When deciding what seeding rate to use for establishing a new forage seeding, you need to consider the percentage seed germination, seedling vigor, and the size of the mature plant. The pure seed and seed germination percentage are listed on the bag's tag for certified and inspected seed. Vigor of the seedling that germinates depends on the species and age of seed. Larger seeded plants usually have more vigorous seedlings than small-seeded plants. Seed are more vigorous the year after harvest than they are if they have aged. The size of the mature plant depends on the genetic ability of the species to increase in size and by the amount of open space around the plant. Some forage species can increase in size by tillering (Kentucky bluegrass, orchardgrass, tall fescue, timothy) or by growing larger crowns (alfalfa, red clover, birdsfoot trefoil, lespedeza). Other species are able to use open areas of the stand by moving growing points underground (Kentucky bluegrass, tall fescue, bromegrass, reed canarygrass) or above ground (common and ladino-type white clover).
Increasing the seeding rate to compensate for poor seedbed preparation is usually not justified. If seeds fall on an area of ground that is not suitable for germination and survival, two seeds will do no better than one. If two seedlings emerge close to each other, they will compete with each other and may do no better than one seed.
In general, seeding rates of individual species are reduced when combined in a mix but the total seeding rate of the mix may be higher. When mixing forage species, use ones that are compatible in growth habit and palatability and complement each other in growth distribution and ecological niche.
Growth habit determines the forage specie's response to grazing or machine harvest management. Orchardgrass, tall fescue, bluegrass, and redtop are similar in growth habit. These species head in the spring then tiller in later growths keeping the growing point near the ground. They can tolerate close, frequent defoliation. Orchardgrass is less tolerant of repeated close, frequent defoliation than the others. Timothy, smooth bromegrass, and reed canarygrass are different. These forages go to joint (the growing point grows up above the soil surface) in every growth cycle and can be injured if grazed or hayed at the wrong time.
Alfalfa, red clover, and upright birdsfoot trefoil (Viking type) are good legumes to use in hay mixtures with orchardgrass, tall fescue, timothy, bromegrass, or reed canarygrass. Ladino and common white clover, red clover, alsike clover, and prostrate-type birdsfoot trefoil (Empire type) are good legumes to use with orchardgrass, tall fescue, bluegrass, and redtop where grazing is the primary harvest method.
Growth distribution in forage species is a response to weather and day length. Some forages grow better in cool weather; others grow better in warm weather. Tall fescue is more tolerant of hot and dry weather than orchardgrass; timothy is the least tolerant. The flush of spring growth in grasses is related to day length and differs among species. Orchardgrass heads out under shorter day lengths than does timothy. Redtop is one of the latest of cool season grasses to go to head. There are differences between varieties within a species. Hallmark orchardgrass goes to head sooner than Pennlate and has more vigorous fall growth.
Ecological niches of forage species differ and are related to climate, soil fertility, soil drainage, harvest management, and pest pressure. The plants growing in an established pasture are usually the ones best adapted to the current combination of site and management. If you want a different plant cover you will have to change the management, soil fertility or soil drainage. Some species will not grow well on some soils. An example is alfalfa on a shallow shale soil. In these cases you need to change the forage species or go to a different soil (field) to grow the crop.
When soils are variable in drainage it is often beneficial to mix two species that complement each other relative to drainage. Birdsfoot trefoil and ladino clover mix well with alfalfa on fields with variable drainage. The trefoil or ladino clover will predominate in poorly drained areas of the field and the alfalfa will thrive in the well-drained areas of the field. Likewise when seeding Kentucky bluegrass use varieties tolerant to different leaf diseases to improve the quality of forage over the year. One advantage of planting ladino clover in an alfalfa stand is to ensure the presence of a desirable forage species which will fill in open areas where weeds would otherwise invade.