Field Crop IPM Program Lead & Grazier Specialist
Frost seeding is used to improve productivity and forage quality of pastures and hay fields by broadcasting seed on frozen ground. Conventional tillage, minimum tillage and no-till usually have higher establishment success rate than frost seeding. However, frost seeding can be an economical way of rejuvenating an existing forage stand when tillage or no-tilling seeding are not viable options because of soil depth, variable soil drainage, stoniness, risk of soil erosion, cost or immediate forage needs.
Time of Seeding
For most of Ontario, the best time to frost seed is from mid-March or early April, once the snow is all or nearly all melted and the ground is frozen enough to support equipment. Ideally, the ground freezes and thaws at least 2 to 3 times after the seed is broadcast. This freeze-thaw action helps to incorporate the seeds into the soil surface. Avoid frost seeding on top of snow where any run-off from rapid snow melt will wash the seed away.
Frost seeding is often done using a spinnerspreader on an all terrain vehicle (ATV), a snowmobile or a tractor. In particularly rough or small areas, a hand-held broadcaster may be the preferred option.
For the seeds to germinate there needs to be good seed to soil contact. The best sites for frost seeding are thinning grass stands with some soil exposed. Seedling establishment can also be improved by overgrazing or clipping to 5 cm the previous fall to open the stand, weaken the existing plant growth and allow for better freezing and thawing action. Frost seeding is least successful in fields with thick sod.
Species Selection and Seeding Rates
Red clover is the easiest specie to frost seed. The seed is dense, which improves seed-soil contact, it germinates at low temperatures and has high seedling vigour, allowing it to start growing early in the spring. Birdsfoot trefoil and white clover have been frost seeded with varying degrees of success. Birdsfoot trefoil is more difficult and slower to establish than red clover, but it is non-bloating. Once established, it will grow well under a wide range of growing conditions, and will persist longer than red clover.
Grasses are rarely frost seed successfully. However, research at the University of Wisconsin by Dr. Dan Undersander demonstrated greater establishment success with orchardgrass and Italian (annual) ryegrass than with timothy or reed canarygrass. Smooth bromegrass was intermediate for establishment, but is more winter hardy than orchardgrass and Italian ryegrass.
Because of auto-toxicity, which will prevent new alfalfa seedlings to grow in the presence of a mature alfalfa plant, alfalfa is not well suited to frost seeding.
Frost Seeding Rates
Species Seeding Rate (lbs/acre)
Red clover 3 6
White clover 2 3
Birdsfoot trefoil 3 6
Orchardgrass 3 4
Italian ryegrass 4 8
Use the higher seeding rates when significant bare ground is visible
While phosphorus fertilizer benefits new seedlings, in a frost seeding situation, fertilizing the field will provide the advantage to the existing plants. A better option is a late summer application of phosphorus and potash to promote growth and winter persistence of the newly established legumes. In the year of seeding, if an adequate stand (40% or more legume) is established, avoid the application of nitrogen fertilizer. Nitrogen fertilizer will increase the competition from grasses. In stands where there is a low level of legume, there will be a yield response from the grasses to additional nitrogen. If nitrogen must be applied to increase production, it should be limited to less than 50 kg/ha (actual) during the first season.
Once the new seedlings are established, regular grazing or harvest will reduce competition from existing grasses and allow light penetration into the canopy. In the year of establishment, avoid overgrazing by keeping at least 5 to 8 cm (2 to 3 inches) of top growth.