Seed bombs are small balls of growing medium (most often soil), fertilizer and seeds that were originally used for aerial reforestation in hard-to-access areas. The most common recipe for home-made seed bombs is credited to Fukuoka, a Japanese biologist who used them in his fields for "no-work" farming. Those seed balls allowed him to seed his farm without equipment or the need for tilling. Today, seed bombs are popular for their use in guerilla gardening, i.e. the practice of adding plants to neglected, vacant or otherwise underused (often urban) spaces, private or public. The aim of an operation of guerilla gardening can either be to beautify a public view, or the seeds can be carefully selected to cause damage to a property (e.g. planting flowers in a local army reserve). Seed bombs can also be used in the home garden for a precise seeding.
Fukuoka's recipe used simple ingredients, namely clay, compost and seeds. The clay in the seed bomb helps hold the mix together and prevents birds and insect from nibbling on seeds. The compost ensures the seeds have good nutrients right from the start. The clay will begin to break down after a few rainfalls and the seeds should start to sprout. It’s best to use seed bombs when they’re fresh, but they can be stored up to several weeks in cool, dark place (otherwise will start sprouting! and will die without right conditions). Seedlings usually visible in 1-3 weeks.
Here's how to make your own!
-large bowl or tray or container of some sort
-clay (if you're in Montreal, you can find some here)
-good compost (old, completely decomposed)
-seeds of your choice (we suggest native plants, but make sure whatever you're planting is not invasive)
There is a cornucopia of seed bombs recipe, calling for a ratio clay to compost to seeds anything from 1:1:1 to 3:1:1 or 5:3:1 or anything in-between. You can test different ratios until you find a recipe that suits your needs, but the minimal requirements are that the bomb hold together once dry, but that it also breaks down easily under rain.
The correct ratio will also depend on the seeds used in the recipe. The ratios above are good for medium-sized seeds (think sunflower seeds). Bigger seeds, like bean seeds, will probably prefer being added individually in the balls after they're formed, at a rate of about one seed per golf-ball-sized seed bomb. Smaller seeds (most flowers and greens; anything smaller than rice) will probably benefit from a 2:2:1 ratio in small balls, or they can simply be added on formed seed bombs and then pressed into the ball (not too deep).
1) Measure all your ingredients (clay, compost and seeds) and put them in a container. Mix well.
2) Add water, a small amount at a time, until you obtain a dough that holds well together (like cookie dough; try pressing it in flat disks to see how well it sticks together) but that is not too wet (wet seed balls may cause the seeds to germinate prematurely, especially if using small seeds).
3) Form in balls of any size and shape.
4) Let dry for at least 2 days. Some people suggest drying in sun, but clay tends to crack and crust when it is exposed to sunlight and dries too fast. For a safe drying process, put the balls in a warm, dark place with good ventilation. Turn the balls once or twice per day so they can dry uniformly. If the seeds germinate prematurely, plant them or lose them.
5) Throw! (Or use a slinger!)
Note on seeds: It is possible to mix seeds in a seed bomb. Important things to consider, though, are the size of the seeds, their temperature/season of germination, their rate of germination and the needs of the plants in terms of soil and sunlight. Seeds of unequal size are not likely to germinate at the same time, since bigger seeds need more water than smaller seeds in order to activate the germination process. Likewise, any combination of seeds that do not germinate in similar conditions, or of plants that do not grow in the same conditions (e.g. do they need well-drained soil? can they tolerate drought? do they do well in poor soil? does one prefer shade while the other needs full sun exposure?), are likely to favor one plant over another, in which case one will survive and the other will die or won't grow well.