2002 Specialty Crop Grower Program
Final Report
Project Title: Colorado Garlic: Expanding Markets Through Improved Cold Storage Methods
Specialty Crop Addressed: Varietal Garlics
Producer(s)/Organization (Project Leader)
Name:Walter A. Lyons, Ph.D.
Producer: Yucca Ridge Farm, Inc./
Address: 46050 Weld County Road 13, Fort Collins, CO80524
County: Weld
Telephone: 970-568-7664Fax: 970-482-8627
E-Mail: or
Technical Advisor:
Name and title: Dr. Gayle Volk, Plant Physiologist
Address: USDA-ARS, NationalCenter for Genetic Resources Preservation,
1111 S. Mason St., Fort Collins, CO80521
Telephone: 970-495-3205 Fax: 970-221-1427
E-Mail:
Submitted
Walter A. Lyons, Ph.D., President, Yucca Ridge Farm, Inc. Project Leader Date
1. SUMMARY
Varietal garlic bulbs (Allium sativum L.) are commonly stored at room temperature after harvest (mid-summer) and curing. The bulbs are then either consumed or used as planting stock in the fall. Thereafter, the quality of the bulbs usually deteriorates rapidly within four to six months of harvest. Come the following spring and early summer, there are few, if any, domestic sources of “fresh” garlic, especially from small organic growers (the main producers of varietal and specialty garlics). If a cold storage technique could be demonstrated to prolong quality into the following year, this would greatly enhance marketing opportunities for small growers. Moreover, if the garlic stock remained viable into the following spring, this would provide an opportunity for spring planting. Spring planting may be highly desirable for Colorado growers, for whom overwintering a garlic crop imposes significant demands for mulching and maintaining soil moisture. On 20 September, several hardneck and softneck varieties from the fall, 2001 harvest were cold stored at 0ºC and –3ºC at the USDA-ARSNationalCenter for Genetic Resources Preservation. With removals beginning on 6 April 2002, we demonstrated that most varietal garlic bulbs stored at –3ºC for 6 months successfully formed cloves within bulbs when spring planted (6 and 26 April). While mean bulb size was somewhat reduced when compared with their fall counterparts, the bulbs were of high quality and commercial size. After 9 months of –3ºC storage, bulbs then held at room temperature retained the quality characteristics of recently harvested garlic (firmness, taste) for at least two months, often longer. Garlic bulbs stored at warmer temperatures (0ºC, 5ºC, 15ºC, 23ºC) exhibited a higher rate of shoot elongation within the cloves than bulbs stored at –3ºC. These studies suggest that varietal garlics can be spring planted and consumed year round when bulbs are stored at –3ºC after the curing process is complete.
2. MATERIALS AND METHODS
Varietal garlic is a high value crop that can be grown successfully in Colorado. Almost all the highest demand varieties, however, have rather short shelf lives. After harvest in August, most garlic begins to lose its viability as culinary food by December and as planting stock by January. Fresh, locally grown garlic could be offered to consumers during the spring and early summer before new domestic supplies become available if garlic could be successfully stored over-winter. Moreover, over-winter storage would enable growers to plant garlic in the spring, rather than in the fall. Garlic is traditionally planted in the fall and this creates a number of practical problems for small Colorado growers. Very high winter winds often blow away the required mulch, while the need for irrigation during our dry but cold winters presents significant operational challenges. If cold stored garlic remains viable for up to six months, then the cloves could be used as stock for spring planting. Our experience is that there is great demand not only in Colorado, but from growers nationwide, for a spring planting option. However, there is little if any published research on the commercial viability of spring planted garlic. We note, however, that a preliminary test at Yucca Ridge Farm this past growing season yielded encouraging results. If spring planting of garlic can be successfully demonstrated, it would have important implications for both small growers and their customers for garlic planting stock.
The experiment involved the viability testing of cold stored garlic harvested in the summer of 2001 and subsequently stored at 0ºC and –3ºC in commercial coolers at the USDA-ARS NationalCenter for Genetic Resource Preservation (NCGRP) in Ft.Collins.
Yucca Ridge Farm provided two softneck varieties [Inchelium Red and Silverwhite] from the 2001 harvest. In addition, eight hardneck varieties [Chesnok Red, German Porcelain, GSF#65, Polish Hardneck, Romanian Red, Siberian, Spanish Roja, and Zemo] were provided. All the garlics were grown organically.
After the harvest in early August, 2001, the bulbs were air cured in the drying shed at Yucca Ridge Farm, Inc., and thereafter kept at ambient temperatures. They were then placed into cold storage at 0ºC or –3ºC on 20 September 2001 at NCGRP. Garlic was stored in each cooler within closed cardboard boxes packed lightly with crumpled newspaper.
In addition, bulbs of four garlic varieties were provided by Gilroy Foods (Gilroy, CA): California Early and California Late (softnecks) and Chinese and Spanish Red (hardnecks). The 2001 crop of garlic from Gilroy Foods was cured and kept at ambient temperatures until 5 September 2001, at which time it was placed in controlled temperature storage conditions at 23ºC (32% RH), 15 ºC (35% RH), 5ºC (85% RH), 0ºC (43% RH), and –3 ºC (76% RH).
Quality evaluations (color, firmness, taste, edibility) were performed biweekly on bulbs from garlic varieties that were returned to ambient temperatures after storage at 0ºC or
–3ºC for 7, 8 or 9 months. The cold stored Yucca Ridge garlic were removed and returned to room temperature storage in three stages, 6 April, 12 May and 9 June 2002. Five bulbs of each variety were placed in brown kraft paper bags, similar to the normal storage medium used by Yucca Ridge Farm after curing. Materials were kept in three home environments between April and September 2002 (temperatures fluctuated between 21ºC and 30ºC). Several bulbs of each variety were distributed to three taste testers: Liv Lyons (Yucca Ridge Farm), Leigh Towill (CSU) and Kate Cross (CSU). At two week intervals, until samples ran out, the garlics were taste tested. The latest test was conducted on 15 September (for the 9 June sample). The cloves were visually inspected, and taste tested both raw and after gentle sautéing in canola oil. Figure 1 shows the forms that were filled out for each test.
The second component of the experiment was to test the viability of spring planted, cold stored garlic. The bulbs were planted on two dates, 6 April (S1) and 26 April (S2). Garlic for the S2 planting was kept at 5ºC until planting after it was removed from cold storage at the time of the S1 planting. We chose to remove those bulbs from storage at 0ºC or –3 ºC at the earlier planting date and keep them at 5ºC for 20 days to increase the probability of a successful harvest from late-spring planted garlic. For each temperature storage regime and planting date, immediately before planting, all the bulbs of a variety were cracked open and uniform cloves were selected for inclusion in experiments. Sixteen cloves were planted in three replicate plots measuring 1 ft square (in a 4x4 pattern). Plots were randomized within a portion of the commercial garlic field at Yucca Ridge Farm, Inc. where the fall crop had been previously planted and mulched (Figures 2 and 3).
Watering (via overhead sprinklers) was identical for all samples. Fertilization of all plantings included two foliar feedings (liquid seaweed and fish emulsion) in early and late May. Bone meal was incorporated into the soil for the S1 and S2 plantings, as it was for the prior fall planting. Mulch was added to the growing area of the S1 and S2 crop once shoots had emerged to 4 to 6 inches. Hardneck scapes were cut at approximately the same stage for the Fall, S1 and S2 plantings (as the curl began to straighten). Garlic varieties matured at approximately the same time (more dependent on variety than planting date). The harvest date for all varieties occurred within 7 days of 26 July 2002, after the lower half of the leaves had significantly browned. Bulbs were cured for 14 days prior to cleaning and data collection. Circumference and bulb weights were determined for five bulbs from each plot and the number of cloves per bulb (total number of cloves) and individual clove weights (average of five representative plantable cloves) were determined for 3 bulbs from each plot. The varieties were pooled to determine the significance of planting date on yield characteristics. For each phenotypic character, comparisons among storage temperatures and planting dates were made within each variety. ANOVA tables were generated and Tukey HSD means separation tests were performed using JMP (SAS Institute, Cary, NC). For details, see attached paper.
Figure 1. Taste Testers’ form.
- RESULTS
a. Table Garlic
Qualitative evaluations of the suitability of the bulbs for consumption were performed on several garlic varieties that were removed from storage at 0ºC or –3ºC after 7, 8, or 9 months. The three tasting panel members agreed that the two softneck varieties, Inchelium (-3ºC) and Silverwhite (-3ºC), retained high quality characteristics (firmness, flavor, color), showing little or no degradation for at least 3 months storage at room temperature. This is consistent with the longer shelf lives of softnecks in general. In fact, several of the bulbs remained eminently edible through the end of December, 2002, or more than 16 months after harvest.
Some hardnecks began to show declines in key parameters (especially clove firmness) after about two months of storage at room temperature. This is again consistent with the generally shorter shelf life of hardnecks. The first to exhibit noticeable degradation were the German Porcelains (-3ºC) and Romanian Reds (-3ºC), which we should note were of lower quality upon harvest. They remained edible for only 2 months at room temperature storage. There were no differences observed in bulb quality among bulbs retrieved from storage after 6 or 8 months at –3ºC. In addition, the flavors of stored garlics did not change significantly at room temperatures until the garlic began to discolor and shrivel. Bulbs stored at –3ºC were of overall higher quality and had a longer shelf life than those stored at 0ºC, especially the Chesnok Red, Zemo, and Inchelium Red.
Our studies demonstrate that varietal garlics that have been cold-stored can be consumed throughout the spring and summer months. In fact, varieties that have been stored at –3 ºC for 9 months can be returned to room temperature and kept until the fall planting season. These results contrast those described by Kline (1990), in which cold stored garlics lost quality characteristics within 2 weeks after return to ambient temperatures. Furthermore, we demonstrated that garlic can be stored at –3ºC for longer than the one month suggested by Hardenburg et al., 1986. Additional details are contained in the article by Volk et al. (2003) submitted for publication in HortSci (see appendix).
- Spring Planting
Garlic varieties can be stored at 0ºC or –3ºC and produce bulbs under Colorado Front Range Colorado conditions when planted in the spring (see Tables 1 and 2 of Volk et al., 2003). Compared to fall plantings, there is a cost to spring planting: bulbs have somewhat smaller circumferences, lower bulb weights (by an average 35%) and, in some cases, fewer cloves per bulb and smaller cloves (S1 crop). The degree of response was variety dependent, since there was a significant variety by planting date interaction as indicated by ANOVAs. The earlier (S1) planting was more successful than the very late S2 planting. This may be in part due to aggressive competition by weeds as mulch had a more limited impact on the late planted garlic. The –3ºC stored garlic fared somewhat better for almost all varieties. In general, the number of cloves per bulb was the least responsive character, with significant differences observed in half of the garlic varieties.
Although yields are reduced, these data indicate that spring planting is possible in Colorado. We note that 2002 was a poor garlic growing season on the Front Range due to extreme heat stress. Thus the Fall planting results were also small that the parent cloves (Figure 6). Though sizes for the 2002 harvest were reduced across the board, the quality of the bulbs remained high. The quality (firmness, wrapper appearance and heft, lack of splitting) for the S1 and S2 plantings was generally on a par with the fall planting, with a few exceptions (below). Thus, stock can be maintained by keeping bulbs at –3oC if materials are not planted in the fall. The April 6 planting date was rather late for spring planting, and yields may have been higher if planted after mid-March. Figures 4 and 5 show representative differences between the fall, S1 and S2 plantings.
There are several reports of increased bulb size when bulbs were kept at 5ºC for 30 to 60 days before planting (Rahim and Fordham, 1988; Siddique and Rabbani, 1985; Bandara et al., 2000). Future studies are needed to determine the optimum storage duration until planting for bulbs removed from 0ºC and –3oC storage.
The yields of early spring planted bulbs were compared to determine whether 0ºC or –3 ºC storage temperatures were preferable. The bulbs stored at –3ºC had slightly larger circumferences and weights. There were no significant difference in the average clove weights and number of cloves per bulb since responses were quite variable across varieties.
While most varieties did form cloves within bulbs, Spanish Red and Polish Hardneck varieties were sensitive to storage at low temperatures and formed rounds instead of cloves when planted in the spring (Table 1). The fall planted Spanish Red variety also exhibited roughness characteristics that included loose papers and side clove formation. This garlic variety may be particularly responsive to storage temperatures and harvest date. Roughness characteristics were also exhibited in some varieties planted in the spring. Side cloves formed on many of the bulbs of California Early, California Late and Chinese varieties of garlic that were stored at 0ºC, while they were absent in garlic stored at –3ºC. While many varieties exhibited no signs of roughness, some bulbs of S1 planted Spanish Roja and both S1 and S2 planted Inchelium Red had either loose papers or side clove formation.
Roughness characteristics occur most commonly in bulbs that are stored at 4ºC to 5ºC prior to planting or that are harvested past maturity (Lammerink, 1990). During storage at 4-5ºC, dormancy is broken and shoot elongation occurs. When planted, these bulbs quickly sprout and mature earlier than bulbs that have not experienced temperatures that accelerate shoot elongation. Additional auxiliary buds are initiated during storage and side cloves form (Rahim and Fordham, 1998). The bulbs stored at 0ºC for extended periods of time also exhibited shoot elongation within the bulb, and probably matured more quickly than those stored at –3ºC. If bulbs of susceptible garlic varieties that had been stored at 0ºC or 5ºC were harvested at a more optimal time, loose papers and side clove formation probably could be minimized.
c.Shoot elongation during storage
Several bulbs of California Early, California Late, Chinese, and Spanish Red garlic were removed from the storage conditions periodically and the length of the shoot within the clove was measured. A percent shoot elongation was calculated by dividing the length of the shoot by the length of the clove and multiplying by 100. A minimum of 10 average sized cloves was measured for each time point.
In general, bulbs of the four varieties (Chinese, Spanish Red, California Early, and California Late) included in this study responded similarly to the 23ºC, 15ºC, 5ºC, 0ºC, and –3ºC storage temperatures. Shoot elongation occurred most quickly at 15ºC and 25oC, followed by 5oC. California Late and Spanish Red bulbs stored at 25ºC became severely dehydrated and perished after 150 days in storage. Bulbs in the 0ºC storage temperature did not show significant elongation until after 70 days in storage, at which time shoots began to elongate at a rate that was specific to each variety. We are confident that shoots within the bulbs had not yet started to elongate when they were placed into storage since the shoots within bulbs stored at –3ºC did not ever exhibit significant elongation until removed from storage. Although shoots showed no sign of elongation within the cloves after more than 200 days of storage at –3ºC, the cloves remained viable, as was demonstrated in the spring planting field trials. In many cases, shoots elongated to the tip of the clove, but did not protrude from the clove in storage conditions.
4. CONCLUSIONS AND DISCUSSIONS
Using garlic from both the 2001 Yucca Ridge fall harvest plus samples from California growers, we demonstrated that cold storage is a viable option to extend the shelf life of varietal garlics into the following year for the purposes of both table consumption and spring planting. Of the several temperatures tested, the –3ºC (27ºF) value appeared to be optimal. The cold storage period began on 20 September 2001 and continued though the spring and early summer of 2002.