While there are lists of fire-hazardous and fire-smart plants from many sources, there is no good, reliable database for plant ignitability (how easy it is for a plant to ignite).
There is, however, an interesting source of ad hoc data for native plants. In 2005, someone at Las Pilitas nursery did a series of tests on the native plants kept at the nursery. The procedure was ad hoc, yet useful:
- “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…”
- “Using a propane torch with a one centimeter length flame (+/- 1mm), the blue tip of flame was placed on to a leaf, if [the] leaves [were] large, or [on to the] first leaf cluster if [the] leaves [were] small, until the leaves ignited and held a flame longer than five seconds. Some leaves would flash. If they held a flame or carried [flame] to other leaves that was counted… I settled on collecting a few stems of a few plants and testing those in a closed barn within minutes of collection.”
- “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.”
Caveat
There is a significant caveat, though. In fall 2024, during fire season, we attempted to duplicate the results obtained by Las Pilitas for a small number of plants. The results we obtained were different from those obtained by Las Pilitas. We were in general interested in plants that showed low ignitability, and more particularly in those with a reputation for fire danger but that showed good results at Las Pilitas. In the general case (with quite a few exceptions) we obtained worse or much worse results than Las Pilitas 
. Because both their procedure and ours were very much ad hoc, this is not a truly concerning issue—but it does point out that this data must be taken with a grain of salt.
So, while we find the data interesting , we are concerned that it may not be reliably duplicated in different conditions than those that existing at Las Pilitas that year—in particular in the conditions that will exist in our gardens during fire season.
Link
Appendix: a brief comparison of results
Our own experiments on ignitability were also very much ad hoc, and we do not believe had a reliable process (nor, do we think, is the process for Las Pilitas, though). We do not purpose to prove anything with them.
Our procedure:
- We used a propane torch with a blue flame of approximately 1 cm
- For the samples we used a few plant stems very recently cut.
- We stopped after two roughly identical results.
- Our records kept track of results as Success/Fail as compared to Las Pilitas (i.e. success = as good a result).
- The plants selected had to be easily accessible, and were, when possible, those where Las Pilitas results indicated low ignitability (in particular when the low ignitability was surprising to us).
For illustration purposes only, these are the plants we tried where our results were worse or much worse than those obtained by Las Pilitas for the same genus and species:
- Adenostoma fasciculatum [Chamise]
- Arctostaphylos (several species) [Manzanita]
- Artemisia californica [California Sagebrush]
- Erigeron glaucus [Fleabane]
- Erigeron glaucus Cape Sebastian
- Eriogonum fasciculatum [California Buckwheat]
- Penstemon heterophyllus (tested: Blue Springs)
In addition, here are the plants, with similar genus, but different species, where our results were also worse or much worse:
- Acacia cognata
- Clematis Armandii
- Cupressus Leylandii [Leyland Cypress]
- Fremontodendron (unknown species)
- Juniperus procumbens “Nana” [Juniper Nana]
- Pinus Radiata [Monterey Pine] (compared to attenuata or flexilis)
There were a few cases where our results were similar:
- Aesculus californica [California Buckeye]
- Aristolochia californica [California Pipevine]
- Carpenteria californica [Bush Anemone]
- Ceanothus Ray Hartman
This article was written by HelpBerkeley.org in collaboration with BerkeleyFirewise.org.