Hedges: Essential Design Tool or Fire Trap?

Articles: Hedges: Essential Design Tool or Fire Trap?

Contributor

Jennifer de Graaf

Topics: Drought and Fire Resilience

Summer 2025

Hedges have graced gardeners’ landscapes for hundreds of years. Most hedges are built from rows of shrubs, but they can also be rows of small-statured trees if kept to size. They can include ornamental grasses, bamboo, or even large fleshy perennials, like giant bird of paradise (Strelitzia nicoli).

Depending on size and placement, hedges have a plethora of uses. Small hedges can create a border and visual distinction between areas in a garden. They can be a physical barrier, controlling movement through a landscape and reinforcing pathways. When larger, they can define sightlines, frame views, provide an aesthetic foil behind other plants, and offer privacy from prying eyes. Hedges may provide benefits to wildlife, stand as a stately monoculture, or combine multiple species in a tapestry of colors and textures. Big or small, hedges have a place in our gardens.

To shear or to prune?

Shearing involves cutting many branch ends together to trim a plant into a shape. Like removing fleece from a sheep, it involves many simultaneous cuts without concern for any individual piece.

Plants have evolutionary responses to shearing. First, shearing causes the remaining buds and stems to spring forth with new growth. The growing tip contains a hormone that suppresses the growth of lateral buds and stems. Removing that tip excites the lower buds and stems into action. Second, many plants experience what is called compensatory growth. A plant will compensate for the loss of foliage by quickly growing more, even though that often means the growth is not as stout or sturdy. When shearing, these responses combine, resulting in a plant with a mass of foliage flushed out at the ends of branches and stems, leaving the interior of the plant choked with fine stems and fallen leaves.

Unfortunately, these dry underbellies make that plant easier to ignite, effectively having collected tinder. Additionally, the weaker new growth and lessened air circulation through the plant makes the plant more prone to diseases and pests.

Pruning, on the other hand, selectively removes vegetation with the intention of fostering plant health. Thoughtful pruning encourages air circulation, makes room for leaf litter to fall to the ground, and supports a healthy structure. We prune with an eye toward the four D’s—remove dead, damaged, diseased, or demented (out-of-place) foliage. By targeting these problems, we’re supporting a healthy plant’s continued good health.

What about fire?

When we smell smoke in the air or hear about fire in the news, we start seeing our garden with a more critical and fearful eye. It’s fair to ask ourselves what traditions to keep and which ones we might want to rethink. Sheared hedges are a good place to start thinking more carefully about what we are doing, as well as how and why we do it.

In my (Doug’s) post-fire wanderings, sheared hedges stand out as often being the first group of plants to ignite in a firestorm. It wasn’t the plant selection or design intent, but the maintenance that caused a less-than-ideal condition. You can imagine that these sheared hedges’ interiors were easily enflamed by firebrands. Their dense, twiggy interiors likely behaved like a butterfly net perfectly designed to catch and hold embers, then they burned from the inside out. This is also challenging for firefighters to extinguish because of the mass of green leaves protecting the dense interior.

What to do?

An artful and patient gardener can grow an effective hedge without endangering structures and exit routes. The most important thing we can do is to refine our habits to prune plants, not shear them. Switching to this practice will create a hedge that is loose and more natural-looking, but less uniform. Depending on the design intent and a hedge’s proximity to escape routes, this may be essential to finding a safe way out in an emergency. We also need to stop planting hedges and “shrubbing it up” merely out of habit, when we can instead use them intentionally and to great effect.

The photo below shows a hedge with informal pruning and thinning, often referred to as lacing. The interior has been regularly cleared of the fine twigs and branches, and the leaf litter has been removed. Leaves sprout along the length of the branches, not just the tips, because of the gardener’s artful hand. This hedge did more than survive the Eaton Fire, it robbed some of the fire’s energy, providing a small degree of protection downwind both by being a windbreak and refusing to catch and hold embers.

A caring gardener does more than prune with skill, they also provide nourishment. In fire country, this nourishment must include appropriate moisture. It is essential that the plants around our homes are not water stressed during fire weather. Supplemental irrigation should be applied in time for the plants to take the moisture up into the foliage. Too late, and there won’t be enough moisture in the plant tissues.

We want our plants to defend against fire as much as they can, and not succumb too easily. Providing nourishment should also include testing the soil to discover what, if any, nutritional gaps there are for the kind of plant you are growing. Fertilizing without knowing what is deficient is tantamount to over-fertilizing and can damage the very root systems we are relying on to bring moisture into the foliage.

Foundational plants, the “bones” of a garden, such as hedges and large trees, rarely get the same care as the plants below them. Splashy, colorful bedding plants get the attention. Protecting the elders in a garden can be an important protection for the garden itself.

For most species, we don’t want to let the soil dry beyond three inches down before and during fire weather—with a caveat. Not all plants want water during the dry months, so be sure to check the water needs of each plant and find out if it resents summer water. Watering a plant too much can have the same effect as underwatering. The root zone relies on gas exchange known as soil respiration. The goal is to provide an amount of water that keeps plants hydrated without introducing drought stress, pest vulnerability, or root suffocation.

Every plant has a lifespan, and every plant will need replacing at some point. Sometimes it is an individual plant within a hedge, sometimes the whole thing is ready to go altogether.

From my experience, the best plants for hedges in fire country have three characteristics. Broad-leaved plants are better than conifers and grasses due to their reduced surface area per mass of foliage. To avoid any additional stresses, plants must have a high tolerance for localized conditions, such as soil acidity or alkalinity, soil compaction, available nutrients, wind tolerance, and sun exposure. If a plant will be part of a hedge, it must respond well to human interactions, such as pruning and brushing against. It should be spaced far enough from paved surfaces that nobody will need to shear it to keep it out of the way.

Pictured below is Christmas Tree Lane in Altadena, California. It houses two blocks of towering and closely grown deodar cedars (Cedrus deodara) that make one giant hedge. Surprisingly, not one tree or home here was lost in the Eaton Fire, despite the destruction surrounding the iconic area. These trees are beloved, and the care they receive is what I believe saved them. People provide plentiful nourishment, remove deadwood, and fight pests. Care, whether for people and their rituals or plants and their expansive reach, allows these cedars to flourish with attention, ultimately protecting all.

Hedges as design tools aren’t the enemy. With considered design, informed maintenance, and thoughtful irrigation practices, they can bring more benefit than risk.