I love the idea of seed bombs. The first time I heard about them I wanted to go out and toss them everywhere, but at the same time, 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, people are encouraged 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.
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 repeated and 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 hard or impossible for seeds to start. The compaction itself can prevent tender young roots from penetrating the soil, and the layer can act as a barrier to water and air, causing puddling above and dryness below. Certain plants manage to break through these dense layers, but they are usually not the ones you want. Most often, 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 fail to penetrate the soil or when they are washed away by a heavy rain.
The things we don’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. They may still 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.
Roadsides are often sprayed by city or county agencies in the name of weed control, so planting seeds in these areas may be for naught. Utility easements are often sprayed as well, usually to keep down fast-growing trees, but the herbicides they use are not selective for one particular kind of plant. 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 much better
Although it may seem counterintuitive, abandoned fields—especially those that were fertilized in the last decade or so—are also poor places for seed bombs. Many wildflowers such vetch and clover are nitrogen fixing. Since these plants can produce all the nitrogen they need, they can effectively compete against other plants in areas where nitrogen is otherwise scarce. All else being equal, plants like the grasses can’t even get started in these areas. But once a field is artificially fertilized, the grasses take over with a vengeance and quickly out-compete the wildflowers.
In his engrossing book, A Sting in the Tale: My Adventures with Bumblebees, Dave Goulson explains this conundrum in detail, and he emphasizes just 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 goes on to explain how the process of reducing soil fertility can take many, many years.
Placement makes a difference
I’ve had people protest that 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 a happy thought that is mostly just that, 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 would go a long way to achieving success.
Honey Bee Suite