According to an article in The Guardian, seed bombing (the technique of introducing vegetation – often wild plant species – into derelict/abandoned urban sites using compressed balls of earth containing a variety of seeds) can be traced back to Japan and the ancient practice of tsuchi dango (literal translation – ‘earth dumpling’).
There are various recipes for creating seed bombs, including this one – which The Guardian article draws from Josie Jeffery’s book, Seedbombs: Going Wild with Flowers:
Makes about 6 earth dumplings:
* 5 tablespoons of seed compost
* 4 tablespoons of terracotta clay powder
* 1 teaspoon of seeds (Note: Base this on poppy seeds as a size guide and add half a teaspoon more as the seeds go up in size.)
* 1 teaspoon of chilli powder as a pest deterrent (optional)
* Sprinkles of water at intervals (about 20ml)
You can also find advice on how to make an earth dumpling here.
We’d like to invite you to donate a earth dumpling (containing where possible seeds of indigenous species of wildflowers – remember, this is quite impoverished soil) to Furnace Park. Even better – donate an egg box containing 6 dumplings!
Your contributions will frame Furnace Park, bringing the whole length of the internal perimeter to life with flowers that will help maintain and increase the site’s biodiversity. (We’d really like to encourage planting that will attract butterflies and bees.)
It would be great if you could make a postcard about what’s in your seed bomb, perhaps with illustrations/poetry/words/haiku, etc, so that we can exhibit them on site in the summer, when the flowers begin to appear.
If you’d like to contribute an earth dumpling and postcard, please contact a.j.jackson@sheffield.ac.uk for more info
If you’re interested in gardening/landscaping and would like to get involved in designing and growing this site, along with our existing volunteers, then please contact a.j.jackson@sheffield.ac.uk
occursus 
Brilliant idea Amanda, will be a great process and exciting to see which flowers enjoy their new surroundings!! You are quite correct the soil is very poor, ideal for most indigenous wild flowers. Try and get some Yellow Rattle seeds if you can they are semi-parasitic and will increase diversity of the other wild flowers.Yellow rattle will also prevent grass smothering the flowers. Looking forward to seeing the transformation of the site in 2014, please be patient though a lot of wildflowers take a year before they appear and give you an abundance of flowers!! Hopefully you will start to see some life in the wildlife pool area in the spring as well, I’m sure the rain has filled the little pools up ready for their new tenants!!
Warm regards
Sally
Seed bombing is a more appropriate technique when you have limited access to the site. Proper guerrilla gardening! If you have regular access, you can save yourself a lot of trouble by simply scattering. We do this a lot a Woodbank. We collect seed in Autumn from gardens we like. A favourite is Bolton Percy, the no-dig aesthetic of which seems applicable to what you have to do. http://www.nodiggardener.co.uk/2012/08/bolton-percy-churchyard.html
http://www.nodiggardener.co.uk/2012/08/bolton-percy-churchyard.html
Of course, spring is the wrong time to be seed collecting. I’ve got a lot of Iris foetidissima seed, which is an ideal plant for you.
But as Sally said, some of these things take forever. I’d guess at five years from iris seed to flower.
Another good trick is to join the Alpine Garden Society who have an awesome seed list (~5500 species) that comes out at christmas. Its not just alpines either. After the main distribution, you can buy surplus seed very cheaply. You just specify genus blocks and number of packets and they pick from whats left at random. A marvelous way to increase your biodiversity….
Anna Pavord on Bolton Percy:-
http://www.independent.co.uk/property/gardening/gardening-pushing-up-daisies-lilies-poppies—-anna-pavord-visits-a-north-yorkshire-churchyard-where-the-dead-can-rest-in-peace-beneath-a-herbaceous-heaven-on-earth-1493905.html
Worsborough village cemetery is worth a look too
http://www.nodiggardener.co.uk/2013/06/worsbrough-village-st-marys-cemetery.html
whoops, second Bolton Percy url was supposed to be Anna Pavord:
http://www.independent.co.uk/property/gardening/gardening-pushing-up-daisies-lilies-poppies—-anna-pavord-visits-a-north-yorkshire-churchyard-where-the-dead-can-rest-in-peace-beneath-a-herbaceous-heaven-on-earth-1493905.html