Establishing a Beneficial Ground Cover in Fraser Fir Christmas Trees: Dutch White Clover Seed Sowing Protocol

Many NC Fraser fir growers can produce stands of naturalized white clover under their trees simply by reducing the rate of glyphosate herbicide that they use to control weeds. Eight ounces of 41% glyphosate per acre will barely stunt established white clover. By suppressing weeds instead of killing them, the more glyphosate-tolerant clover recovers sooner, spreads faster, and dominates the ground cover. However, many fields do not have enough natural clover to achieve dense stands in the first year. Nor does the “native” clover provide as much nitrogen as inoculated sown clover. To rapidly establish a dense stand of clover and to reap full benefits of the clover nitrogen contribution, a grower must sow inoculated Dutch white clover. Further, if the location is prone to drought stress, the grower may choose to invest in Pennington Seed Company’s drought resistant selection of Dutch white clover, “Durana” Clover. Plots of Durana clover have survived and recovered from periods of drought better than either natural stands of clover or sown Dutch white clover. Separate seeding rates are listed in the protocol below for both Dutch and Durana clover seed.

Optimum sowing windows for the NC mountains:

• Winter / frost sowing – January 1 – February 28
• Spring seeding March 1 – April 15
• Fall seeding August 15 – September 15

Ideally, sow your clover seed when there is adequate moisture in the soil. Avoid sowing during dry spells that can diminish germination and seedling survival. Also avoid sowing seed prior to predicted heavy rains such as hurricanes. Clover seed will float and wash down slope. Consider winter sowing to allow freezing and thawing to improve soil contact of seed in no-till conditions. Choosing the right weather is as important to establishing clover as it is to any cash crop you can grow.

Prepare the site

• Fall seeding: Apply herbicide 1-7 days before seeding.
• Spring seeding: Apply glyphosate herbicide the fall before in late September or October.
• If you did not prepare the site in the fall but need to sow clover seed in the spring, apply herbicide 1-7 days before seeding.

The optimum herbicide strategy depends on existing weed cover and height.

• If field has little or no desirable ground cover, broadcast a killing rate of glyphosate (24-32 oz/acre of a 41% formulation). You can add 8 -16 oz/acre of triclopyr (Garlon) if bindweed, poison oak, or other woody vines are present. Triclopyr has a 3 to 4 week residual effect. If you use triclopyr, wait at least 30 days before seeding clover.
• If the field has plenty of desirable ground cover, apply a broadcast suppression rate of glyphosate (8 oz/acre of a 41% formulation).
• If there are only spots of problem weeds or vines, spot-treat those areas with killing rates of herbicide while the majority of the field receives a broadcast suppression treatment.
• If existing ground cover is tall and dense, mow it at least 3 days after spraying.

Purchasing your seed

• Only purchase “Dutch white clover” or a named short variety such as “Durana.”  Some white clovers grow too tall and aggressively to be a desirable ground cover under Christmas trees. “Dutch” is most likely to be a short-growing white clover seed.
• Try to purchase uncoated or un-inoculated seed to inoculate yourself.
• Plan to inoculate your seed right before sowing even if it was “pre-inoculated,” because the inoculum will often die over extended storage even if the seed is still good.
• Be sure to buy inoculant along with your seed.
• Keep stored seed cool and out of direct sunlight.
• Keep inoculum cool and out of direct sunlight as well.

Per acre sowing rates

• Dutch white clover seed: 10-15 pounds per acre
• Pennington Seed  “Durana” white clover:  5 -7 pounds of seed per acre

Tools required

• Earthway 3100 seed spreader
• Clean 5 gallon bucket
• 32-64 oz. measuring cup
• ¼ cup measuring cup
• Kitchen tablespoon
• Non-diet soft drink
• Calculator

Inoculation process

1. Measure out 1 gallon of clover seed with measuring cup, pour into 5 gallon bucket.
2. Add 1½ tablespoons of soft drink to the bucket of clover seed and stir well.
3. Measure ¼ cup of inoculant and add to the moist clover.
4. Stir again, mixing well to coat all the seed with inoculant.

Using the spreader

1. Pre-set the Earthway 3100 spreader to a setting between #7 and #8. Close the trigger.
2. Empty the 1 gallon of inoculated seed into spreader.
3. With the trigger closed, practice turning the crank at the rate of a full rotation per second.
4. Walking at a steady pace, open the trigger and walk down the second row in field.
5. The spreader should throw a 12-foot-wide pattern to cover 3 rows of trees: one to your left, the one you are walking along, and one to your right.

Check your calibration

After you empty the spreader with the first gallon of seed, stop. Pace or step off the area you have just seeded. Estimate the length and width of the area in feet. Then, using your calculator, multiply them to get the square feet sown. A gallon of seed will weigh about 5 – 7 pounds and should cover about 20,000 to 25,000 square feet (around one-half acre). This equates to a per acre rate between 10 and 15 pounds per acre. For practical purposes, that is close enough. If your measured area is outside of 20,000 to 25,000 square feet, adjust the setting on the spreader. Sow another gallon of seed. Continue checking your calibration until you achieve your target per acre rate. Periodically recheck your calibration.

Problems to be aware of

• Sometimes the openings in the bottom of the spreader become clogged. You may hear a “clanging” sound from your spreader and observe a reduction in seed flow. You can stop and clear the clog any time you suspect this of happening.
• Use common sense when stopping or making slow turns — shut off the spreader trigger.
• If you change Earthway spreaders or change the person spreading, recalibrate.
• Remember to use Garlon only if absolutely necessary and only if you allow for the 3 to 4 week residual effect on clover germination!

Post-germination ground cover management

Use suppression rates of glyphosate (8, 4, & 8 oz. per acre sequentially) during the normal weed suppression (chemical mowing) windows in May, June, and July. Suppression rates should not harm established clover seedlings. However, use of rates above 8 ounces per acre will most likely kill tender clover seedlings and should only be used as spot sprays to control problem weeds. See the note on “Calibrating your backpack sprayers” for more details about weed suppression with glyphosate.

Note to growers in other regions

In the cool mountains of NC, white clover usually germinates soon after sowing. Growers can find new clover seedlings within weeks of spring or fall sowing. In the Piedmont or Coastal Plain of NC, there may be a delay of one year or more before clover becomes visible. Under warmer conditions, clover seedlings may be growing below the soil surface the first season in a similar fashion to subterranean clover. This pattern has been observed over several years of trials on several farms where first season failures turned around the second year. This clover sowing protocol was developed for Fraser fir in the mountains, but with patience, can work in other regions and other species of Christmas tree. In hotter climates, Durana or another drought-hardy variety of white clover would be the optimum seed selection.

Glyphosate herbicide can behave “hotter” in hotter climates. Where 8 ounces has proved to be the optimal suppression rate used to encourage white clover ground covers in typical mountain temperatures, a 6 ounce rate may provide better results when daytime temperatures exceed 85 degrees Fahrenheit. There is often a fine line between weed suppression and killing your beneficial ground covers.