Does Wildfire Smoke Harm Flowers? A Gardener's Guide

For several days, the sky over the Hudson Valley has looked unfamiliar. The sunlight has been muted, the horizon obscured, and the air quality has at times reached levels considered unhealthy — or worse — for the people breathing it.

The smoke began with wildfires in Canada, but it did not remain there. Carried south by prevailing winds, it now sits over just over a third of the United States, bringing with it fine particulate matter and an understandable question for anyone who grows things:

If this air is hazardous for us, what is it doing to the flowers?

The reassuring answer is that a short period of wildfire smoke is unlikely to cause lasting harm to most established garden plants. Flowers cannot leave the field, of course, nor can they retreat indoors beside an air purifier. But plants and people do not respond to air pollution in quite the same way.

That does not mean smoke has no effect. It means the effect is more complicated — and usually less dramatic — than the sky suggests.

Smoke Changes the Light

The most immediate effect of a smoke-filled sky is a reduction in direct sunlight. Plants rely on light to grow, form roots and produce flowers. Dense smoke can reduce the amount of light reaching the leaves, which may temporarily slow that process.

For flowers such as dahlias as an example, which require considerable energy to produce continuous growth and bloom, several heavily smoked days could mean buds that take longer to open and new growth that comes in less vigorous while the haze remains.

But smoke also scatters light. On a clear day, direct sun mostly reaches the top of a plant, leaving lower leaves in some shade. Scattered light travels in every direction, reaching leaves that would otherwise stay shaded. Cornell Cooperative Extension has noted that during temporary smoke events, plants generally continue to receive enough of this diffuse light to maintain growth, and the overall effect is likely to be minimal.

The grayness that feels so oppressive to us does not necessarily mean the garden has gone dark.

Will the Particles Clog the Leaves?

Wildfire smoke contains extremely fine particles, including PM2.5 — particles small enough to travel deep into the human respiratory system.

It is reasonable to imagine those particles settling over a garden and sealing the pores through which leaves breathe. In most circumstances, however, a few days of smoke are unlikely to clog them.

A visible coating of ash or soot is a different matter. A heavy accumulation can shade the leaf surface and interfere with normal function. Once the air has improved, foliage covered with obvious residue can be rinsed gently with clean water. There is no need, however, to wash every leaf simply because the air has been smoky. In a large garden or flower field, that would consume a great deal of water while accomplishing very little.

Ozone May Matter More Than the Visible Smoke

The pollutant of greater concern to plants may not be the one we can see. Wildfires release gases that help form ground-level ozone, which enters leaves and can damage tissue, reduce photosynthesis and slow growth. The degree of injury depends on the concentration, the sensitivity of the plant, and — most of all — the length of exposure.

Ozone does its damage over repeated or prolonged exposure, not a single smoky afternoon. Sensitive plants may develop stippling, bronzing or premature aging of the foliage, although those symptoms can easily be confused with insects, disease, drought stress or nutrient problems.

We would therefore be cautious about attributing every imperfect leaf to wildfire smoke. A garden is rarely responding to one condition alone.

What Should Gardeners Do?

There is no special treatment that can remove smoke from a field, nor is there a product that will replace the sunlight lost behind a smoky sky.

The best response is the least dramatic one: keep the plants otherwise healthy.

Maintain adequate soil moisture, particularly during hot or dry weather. A plant with access to sufficient water is better able to withstand environmental stress. Water deeply and according to the needs of the soil rather than applying frequent, shallow irrigation. Containers deserve particular attention, since they dry much faster than plants growing in the ground.

Avoid compensating with additional fertilizer. It cannot make up for diminished light, and forcing soft growth during a stress event may create other problems.

Do not spray foliage merely as a gesture. If there is a clear deposit of ash, rinse it after the smoke has passed. Otherwise, continue your usual growing practices and observe the plants over time.

Most importantly: do not remain outside caring for the garden when the air is unsafe for you. Flowers can tolerate a few days without deadheading. Dahlias can wait to be tied. Weeds will still be there when the air clears. An AQI warning is a public-health warning, not a challenge to see how much work can be completed before breakfast.

What We Are WWatching at Bear Creek Farm

At Bear Creek Farm, we are not making major changes in response to a temporary smoke event. We continue to watch soil moisture, temperature, disease pressure and the general vigor of the plants. We are attentive to any unusual changes in the foliage or the pace of bud development, but we are also careful not to mistake coincidence for cause.

Should smoke and elevated ozone persist for weeks rather than days, the concerns would become more significant. For now, though, the evidence suggests our flowers are likely to endure this episode far better than we might expect.

A Garden Grows in the World as It Is

Those who garden long enough eventually surrender the idea of a perfect growing season. There are years of drought and years of relentless rain. There are late frosts, early heat waves, hungry insects, and August nights that feel more like October. Now, increasingly, there are days when smoke from fires hundreds or thousands of miles away turns the sun overhead into a deep, hazy orange, barely recognizable and hard to look away from.

Gardening is sometimes described as an escape from the world. In truth, a garden is deeply connected to it. The atmosphere, the soil, the water and the shifting climate do not stop at the garden gate. Flowers grow within those conditions — not because the conditions are always ideal, but because plants are remarkably practiced at adapting to an imperfect world.

For the moment, the most useful things we can offer them are good soil, adequate water, and our careful attention. And while the air remains hazardous, we should extend that same care to ourselves.