Before you can restore your parcel, you must obtain seed. The amount of seed you will need is directly related to the size of your parcel. When our school did its restoration, the area available to us was a bit larger than a full sized tennis court, about 15 meters by 40 meters. When seed was spread, each square meter of soil needed, by volume, about 500 cubic centimeters of seed to cover it adequately. This is roughly equivalent to a full 8-ounce plastic cup of seed for each square meter quadrat.(A quadrat is a term used in field studies meaning a measured off square of conveniently sized dimensions.) All together the total amount of prairie matrix (a mixture of all types of prairie seeds) we needed, fit easily into about 2 large plastic trash can liners (30-gallon size). For another comparison, a large (gallon size) zip-lock bag full of prairie matrix can easily be used to cover a small plot of 10 square meters (2 by 5 meters).
When acquiring seed, try to obtain seed that has come from locally grown plants. Local seed stock is obviously adapted and well suited to grow and reproduce in your area. Seed acquired from seed companies may and usually do include seeds from distant areas and might not be suited for growing well in your area. (For list of seed and plant sources, see section included an the end of this report.)
Through my affiliation with Fermilab, I was able to acquire enough seed for our restoration project. Fermilab seed was originally hand collected from prairie remnants and collecting your own seed in this fashion is also an option. Prairie remnants include areas like abandoned cemeteries where the ground has not been worked. A more common site for these remnants are railroad right-of-ways. The soil was never worked or planted for crops and the sparks from passing trains actually aided the burning, and therefore, the maintenance of native species aided.
If you are planning to collect seed from a remnant, be sure to obtain permission to do so. Digging up specimens from remnant sites is usually not done because it can destroy the intricate associations established by the plants and lead to the death of many plants.
Obtaining seed from the restored prairie at Fermilab can be one your options. The Lab has been known, on a limited basis, to donate seed for a project. Contacting the Education Office there will get you in touch with someone who may be able to assist you. Seed from the Lab is limited by availability and will require some proof of intended use. A letter on school letterhead paper from your building principal or any other authorized administrator indicating his knowledge and approval will be very helpful in you possibly obtaining some seed.
Another thing to consider is whether to include seedlings as part of your planting. You can start germinating some of your seeds as a class project around mid-March (8 weeks or so before planting) and plant them when conditions are right. It's important to note that seedlings will need to be watered frequently and on a consistent basis, and transplants will need to be hardened for at least a week before being planted. For large scale projects this option may not be very practical. (Hardening is the process of acclimating your plants to the out of doors. It usually only means taking your transplants out to the site and leaving them there for a while. For the first few days leave them out just during the day, then leave them day and night for a few more days, eventually totaling about a week.)
When obtaining seed from anyone, be sure to ask them if the seed is "stratified." Stratification is the natural process plants have developed to protect the seeds that it has produced from germinating in late fall and winter. Seeds that would germinate at these times would be killed by freezing. The seeds you collect from the field need this stratification in order to germinate at acceptable rates. Usually all that is needed to stratify your seeds is to keep them in your garage or other protected, but unheated, area over the winter months. If you want to plant collected seeds earlier, there are artificial methods of stratifying, such as storing the seeds, usually dry or sometimes damp, in the refrigerator for a period of time. Most seeds need about 8-10 weeks to become stratified, but some like Boneset (E. perfoliatum) need up to 16 weeks.
In addition to stratification, some seeds, usually from the legume family may need to be "scarified". Scarification is the mechanical scratching or cutting of the outside coverings of seeds. Some seeds will not germinate unless this action has taken place. As you probably have already determined, these seeds have a thick hull to resist the chemical and mechanical processes associated with being eaten and digested. Scarifying seeds usually only requires that you grind these seeds between sandpaper blocks for about 15 seconds or so. Rubbing them against screening material usually obtains similar results. An example of a common plant that would need its seeds processed like this would be Wild Indigo (Baptisia leucophaea). Since seeds of this type are in the minority, scarification is really not an issue that should worry you.