ONION PRODUCTION FROM TRANSPLANTS GROWN IN A
LOW TUNNEL COLD FRAME AND IN A GREENHOUSE

 

Clinton C. Shock, Erik B. G. Feibert, and Lamont D. Saunders
Malheur Experiment Station
Oregon State University
Ontario, OR, 2009

Bob Simerly
McCain Foods
Fruitland, ID

 

Introduction

Increased interest in an earlier start for the onion harvest season has led to interest in growing onions from transplants.  Our earlier research showed that onions, grown from transplants started in the winter in a greenhouse, can be harvested in July (Shock et al. 2004).  Through 2009 transplants were grown locally as required by the local onion white rot quarantine that prohibited importation of onion transplants from areas outside the Treasure Valley.  Onion transplant production in the Treasure Valley is relatively expensive due to the need for a heated greenhouse during the winter.  Transplants produced from field-grown, over-wintering varieties performed inconsistently and the available over-wintering varieties do not have adequate bulb quality and appearance (Shock et al. 2006, 2007). 

Another alternative to greenhouse-grown transplants is to grow transplants in unheated “low tunnel” cold frames (Shock et al. 2008, 2009).  In 2007 and 2008, transplants produced in unheated “low tunnel” cold frames performed poorly compared to transplants produced in a heated greenhouse.  Onion seed in the low tunnels emerged in early February which resulted in small plants at transplanting time.  Onion seed in the low tunnels was planted on January 17 in 2007 and on December 17 in 2008 and the seed emerged emerged on February 12 and 18 in 2007 and 2008, respectively. 

For the 2009 season, onion seed was planted on December 3, 2008 in the low tunnels to try again for earlier emergence.  The 2008-2009 trial compared the performance of onion from transplants produced in low tunnels and in a heated greenhouse. 

Materials and Methods

A 44-inch bed was made in a field of Nyssa silt loam on December 2, 2008.  Two drip tapes were laid 11 inches to each side of the bed center.  Seed of cultivar ‘Ranchero’ (Nunhems, Parma, ID) was broadcast on the bed surface at a rate of 144 seeds/ft2 on December 3.  The onion seed was covered with 0.25- to 0.5-inch depth of shredded bark mulch.  The low tunnel was made by laying a 6-ft-wide plastic sheet over wire hoops leaving about 6 inches of plastic on the outside of each bed side.  The excess plastic was covered with soil to secure the plastic.  The 76-inch-long hoops were made from number 10-gauge smooth galvanized steel wire.  The hoops were inserted 6 inches into the ground at the bed edges.  The low tunnel was 20 inches high at the center. 

The low tunnel was irrigated after planting to wet the soil surface.  Thereafter the field was irrigated when the soil water tension at 4-inch depth in the bed center reached 20 cb (1 cb = 1 kPa)(Shock et al. 2005).  Soil water tension was monitored by 6 granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 200SS, Irrometer Co. Inc., Riverside, CA) centered at 4-inch depth below the bed center.  The sensors were automatically read three times a day with an AM-400 meter (Mike Hansen Co., East Wenatchee, WA). 

In addition to the low tunnel cold frame, transplants of variety Ranchero were also grown in a heated greenhouse (65°F day, 45°F night air temperatures).  Onion seed of Ranchero was planted in flats with a vacuum seeder at 72 seeds/flat on January 23, 2009.  The seed was sowed on a 1-inch layer of Sunshine general purpose potting mix.  The seed was then covered with 1 inch of potting mix.  The flats were watered immediately after planting and were kept moist. 

On March 31, transplants from the low tunnel and from the greenhouse were transplanted to a field of Owyhee silt loam. The seedlings were planted in double rows spaced 3 inches apart on 22-inch beds.  The spacing between plants in each single row was 6 inches (3 inches apart in each double row), equivalent to 95,000 plants per acre.  Plots of each treatment were 20 ft. long by 4 double rows wide arranged in a randomized complete block design with 5 replicates.

The onions were managed to avoid yield reductions from weeds, pests, diseases, water stress, and nutrient deficiencies.  On April 27, Prowl® at 2 pints/acre and Select® at 10 oz./acre were broadcast for weed control. On May 11, Goal® at 10 oz./acre, Buctril® at 12 oz./acre, and Poast® at 1.2 pints/acre were broadcast for weed control.  Aza-Direct® at 8 oz./acre and Success® at 16 oz./acre were broadcast on June 9 and June 18 for thrips control.  Lannate® at 3 pints/acre was broadcast on July 10 for thrips control. Not all of these late cultural practices were necessary for these onions, but the transplants were planted in a large  field of onions to be harvested in September and so the transplants received all cultural practices appropriate for the full-season onion trials.

The field was furrow irrigated as necessary to maintain soil water tension at 8-inch depth at 25 cb.  Soil water tension was monitored by six granular matrix sensors centered at 8-inch depth below the onion row (Shock 2003) .  The sensors were automatically read three times a day with an AM-400 meter.

The field was fertilized with a total of 150 lb. nitrogen (N)/ac as urea.  Fifty pounds of N/acre were water run on May 14 and 100 lb. N/acre were sidedressed on May 23.

At each harvest date, onions in each plot were evaluated subjectively for maturity by visually rating the percentage of onions with the tops down and the percent dryness of the foliage.  The percent maturity was calculated as the average percentage of onions with tops down and the percent dryness.

On July 22, July 29, and August 6, 6.7 ft. of the middle 2 double rows in each four row plot were topped and bagged.  Decomposing bulbs were not bagged.  Following each harvest the onions were graded.  Bulbs were separated according to quality: bulbs without blemishes (No. 1s), split bulbs (No. 2s), bulbs infected with neck rot (Botrytis allii) in the neck or side, plate rot (Fusarium oxysporum), or black mold (Aspergillus niger).  The No. 1 bulbs were graded according to diameter: small (<2.25 inches), medium (2.25-3 inches), jumbo (3-4 inches), colossal (4-4.25 inches), and supercolossal (>4.25 inches).  Bulb counts per 50 lb. of supercolossal onions were determined for each plot of every variety by weighing and counting all supercolossal bulbs during grading. 

Onion bulbs from all harvests were rated for single centers.  Twenty-five onions ranging in diameter from 3.5 to 4.25 inches from each plot were rated.  The onions were cut equatorially through the bulb middle and, if multiple centered, the long axis of the inside diameter of the first single ring was measured.  These multiple-centered onions were ranked according to the diameter of the first single ring: “small” had diameters under 1.5 inch, “medium” had diameters from 1.5 to 2.25 inches, and “large” had diameters over 2.25 inches.  Onions were considered “functionally single centered” for processing if they were single centered or had a small multiple center.

Treatment differences were compared using repeated measures analysis of variance.  Means separation was determined using Fisher’s least significant difference test at the 5 percent probability level, LSD (0.05). 

Results and Discussion

Emergence

Onion seed in the greenhouse emerged on February 2 (10 days after planting) and onion seed in the low tunnels emerged on February 16 (75 days after planting).  The earlier planting (Dec. 3, 2008) did not result in earlier emergence than in 2007 or  2008.  The greenhouse transplants were substantially larger than the low tunnel transplants.  At the time of transplanting, the greenhouse transplants had two to three true leaves while the low tunnel transplants had only one to two true leaves. 

July 22 Harvest

On July 22, onion bulbs grown from the low tunnel and the greenhouse had marketable yields of 377cwt/acre and 695 cwt/acre, respectively (Table 1).  The onions from  greenhouse transplants had significantly higher jumbo yield (624 cwt/acre) than those grown from low tunnel transplants (296 cwt/acre).

 July 29 Harvest

The onion bulbs grown from greenhouse transplants had significantly higher colossal and jumbo yield than those grown from low tunnel transplants (Table 1).

August 6 Harvest

The onion bulbs grown from greenhouse transplants had significantly higher total, supercolossal and colossal yield than those grown from low tunnel transplants (Table 1).

Single Centers

Averaged over the three harvests, the onions grown from low tunnel transplants had significantly higher percentage of large multiple centers and a significantly lower percentage of functionally single-centered onions than those grown from the greenhouse transplants (Table 2).

Planting the seed early (Dec. 3) in the low tunnels in 2008 for 2009 transplants did not result in earlier emergence and larger transplants than January 17 or December 17 plantings the previous 2 years.  We do not know whether an earlier planting date (earlier than Dec. 3) in the low tunnels might result in earlier emergence and adequate growth.  Over the 3 years of these studies, the onions from greenhouse transplants have had higher yields and grade than those from the low tunnel transplants (Table 3).

References

Shock, C.C. 2003. Soil water potential measurement by granular matrix sensors. Pages 899-903 in B.A. Stewart and T.A. Howell (eds.). The Encyclopedia of Water Science. Marcel Dekker.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2004. Onion production from transplants in the Treasure Valley. Oregon State University Agricultural Experiment Station Special Report 1055:47-52.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2006. Onion production from field-grown transplants. Oregon State University Agricultural Experiment Station Special Report 1070:64-67.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2007. Onion production from transplants. Oregon State University Agricultural Experiment Station Special Report 1075:45-50.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2008. Onion production from transplants grown in a low tunnel cold frame and in a greenhouse. Oregon State University Agricultural Experiment Station Special Report 1087:26-33.

Shock, C.C., E.B.G. Feibert, and L.D. Saunders. 2009. Onion production from transplants grown in a low tunnel cold frame and in a greenhouse. Oregon State University Agricultural Experiment Station Special Report 1094:32-40.

Shock, C.C., R. Flock, E. Feibert, C.A. Shock, A. Pereira, and L. Jensen. 2005. Irrigation monitoring using soil water tension. Oregon State University Extension Service EM 8900.

Acknowledgments

Support for this research was provided by McCain Foods, onion seed companies, and Oregon State University.

Table 1. Performance of onions (cv. Ranchero) grown from transplants produced in unheated low tunnel cold frames and in a heated greenhouse at three harvest dates, Malheur Experiment Station, Oregon State University, Ontario, OR, 2009.

Harvest date Transplant source   Marketable yield by grade Bulb counts >4¼ in        
Total yield  Total >4¼ in  4-4¼ in  3-4 in  2¼-3 in Small No. 2 Rot Maturity
---------------------------- cwt/acre --------------------------- #/50 lb. --- cwt/acre --- ------- % -------
22-Jul
Low tunnel 385 377 0 5.8 296 75.3 0.0 8.0 0.0 0.8 12.5
Greenhouse 695 694 0 40.8 624 29.1 0.0 1.0 0.0 0.0 4.5
Average 540 536 0 23.3 460 52.2 0.0 4.5 0.0 0.4 8.5
29-Jul
Low tunnel 483 482 0 47.5 403 31.5 0.0 1.0 2.9 0.0 23.0
Greenhouse 852 851 0 186.6 659 5.7 0.0 0.9 0.0 0.0 15.0
Average 668 667 0 117.1 531 18.6 0.0 1.0 1.5 0.0 19.0
6-Aug
Low tunnel 535 528 0 63.6 454 11.1 0.0 6.9 0.0 0.0 30.0
Greenhouse 936 935 105.2 392.8 435 1.5 25.1 1.0 0.0 0.2 29.0
Average 736 732 52.6 228.2 445 6.3 12.6 3.9 0.0 0.1 29.5
Average
Low tunnel 468 463 0 39 384 39.3 0.0 5.3 1.0 0.3 21.3
Greenhouse 828 827 35.1 206.7 573 12.1 25.1 1.0 0.0 0.1 16.3
LSD (0.05) 
Treatment 78 81 16.3 55.8 77 7.2 NS 4.3 NS NS NS
Harvest date 88 87 16.6 56.8 NS 12.1 NS NS NS NS 6.1
Trt X date NS NS 23.5 80.3 151 17 NS NS NS NS NS

Table 2. Bulb single centeredness of onions (cv. Ranchero) grown from transplants produced in unheated low tunnel cold frames and in a heated greenhouse at three harvest dates, Malheur Experiment Station, Oregon State University, Ontario, OR.

Harvest date

Transplant source

Multiple center

 

Single center

Large

Medium

Small

 

Functionalb

Single

>2¼ inchesa

1½ to 2¼ inches

<1½ inch

 

 

 

22-Jul

----------------------------------------- % -------------------------------------------

Low tunnel

8.0

4.0

5.6

 

88.0

82.4

Greenhouse

4.0

7.0

7.0

 

89.0

82.0

Average

6.0

5.5

6.3

 

88.5

82.2

29-Jul

 

 

 

 

 

 

Low tunnel

13.3

10.0

8.0

 

76.7

68.7

Greenhouse

5.0

5.0

7.0

 

90.0

83.0

Average

9.2

7.5

7.5

 

83.3

75.8

6-Aug

 

 

 

 

 

 

Low tunnel

8.0

14.5

5.3

 

77.5

72.2

Greenhouse

2.5

9.5

8.0

 

88.0

80.0

Average

5.3

12.0

6.7

 

82.7

76.1

Average

 

 

 

 

 

 

Low tunnel

9.9

9.8

6.4

 

80.3

73.9

Greenhouse

3.8

7.2

7.3

 

89.0

81.7

LSD (0.05)

 

 

 

 

 

 

Treatment

4.5

NS

NS

 

8.7

NS

Harvest date

NS

NS

NS

 

NS

NS

Trt X date

NS

9.3

NS

 

NS

NS

a diameter of the first continuous ring.

b single center plus small multiple center.

 

 

Table 3.  Onion yield for variety ‘Ranchero’ grown from transplants produced in a heated greenhouse over 6 years compared to those produced in low tunnels over 3 years. Malheur Experiment Station, Oregon State University, Ontario, OR.

Year Transplant source Transplant date Harvest date Total yield Marketable yield by grade Bulb counts  Functional single centera
Total >4¼ in 4-4¼ in >4¼ in
-------------- cwt/acre --------------- #/50 lb. %
2002 greenhouse 15-Mar 23-Jul 921 921 102 328 29.1 100.0
2003 greenhouse 19-Mar 22-Jul 945 942 71 459 32 82.0
2006 greenhouse 12-Apr 19-Jul 580 561 0 43 98.4
2006 greenhouse 12-Apr 3-Aug 693 691 0 133 92.0
2007 greenhouse 29-Mar 30-Jul 944 944 89 443 31.5 77.0
2007 low tunnel 29-Mar 30-Jul 686 683 21 155 35.1 90.0
2008 greenhouse 8-Apr 1-Aug 683 680 102 99.2
2008 low tunnel  8-Apr 1-Aug 524 516 13 85.0
2009 greenhouse 31-Mar 29-Jul 852 851 0 187 90.0
2009 low tunnel 31-Mar 29-Jul 483 482 0 48   76.7

asingle center plus small multiple center.