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Empire State Fruit and Vegetable Expo Report

Plant Populations and Spacing: How Important Are They?

The Tomato Magazine
June 2006

How important are pepper plant population per acre and plant spacing on insect and disease incidence, effectiveness of pesticide applications and yield?

Mark A Bennett, a professor with the Department of Horticulture and Crop Science, Ohio State University (OSU), reviewed recent research shedding light on the question during the Empire State Fruit & Vegetable Expo in Syracuse, N.Y. The tomato, pepper and eggplant session took place Feb. 15 at the Oncenter Convention Center.

Bennett’s report was based on research done in collaboration with Celeste Welty, Sally Miller, Richard Derksen, Salvador Vitanza and Elaine Grassbaugh, all of OSU.

While there has been little research done recently in the Great Lakes region to determine the most economically advantageous plant populations for currently used pepper cultivars, Bennett summarized the following key research points from other states:

Batal and Smittle (1981 – Georgia): These researchers compared 27,000, 40,000 and 60,000 bell pepper plants/ha (~11,250, 16,670 and 25,000 plants/acre). The biggest yield increase occurred when populations were increased to 16,670 plants/A, but yields decreased when plant populations were increased to 25,000 plants/A.

Locascio and Stall (1994-Florida): The two compared one, two and three rows on two bed widths (48 and 72 inches wide) and in-row plant space of nine and 12 inches between plants. Highest yields were from single row orientation and wider in-row spacing. Best yields were achieved with fewer plants/row. The number of rows per bed and the overall raised bed width had more influence on yield than in-row spacing. Bell pepper fruit yields per plant were also greater with the wider spaced in-row spacing. Two rows per bed versus three rows resulted in non-significant yield differences probably due to better light use. This is also confirmed with the three-row orientation where plants in the middle row produced the lowest yields compared to the outside rows on the same raised bed.

Stoffella and Bryan (1988-Florida): The team compared populations of plug-mix seeded bell peppers planted at 21,500 to 258,000 plants/ha (9,000 to 107,000 plants/A). Variable in-row spacings of 13, 25, 38 and 50 cm (5-20 inches) were compared. As plant population increased, shoot:root rations generally declined. This suggests that the decrease in shoot weight was greater than the decrease in root weight. At higher plant populations, the larger root system to shoot mass is perhaps required to improve water and nutrient absorption since root competition between plants is higher. Marketable pepper fruit number and weight generally decreased per plant and increased per hectare as plant populations increased.

Decoteau and Graham (1994-South Carolina): The researchers compared plant spacing of cayenne pepper for mechanical harvesting. Plants were arranged in single and double rows on raised beds at a plant spacing of 15 to 60 cm (6 to 24 inches) apart. As spacing increased from 15 to 60 cm, the total fruit weight and number per plant increased linearly. As in-row spacing increased, total fruit production per hectare decreased. In-row spacing effected plant growth and fruit production. Closer plant spacing generally produced more dry weight per plant, taller plants, thinner stem diameters and fewer fruit set per plant but more plants per hectare. Plants in double rows produced more fruit on the top of the plants compared to single rows where more fruit developed lower on the plant. The double row orientation may increase the probability of harvesting more fruit mechanically.

Motsenbocker, et al., (1997 – Louisiana): The two evaluated the effect of in-row spacing on two cultivars of machine-harvested jalapeno peppers. Plants were spaced four, eight, 12 and 16 inches apart in-row. Yields, in general, increased with reduced plant in-row spacing. This effect, however, may be cultivar dependent. One cultivar, ‘Jalapeno-M,’ had highest yields with four inches between plants vs. cultivar ‘TAM Mild-1’ that obtained the highest yields with a 12-inch in-row spacing, but was not significantly different from the four- or eight-inch spacing. Closer in-row spacing may provide increased marketable yield of jalapeno peppers. Both cultivars had more plant lodging with increased in-row spacings.

As for the Ohio situation, commercial practices vary from staggered twin rows on raised beds with bed center five feet apart to single rows, three to four feet apart, without raised beds, Bennett told the group. In-row spacing ranges from 12 to 18 inches. Total populations range from 8,000 to 25,000 plants per acre.

“Hybrid pepper seed is expensive, particularly for processing peppers where profitability margins are relatively slim,” the speaker said. “Growers are seeking information to determine if plant populations can be adjusted to reduce hybrid seed costs without significantly reducing yield, particularly if this is associated with better insect and disease control and thus fewer culls.”

Plant spacing affects the microclimate in the plant canopy that, in turn, may influence the incidence and severity of a number of diseases as well as the attractiveness for egg laying by European corn borer, Bennett said. No data are available on the effect of plant density on the epidemiology of anthracnose (C. acutatum) on peppers. However, plant spacing and microclimate are known to affect the severity of anthracnose disease on other crops (Boudreau and Madden 1995; Koech and Whitbread 2000).
In a 2005 field study near Fremont, Ohio, single-row pepper plots with 10,500 to 14,000 plants/A equivalent provided the best pepper yields and quality in general, Bennett said.

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