"What is the best pasture mix" is a question that crosses my desk on a frequent basis. The answer is simple, "that all depends". Each situation needs to be looked at for the specific characteristics and then look at the grass and legume species that best match.
Is hay going to part of the management of this field? Are you looking to take a 1st-cut of hay and then graze the second growth? Or is it going to be hay for a couple of years and then become a pasture? If hay is going to be part of the management plan, then alfalfa is likely a good choice for the legume component of the mix. Alfalfa does best in well drained soils. Trefoil can tolerate more uneven drainage, so it could be a possibility if the field is poorly drained. Clovers might be considered, but keep in mind that they are slow to dry if you want to make hay. White clover is excellent for pasture. Its spreading growth habit will fill in some open spaces between bunch grasses. Red clover will only last for 2 years in a stand.
Bunch Grasses & Sod Forming Grasses
Including both bunch grasses and sod forming grasses in a pasture mix will be beneficial. Bunch grasses include orchard grass, meadow brome, timothy, perennial rye grass and tall fescue. Sod forming grasses include smooth brome, reed canary grass, Canada bluegrass, Kentucky bluegrass and creeping red fescue.
Orchard grass is a very productive grass that works well for both grazing and stored forage. For pasture, an advantage of orchard grass is that once the seed head is removed the plant stays vegetative for the rest of the growing season. Orchard grass is reasonably productive in dry conditions. Orchard grass starts to grow very early in the spring, well before any of the other species. The disadvantage is that when it heads out, the forage quality drops very quickly and dramatically.
Meadow brome is almost as productive as orchard grass. Similar to orchard grass, it stays vegetative after the first seed head is removed. This is a big benefit in a pasture situation.
Reed canarygrass makes excellent pasture. It does well in moist soil conditions. Because of its big root system, it can be productive in dry conditions as well. The disadvantage of reed canary grass is that it is slow to get established. It typically takes 2 or 3 years before you see very much reed canarygrass in the stand. Reed canarygrass stores energy in the base of the stem and re-grows from the top of the cut stem. For this reason, if cutting reed canary for stored forage, the cutting height should be fairly high at 3 - 5 inches (7-10 mm).
Perennial Ryegrass and Tall Fescue
Perennial ryegrass makes excellent pasture, but generally does not last more than 2-3 years in our Ontario environment. Perennial ryegrass prefers cool temperatures and good moisture levels. Tall fescue is the best grass for stockpiling forage for late-fall and early-winter grazing. If the pasture you are seeding will be used in this way then consider tall fescue as one of the species for the mix.