Creating a seed mix
Most tallgrass prairie seed mixes start with a 50:50 grass to forb ratio. Forbs include wildflowers and shrubs that behave like wildflowers, such as New Jersey Tea. A mix with too much grass seed becomes too dense for the wildflowers to survive. However, a mix with too little grass does not contain enough fine fuel to burn properly. A 50:50 ratio gives enough wildflowers to cerate a diverse and showy habitat, and enough grass to carry fire.
The amount of seed (weight) depends on the site. The more competition you expect the prairie plants to have the more seed you will need. A typical rule of thumb is 10kg/hectare (10,000 square meters). This is a typical amount for broadcasting. If a seed drill is involved less seed can be used. Perhaps 7 kg/hectare. Seed should always be cleaned, with awns and husks removed. Doing so will allow for a lesser rate of seed to be used and a greater germination can be achieved in you planting.
Another way to create a seed mix is to create a spreadsheet. For each species you assign a percentage of the mix you want it to be. Common species, such as Black-eyed Susan and Wild Bergamot can be given a higher percentage than rarer species, such as Butterfly Milkweed. You then must research the amount of seed per gram. The internet can be used for this, although it maybe in ounces and you will have convert. Lastly you need to assign a value to the number of seeds per square meter you would like. 50 seeds per square meter seems to work. Then you multiply the number of square meters your site is (10,000 square meters for example) by the number of seeds per square meter you choose (50 x 10,000 = 500,000) Therefore you need 500,000 seeds. Then you take the percentage of the mix for each species (for example 10% for Black eyed Susan). 10% of 500,000 is 50,000. therefore you need 50,000 Black-eyed Susan seeds. If you know the number of seeds per gram (in the case of Black-eyed Susan it is 3570) you divide the total seeds required by the seeds per gram to get the total weight required (50,000/3570 = 14 grams of Black-eyed Susan seed required). By doing this you can calculate more accurately the amount of seed for each species required. Otherwise you have to estimate by volume, and it is much less accurate, because seeds differ significantly in size.
Deciding on the species to use in the mix and the percentage of each depends on a lot of things:
How much does the seed cost?
How much seed is available?
What is your goal – are you trying to recreate a certain type of prairie or creating wildlife habitat, creating a buffer strip along a water course? Is the target wildlife pollinating insects, upland game birds or rare songbirds?
What is the soil type and moisture level?
What species are found in your area?
One rule of thumb is that there are certain species that will perform the best initially. Generally these species are lumped together as early successional, meaning they naturally show up first and then disappear or become much less common. Early succession prairie species include Black-eyed Susan, Wild Bergamot, Hoary Vervian, Showy tick-trefoil and Canada Wild Rye. The next species to appear are the mid successional species- such as Butterfly Milkweed, Round-headed Bush-clover, Big Bluestem and Indian Grass. The last species to appear are the most conservative species. These species are typically only found in prairie remnants and generally do not inhabit creations. Plants on this list are Pink Milkwort, Gatinger's Agalinis and White Fringed Prairie Orchid. A species mix with lots of early succession and a some mid succession species will do the best. If appropriate the most conservative species can be added last. But research indicates that a it may take a prairie at least 50 years to be ready for the conservative species.
For more information on creating a seed mix refer to the book:
The Tallgrass Restoration Handbook for Prairies, Savannas and Woodlands
Edited by Stephen Packard and Cornelia F. Mutel