These are brief notes from a presentation given at Creston Firewise’s 2025 annual meeting, combined with some of the questions. This should NOT be considered advice from a specialist, but simply the opinion of a well-informed neighbor.
Old landscape schemes do not apply anymore
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The most fundamental issue is the actual landscaping design itself. I landscaped both my front and back yards between 1998 and 2003. At the time, I planted essentially 50% of my shrubs and trees right alongside the house, and 50% right alongside the property line and the fences. This type of design, unfortunately has to go.
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The same thing applies to the density of the design. In 2003, I planted a very lush landscape, where, eventually, all but a small percentage of the land would be covered by luxurious plant canopies, and many types of green color and texture. This, also has to go: the whole concept of defensible space means that we have to create gaps and buffers between trees and shrubs. Viewed from above, you need to see many gaps in the landscape.
Buffers
What kinds of buffers are required in California (and, essentially, in most of not all wildland urban interfaces around the US)?
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In Zone 0, that is, within 5 ft of any structure (particularly your home and garage, but any other as well), we cannot have ANYTHING that is combustible (including fences, furniture, gates etc.), with one single exception: a bare trunk running up within zone 0 is acceptable, as long as its foliage is at least 10 ft away from your roof line. There are no exceptions.
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In zones 1 and 2, that is, from 5 to 100 ft from any structure, any tree canopy needs a buffer of 10 ft from any other tree canopy in flat land, 20 ft in 20-40% slope, 30 ft in >40% slope. According to CA regulation, any shrub must be at least 2x Height away from another shrub in flat land, 4x Height in 20-40% slope, 6x Height in >40% slope. Other regulations apply to combustible materials which I will not discuss at this time. The idea is that we do not want the fire the ability to follow a horizontal ladder from one side of your property to the other, through proximous foliage.
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However, in this respect IBHS (an insurance consortium that defines acceptable norms), which is typically harsher than CalFire, has a better regulation. They allow 3 shrubs to be within a 10 ft diameter pod, which must be, collectively, at least 10 ft away from the next green pod.
In zones 1 and 2, there is also a concept of vertical laddering that must not happen. We do not want fire that runs on the ground to be able to go up into trees and turn into a canopy fire. For this reason, we need to limb trees to 8 ft, and shrubs to at least 1/3 of their height. If there are shrubs under trees, the trees must be limbed to 4x shrub Height.
How can we design new landscaping in 2025?
It took me a while to figure it out. Normally, I would suggest that we should design to the toughest regulation, so as to be sure to be OK in the end. However, in our case, we are generally dealing with mature landscapes: we must play the hands we are dealt. In this case, I think it is acceptable to use the IBHS regulation as the basis for design. I do not believe that we will face pushback if we satisfy the IBHS regulation 100%. Besides, who will enforce zones 1 and 2 first, the fire department or our insurance companies?
The new landscape scheme and methodology: green islands
If you are looking to make your garden look like a high desert or a southern California garden, this may not apply to you, because it is possible for you to landscape to this ideal within the kind of buffers we need. The problem is—if you are looking for as mush green as possible, what can you do?
The key is the concept of green islands. You can design green islands in your property anywhere you want, as long as (a) they do not penetrate Zone 0, and (b) they have a 10 ft canopy buffer from the next green island. If a tree, the canopy can have any diameter you want. If a group of shrubs, it cannot be more than 10 ft in diameter.
So the game becomes: how many green islands can you pack in your yard? What large islands (trees) can you have, and what smaller islands (shrubs or groups of shrubs) can you use? In the middle, you can still plant non-woody plants to link them, although the IBHS is VERY strict of what constitutes a non-woody plant. For instance, an average succulent does not count.
Dealing with existing trees and shrubs
There are almost no rules… Here is my process: it may work for you, or not.
- I start from my own taste. There are trees and shrubs I love, and others I just like. Well, as things go, pretty much everything I just like needs to go, and I typically need to get rid of more.
- Then I look at my green island scheme. Why green islands will optimize the overall design? There are many choices to be made: do you go with tree 1 and shrub 1 and 2 in the island, or tree 2, shrub 2 and shrub 4? What gives you the biggest heartache? How do you keep the most and also the most beloved? You rarely get to have perfect choices.
- Sometimes, there are existing shrubs that are just a few feet too far in one area or another. For me, for instance, I have a datura that makes a green island 13 ft wide, and a loropetalum alba that makes another green island 14 ft wide. I am keeping the datura for a couple more years, but planted another one in a location that will work. In a couple of years, I will cut the old datura, and the new one will be mature: a win! As for the loropetalum, big heartache: I cut it, then planted a small one and a tall one (or one that will become taller) in the original location. Another 5 years, and I will have the perfect green island. Maybe…
My new landscaping ideas for my own yard
In the front, I have a Japanese garden, which I have already practically wrecked with my cutting. I definitely am going the green islands way.
In the back, in several parts of the garden, I have essentially denuded everything. What I have done:
- in some areas, I have recreated a green zone centered about 10 ft away from the walls. For instance, I was able to transplant an evergreen hydrangea that I love. I think it will do wall.
- in an other (central area), I am radically changing the scheme. I am creating a big island right in the middle of the yard, and keeping the edges totally free. We will relandscape our ipe landing into a hardscape landing, and have the green island right abut this landing. I can do it because… IBHS does not count hardscape landings as part of the house!
What are we going to do where nothing can be grown? We are doing a lot of things with rock, moss rock from American Soil ($180/ton), that is small enough to handle with two people: it is pretty sizable already. We are also looking at water: can we create water features and ponds, without spending too much money? Finally, we’d love to have metal sculptures that we can position in these areas. We have not had much luck so far.
The evil of street-side privacy hedges
@JenniferBraun of Berkeley Woods woke me up to this truly horrible, person-killing problem.
First, I should simply admit that all of us have privacy hedges, and I have had some for many years. In front of my property, street side, running right along the street, for about 40 ft I have a lovely, dense jasmine vine, dense, running all the way on top of an ancient fence. The debris build-up under this fence must be seen to be believed. When Kevin R and Duncan A from Berkeley Fire Department (BFD) came to give us mock inspections, to show us how to do them, the very first thing that Duncan did was knock me on the phalanges with this hedge (and a wood gate right by my house).
When wildfire comes to my property, it will catch at one end of my hedge, and, in a few seconds, run through the whole hedge. When the hedge is in flames, in will shrink Creston Rd by 5-10 feet because of radiated heat. There si NO WAY that a firefighting vehicle, which is already much wider than regular vehicles, can make it through this section once it is on fire.
And what about people evacuating? Their vehicles, while narrow, run in both directions, and are much less able to resist radiated heat. It is possible that my hedge will kill evacuees. For sure, it will stop firefighters from passing by my property, and essentially condemn my neighbors (and me) to structure fires.
As for the firefighters, which one of them will be willing to fight a hedge fire before being able to defend my house? The simple fact is that street-side [privacy fences are neighborhood killers, and possibly people-killers. I am really sorry because I love my jasmine hedge. But it has to go, and yours probably should too.
The evil of privacy side-hedges
Fire research indicates that any house within 50 ft of another structure is at danger of ignition from radiated heat, i.e. from the next-door structure’s heat when burning. Within 20 ft, the danger is particularly acute. Many, of not most of our houses, are within 20 ft of a neighborhood house. If you are within 20 ft of the neighbor’s house, how much closer are you to the privacy hedge between the two?
A street-side privacy hedge endangers the whole street, and the firefighters who come to save your house. A privacy-side hedge, beyond giving the fire a very fast shortcut from one end of your property to the other, endangers your home and your neighbor’s.
My house is separated from one of my neighbor’s houses by about 20 ft. We just agreed, my neighbor and I, to take out the hedge and fence, and to build a concrete-footed aluminum privacy fence between the two of us. I hope you make the same kind of decision.
What is allowed about hedges?
Calfire, and Berkeley, allows NO hedges: each shrub foliage must be separated from another by 2x Height. IBHS allows 10 ft islands of hedges, separated by 10 ft canopy buffers. In this case, I feel that the CalFire rule is the right one to adopt, because it is not only putting you at risk: it puts many of your neighbors at risk.
Wood mulch in Zone 0
Everyone agrees that wood mulch is strictly forbidden in Zone 0. When Duncan A of BFD was discussing what to do with a budget of $500, he listed removing wood mulch in zone 0 as a very cost effective measure.
Wood mulch in Zones 1 and 2
Let’s be clear: wood mulch is a racing circuit for wildfire. It is an accelerant that will carry a wildfire very fast across your whole yard. It is all the more curious that generally reputable websites actually allow it in limited circumstances:
- generally, wood mulch is allowed in less than 2" thickness, in no more than 10 ft islands separated by 10 ft, and only if it is composted mulch.
- The incredible fact about this shoddy research, is that ONE study ever has shown this result, about a very specific proprietary wood mulch from a specific provider, and where the wood mulch, instead of allowing wildfire progressing at 15 ft/min, allows it at 1.3 ft/min. So instead of eating up your yard in 5 minutes, it will eat your yard in 50, if the study is even believable.
- The is a perfect example of shoddy due diligence by reputable websites, who build upon each other’s shoulders without ever going back to the original study.
What to use instead of wood mulch
- My opinion is that nobody should use any wood mulch ever. Instead, depending upon the circumstances, we are faced with several options:
- On steep hillsides, we have fewer options. We need to use larger pebbles, possibly 5/8" or more, in thick layers (4" or more), possibly using larger rocks here and there to play a terracing role. Another option is volcanic rocks of larger size, that have the advantage of being very light and being rake-able easily, if you decide to dress your soil.
- On not-so-steep hillsides, it is probably possible to use smaller diameter stones, such as nicely colored pea gravel, or smaller diameter volcanic rocks. Volcanic rocks have the advantage of immediately showing what is irrigated and what is not, since they chance color in the presence of water.
- In flat land, we have many choices. We can use fine decomposed granite that is pounded flat. For aesthetic reasons, I find that I prefer a thin layer of coarse granite on top of the fine layer. We can use pea gravel or equivalent diameter stone. Or, we can use any size stone we want, keeping in mind that weed-preventing ability requires the smaller size whenever possible and aesthetically acceptable.