Penstemon

heterophyllus



>60



Penstemon

incertus



10



Penstemon

newberryi



>60


nothing left of plant

Penstemon

spectabilis



20-30



Philadelphus

lewisii



>60


lit once in 5 tries

Physocarpus

capitatus



5

1

low to moderate fuel load

Pickeringia

montana



>60



Pinus

attenuata



15



Pinus

flexilis



20



Pinus

jeffreyi



40



Pinus

monophylla



45



Pinus

muricata



>60

1

live leaves fall off instead of igniting

Pinus

ponderosa



>60


lit once in 10 tries

Pinus

sabiniana



45

3


Platanus

racemosa



>.60


kinda burned at 60 secs., if leaves rolled right and the angle was right

Pluchera

odorata

odorata


>60


not even coal

Populus

fremontii



60

1

dead leaves burn very well

Populus

tremuloides



5


poof!

Populus

trichocarpa



30

1


Potentilla

glandulosa



>60



Prosopis

glandulosa

torreyana


15



Prosopis

pubescens



>60



Prunus

ilicifolia



7



Prunus

lyonii



45

2


Prunus

virginiana

demissa


20



Prunus

virginiana

melanocarpa


avg 40


ignited twice in 5 tries

Pseudotsuga

menziesii



40



Psoralea

orbicularis



>60



Ptelea

crenulata



25

1


Pteridium

aquilinum

pubescens


>60

1


Purshia

glandulosa



50


unwatered and very dry

Purshia

tridentata



>60



Pycnanthemum

californicum



30-60



Oaks are pretty flammable, but with management are not a problem. Do not run out and cut all your oaks down, but do make sure there are no weeds or upright twiggy dead debris under them and prune the limbs up so you can walk under them.

Quercus

agrifolia



10 sec.


watered sample = 10 seconds

Quercus

berberidifolia



20



Quercus

chrysolepis



5



Quercus

douglasii



>60


I have no idea, tried repeatedly

Quercus

engelmannii



7



Quercus

garryana

breweri


15

10


Quercus

kelloggii



10



Quercus

lobata



avg 15



Quercus

tomentella



25

2


Quercus

wislizenii



5


watered sample

Rhamnus

californica



>60


smoulder only

Rhamnus

californica


San Bruno

30


with some watering = >60

Rhamnus

californica

Eve Case


>60


will not sustain ignition

Rhamnus

californica

Tranquil Margarita


>60



Rhamnus

crocea



>60


both watered and unwatered didn't light

Rhamnus

crocea

ilicifolia


15


bigger leaves burn more easily?

Rhus

integrifolia



>60



Rhus

laurina



>60


tried repeatedly, got one flash out of five+ tries suspect dead leaves for its reputation of being flammable, so tidy!

Rhus

ovata



>60


popped a lot

Rhus

trilobata



>60



Ribes

aureum

gracillimum


50

3

if dead leaves are allowed to pile up or linger, that can be a problem

Ribes

californicum



>60



Ribes

indecorum



>60

3


Ribes

malvaceum



>60


can burn in 30 seconds but doesn't carry flame

Ribes

menziesii



>60

3


Ribes

nevadense



30


poor ignition

Ribes

quercetorum



>60



Ribes

sanguineum

glutinosum


>60



Ribes

speciosum



>60

10


Ribes

viburnifolium



>60


vaporized to little ash

Romneya

coulteri



>60

1


Rosa

californica



>60



Rosa

gymnocarpa



>60



Rosa

pinetorum



>60


got one leaf to light, not repeatable

Rosa

woodsii

glabrata (mohavensis)


45



Rubus

parviflorus



45



Salix

laevigata



15



Salix

lasiolepis



10



Salvias are very flammable, if you do not keep them clean and wash the foliage off occasionally. Just washing the leaves off every two weeks and keeping them tidy is enough to make them almost fire proof.

Salvia



Bee's Bliss

10

5

tidy!

Salvia



Celestial Blue

12


very little fuel watered and trimmed = >60 secs.

Salvia



Daras Choice

50

3


Salvia



Gracias

10

3

tidy! watered sample = 40 secs.

Salvia



Pozo Blue

see notes


young leaves = 30 secs. old leaves = 15 secs. trimmed and watered = >60 secs.

Salvia

apiana



20


on edge of watered area = >60 secs.

Salvia

apiana

compacta


10



Salvia

brandegei



>60


very clean

Salvia

clevelandii


Alpine Cleveland sage

7-15


watered sample = >60 secs.

Salvia

clevelandii


Winifred Gilmam Cleveland Sage

15


watered = >60 secs., but erratic

Salvia

dorrii



>60



Salvia

leucophylla



12



Salvia

leucophylla


Pt. Sal

15



Salvia

mellifera



20



Salvia

mellifera

repens


>60


at edge of watered area

Salvia

munzii



>60


not even charcoal

Salvia

pachyphylla



>60


smells good!

Salvia

spathacea



15


summer deciduous, needs to be tidied. watered sample = >60 secs.

Salvia

spathacea


Powerline Pink

20



Salvia

spathecea


Las Pilitas

>60



Sambucus

caerulea



>60



Sambucus

mexicana



>60

1

keep tidy

Satureja

douglasii



>60



Satureja

mimuloides



10



Scrophularia

atrata



>60



Scrophularia

californica



>60



Scutellaria

austinae



>60



Sedum

oreganum



>60


water expelled from leaves

Senecio

douglasii



>60


leaves melted

Sequoia

sempervirens






Sisyrinchium

bellum



>60


watered sample

Sisyrinchium

californicum



>60


watered sample

Solanum

xanti



>60


smells like bad goat cheese

Solanum

xanti

hoffmannii


>60


old pig smell

Solidago

californica



>60


some unsustained ignition

Solidago

canadensis

elongata


7-15



Solidago

confinis



>60



Sphaeralcea

ambigua



30

3

need to tidy

Spiraea

douglasii



5



Stachys

ajugoides

rigida

Persnickety Pink

>60



Stachys

bullata



>60



Stachys

chamissonis



>60



Stanleya

pinnata



>60



Styrax

officinalis

fulvescens


7


watered sample

Symphoricarpos

albus

laevigatus


>60



Tellima

grandiflora



>60



Thalictrum

fendleri



>60

1

need to tidy!

Thuja

plicata



15


very oily

Toxicodendron

diversilobum



>60


held breath

Trichostema

lanatum



10



Trichostema

parishii



10



Umbellularia

californica



15



Vaccinium

ovatum



>60


foliage melted

Venegasia

carpesioides



>60

1


Vitis

californica



55

3

dead burning leaves go out after 5 secs.

Vitis

girdiana



>60



Wyethia

ovata



>60

1


Xylococcus

bicolor



45


varied from 15- 60+ secs.

Yucca

whipplei

percusa


>60



The California fuchsias are not flammable, but any of their debris is. Mow them down every December or January and you should be fine.

Zauschneria

californica


Catalina

>60



Zauschneria

californica


Ghostly Red

>60

5

debris doesn't carry flame

Zauschneria

californica


Pink

>60



Zauschneria

californica


White

>60



Zauschneria

californica

Uvas Canyon


>60



Zauschneria

californica

mexicana


>60

10


Zauschneria

cana



>60



Zauschneria

latifolia

johnstonii


>60

15


Zauschneria

latifolia

viscosa


>60



Zauschneria

septentrionalis


Mattole River

>60

5


Non-Native Grasses and Weeds

The numbers explain why brush fires slowly spread in comparison to grass/weed fires. Grass/weed fires can kill you. Look at it this way (and there are no absolutes in nature): when a field is in annual grass and mustard, and the ignition time per plant is almost instantaneous, you'll get what appears to be area ignition.  On the Las Pilitas fire we had an area by Santa Margarita Lake where the fire moved through miles of grass in a few minutes. You can't outrun something that basically blows up.
Brush burns at, on average, 45 seconds per plant and makes a very hot creeping fire,(with some dramatic flashes); you can't be within one hundred feet of it and be comfortable, but you can usually move to one side or the other.  Houses can tolerate a great deal more heat than humans and can be undamaged  in spectacular fires.
In contrast, if you have weeds in brush, you get a very fast, erratic, spotty, and hot fire.
In fire training one of the points they drilled into the concrete of our heads was,  "firemen rarely die in brush fires...all the recent deaths in California have been in grass fires".Back in the 1980's during the Chispa fire we (volunteer and paid firefighters) were back-firing into the main fire to stop it. We could not light the brush; the torch made a fire ball in the brush, and it would go out and not stay lit. After about thirty minutes of this frustration (hey, we were exhausted and a little slow) we figured out that if we looked for weeds (mostly annual grasses), we could light them and they would light the brush. That worked!
Plant
state of plant
ignition speed in seconds
comments

Annual grass (Bromus diandrus)

dead since May

instant, so fast impossible to time. Whole plant gone in a second.

weed control is very important

Melilotus

dead Yellow Sweet Clover

2

these can be big plants

Mustard

fields of dead mustard

3


Star Thistle (Centaurea solstitialis)

dead

2

the back of one of the parcels was covered with this, 30 foot flames, looked like oil fire



Typical non-native landscape plants. These are not NATIVE!

Plant

Live leaf ignition
(in seconds)

dead leaf ignition (in seconds)

Notes (times in seconds)

Abelia

30


watered planter in Atascadero, California

Apple, Improved Pippin Here's how many different apple varieties have grown here.

30-60

2

very variable, this one was watered regularly. Under drought, is flammable

Blackberry

50-60


regular water

Bottle bush ( Callistemon)

12


regular water on drip

Bottle Tree(Brachychiton)

>60


regular water

Buddleja davidi ('Butterfly bush')

5


very flammable in watered greenhouse, this was a WOW one, looked so moist, burned real fast

Cistus villosa

new growth 45, old growth 10


watered planter in Atascadero, California

Cotoneaster, groundcover

>60


watered sample from SLO (San Luis Obispo)

Cotoneaster, shrub

10


watered sample from SLO

Day Lilly

>60


dead material does burn

Elm, Chinese

30


watered sample from SLO

Eucalyptus, Red Flowering Gum

15


these can be big trees and make spot fires for a mile or more.

Eucalyptus, Red Gum

5


watered sample from SLO, "

Gamolepis daisy

>60


watered planter in Atascadero, California

Gazania

>60


these accumulate a lot of dead material that is very flammable.

Grape, Thompson Seedless

>60

3

hygiene is important

Ivy, Algerian

20


In a watered flower bed. A little wind, drought, and slope, this would be interesting.

Juniper, Pfitzer

15


hot fast fire

Lavender, English

20


dead stuff lights easily, live stuff burns easily all year.

Lavender, Hidcote

20

1

dead stuff lights easily, live stuff burns easily all year.

Lavender, Munstead

>60

1

dead stuff lights easily

Lavender, Spanish

>60

1

live foliage with breeze = >30 dead stuff lights easily

Lemon Verbena

5


some of the tropical stuff ignites readily

Lilac, common

3


plant was very dry, I've seen similar in dry gardens

Myoporum parvifolium

>60


watered sample from SLO

Nandina

10


watered planter in Atascadero, California

Oleander

10


on drip

Peach, Elberta

45


regular water

Pear

20


very lush and regularly watered.

Persimmon

>60


looked lush and had regular water

Pittosporum Tobira

7



Plum, Santa Rosa

15


looked lush and had regular water

Quince, Pineapple

30


looked lush and had regular water

Raphiolepis sp.

12


watered planter in Atascadero, California - popped and snapped

Thyme (Thymus sp.)

<60




Mulch

time to ignite for sustained 5 seconds

dry Chipped Cedar leaves

1 sec. -flame height six inches

dry Redwood shavings

1 sec. -flame height one inch

dry Oak and Pine chips

10 secs.- flame height one inch. Pieces too large and random to lay flat

dry Shredded redwood bark

loosely laid single grind = 15 secs.- flame height 3 inches. properly laid single grind = 20-30 secs.- flame height one inch.
(the sticks ignite) loosely laid double grind = 15 secs.- flame height 2 inches.
 Properly laid double grind = 60 secs.- flame height one inch. Mulch needs to lay flat and compact with no twigs or debris (a heavy watering at application will help accomplish this)
Dry shredded redwoodbark should not run up to structure. Embers will ignite in fire  storm, but flame heat is so low  vegetation seldom ignites.

Materials. Don't forget the fence, deck and siding. 

Material

time to ignite for sustained 5 seconds

1X cedar board

35 seconds

daily newspaper laid flat

5 seconds

cardboard

1 second

stained 1X pine

5 seconds

1X redwood

50-60 seconds

1X linseed treated (cured) redwood

10 seconds

9/16 plywood

30 seconds

1X4 and 2X4 doug fir

30 seconds

In conclusion,  you want to work towards a  weed-free landscape, with no leaves on the roof, no flammable wood furniture or lath type structures near the house, and no wood shingles or any other flammable item within thirty feet of the house.  Picture a hot day with 20 mph winds and a helicopter flying over your home throwing out buckets of lit matches. Hygiene is the most important thing to remember.
Really stupid things cause  most problems in a fire situation; that corner of the yard that you never weeded, where you left the old cardboard box and tree trimmings, the rattan furniture under the bamboo overhang,  and the rabbit that was on fire and ran under your lath- covered deck.
Choice of plant material matters;  native plants are generally less flammable than non-native plants. For many species, watering makes no difference. Mulch is ok as long as it doesn't run right up to within about a foot of the house.  The trade off is the mulch can smolder and cause some heart burn, but the plants will have better moisture retention and be less likely to burn.
A fire landscape should contain only enough plants to stabilize the site.  Be very limited in plant material; rocks and concrete do not usually burn.  Decomposed granite walkways are a wonderful addition to a native plant garden.
Plan on not having any water during a fire, even for months leading to a fire. It's common for the power to go out in fire areas along with water pumps and for the fires to occur during water rationing.  In urban interface areas it's also common for all the people a mile ahead  of the fire to water their houses down and the water not to be available to homes nearest the fire. On one fire we pulled the engine up to a hydrant on one of the higher streets, hooked up the hose, turned on the hydrant to listen to a sucking sound as our hose went flat.
Cohen, Jack. Structure Ignition Assessment Model (SIAM),  USDA Forest Service Gen. Tech. Rep. PSW-GTR-158. 1995.