Seed bombs: Weapons of mass germination

Here’s how to create seed bombs for some explosions of colour in your own patch, or for a touch of guerilla gardening this spring.

Pre-packaged seed bombs can be found in gardening and gift shops, but they are also very easy to make at home. The idea is to provide everything the seed needs to germinate within the mix, making it easy to create a throw-and-forget garden or to add some biodiversity to roadside verges and empty lots. Most of the store-bought bombs are wildflower-based but you can also make a native mix with a little bit of prep.

How to make seed bombs

These little biodiversity balls can make excellent, eco-friendly gifts and are very easy to make. Children will love getting their hands dirty while helping out!

You will need:

• One cup of seeds
• 5 cups of compost
• 2-3 cups of clay powder or dense soil.

If you have some clay soil on your property or nearby, you can pound this into a powder using a mallet or a piece of wood, or clay powder can be purchased from pottery supply stores.

Select your seeds. If you are using wildflowers, this could be a pre-mixed packet blend or saved seeds from your garden. Mix in herbs like parsley or dill to create some scent and greenery, along with the usual wild suspects, such as cornflowers, Sweet William and Californian poppies.

If you’re bombing with the goal of spreading native plants, try Carex grass seeds, flax seeds, tussock seeds and berries from any of the Corokia species. Give these a gentle grind with the mortar and pestle to loosen the outer shells. Harder seeds like kōwhai will take a little more prep – clip their hard outer shells with a nail clipper to help them along with germination.

It also helps to pre-soak the seeds for a few hours before shaping your green grenades.

Add the compost, along with a little water, then add your clay and mix together. The clay should help with binding so your bombs don’t fall apart too easily.

Shape into balls and leave in a cool, dry place to harden. Collect up and get throwing!

Where to bomb

Choose sunny spots, preferably with bare, fertile soil. Roadside areas can be great for guerilla gardening but make sure you’re not throwing these into anywhere that is likely to be sprayed or on conservation or farmland, where some plants may be kept out for a reason. 

If you are using seed bombs at home, toss them into bare spots among your garden to add colour and biodiversity. Doing so in spring should bring you results in the summer, as they will have the chance to take root as the weather warms. Don’t forget to water your soil, if possible, to give your bomb the best chance of exploding into life! The bees and birds will thank you for it.