Winter Survivability and Subsequent Performance of Fall-Planted Flax (Linum usitatissimum L.) in Mid-Central Virginia

Abstract

Winter cropping can be used to achieve a double benefit for producers: as soil cover and an additional economic crop cycle. Flax (Linum usitatissimum L.) is a spring crop growing in the northern region of the US and used as a fall cover crop in some southern states. In this study, eight seed-type flax varieties were evaluated for production as a fall/winter crop for the Commonwealth of Virginia, a mid-latitude region. Mixed results were obtained; however, the crop showed winter tolerance and potential productivity, especially when the frequency of sub-zero winter temperatures was low. Planting too early in the fall allows for significant stem development that increases susceptibility to physical damage by snowstorms and winter frost. Seed yield was low compared to spring-planted crops; however, it reached up to 400 kg ha⁻¹ in some varieties. Seed weights were comparable to those found elsewhere for the same or other varieties, and seed protein and crude fat content ranged from 228–270 and 189–234 g kg⁻¹, respectively. Across years and varieties, P, K, Mg, Ca, and S averaged 7.74, 9.88, 3.88, 2.86, and 2.35 g kg⁻¹, respectively. Mineral elements Fe, Zn, Mn, Cu, and B averaged 95, 62, 21, and 10 mg kg⁻¹, respectively. However, early maturity in spring ahead of other grains subjected it to significant losses to wild birds. Fall-planted flax has potential as a cover crop and may be harvested for seed, which in addition to a summer crop, provides a producer with economic returns from two crop cycles per year.

1. Introduction

Flax is an annual herbaceous crop originally from Europe and introduced to North America by European colonial powers [1]. In the early part of the 20th century, flax was planted in spring and harvested for fiber in the summer in Oregon state, and was also in rotation with warm-season crops, corn, and forage legumes [2,3]. Yields of up to 7500 kg ha⁻¹ of straw and 795 kg seed ha⁻¹ were produced in Georgia in the 1920s [4]. In recent years, straw yields of 9600 kg ha⁻¹ that produced about 2000 kg ha⁻¹ of fiber were obtained in Oregon [5]. Flax does well in cool climates and, in North America, it is produced mainly in the northern US states and Canada. The crop whose stem consists of 30–40% fiber and 60–70% wood pulp [6] is produced mainly for its seeds and fiber content. Flax seed oil content of about 300–480 g kg⁻¹ [5,7,8,9] is composed of 92–96% unsaturated fatty acids. Compared to cotton and hemp, flax seed oil has a larger proportion of omega-3 fatty acids. Additionally, flax fiber’s tensile strength is greater than those of cotton and hemp [10] and is good for producing high-quality linen. The US market demand for flax seed exceeds the supply and the country’s imports of flax seed and linseed oil had a combined total of about USD 250 million as of 2022 [11]. This high US flax demand and the recent removal of federal restrictions on the production of industrial hemp and its promotion in the Commonwealth of Virginia make evaluating the productivity of flax, a crop with comparable industrial uses, an appropriate decision. Having flax as an alternative or in addition to hemp and producing multiple crops that have similar qualities during the same production cycle or in rotation with each other and/or with other crops will increase the supply and may satisfy the market demand.

Flax oil is rich in alpha-linolenic acid (ALA), an omega-3 fatty acid important for nervous system development, visual acuity [12], and for reducing incidences of diabetes, cancer, and other diseases in humans [13]. Fish-fed omega-3-fatty acid-rich flax seed showed an improved performance and fatty acid profile [14,15]. Similarly, dairy animals fed flax seeds produced more milk with a high omega-3 fatty acid content [16], while beef animals showed increased omega-3 fatty acid levels in their muscle fat [17,18]. Feeding flax seed and/or seed oil increased the omega-3 fatty acid content in poultry and hog carcasses [19,20,21] and also increased the reproductive performance and weaning weights of sows [22]. However, fish meal, an omega-3 fatty acid-rich feed source for aquaculture and other animal production systems, is becoming expensive and insufficient to meet the demands from expanding farm productions. The producers are seeking cheaper plant-based alternatives, and flax seed with its high omega-3 fatty acid content is increasingly becoming a preferred choice to meet this demand. Therefore, a need exists to evaluate the flax production potential in the mid-Atlantic, a region historically used for cotton farming. In the mid-Atlantic, with its good road and rail networks, the delivery of producers’ flax crops to markets on the east coast is an easy task. Despite this potential market, there remains a lack of data on flax production in the region, which this study seeks to address and thus contribute towards reversing the lack information on the importance offlax production.

Although the crop has been produced with success in several northern states, including Oregon, North Dakota, Montana, and Minnesota, and in the southern states of South Carolina and Georgia [23], production strategies, including planting date, vary due to latitudinal differences. In the north, flax is planted in early April and harvested during the summer months. In the southern states, flax is planted as late as December as a winter crop [24,25] and harvested for its fiber and seeds 140 and 160 days later, respectively [25]. Flax seed and oil yield potential values are reportedly influenced by both variety and planting dates [26,27] and by fertilizer management and harvest timing [25,28,29]. In fact, in Italy, planting flax in the fall was found to be favorable compared to spring and resulted in greater seed yield and seed oil content [30]. While planting in the fall allows the seed to germinate while temperatures are favorable, an inappropriate planting date may subject the seedling to frost damage during winter months. Flax takes a few months to mature and can be included in rotation with cereal grains and seeds or forage legumes. Research in North Dakota showed that flax following legumes, such as soybeans, field peas, or field beans, produced a greater yield compared to that following flax or hay crops [31]. If planted in the fall, flax can be followed by a summer crop, such as corn, then a winter forage legume/or cover crop. In the Commonwealth of Virginia, where cotton production is historically the crop of choice, rotation that includes fall flax and spring cotton and/or industrial hemp, crops with similar applications, are beneficial because there is an efficient use of harvest and processing machinery by reducing idling time. Additionally, due to the differences in their rooting patterns, rotating flax with cotton, legumes, or industrial hemp allows for a good and balanced utilization of water and soil nutrients from different depths. The potential to recycle nutrients from a depth below the root zone of a previous crop prevents leaching losses that may affect the Chesapeake Bay waterways.

Therefore, there is a need to obtain data for fall flax-planting dates in the mid-latitude states of the US. Such data allow for the determination of whether the rotation of fall-planted flax with warm-season crops may be a possibility. This study aims to determine the appropriate flax-planting dates so that comprehensive planning for flax production and inclusion during appropriate crop rotations can be performed. The objectives are to evaluate flax-planting dates and their impacts on (i) winter survivability and (ii) spring-growth performance, seed yield, and quality.

2. Materials and Methods

2.1. Experimental Site, Layout, and Planting Material

The experiment was conducted at Randolph Farm, the Virginia State University Research and Extension Farm in Chesterfield County, Virginia (37°13′43″ N; 77°26′2″ W). The soil from the farm was a Bourne series fine sandy loam (mixed, semi-active, thermic Typic Fragiudults). The site was previously covered by stinging nettles (Urtica dioica). Prior to the project’s initiation, soil samples were obtained from the topsoil (0–15 cm) for a routine analysis and to determine nutrient fertilizer needs. Flax crops were planted in the fall and harvested in the spring of the following year, and the two production periods were 2020–2021 (considered as 2021) and 2021–2022 (considered as 2022). Planting was performed on three different dates (planting dates 1, 2, and 3), about 10–14 days apart from early October through to early November. The experiment was presented as a randomized complete block design (RCBD) with cultivars assigned to the block randomly and replicated four times. Eight flax seed varieties normally produced for oil, Bison, Carter, Gold ND, ND Hammond, Nekoma, Omega, Pembina, and York, were obtained from the North Dakota State University Research Station and planted. These varieties originated from North Dakota and were developed mainly by breeders at North Dakota State University and, in some cases, similar to the variety, Omega, with collaborators from USDA Agricultural Research Station. The regional varieties were evaluated for their plasticity to the mid-latitude locations.

The number of seedlings that survived the winter temperature to emerge in spring was determined by a before and after sampling procedure. In the fall, prior to killing freeze, two locations, each on a different row within a plot, were selected and marked with flags. The selected sections were those with a significantly greater number of emerged seedlings and not necessarily representative of the whole plot. All emerged seedlings in the selected row–segments were counted and recorded. After the soil temperature warmed up and the plants regrew in spring, a second seedling count in the same flagged segments was determined, taking care not to include branches as independent seedlings. Seedling survival percent was a proportion of seedlings in spring × 100.

At seed maturity, all plants in the two middle rows were hand-harvested, bagged, dried in a Grieve forced-air oven at 65 °C for 48 h, and seed-threshed and shelled using a Haldrup LT-35 stationary thresher (Haldrup Co., lsofen, Germany). The weight of the seed was obtained and a thousand seeds were counted using a seed counter, and 1000 seeds’ weights determined on a weighing scale. Another seed sample was ground and analyzed for crude protein, crude fat, and macro- and micro-nutrient element contents using methods as employed by Waypoint Analytical Inc., Peoria, PA, USA. Crude protein was determined using the combustion method AOAC Official Method 990.03 [32], crude fat using the diethyl ether extraction AOAC Official Method 920.39 [33], and elemental analysis was performed using the metals in plants AOAC Official Method 953.01 [34].

2.2. Data Analysis

The data were organized and subjected to analysis of variance (ANOVA) as an RCBD with, year, planting date, and varieties as fixed factors. Because of planting date × year and variety × year interactions, each production year was analyzed independently. For the survival percent, there was a cultivar and planting date interaction during the second year and, therefore, cultivar survival comparisons were performed within a planting date. Across years and planting dates, another analysis was conducted to compare the seed-quality attributes of planted versus harvested seeds. Means were compared by Fisher’s least-significant difference test at α = 0.05.

3. Results

3.1. Soil Characteristics

The soil at the research site had pH levels of 6.2 and 5.9 in 2021 and 2022, respectively (

Table 1. Soil chemical characteristics at the experiment site.

Year	pH	P	K	Ca	Mg	Zn	Mn	Cu	Fe	B
		mg kg−1
2021	6.2	34	82	337	53	0.8	9.8	0.9	18	0.2
2022	5.9	50	73	288	42	1.0	10.8	1.0	19.8	0.1

). Additionally, across two years, mean site soil P, K, Ca, and Mg contents were 42, 77.5, 312.5, and 47.5 mg kg⁻¹, respectively. Soil Zn, Cu, Fe, and B, averaged 0.9, 9. 0.95, 18.9, and 0.15 mg kg⁻¹, respectively.

3.2. Winter Seedling Survival

The initial seedling counts prior to killing frost were similar across the planting dates and cultivars and averaged 28 and 20 in 2021 and 2022, respectively. In 2021, seedling winter survival did not differ (α = 0.05) for the cultivars and was greater than 89.5% for all flax cultivars (

Table 2. Percentage of emerged flax seedlings that survived the winter months in 2021 and 2022.

Flax Cultivar	Percentage of Emerged Seedlings That Survived the Winter Months
	2021		2022
		1 *	2	3
Bison	91.4	47.6 ab	52.3 ab	28.7 c
Carter	91.7	17.3 cd	39.3 bc	88.8 a
Gold ND	89.5	29.0 bcd	58.3 ab	34.7 bc
ND Hammond	90.0	66.0 a	56.0 ab	83.3 a
Nakoma	91.0	33.7 bcd	75.0 a	51.7 ab
Omega	96.1	12.3 d	58.3 ab	82.0 a
Pembina	94.5	37.0 bc	51.0 ab	71.3 ab
York	97.9	15.3 cd	17.7 c	38.0 bc

* Planting dates in 2022. Means within a planting date followed by different letters are significantly different at α = 0.05.

). However, in 2022, the degree of survival was affected by the planting date and cultivar and their interaction. Across cultivars, the magnitude of survival percent was low for seedlings planted early compared to those planted later. For each planting date, variety York, in general, consistently registered a low survival rate that reached a value less than 20% in plantings one and two. For all planting dates, ND Hammond exhibited a greater survival percent, over 50 percent in all cases. The plants that survived continued to grow in spring and formed seeds whose mean weights were comparable to and, in some cases, heavier by up to 5% compared to the planted seeds (

Table 3. Seed yield, seed weight, seed crude protein (CP), and crude fat (CF) content of different flax cultivars in 2021.

Flax Cultivar	Seed Character
	Yield (kg ha−1)	1000 Seed Weight (mg)	CP (g kg−1)	CF (g kg−1)
Bison	407	5923 c	229.6 b	220.4
Carter	347	5862 c	232.7 b	222.7
Gold ND	299	6340 a	226.0 b	223.3
ND Hammond	298	5794 c	242.0 a	232.7
Nakoma	408	5840 c	228.4 b	224.0
Omega	374	5862 c	232.9 b	229.1
Pembina	358	6075 b	232.8 b	234.7
York	391	5938 c	229.0 b	222.7
Planting date
1	382 b	6026 a	223.2 b	206.3 b
2	523 a	5912 b	226.5 b	254.8 a
3	177 c	5924 b	245.3 a	217.5 b

Means within a column followed by the same letter are not significantly different at α = 0.05.

). While in the 2021 winter crop year there were a few days with temperatures below −5 °C, a significant number of days in 2022 reached below −5 °C and even below −10 °C [Figure 1]. Additionally, in 2022, plants that were planted earlier (first planting) showed the lowest survival rates compared to those planted later. In addition, there was observable physical damage to a significant number of these plants showing broken stems. However, despite the evidence of necrotic foliage during the winter months (Figure 2), some recovered as spring set in and there were observable differences in recovery for ND Hammond, Bison, Nakoma, and Gold ND showing better regrowth potential (Figure 3). Foliage during the winter months recovered as the winter temperature increased, and observable differences in recovery were evident for ND Hammond, Bison, Nakoma, and Gold ND showing better regrowth potential (Figure 3).

3.3. Seed Yield, Seed Weight, Seed Protein, and Fat Content

In 2021, the seed yield obtained was around 300–410 kg ha⁻¹ with a mean across all cultivars of 360 kg ha⁻¹, with no significant differences observed among the cultivars (

Table 4. Seed yield, seed weight, seed crude protein (CP), and crude fat (CF) content of different flax cultivars in 2022.

Flax Cultivar	Seed Character
	Yield (kg ha−1)	1000 Seed Weight (mg)	CP (g kg−1)	CF (g kg−1)
Bison	58	5372	262.8 ab	228.3
Carter	103	5528	265.3 ab	195.7
Gold ND	126	5264	257.3 b	230.5
ND Hammond	85	5596	270.0 a	189.0
Nakoma	87	5725	259.3 b	229.6
Omega	53	5584	265.0 ab	218.0
Pembina	137	5563	259.7 ab	223.4
York	60	5642	254.5 b	189.9
Planting date
1	82	5653	264.4	20.63
2	110	5317	261.8	21.87
3	72	5637	259.3	21.10

Means within a column followed by the same letter are not significantly different at α = 0.05.

). Across cultivars, the second planting produced a greater seed yield averaged at 523 kg ha⁻¹. There was a significant difference between the cultivars in average seed weight with a mean weight of 5.95 g seed⁻¹ across cultivars. ND Hammond had a greater crude protein content at 242 g kg⁻¹, while other cultivars had lower and similar contents averaged at 230 g kg⁻¹. There were no significant differences in crude fat content that averaged 226 g kg⁻¹ across cultivars. There were differences between the planting dates for all parameters. In 2022, the seed yield was low and averaged 89 kg ha⁻¹, and no differences among the cultivars were observed for seed weight and crude fat, which averaged 5.53 mg seed⁻¹ and 213 g kg⁻¹, respectively. However, similar to 2021, ND Hammond produced the greatest crude protein content at 270 g kg⁻¹. All planting dates had comparable crude protein levels and seed weight values.

3.4. Seed Macronutrient Element Content

In 2021, seed P content among flax cultivars ranged from 7.14–7.77 g kg⁻¹ and K ranged from 9.30–10.80 g kg⁻¹ (

Table 5. Seed macronutrient element contents of different flax cultivars in 2021.

Flax Cultivar	Macronutrient Element Content (g kg−1)
	P	K	Mg	Ca	S
Bison	7.51 abc	10.26 b	3.72 bc	2.63 c	2.28 ab
Carter	7.37 bcd	10.11 bc	3.83 ab	2.64 c	2.27 ab
Gold ND	7.14 d	9.30 d	3.64 d	2.57 c	2.11 c
ND Hammond	7.77 a	9.66 cd	3.91 a	2.79 b	2.36 a
Nakoma	7.28 bcd	9.72 cd	3.68 c	2.64 c	2.23 b
Omega	7.52 abc	9.31 d	3.96 a	3.03 a	2.23 b
Pembina	7.63 ab	10.21 b	3.77 bc	2.38 d	2.24 b
York	7.59 abc	10.80 a	3.83 ab	2.62 c	2.90 ab
Planting date
1	7.51 b	9.57 c	3.72 b	2.85 a	2.20 b
2	7.13 c	9.96 a	3.67 b	2.39 c	2.16 b
3	7.79 a	10.16 a	3.99 a	2.75 b	2.40 a

Means within a column followed by the same letter are not significantly different at α = 0.05.

). Seed Mg, Ca, and S content ranges were 3.64–3.96, 2.57–3.03, and 2.11–2.36 g kg⁻¹, respectively. For all nutrient elements, the cultivars with the greatest and lowest content differed from each other for the element in question. However, ND Hammond presented one of the greatest contents for all elements, except K. Seeds planted on different dates differed in their mineral element contents in 2022. Except for Mg and Ca, for which only two cultivars in each case differed in their contents, all other elements were similar in concentration among the cultivars. Across cultivars, P, K, Ma, Ca, and S averaged 8.00, 9.84, 3.96, and 2.44 g kg⁻¹, respectively. The seeds from plants grown on different dates showed similar element contents (

Table 6. Seed macronutrient element contents of different flax cultivars in 2022.

Flax Cultivar	Macronutrient Element Content (g kg−1)
	P	K	Mg	Ca	S
Bison	8.27	10.41	3.99 ab	3.06 ab	2.52
Carter	8.09	10.40	4.09 a	3.08 ab	2.57
Gold ND	8.05	9.67	4.07 a	2.91 ab	2.45
ND Hammond	7.93	9.81	4.00 ab	2.86 ab	2.54
Nakoma	7.76	9.59	3.93 ab	3.01 ab	2.44
Omega	7.79	9.50	3.91 ab	3.24 ab	2.41
Pembina	7.91	9.76	3.90 ab	2.69 b	2.40
York	8.14	9.58	3.79 b	3.54 a	2.23
Planting date
1	8.06 ab	10.35 a	4.00 a	2.91 b	2.51
2	7.83 b	9.44 b	3.87 b	2.83 b	2.43
3	8.14 a	9.81 ab	4.04 a	3.42 a	2.41

Means within a column followed by the same letter are not significantly different at α = 0.05.

).

3.5. Seed Micronutrient Element Content

In 2021, seed Fe, Zn, Mn, Cu, and B contents were very similar across flax cultivars, but with at least two of the cultivars showing significant content differences. ND Hammond showed a greater content for all micro-element contents. Values for Fe content ranged from a low of 63.9 mg kg⁻¹ in York to a high of 73.4 mg kg⁻¹ in ND Hammond. Zinc and Mn averaged 58.6 and 19.5 mg kg⁻¹ across the cultivars, respectively. ND Hammond had a significantly greater Cu content than Carter and Nakoma, which had greater contents than Bison, York, Gold ND, and Omega. Except for Zn, there were differences in the seed micronutrient element content according to the planting date (

Table 7. Seed micronutrient element contents of different flax cultivars in 2021.

Flax Cultivar	Micronutrient Element Content (mg kg−1)
	Fe	Zn	Mn	Cu	B
Bison	66.8 ab	57.6 ab	20.0 a	15.6 de	10.1 ab
Carter	67.2 ab	59.0 ab	20.1 a	17.1 b	10.5 ab
Gold ND	64.3 ab	55.4 b	17.0 b	15.3 de	9.5 b
ND Hammond	73.4 a	61.0 a	20.1 a	16.9 a	10.6 a
Nakoma	64.0 b	58.5 ab	19.6 ab	16.9 bc	10.3 ab
Omega	69.0 ab	59.7 ab	19.1 ab	15.2 e	9.8 ab
Pembina	65.8 ab	58.7 ab	19.4 ab	16.2 cd	9.7 ab
York	63.9 b	58.6 ab	20.3 a	15.8 de	10.1 ab
Planting date
1	74.8 a	57.6	18.8 b	16.1 b	11.1 a
2	54.6 b	59.7	21.9 a	15.9 b	9.6 b
3	71.0 a	58.4	17.8 b	17.1 a	9.6 b

Means within a column followed by the same letter are not significantly different at α = 0.05.

). In 2022, similar trends to those in 2021 were observed for seed micronutrient element contents in flax cultivars. Across the cultivars, Fe, Zn, Mn, Cu, and B averaged 123.1, 66.2, 22.4, and 10.3 mg kg⁻¹. However, the concentrations, with the exception of Boron, were relatively greater than those found in grains harvested in 2021. Additionally, differences in the micro-element contents were observed for different planting dates, except for seeds Zn and Cu, in 2022 (

Table 8. Seed micronutrient element contents of different flax cultivars in 2022.

Flax Cultivar	Micronutrient Element Content (mg kg−1)
	Fe	Zn	Mn	Cu	B
Bison	117.4 b	68.4 a	23.7 ab	21.6 ab	12.3
Carter	118.2 b	66.8 ab	20.5 b	22.8 ab	9.5
Gold ND	123.7 b	66.8 ab	25.2 ab	20.0 b	10.2
ND Hammond	124.5 b	68.8 a	26.1 a	23.0 ab	10.7
Nakoma	119.5 b	66.4 ab	24.1 ab	23.1 ab	10.6
Omega	116.8 b	65.1 ab	23.1 ab	19.7 b	9.4
Pembina	166.4 a	67.0 ab	25.7 ab	22.0 ab	9.9
York	98.4 b	60.3 b	20.9 ab	26.8 a	9.5
Planting date
1	127.8 a	64.4	19.2 c	22.7	9.5 b
2	132.9 a	68.7	28.4 a	21.4	9.4 b
3	107.5 b	64.9	22.2 b	23.6	12.0 a

Means within a column followed by the same letter are not significantly different at α = 0.05.

).

4. Discussion

The observed lack of significant frost damage to the fall 2021 crop and the observed damage to flax in 2022 can be attributed to the differences in winter conditions, including the presence of snowstorms, the lowest winter temperatures, and the duration of such temperatures, whereas in 2021, there were a few days with temperatures below −5 °C, a significant number of days in 2022 reached below −5 °C, and some reached about −10 °C (Figure 1). While flax seedlings are reported to withstand temperatures up to −3 °C [35,36], it was reported that temperatures below −5 °C were injurious to flax stems [35,37,38]. This supports the observed damage to the crops in 2022 (Figure 2) where, in addition to January and February temperatures dropping below −5 °C, they remained at this temperature for more than 48 h, in some cases. Moreover, there were extreme daily swings between the maximum and minimum temperatures, a scenario reported to exacerbate frost damage [39]. Such damage at temperatures below −5 °C have been reported in Texas, where 100% mortality occurred for North Dakota-developed varieties Nakoma, Pembina, and York [40]. Additionally, in 2022, plants that were planted earlier (first planting) showed the lowest survival rates compared to those planted later. This can be attributed to significant stem development by these plants by the time of killing frost that was subject to damage by temperatures below −5 °C, as explained earlier. In addition, there was observable physical damage to a significant number of plants showing broken stems. Some of the plants that visually showed necrotic foliage during the winter months recovered in winter as temperatures increased, and observable differences in the recovery rates were evident with York, which was severely impacted, and ND Hammond and Bison showing better regrowth potentials (Figure 3). Nakoma and Gold ND also showed good recovery rates in spring.

The yields for some varieties compared well to those found for fall crops in south-east Texas [40,41] and to those reported for flax crops in the stacked crop-rotation system in the northern Great Plains [42]. Seed yields were slightly lower than those reported for Lithuanian varieties ‘Snaigiai’ and ‘Hermes’ that averaged 670 kg ha⁻¹ [43], and were also much lower than the value over 1000 kg ha⁻¹ obtained for flax grown as a winter crop [27,29]. The seed yields were much lower than those reported for the same varieties planted in spring in North Dakota [44]. The low seed yield obtained may also be a result of the losses that occurred from wild-bird feeding and shedding. The protein and oil content were greater and lower, respectively, when compared to those reported for some varieties grown during the winter months in eastern Texas [41]. The seeds matured earlier in summer when most other small-seed crops and wild species were not ready. The crop, therefore, experienced above-normal infestations by wild birds. Additionally, coupled with this, is the field moist condition that prevented machine access to the field on time for harvest and exacerbated field seed loss. The much lower yield experienced in 2022 was mainly due to the impact of winter months on plant survivability. The extremely cold temperature led to plant kill and reduced plant density. In addition, as was the case in 2021, bird infestation and associated field seed losses were experienced in 2022. The plants that survived and continued to grow in spring produced seeds with sizes comparable to those reported elsewhere [29,43,45,46]. The lack of flax cultivar and planting date interaction in 2021 may be attributed to the relatively mild winter. In this case, all seedlings that emerged remained dormant during the winter months and they all resumed growth under similar conditions in spring. However, in 2022, the interaction could be linked to the differential variety tolerance to the harsher winter conditions experienced during this production year. There was no strong correlation between planting date and variety seed yield, despite the survival difference in 2022. Other factors, such as a variety’s physiological process including capsules per plant and seed per capsule, can significantly affect seed yield [47] and, in addition to the weather and field factors, may have contributed to a wider spread in yield distribution, resulting in non-statistical differences in yield.

The mineral macronutrient contents observed in this study were comparable to those reported for multiple flax varieties evaluated for their element composition [48,49]. The seed P and K contents were slightly greater than those reported in flax (cv. Norlin) receiving P and Zn fertilizer [50]. These differences in seed P and K may be a result of the difference in the available nutrients in the soil at these two sites. Whereas soil pH at the site of this study was low (~pH 6.0) and the plant available P content was 34 mg kg⁻¹, in the referenced study above, the pH was high (~pH 7.5) with a soil P content of 11.4 mg kg⁻¹. While these micro-nutrient element contents compared well to those reported elsewhere [48,49], the Fe, Mn, and Cu contents were greater than those reported elsewhere [46]. These differences in elemental contents between years are not surprising since weather conditions, including temperature, have been found to impact the levels of mineral elements in flax seeds [49]. Differences in micronutrient content from those reported by [46] may be a result of a low pH value. Unlike pH 7.5 at the site of the [50] study, the pH in the current study was low and within the range in which most of the listed elements are relatively plant-available. However, no strong correlation was observed between planting dates and seed nutrient concentrations. Plants that survived low winter temperatures continued their growth under the same climate and soil conditions, hence the similarities in element content in seeds.

5. Conclusions

A fall-planted flax seed crop showed mixed results. Although the seed yields were lower than those found elsewhere, there was an appreciable crop performance, especially when winter snowstorms were mild and temperatures remained above −5 °C. An emerged seedling with little stem development by the time of killing frost seemed to tolerate winter temperatures better. Other than the cultivars’ tolerance potential, the appropriate timing for planting may be key to a successful winter survival. Despite the low seed yield, having flax as a cover crop in winter may be beneficial for soil cover and could be harvested for seed when winter survival is high. However, given the possibility of below −5 °C temperatures, and crop death from winter frost, the production of flax in winter for seed may not be possible, and more research over several years needs to be conducted, including economic analysis to determine whether it is worth the effort.