The label on a seed bomb can read like a soil science textbook. Mycorrhizal inoculant. Humic acids. Biochar. Native species. These are real things with real functions, and understanding what they do is the fastest way to understand why some seed bombs work and others don't. This is a plain-language glossary of every term we use in our formula and on our packaging.

Biochar

Biochar is charcoal produced by burning organic material: wood, plant matter, agricultural waste at high temperatures with limited oxygen. The result is a porous, stable carbon structure that doesn't break down quickly in soil.

In a seed bomb, biochar does two things. It holds moisture in the root zone, which matters in the dry, compacted urban soil where most seed bombs land. And it creates physical pore space in that same compacted ground, giving roots somewhere to go. It also acts as a long-term habitat for the microbial life that makes soil productive. Once those populations establish, the soil around the plant improves over time rather than staying depleted.

Biochar is not a fertilizer. It doesn't feed plants directly. What it does is make the soil around a seedling more hospitable, which is exactly what you need when you're planting in ground that hasn't supported anything in years.

Mycorrhizal Inoculant

Mycorrhizae are fungi that form a symbiotic relationship with plant roots. The fungal network extends far beyond what the root system can reach on its own, pulling in water and nutrients, especially phosphorus, and delivering them to the plant. In exchange, the plant feeds the fungi sugars produced through photosynthesis.

This relationship exists in the roots of most plants in healthy natural soil. The problem with urban ground is that construction, compaction, and years of neglect destroy the fungal networks that would normally be there. A seedling trying to establish in a vacant lot has no existing network to connect to.

A mycorrhizal inoculant introduces fungal spores directly into the growing environment. We use a concentrated inoculant that colonizes roots shortly after germination. Once the connection forms, the seedling has access to a much larger effective root zone than its physical roots would allow which is the difference between a seedling that stalls out at two weeks and one that keeps growing through its first summer.

Humic and Fulvic Acids

Humic and fulvic acids are naturally occurring compounds produced by the decomposition of organic matter. They're found in healthy soil, peat, and leonardite, and they play a foundational role in how plants access nutrients.

Humic acid improves soil structure and helps bind nutrients so they don't leach away with rain. Fulvic acid has a smaller molecular size and works at the cellular level. It helps nutrients cross the plant's cell membranes more efficiently, which means the plant can absorb what's already in the soil around it rather than leaving it locked up and unavailable.

We use humic and fulvic acids in our formula, dissolved into the mixing water before the clay is shaped. The result is a seed bomb where both compounds are distributed evenly throughout the substrate, close to the seed from the moment it starts to germinate.

Worm Castings

Worm castings are the digested organic matter that passes through an earthworm. They're one of the most nutrient-dense natural soil amendments available rich in nitrogen, phosphorus, potassium, and a range of micronutrients and they release those nutrients slowly over weeks rather than all at once.

In a seed bomb, worm castings serve as the primary slow-release nutrition source for the seedling in its first weeks of growth. They also introduce beneficial microbial populations that support root health and help break down other organic matter in the surrounding soil.

Worm castings are gentle enough that they won't burn seedlings at high concentrations, which makes them well-suited to a formula where the growing medium is in direct contact with the seed from the start.

Native Wildflower Species

A native species is a plant that evolved in a specific region and has been part of that region's ecology for thousands of years. Native plants are adapted to local climate, soil conditions, and seasonal patterns. More importantly, they have co-evolved with the insects, birds, and other wildlife in that region which means local pollinators have learned to forage from them, and local birds have learned to nest near them.

In Canada, many commercial wildflower mixes contain non-native species some of which are actively invasive. Baby's breath and dame's rocket are two common examples. They germinate reliably and look attractive, which is why they end up in cheap seed mixes, but they compete aggressively with native plants and provide less usable forage for native bee species.

Our seeds are sourced from Canadian suppliers and matched to the region each product is sold in. A seed bomb sold for use in Ontario contains species native to Ontario. The goal is not just to put plants in the ground  it's to put the right plants in the ground for the insects and birds that are already there.

Coco Coir

Coco coir is the fibrous material processed from coconut husks. In horticulture, it's used as a growing medium because it holds moisture consistently, resists compaction, and has a neutral pH. It's also pathogen-free, which matters in a handmade seed bomb formula where introducing weed seeds or disease from unsterilized soil would undermine the whole product.

We use coco coir instead of screened garden soil as the bulk substrate in our formula. It gives the seed bomb a consistent texture across every batch and ensures that what's growing out of each bomb is what we put in not whatever happened to be in a bag of outdoor soil.

Clay

Our clay is used as the structural shell of our seed bombs. It's the material that holds everything together, gives the bomb its weight, and breaks down gradually in soil as moisture penetrates the outer layer.

The clay shell is what makes a seed bomb different from a pellet or a pressed seed disc. It survives being thrown, handles rain without dissolving immediately, and creates a stable microclimate around the seed during the early stages of germination. The gradual breakdown over days or weeks depending on rainfall is what gives the seed inside a slow, sustained moisture release rather than a single wet event.

For a fuller breakdown of how all of these ingredients work together in our specific formula, the previous post on whether seed bombs actually work goes into the reasoning behind each one. And if you want to see the formula in action, our seed bombs are available here, made in small batches in Canada