How Does Wildfire Smoke Impact Gardens?

How Does Wildfire Smoke Impact Gardens?

“I live in northern California where we had a lot of fires and smoke. The sky was thick with smoke for quite a few days.  How will this impact my flowers?” Question from Jenna of Magalia, California

Answer: What a crazy season it has been! I have watched several of my western gardening friends struggle through the impacts of wildfires. Thankfully, many have been spared the damage caused by fire, but none are spared the ill effects of ash and smoke, which does impact plants in several ways.

Wildfire Smoke and Ash Impacts on Gardens

  1. Ash Effects: Ash can be very destructive, but it also has the potential to benefit plants. On the downside, hot ash will burn foliage. If fine and dense, it can cover foliage and keep plants from photosynthesizing as well. Rinsing it off will stop this problem. On the flipside, ash can raise soil pH, add extra minerals to the soil, and increase microbial activity and plant growth. So, it’s not all bad.
  2. Smoke Effects on Air Quality: Smoke increases carbon dioxide levels, which actually benefits plants. Plants use CO2 to convert sun to energy and release oxygen.
  3. Smoke Effects on Light Quality: Smoke lowers light levels, which can be harmful to plants growing under severe smoky conditions for extended periods of time. There is really nothing gardens can do but wait until the smoke passes.

Smoke is also drying, so be sure to irrigate your plants during these times, if you can.

I wish you the best and hope the fires stop soon. A moist, cool winter would certainly be a blessing.

Jessie Keith

Black Gold Horticulturist

Transformative Grasses: Anchoring Gardens and Soils


This hardy fountain grass is in full summer bloom, releasing pollen in the breeze. (Photo by Maureen Gilmer)

Over the past year, California has experienced drought, wildfires, floods, mudslides, and extreme cold.  The rest of the Southwest has seen the same crazy extremes and has experienced high-damage potential within a short time span.  Everyone will have some rethinking to do, whether making structural repairs or just replanting to return beauty to the landscape.  For others, it may require a whole new assessment of site planting and soil protection.

There is just one group of important plants that are called for this spring to heal the land.  John James Ingalls tells us why in a most eloquent quote:

Grass is the forgiveness of nature–her constant benediction. Fields trampled with battle, saturated with blood, torn with the ruts of cannon, grow green again with grass, and carnage is forgotten. Streets abandoned by traffic become grass-grown like rural lanes and are obliterated. Forests decay, harvests perish, flowers vanish, but grass is immortal. – John James Ingalls, Yearbook of Agriculture, 1948

The Power of Grasses

Empty garden spaces can easily be transformed or revegetated by large, ornamental grasses. (Photo by Maureen Gilmer)

Grasses are natural colonizers.  They are nature’s repair mechanism for soil disturbance.  Soil bound by grass roots underground and broad foliar coverage above protects the surface from raindrop particle displacement (erosion).  On slopes, they are excellent for slowing runoff velocity as well; the slower the water flows, the lower the erosion potential.

This makes grasses the most natural quick fix for gardens and home sites damaged by extreme weather and disasters.  Not only are they the ultimate problem solvers for damaged ground, but large ornamental grasses will also turn sparse drought plantings into lush, beautiful landscapes this year.  When planted in spring, they flower by mid to late summer with tall animated stems that grow more beautiful as they complete their life cycle.

Grasses produce flowers held well above the foliage to catch the wind, which is integral to their reproduction. When pollen flies from grass plumes amidst prairies or drylands, it is caught on sticky flower parts called pistils for pollination and seed set.  In the fall, dry winds help distribute seed far and wide.  The remaining seed structures stand barren into winter until knocked down by snow or heavy rain.

Because grasses are found on every continent, their range of tolerances is significant.  In dry areas of the Southwest, the soils and water supply are too lean for many species that originate in summer-rain climates.  The key is growing grasses that will thrive in our heat and potential drought, so you need not increase irrigation.  They should be sufficiently adapted to drought to survive nicely when the wet cycle wanes.

Planting with Grasses

Grasses are such incredibly transformative plants due to fast growth and significant seasonal change.  They are the stars of late summer gardens when the flowers are heavy and stems nod and sway in the slightest breeze.  Designers know how important this “animation” can benefit an otherwise static garden dominated by rigid cacti, succulents, and arid species.

There are four easy ways to add adaptable grasses to your western landscape this spring.

Create Fast and Easy Fillers

Early in the year, upright maiden grass makes a lush, green single specimen. (Photo by Maureen Gilmer)

Tall grasses with a significant diameter at maturity, like maiden grass (Miscanthus sinensis ‘Gracilimus’, 7-feet high, USDA Hardiness Zones 5-9), are the fastest way to fill gaps in your planting caused by frost death, washouts, and slope failure.  Provided these grasses spots in full sun, and plant to fit a given space.  If garden space is too large for just one single specimen, plant a group of three or five for a bigger visual impact.

Add Texture to Succulents

Blue fescue is the perfect low-growing, fine-textured grass for planting among succulents.

Succulent plants are coarsely textured and physically stable.  Blend them with fine-textured shorter grasses that are of similar height to contrast the character of each. Try Mexican feather grass (Nassella tenuissima, 3-feet high, USDA Hardiness Zones 7-10) or blue fescue  (Festuca glauca, 1-foot high, USDA Hardiness Zones 4-8) for fine-textured appeal.

Enhance Boulders and Rock Gardens

Pennisetums are reliable anchoring grasses for rock gardens.

Boulders are always more natural when anchored by grasses.  Planting right at the edge allows roots to reach underneath and draw up cool moisture trapped beneath the stone far into summer.  Where rocks are plentiful, the roots of grass tend to do better in shallow soils where they find fissures of much greater depth where the water hides. Two kinds of grass for the task are tender fountain grass (Pennisetum setaceum, 5-feet high, USDA Hardiness Zones 9-10) and hardy fountain grass (Pennisetum alopecuroides, 4-high, USDA Hardiness Zones 6-9).

Enhance Background Seasonal Color

The Southwest native deergrass is our best large grass for the dry southwestern US and California. (Photo by Maureen Gilmer)

Bedding plant and succulent displays are animated by taller grasses in the background, particularly after blossoms fade. In the fall, when ephemeral annuals wane, the tall flowers of upright or airy ornamental grasses become sculptural. With this background, you’ll never be without interest except in the dead of winter. Deergrass (Muhlenbergia rigens, 4 to 5-high, USDA Hardiness Zones 7-9) is a good selection that offers a cloud of pinkish seasonal color.

Planting Grasses

Because grasses are very active rooters, gardeners planting in clayey soils that tend to clod-up should generously add Black Gold Garden Compost Blend to their backfill at planting time.  With heavy clay, like Adobe, mix compost in at a 50/50 ratio with excavated soil.  This introduction of copious organic matter will wake up the army of dormant microbes that exist in fertile clays and work with plants to make them more resilient. The organic matter allows new roots to grow much faster and penetrate deeper. Adding compost also helps prevent surface cracking as wet, clayey soils dry out.  Cracks in hardpan clay allow water to skim the surface or penetrate too fast in the wrong places, causing irregular saturation.

Let grasses make your garden immortal this year. Celebrate the repair and renewal opportunities that grasses offer to rethink landscaping after a very difficult winter. For those who have suffered from wildfire and flood, turn to Mother Nature’s repair mechanism for all things soil-related to receive her constant benediction.

Fight Fires with Garden Flowers

Cistus ‘Brilliancy’ is a low-fuel-volume shrub with lovely magenta flowers.

You can fight fires with flowers. When landscaping around high-fire-hazard homes, the key is to think about minimizing fire fuel volume, or the amount of burnable material that plants provide to oncoming fire. For example, a pine tree has a huge fuel mass, but a sage plant, with its lovely lavender-blue flowers, has negligible fuel mass.

To further understand the concept of fuel mass, imagine the plant on fire. The overall flame produced is roughly three times the plant’s height; the greater the overall mass and size, the greater the fuel volume. (Chemical composition also play a role in fire susceptibility. For example, creosote bush (Larrea tridentata) contains many resinous, volatile oils that are highly flammable.) This demonstrates the problem with woody trees and shrubs that are taller and have enormous fuel volumes.

Plants for Firescaping

Native penstemons are timed for winter and spring bloom and gone by the fire season. (Maureen Gilmer)

The good news is that annuals, perennials, biennials, and low-growing shrubs are all better landscape candidates for firescaping. Ornamentals below 2-feet in height are better choices for areas with fall or winter fire seasons. Early frosts often cut these plants back, or the heat of late summer makes them listless in the arid West. Many western natives are also fully dormant by fall, an adaptation that allows them to withstand the dry heat and drought of this season. Once the plants have died back, gardeners can cut them back to further reduce fuel mass around the home.

Some flowers are also fire resistant, but are these the best for the arid West? Scientific research has yielded data on plant fire susceptibility and fuel mass with simple testing.  The tests are done by placing plant samples in a furnace and timing how long it takes for them to catch fire and burn. This makes no allowances for weather, wind, and topography, so in a real fire situation, the test results may be deceiving. All plants burn in catastrophic wildfires. The ” fire-resistant” plants may simply ignite a second or two later than non-fire-resistant plants, so gardeners should not worry about just planting fire-resistant plants.

The key is choosing drought-tolerant landscape plants that also have a low fuel volume. What you can grow locally is dictated by your rainfall and winter cold. You must choose plants adapted to your growing region. Every elevation and geographic area will have its own list of suitable native and non-native herbaceous flowers and subshrubs that fulfill both the fuel height and drought requirements.

Select Flowers for Firescaping

Avoid shrubs and plant blooming succulents, like rock purslane. (Maureen Gilmer)

Drought resistant, low-fuel-volume flowering landscape perennials:

Botanical Name          Common Name           USDA Zone            Color

Achillea tomentosa         Wooly Yarrow            3-8                         Yellow

Arctotis hybrids               Cape Daisy               9-11                        Many

Cistanthe grandiflora      Rock Purslane          8-11                        Magenta

Cistus ‘Brilliancy’             Rock Rose               8-11                        Magenta

Penstemon spp.              Penstemon              Varies                      Varies

Rosmarinus ‘Prostratus’ Rosemary                 7-10                        Lavender

Santolina spp.                 Lavender Cotton      6-10                          Yellow

These are just a few select perennials for starters. Any of these will grow best with drip irrigation in the arid West. You might also plant spring bulbs and wildflowers, which are already naturally adapted to survive fire due to their seasonality; they bloom and grow in the low-fire season. Succulents are also recommended because they contain so much water, they rarely burn. In wetter areas, low fuel volume options include bearded iris (Iris hybrids), sea thrift (Armeria maritima), and many other beauties.

To boost flower production in your newly planted low-fuel-volume flowers this year, generously work Black Gold Garden Compost Blend or Just Coir into the soil to increase water holding capacity, drainage, and fertility. This superior growing amendment is also OMRI Listed for organic gardening.

This garden features the best drought-resistant, low-fuel-volume flowers for firescapes. (Maureen Gilmer)

Planting to Reduce Fire

The commonly used term for firescaping, “planting for fire”, is actually an oxymoron. It should be “planting to reduce fire”. The less fuel there is, the safer you are, but homeowners in high fire zones should not be afraid to have beautifully landscaped gardens. Human beings want beautiful home landscapes with diversity and color, so the hyper-safe fuel-free parking lot approach is not appealing to anyone. Instead, think it through yourself, select wisely chosen low-fuel plants, then start flower gardening in your high-fire zone today.

The final caveat is what’s lying on the ground.  Thick leaf litter and duff ignites quickly from embers, then smolders for many days afterward.  So, another key to fire survival is managing the property so these organic accumulations remain thin or absent. You can also reduce unnecessary top growth. Cutting back plants at the start of fire season should be an annual ritual for reducing overall fuel loads.

There are no easy answers to the new wind-driven fires in the American West, and the future is uncertain. What we can do is realize that survival can rest in your landscape. Plant the flowers you love, explore new plant discoveries, and choose anything else with low fuel volume, so you are ready to fight fires after the flowers bloom.

Arctotis ‘Louise’ is a tough, cool-colored perennial that’s good for firescaping.