Spinach Cultivar Trial in a 3-Season Haygrove High Tunnel

Expanding Spinach Market

Annual spinach consumption increased in the US from an estimated 0.3 lb/capita in 1970 to 0.9 in 1998 (Heacox, 2000) and 2.5 lb/capita in 2003 (Boriss and Kreith, 2006). The increase is mostly due to consumption of fresh “baby” leaf spinach (Boriss and Kreith, 2003; Heacox, 2000). Fresh, clean, salad ready spinach brings premium revenues (Heacox, 2000). Growers using high tunnels are able to supply some of the market demand for spinach. A survey of growers in the central Great Plains found that leafy greens are a favorite crop for high tunnel vegetable production (Knewtson, 2008).

Kansas growers are interested in recommended spinach cultivars for spring or autumn crops. Spinach production is mainly concentrated in the southwest US, California, Texas and Arkansas. Because of this seed cultivar selections are often based on production in those climatic zones. It was our intention to grow and record observations for spinach (Spinacia oleracea L.) cultivars planted in the autumn in northeast Kansas. Several seed companies provided seed that they either currently market, or are considering for market, in our region.

Materials and methods

Twenty-six spinach cultivars were planted in autumn 2005 in a 3-season Haygrove high tunnel and in adjacent field plots at the Kansas State University Horticulture Research and Extension Center, Olathe [latitude 38 53’N, elevation 1056 ft (322m)]. The high tunnel cover was removed for the winter on 10 December 2005 and replaced on 15 April 2006. From December through February the spinach was protected under a sheet of spun-bonded polypropylene fabric (Typar 580 floating row cover; Ken-Bar, Peabody, Mass.) held in place with sand bags. The spinach grew slowly during the cold winter with little freeze damage. Spinach was harvested twice, once in the autumn and once in the spring.

Six raised beds of 96ft length and approximately 2 ft width were prepared in the north half of one bay of our 4-bay, half-acre Haygrove high tunnel. The distance between beds was 3 ft. Cultivars were randomized within pairs of beds, giving three replicates.

Irrigation was from overhead sprinklers. Raised seedbeds were prepared with a wheel hoe equipped with a furrower attachment. Bradfield Organic fertilizer 3-1-5 (Bradfield Industries, Springfield, Mo.) was applied to supply nitrogen at a rate of 136lb/acre on 2 September 2005. Plots were about 5 x 2 ft, with about six inches of buffer zone between plots within rows. We seeded the beds with two passes of a 4-row pinpoint seeder giving eight rows of spinach per bed. The seeder can deliver a seed per inch of row.

Germination failure

Beds were seeded the first week of September. Germination was very poor. The field plots were a total failure. Under the high tunnel fewer than twenty plants survived in the majority of plots. Only the cultivars Hellcat and Highpack had 50-75 plants in one plot each. The weather was hot and this may have been a factor in the poor germination hat followed. We had used a roller to press the seeds into the bed. It is possible that some of the seed was pushed too deep. We determined that with the second planting we would sprinkler irrigate for short periods throughout the day to cool the soil and not use the roller.

Germination

Spinach was seeded a second time under the high tunnel on 27 September 2005. Germination was much improved, but not excellent in any plot. Based on observation,germination within a plot of less than 50 seedlings was rated as poor, 50 to 70 was fair,70 to 100 was moderate, and 100 to 125 was rated as a good germination. Cultivar PVO172 had the best overall germination with an average of 104 plants per plot. Interceptor, PVO170, Space, Lombardia, Bloomsdale, Emilia, and Hellcat cultivars had moderate germination (Table 1).

Table 1. Germination and seed source of spinach seeded on 27 September.

Besides the effect on harvest yield, germination rate was also important because of the relationship to weed encroachment. Plots with poor spinach germination had more weeds later. Henbit (Lamium amplexicaule L.) was the main weed. Our only method of weed control was pulling by hand. Denser seeding would reduce weed pressure. This could be done by overlapping an increased number of passes with a wheel planter, using a closer spaced planter, or broadcasting seed. The cost in extra seed would likely be worth the reduced time spent pulling weeds.

Leaf texture and growth habit

We harvested the spinach as “baby spinach”. The ideal harvest size and shape is that of a soupspoon. All cultivars conformed to the spoon shape. Leaf texture is described as smooth or savoy (rippled). Some markets have a preference for smooth leaves. Growth habit and leaf texture are noted in Table 2.

Upright petiole growth allows easier harvest, especially if using a leafy greens harvester (consists of a serrated blade on a frame with a bag on the back of the frame to hold the cut greens). Spinach with prostrate growth was harvested by holding bunches in the hand and cutting with a knife. Plots with upright growth were harvested with a leafy greens harvester from Johnny’s Selected Seeds (Winslow, Maine). It is possible that some cultivars that seemed to have more prostrate growth habit could be forced to have upright petioles if more densely seeded.

Table 2. Leaf texture and growth habit of baby spinach planted 27 September 2005 under a high tunnel at Olathe, Kansas.

Spinach was harvested in the autumn on 10 November 2005, and a second time on 11 March 2008. Average yield per 10 ft2 plot is presented for each cultivar in Table 3. The following cultivars were among the ten with highest yield in both harvests: Interceptor, Highpack, Lombardia, Olympia, PVO170, and Tigercat. However, it should be noted that the cultivar with the highest combined yield, Interceptor, had a statistically significantly higher yield than only Spinner, Samish, C2-606, C2-605 and Tyee.

Table 3. Harvest yield of spinach planted on 27 September 2005 under a high tunnel at Olathe, Kansas. Yield is average of three replicated plots.

The second harvest was of greater mass, but the leaf size not much larger than the first harvest. The plantlets seemed to have put on more leaves.

Spring bolting

After the second harvest, on 11 March, the weed population took over. We were not able to devote the time it would have required to hand pull all of the spring weeds. We continued to water the spinach and let it grow long enough to observe how the cultivars responded to warm weather.

On 2 May 2006, observations of spinach bolting were recorded (Table 4). The least objectionable warm weather effect was petiole lengthening. This might make harvest easier and did not detract from the leaf form. At the time of evaluation, some cultivars had developed elongated internodes that are typical of bolting, but had not yet flowered. Some cultivars had developed flowers or gone to seed. Leaves on the cultivar Springer elongated and became arrow shaped. Spinach cultivars that had the best appearance and least bolting effects in warm weather were: Blackhawk, C1-601, C2-606, Interceptor, PVO170, PVO172, Space and Umbria.

Table 4. Spring bolting of spinach as observed on 2 May 2006. Spinach was planted on 27 September 2005 and over wintered in a high tunnel. (n = no bolting effects, e = elongated internodes, p = petioles long, f = flowers, s = seed formation)

Research Continuation

Information presented in this report such as germination, leaf appearance and spring bolting may be of current interest for growers in our climatic zone [Plant hardiness zone 5 (USDA, 1990)]. Harvest yield data will be of more value when added to additional years of cultivar trials. Cultivar trial data are more reliable when results are collected over a few years. Performance of autumn planted spinach may vary from year to year depending on weather (cloud cover, temperature, and early and late frost).

Literature Cited

Boriss, H. and M. Kreith. 2006. Commodity profile: spinach. Agricultural Issues Center, Univ. of California. created Feb 2006. Verified 11 March 2010. http://aic.ucdavis.edu/profiles/Spinach-2006.pdf

Heacox, L. 2000. A new spin on spinach. American Vegetable Grower 48(5):38-39.

Knewtson, S.J.B. 2008. Studies in vegetable and high tunnel production on the Central Great Plains. PhD Dissertation, Kansas State Univ., Manhattan. The dissertation is number AAT3320234 and posted on the Web as:
http://krex.k-state.edu/dspace/bitstream/2097/926/1/SharonKnewston2008.pdf

USDA, 1990. USDA Misc. Publ. 1475. Posted online by the United States National Arboretum Feb 2004. Verified 11 March 2010. http://usna.usda.gov/Hardzone/ushzmap.html