Inside: Seed bombs may not work because the soil is poor or growing conditions are not ideal. Starting seeds takes more than luck.
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I love the idea of seed bombs. The first time I heard about them I wanted to toss them everywhere, but I knew they wouldn’t work. Actually, they will work in places where you don’t need them, but will almost never work in places you do.
More often than not, we encourage people to throw seed bombs into vacant lots, abandoned industrial sites, roadside verges and medians, grassy wastelands, and trampled playgrounds. These places are the least likely to produce results.
First, what is a seed bomb?
Seed bombs (also called seed balls, seed pellets, or earth) are golf ball-sized wads of clay, compost, and wildflower seeds. The ingredients are blended together and then dried so the seeds will not sprout prematurely.
People then toss these balls into places where nothing lives, hoping to grow flowers for bees and other pollinators. The problem is that bare ground is usually caused by factors that inhibit the growth of plants, including those new wildflower seeds.
Why bare ground stays that way
Most bare ground is bare for a reason. To begin with, many of these areas have dense layers of traffic pan. Traffic pan is an agronomist’s term for soil that has been heavily compacted by frequent use. Roads, industrial sites, and fields frequently traversed by tractors, cultivators, harvesters, or trucks all are subject to traffic pan. Even footpaths, playgrounds, and ball fields develop it.
Traffic pan makes it difficult or impossible for seeds to start. The compaction itself can prevent tender young roots from penetrating the soil, and the heavy layer can act as a barrier to water and air, causing puddling above and dryness below. Certain plants (think dandelions) manage to break through these dense layers, but they are usually not the ones you want.
Most often, the traffic pan needs to be broken up by mechanical tilling. If not, seeds landing in these areas may germinate, only to die when the roots cannot penetrate the soil or when they get washed away by heavy rain.
Things in the ground we can’t see
Industrial sites may be polluted with chemicals or waste products that prevent germination or inhibit growth. Toxic substances may have destroyed beneficial soil organisms while other chemicals may have altered the pH. In addition, these areas may be too sunny, too shady, too wet, or too dry.
Some may continue to be driven over, walked on, or peed on by every passing pooch. The seeds or young shoots may be preyed upon by birds, rodents, squirrels, or other hungry city-dwellers. Remember that farmers and gardeners work hard to get results, and they continually fight against the elements, predators, pests, and pathogens. They don’t just stick seeds in the ground and walk away.
City or county agencies often spray roadsides for weed control, so planting seeds in these areas may be for naught. Utility companies spray their easements as well, usually to keep down fast-growing trees, but the herbicides they use are not selective for one particular kind of plant. They may end up killing everything.
And since seed bombs are not (or should not be) made from invasive species, there is no way that seeding a field of invasives will do anything except give the existing flora a little jolt of fertilizer.
Fertile fields are not good for wildflowers
Although it may seem counterintuitive, abandoned fields—especially those that received fertilizer in the last decade or so—are also poor places for seed bombs.
Many wildflowers are naturally nitrogen-fixing, producing all the nitrogen they need through natural processes. That means they can thrive in low-nitrogen soils where other plants can’t survive. As long as the soil nitrogen remains low, they can easily compete against other plants, including grasses.
But once we add chemical fertilizers, grasses take over with a vengeance and very quickly out-compete the wildflowers. Much of that artificial fertilizer lingers for years, making it nearly impossible to grow wildflowers in abandoned croplands.
In his engrossing book, A Sting in the Tale: My Adventures with Bumblebees, Dave Goulson explains this conundrum, and he emphasizes how hard it is to grow wildflowers in a field that was once fertilized. As he says, “There is no easy way to reduce the fertility of soil in a meadow, yet it is impossible to recreate a rich flower community without first doing so.” He explains why reducing soil fertility can take many, many years.
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Careful placement of seed bombs makes a difference
I’ve had people say they planted seed bombs in flower pots and garden beds and they grew “beautifully.” No doubt this is true. But the idea behind a seed bomb—that we can distribute pollinator plants far and wide by throwing clay-encrusted flower seeds into waste areas—is mostly just a happy thought.
The law of unintended consequences is hard at work here. By “improving” the land for various uses, we have destroyed its ability to produce the historic native landscape we are now seeking.
If you want to toss seed bombs, go for it. After all, it is fun to throw things: “Take that, you nasty piece of plantless dirt!” But if you really want to help the pollinators, a little more thought is necessary for success.
Honey Bee Suite