The word “bomb” is not usually associated with positive things. Except in this case, where making seed bombs could help the ecological restoration of your neighborhood.
These marble-sized balls have resurfaced on platforms such as Instagram and TikTok, where guerrilla gardeners use them to promote urban biodiversity by adding vegetation in neglected areas.
Making seed bombs is an easy, cheap, and fun way to help restore your local greenery, as long as you’re tossing them in the right areas and aren’t breaking any laws. Here’s how to go about it.
How to make seed bombs
Clay powder may be the hardest ingredient to find for this project, but a pound of it will be enough to make a few dozen seed bombs. You can easily find soil and seeds at your local hardware store, but you can also source them from mother nature.
Stats
- Time: 20 minutes.
- Material cost: Around $25 for 15 to 20 seed bombs.
- Difficulty: Easy.
Materials
- ⅓ cup or six to 12 packets of native seeds
- 1 cup powdered clay
- ½ cup potting mix
- 1 cup water
Tools
- Large bowl
- (Optional) Mixing spoon
- (Optional) Tray
Instructions
1. Mix the clay and potting mix. In the bowl, pour the clay and potting mix in a 2:1 ratio.
The powdered clay acts as a binder and protects the seeds from direct sunlight, insects, and birds. We used green calcium bentonite clay (which doubles as a face mask), but you can use any kind you find at your local store or have at home. If you want seed bombs that look more natural and blend into the soil, you can use red clay powder.
Meanwhile, the potting mix will provide essential nutrients for seed germination and early plant growth, giving your bomb the best chance to thrive. Any kind will do, but the finer it is the easier it will mix with the clay. If you have a coarser mix at home, sift it out in a strainer before you use it.
- Pro tip: If you can’t find clay or just don’t want to buy some, you can replace it with the same amount of flour or wet, shredded paper. These alternatives will also act as a binding agent, but they will not be as strong as clay when dried.
2. Add water. Slowly pour enough water to turn the dry mix into a dough—it should feel like putty in your hands. The amount you use to reach this consistency will depend on the absorbency of your chosen clay and soil.
If you think you added too much water, you can add more clay and potting mix to compensate for the added moisture. Just keep the ratio of the dry ingredients constant: for every extra part of potting mix, add two parts of clay.
[Related: Save the world by saving your plants’ seeds]
3. Add the seeds. Pour in your seeds in a ratio of 3:1 in relation to the clay mix and combine with your hands or a mixing spoon. You may change this proportion depending on how dense you want plants to grow, but 3:1 is ideal to work in enough seeds.
- Pro tip: You can put multiple types of seeds into your bombs, but be careful how you mix and match: sun-loving plants will thrive in a spot where a shade-loving one will die, while fast-growing greenery might out-perform and suffocate another. Only combine seeds with similar qualities or habitat preferences, or plants that are known to grow well together.
4. Knead and roll the mix into small balls. Use the palms of your hands to shape your bombs. Keep them around half an inch (approximately one centimeter) in diameter. As you finish each one, place them on a tray with enough room between them so they’re not touching—once they dry, it’ll be difficult to break them apart.
- Pro tip: As you shape your bombs, your clay mix might start drying, making it hard to work with. Keep a bowl of water at hand and add it to the mix in small amounts to bring the desired texture back.
5. Let the seed bombs dry and harden. Leave your tray of seed bombs to rest for a couple of days until they’re fully dry and hard. If you want to speed up the process, place them in direct sunlight, and if you’re leaving them outside, make sure they’re covered in case it rains.
6. Start bombing. Once all of your seed bombs are dry, you can plant them in indoor or outdoor pots, your yard, or in neglected patches of soil you’re allowed to access. You can push them slightly into the soil, leaving the tops uncovered in a sunny spot, but if you prefer to toss them like true bombs, soak them in water for 5 to 10 minutes before bombardment.
Pick and plant your seeds wisely
There are two important considerations to keep in mind when using your seed bombs. The first is location: spread your greenery grenades only where you’re allowed to do so. If it’s a public space, talk to whoever’s managing the land to ensure your seed bombs won’t disrupt the existing ecosystem. If you want to plant in a private space or need to enter one to drop your bombs, get the explicit permission of the property owner. You want to make sure you’re not breaking any trespassing laws.
Second, think about the seeds you’ll be using and make sure they’re from native plants. Native seeds are most likely to thrive in your home environment and will provide habitat and sustenance for local fauna.
“Native species have not only relationships with themselves and humans but also lots of the wildlife that is native to this region. By planting native species, you’re able to continue to support all of these relationships and networks,” says Andrea Kramer, director of restoration ecology and conservation scientist at the Chicago Botanic Garden.
[Related: These 142-year-old seeds sprouted after spending more than a century underground]
Finding seeds native to your area is easy. You can follow our guide and collect seeds from the plants around you, or you can get them at your local hardware store or nursery. To know what to get, check out the National Wildlife Federation’s Native Plant Finder, which will show you a list of plants and shrubs local to your specific zip code.
If you’re having trouble finding vendors, you can use the Xerces Society for Invertebrate Conservation’s Native Plant, Seed and Services Directory. After providing information such as your state and some details about the area you want to cover, the site will tell you where you might find the seeds you need for your bombs. If you have any questions, remember to contact your local environmental organizations and ask for their help.
Update, May 18, 2023: This story has been updated to emphasize that readers should not plant seed bombs in spaces they’re not authorized to access.
