Birdsfoot Trefoil Seed Production


There is a strong market for birdsfoot trefoil seed, but extra time and effort is required for proper production. Though not an easy crop to grow - a lot of attention must be paid to local conditions - a successful crop is well worth the effort.

Production of birdsfoot trefoil seed involves three phases:

  • the pre-establishment period
  • the establishment year
  • subsequent production years

Pre-Establishment Year

Site selection - For maximum seed yield, the birdsfoot trefoil planting site should have the following characteristics:

  • a field that is free of quackgrass, clover and other perennial weeds; and
  • clay or loam soils with good water-holding capacity.

When producing pedigreed seed, be sure to isolate the class of seed. Refer to the Canadian Seed Growers' Association Circular 6, Regulations and Procedures for Pedigreed Seed Crop Production for more complete information.

Site preparation - Perennial weeds are very difficult and expensive to control once the crop has been seeded. The site selected should be a clean field without troublesome weeds such as quackgrass, Canada thistle, sow thistle and dandelions.

The final step of site preparation during the pre-established year is a soil test to get recommended fertilizer rates for the establishment year.

Establishment Year

Fertilizers and weed control - Once into the establishment year for birdsfoot trefoil, the field should be fertilized according to soil test recommendations. If phosphate, potassium and/or sulphur are required, broadcasting these fertilizer nutrients into the seedbed is recommended prior to seeding.

On established stands, an annual broadcast application of fertilizer may be made in late fall or early spring. Fertilizer should not be applied on frozen soils subject to water runoff.

There are two pre-plant incorporated herbicides that can be used before seeding. Where no companion crop will be used, Eptam can be applied to control several grass and broadleaf weeds. Eptam must be incorporated immediately after application to the soil, followed by a second incorporation to ensure thorough mixing. The product label carries complete directions.

Avadex BW will control wild oats when birdsfoot trefoil is sown with barley, wheat, flax or canola.

Several post-emergent herbicides can be used to control grass-type weeds when seeding trefoil. Herbicides containing 2,4-DB can be used to control some broadleaf weed control in the seeding year. The options for broadleaf weed control in established trefoil are limited to Princep Nine-T, Simazine 80W or Kerb. The product label should be checked for recommendations and precautions.

For more information consult the Guide to Crop Protection for herbicide recommendations.


Just prior to seeding, birdsfoot trefoil seed should be treated with its own special inoculum. Twice the prescribed amount is recommended when sowing this crop for the first time. There are three common methods to inoculate seed;

Mix inoculum with water in amounts indicated on package to form a slurry, then pour slurry on seed and mix well. When done properly, the seed will imbibe the water leaving an even, dry coat of inoculum.

Adhesive solution
This method is a modification of the slurry method, using an adhesive solution instead of water. The inoculum adheres to seed coated with this solution. The solution also contains nutrients which the nodule bacteria uses for growth. Commercially prepared adhesives are available, or a suitable solution can be made by mixing 2 tbsp. (25 ml) of corn syrup in 1 quart (1 L) of water. Use this solution to make a slurry with the inoculum and apply as described in the slurry method.

Dry application
When applying inoculum dry, use two to tree times the normal rate. The dry application method is not recommended because much of the inoculum is wasted and it is not as successful as the slurry method.

To save time, pre-inoculated seed can be used. This seed is treated or coated with rhizobia by a seed processor or distributor and can be seeded directly. The success of nodulation with pre-inoculated seed depends on proper application and storage techniques used by the seed processor or distributor.


If EPTC has been applied, the trefoil should be seeded without a companion crop. If a companion crop is necessary, choose one such as flax which will not act as a strong competitor. Use a seeding rate of 1 to 2 lb./acre (1 to 2 kg/ha) for birdsfoot trefoil. Once the trefoil crop is established, a series of management practices are necessary during the production years.

General Rate of Nutrient
(imperial measurement)






lb./acre lb./acre lb./acre lb./acre
New stands 0 54-76 58-152 27
Established Stands 0 40-54 40-98 27


  1. Sands, sandy loam and organic soils are frequently low in available potassium. On these soils apply 58 to 152 lb./acre of potash at the time of establishment or 40 to 98 lb./acre of potash (K2O) for established stands.
  2. 27 lb./acre of sulfate sulphur (S) are recommended on well-drained sandy soils and gray luvisal (grey weeded) soils.

General Rate of Nutrient
(metric measurement)







kg/ha kg/ha kg/ha
New stands 0 60-85 65-170 30
Established Stands 0 45-60 45-110 30


  1. Sands, sandy loam and organic soils are frequently low in available potassium. On these soils apply 65 to 170 kg/ha of potash at the time of establishment or 45 to 110 kg/ha of potash (K2O) for established stands.
  2. 30 kg/ha of sulfate sulphur (S) are recommended on well-drained sandy soils and gray luvisal (grey weeded) soils.

Production Years

Management practices should concentrate on obtaining high yields of pure, clean seed. Undesirable weeds, such as sweet clover, should be rogued, since the seed is difficult to separate from birdsfoot trefoil.

A sufficient number of bees are necessary for adequate pollination. Fields in the vicinity of bush land will be well served by wild pollinators. Where no bush is nearby, arrange with a local beekeeper to place bee colonies within or along side the field. The recommended rate is one or two per acre (two to five hives per hectare).

Seed harvesting time is crucial. The field is ready for harvesting when two-thirds to three-quarters of the seed pods have turned brown, but before too much shattering has occurred. Swathing and combining has been shown to be the best method for harvesting trefoil in Manitoba. Fields should be cut when slightly damp with dew as this reduces losses from shattering. Depending on humidity, temperature, size and density of the swath, it will be ready for combining in two to five days. However, complete separation in the combine is difficult because of the seeds' small size and light weight. Try to save as much seed as possible since it can be cleaned up at the seed plant later on.

More information

Growers are advised to contact one of the seed trade companies offering field services for further advice on production matters.