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Garlic- Winter Mulch Study


Fall planted garlic is commonly mulched to protect it from desiccation and to reduce the heaving of cloves and hard freezing. The traditional method of mulching with straw or other organic mulches in northern Colorado is a challenge because there is rarely enough snow cover to hold the mulch in place in our windy climate. In this study we looked at four mulching treatments with two stiff neck varieties; Music and German Extra Hardy.

In addition, our region’s limited availability of irrigation water was addressed by evaluating three irrigation methods, and quantifying water use. We compared drip, over head sprinkler, and furrow.

Null Hypotheses:

  1. There will be no difference in growth or yield between the two varieties: a.) Music and b.) German Extra Hardy.
  2. There will be no difference in winter kill, growth rates, or yield among the four winter mulch treatments a.) bare ground b.) grass hay mulch with bird netting to hold in place, c.) single layer of fleece row cover, and d.) double layer of fleece row cover.
  3. There will be no difference in yield among the three irrigation treatments a.) drip, b.) sprinkler, and c.) furrow.


Bare garlic field at planting time, November 2002
The study area was located in a certified organic field at the ARDEC south, northeast of Fort Collins, Colorado. In early November, 2002, the 0.28 acre study plot (made up of twelve 400′ rows) was planted. The garlic cloves were spaced 6″ apart in-row on 30″ beds with two rows per bed. There were four replications of each winter mulch treatment with a total of 100 cloves planted in each replication (mulch treatments were 25′ long) – see map below.
Garlic field at planting time, November 2002



Drip Irrig.

Furrow Irrig.

B = bare ground, S = single layer of row cover, St = straw mulch, D = double layer of row cover

Each irrigation treatment covered four rows including two rows of buffer on either side of the data collection rows. Each row was planted alternately with the two garlic varieties so that each irrigation type and mulch type also contained both varieties.


At planting in November, approximately 3 inches of water was applied by furrow irrigation to all treatments. Mulches were then applied. Subsequent furrow and overhead irrigation rates were determined by the system limitations rather than specific irrigation requirements, but represent common irrigation practices used.

After the fall planting irrigation of 3.0 inches the different treatments received a total of:

  • 3.6 inches using drip irrigation
  • 6.9 inches using overhead irrigation
  • 9.1 inches using furrow irrigation
  • 6.7 inches of precipitation was received from planting to harvest (nearly historical avg.)

Production, Harvest, and Data Collection:

Row covers and straw mulch were removed on April 17th and all plots were flame weeded at that time and periodically throughout the growing season using a propane torch. Third leaf length, number of leaves, and plant height data were recorded on the drip tape rows once every two weeks from mid-April until the end of June. We chose to make field measurements in only one irrigation treatment due to time restraints. On April 30th and May 30th the garlic plants were foliar fed with fish fertilizer. In early June scapes were removed from the plants. Bare, single and double row cover, and straw mulch treatments
The week of June 30th the field was harvested with a potato digger. The garlic plants were cured for approximately two weeks in an open shed, and then the bulbs were clipped, cleaned, sized by diameter (extra small = <1.5 inches, small = 1.5 to 2.0 inches, medium = 2.0 to 2.25 inches, and large = >2.25 inches) and weighed.    Marketable bulbs are mostly greater than 2.0 inches in diameter. Data was analyzed using Systat (version 10.0, SPSS, Inc.) using ANOVA, two-sample t-tests, and an alpha value of 0.1.
rack for drying garlic
harvesting garlic with a potato digger
Rack for drying garlic
Harvesting garlic with a potato digger
Garlic sizing boxes
Comparison of garlic sizes
Garlic sizing boxes
Comparison of garlic sizes


  • There was indeed no significant difference in growth or yield between the two garlic varieties (Music and German Extra Hardy). The Music variety did appear to produce slightly more large bulbs and German Extra Hardy tended to produce slightly more small bulbs. This trend was not statistically significant but could make a significant economic difference on a per acre basis. (The varieties were combined for the remainder of the analysis.)
  • There was no difference in winter kill between the treatments (94% average survival rate).
  • Early season growth and total plant height under floating row cover was significantly greater early in the season. However, plant height and number of leaves converged as the season progressed:

  • At the time of the removal of the row cover, it was obvious that weed cover was also greater under the row cover compared to the bare ground:
April 17, 2003
Bare mulch treatment
Double layer row cover mulch treatment
weed seedlings at appropriate size for flame weeding
Weed seedlings at appropriate size for flame weeding
  • Scape emergence of plants under the floating row cover treatment was also about 1 week ahead of the bare ground treatment.
  • Regardless of irrigation treatment, bare ground (no mulch) produced the fewest large bulbs and the most small bulbs. This difference was statistically significant for all irrigation treatments. The straw, single layer of row cover, and double layer of row cover were not statistically different from each other in yield for any of the irrigation treatments.
  • Early growth in aboveground biomass gained by having a floating row cover did not appear to result in higher yields, as demonstrated by the straw mulch treatment which developed leaves later, but yielded essentially the same.

  • Yields from sprinkler and furrow irrigation were essentially the same, however furrow irrigation used nearly 30% more water. Too little water was applied to the drip irrigated treatment and yield suffered. In the furrow irrigation treatment where water was not a limiting factor, the clearest differences are demonstrated in the mulch effects. However, in the drip irrigation where water was a limiting factor, the bare ground treatment still clearly produced the most small bulbs and the least large bulbs.

  • As long as the garlic is adequately watered, any of the mulches tried were better than bare soil.
  • Note: Our yields were low compared to average yields for the area, this is presumed to be due to to the highly saline soils (E.C. = >3.5 mmhos/cm) which the garlic plot was located in.
Comparing garlic from double row cover (bottom) to bare ground (top)
Comparing garlic from double row cover (bottom) to bare ground (top)


Music appears to be the superior variety since on a per acre basis it tends to produce more large bulbs which could prove to be economically significant. Drip irrigation is recommended to reduce water waste however higher rates than we used would be advised. Flame cultivation is a viable method and is recommended for a hardy crop such as garlic (see our 2004 Flame Weeding Study).

Bare (left) versus double layer row cover (right)

Luxurious weed growth under double layer row cover

The furrow and the sprinkler irrigation treatments produced the highest yields but this was most likely due to the amount of water applied rather than the application method. Assuming average natural precipiation of about 6.5 inches from October to June, we have found that optimal water application is between 3.6″ (what our drip system delivered) and 6.9″ (what our sprinkler system delivered). Any irrigation system which is able to deliver this amount efficiently may be appropriate.

Regarding winter mulches, since the application of hay required significantly more labor time than floating row cover, and since there was no yield differences between the mulches, a single layer of row cover is recommended. However the single layer of material resulted in more wind abrasion to the leaves than the double layer. Straw/hay may also aid in keeping early weed growth to a minimum if it can be left on longer into the growing season. A mulch should definitely be used, however choice of mulch may depend on hay and row cover costs and labor availability.

Costs of mulching material as well as labor requirements for application and removal of mulch should be considered. Floating row covers may have a multi-year life if properly cared for and anchored in the field. Our experience has been that the widest material requires much less effort to apply and remove than the narrower widths and does not blow away in the wind as readily as organic mulches. We used 2-gallon nursery pots partially filled with soil, and placed them on the edge of the row cover about every 6 feet. When the row cover is removed, the pots can be dumped and neatly stacked for later use, or they can be easily moved to the side if the floating row cover is removed for a short period to allow field access. With this anchoring system our covers resist blowing away even in 70+ mph winds.


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