Martina Decker is developing tactical urbanism tools that come from a lab.

By Zach Mortice

The tools for tactical urbanism seem more likely to be developed in community center meeting halls and anonymous Internet forums rather than university laboratories. But at the New Jersey Institute of Technology (NJIT), an architecture professor is working on ways to give impromptu urban vegetation efforts staying power with hydrogel seed bombs.

Martina Decker, who directs NJIT’s Idea Factory and Material Dynamics Lab, is combining seed bombs—balls of organic matter that protect and help seeds packed within them grow—with hydrogel granulates, polymers that are extremely hydrophilic, sucking in moisture and swelling to up to 400 times their own weight in water. By nestling this water-attracting material amid seeds, young plants have access to moisture that stays in the soil and won’t evaporate.

Decker trained as an architect, but found her way to material science research after realizing how unsustainable many building and planting materials are. By looking at materials at the “molecular level,” she says, “rather than trying to find the right material for an application, we can design materials for the application.”

The hydrogel seed bombs aren’t a fire-and-forget miracle. “It’s really more of a starter medium,” she says. Hydrogel is perfect for inattentive houseplant owners, but successful plants that rely on it still need some added moisture.

Each of Decker’s hydrogel seed bombs places compost, hydrogel granulates, fertilizer, and seeds (she’s been experimenting with wheatgrass, onions, and radishes) inside a water-permeable clay shell. When the bombs are launched and they reach the earth and absorb water, the hydrogel begins swelling with it, pushing seeds out into a wider radius. “You increase the radius by eight inches,” says Decker, who pioneered this research with help from NJIT industrial design student Nahin Shah, the lead designer on the project. It’s a good planting method for large areas that don’t need to be planted with any precision. Moisture is released slowly over time, and is less able to evaporate, especially if the gel makes its way underground. This hydrogel can absorb and release water over many cycles, lasting for several years. Tests with wheatgrass planted with hydrogel resulted in plants that grew faster, larger, and stronger than those with only sparse watering in standard soil.

Decker is beginning to look at combining hydrogel seed bombs with drone technology, investigating ways algorithms can program drones to best distribute seeds. She’s also researching the ways hydrogel could work with green wall systems. “One of the biggest issues that we have with green walls is that they’re fighting gravity more than a green roof,” says Decker. “The moisture immediately drains, and they dry out.” By turning liquid into a quasi solid and helping it resist evaporation, water that makes its way into green walls has a better chance at sticking in its shallow soil.

The seed “recipe” in each seed bomb is also something Decker wants to refine. There are already off-the-shelf seed mixes at garden centers and home improvement stores formulated to attract bees or specific kinds of butterflies. (And you can buy hydrogel itself at the same places.) Why not put hydrogel seed bombs next to them that attract particular bird pollinators, or that draw bees to feed the burgeoning urban beekeeper renaissance?

Decker says her hydrogel seed bombs are “a good tool to reclaim urban surfaces that have been barren.” These seed bombs are portable, covert, and require only a decent throwing arm to use; they’re ideal for grassroots landscape activism. Decker calls it “stealth gardening.”

But hydrogel seed bombs aren’t just useful for gardening vigilantes. In addition to park agencies looking for planting methods that require less water, there is the simple ease and fun of hurling a clay shell to the earth so that it disintegrates and something grows in its place. It’s an inviting tool to get all people—young and old—to take action and ownership of the landscapes in their communities. It’s easy to imagine a class of giddy second graders flinging hydrogel seed bombs in an abandoned empty lot near their school. They will be learning about how the seeds will grow, and how, with a few flowers in a new prairie grass meadow, their neighborhood might, too.

Zach Mortice is a Chicago-based architecture and landscape architecture journalist. You can follow him on Twitter and Instagram.