Time to grow crops vs. day of year planted, part II

Final Report for FNE12-744

Project Type: Farmer
Funds awarded in 2012: $7,497.00
Projected End Date: 12/31/2012
Region: Northeast
State: New Hampshire
Project Leader:
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Project Information


This is the second year of this project. The purpose of the second year was to look at the repeatability of the first years (2011) results. This project measured the time to harvest for many plantings of 2 varieties of lettuce, one variety of broccoli and one variety of corn, and provides a planning tool for scheduling succession planting of crops. The main variables are seen to be temperature above the plants “base growing temperature”, and the amount of light as the calendar year progresses. The temperature is the largest variable, year to year. The amount of light varies through the season but is repeatable year to year.

As more growers practice winter growing, these issues will become even more pronounced. Winter growing was not be addressed by this project, but the results should be useful. For instance, knowing the effects of time and temperature numerically will allow growers to make more educated (calculated) investments in supplemental heating and lighting or crops in the fall, winter and spring.

Results from 2011 and 2012 seasons and data show that the days to harvest, and the time, temperature and light requirements are:
2011 2012
Broccoli, from Seeding.
2011: 74 to 96 days 34,000 GDDf*HD (40 F base)
2012: 76 to 125 days 38,000 GDDf*HD (40 F base)

Corn, from Seeding.
2011: 78 to 100 days 27,000 GDDf*HD (50F base)
2012: 84 to 100 days(limited good data) 30,000-35,000 GDDf*HD (50F base)

Greenstar Lettuce, from Seeding.
2011: 52 to 83 day 25,000 to 30,000 GDDf*HD (40 F base)
2012: 52 to 83 day 29,000 GDDf*HD (40 F base)

Vulcan Lettuce, about from Seeding.
2011: 53 to 84 day 28,000 GDDf*HD (40 F base)
2012: 47 to 79 day 29,000 GDDf*HD (40 F base)


Blue Ox Farm is a certified Organic Vegetable Farm in Enfield NH with 10-12 acres tilled in 2012. We grow for local markets. We grow about 1 to 1.25 acre each of Lettuce and Broccoli, and about half acre of corn. The remaining is a wide variety of crops. Most of the soils are silt loams with relatively high water tables, new fields are sandier and less wet. The first 2-4 plantings were on the drier fields, the rest were on the wetter silt loams.

Becky Sideman was the technical advisor on the project. Cynthia Walthour did the seeding, most of the tracking of the plants through the seeding and transplanting, with Dave Winters doing most of the lettuce harvest. The corn and Broccoli were harvested by Dave Winters, Dave Gagne, Jeremiah Cobb and Steve Fulton through the season (the same people also did the data recording on the cards). Steve Fulton did some of the tracking and most of the analysis of the data, Steve was also responsible for setting up and placing the thermal probes.

Project Objectives:

Planning a years production of crops that are planted in succession requires experience, plus a bit of guessing what the weather might be during the season. This report presents a methodology to eliminate some of the guessing that is based on historical weather information from a growers area.

Plants need time, light, and heat to grow. Growing Degree Days (GDDf) are a relatively well known method to understand biological processes such as when an insect pest will appear, or when a crop will be mature. Data for crop maturity shows that the GDD for a crop to mature is not constant, but varies through the season. Some, or maybe all, of the variation is due to day length variation.

A proposed means to combine the effects of time, light, and heat are the Growing Degree Day * Hours Daylight (GDDf*HD) .
See the 2011 report for more definition of the basis for this, and plots of harvest forecasts.

The data suggests that the GDD*HD (Growing Degree Days * Day Light Hours) is as follows
• Everest Broccoli, 34,000 to 38,000 GDDf*HD (40 F base), from Seeding.
• Mystique Corn, 27,000 to 32,000 GDDf*HD (50F base), from Seeding
• Greenstar Lettuce, 29,000 GDDf*HD (40 F base), from Seeding.
• Vulcan Lettuce, about 29,000 GDDf*HD (40 F base), from Seeding.


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  • Becky Sideman


Materials and methods:

Experimental methods and procedures in 2012 were the same as in 2011. The Lettuce and Broccoli data loggers were placed in the field on 4-26-2012. Unfortunately the corn data logger, and all the data in it was destroyed during the season when it was in-advertently hit by a rotary cutter.

Analysis in 2012 was performed using the same methodology as 2011, with a few minor differences for the time period where crops were started in a greenhouse, and kept in the (heated) greenhouse for a significant amount of the time between seeding and transplanting. This was all at the start of the season. For lack of a better term I have called this data ‘correction’, but it means trying to capture the time at a higher temperature in the greenhouse. This only effects data at the start of the season, the first 2-5 plantings.
In 2011 there was some ‘correction’ to some of the data. I assumed the greenhouse was at 60 F (the setpoint on the thermostat to the heater.

Mathematically there are two general cases:
#1, Start in GH early in season, transplant from GH (may have short time outside)‘Corrected GDD’ = ‘GDD from Transplant to harvest from thermal data’ + (Tgh-40) * (days from seed to transplant), where Tgh = 60 F for 2011 report, and Tgh = 70 for 2012 reporting
#2, Start outside, transplant outside ‘GDD’ = ‘GDD from Transplant to harvest from thermal data’

In 2012 there was ‘correction’ to some of the data. I now recognize that the greenhouse was at a temperature higher than the thermostat set point, so I now assume a 70 F high temperature for the calculations. The comparisons between the twos years (in this report), use consistent methods, any difference is real, not a difference in data analysis.

We did plant Vulcan Lettuce on a different schedule than in 2011, but the methods were the same.

Practical issues with methods, in 2012

We had no issues with the seeding. We did not seed on the exact dates on the seeding schedule all the time, but we use the actual date seeded, not the planned dates for data analysis.
Transplanting in 2012 was done the same as 2011. The first 2 plantings of corn were transplanted and then covered by row cover. Then they froze. The first plantings of lettuce and broccoli were planted onto Bare ground, same as 2011.

Instrumentation used.
Same data loggers and thermal probes as 2011
Data analysis was done with HOBOWARE version 3.1.2 and Microsoft EXCEL. (same as 2011)

Sensor placement

Soil temperature probes were all placed the same as 2011, though in different places in the field
Calculation of Growing Degree Day (GDD).
Same as 2011 with the exception mentioned earlier this report regarding early season plantings.
There are many definitions of Growing Degree Day (GDD). The general concept is that biological activity (growth for plants) is related to the amount of Time at or above a temperature.
Growing degree day for a single day is:
GDD (Growing Degree Day)= ((Max Temp+Min Temp))/2-(Base temp)
(this is the average temperature for the day, less the base temperature. It is never negative.)
Min temp = minimum air temperature that day
Max temp = Maximum air temperature that day
Base Temp = base temperature, below which no plant growth is presumed to occur.

I used the same software and definitions as was defined in the 2011 report.

Base temperatures used were the same as in 2011.
Calculation of Growing Degree day * Daylight Hours (GDDDH)
Same definition as 2011
This is defined (by me) as GDD for a day, times the day length (in hours). Day length is defined by the length of time between actual dawn, to actual twilight. (NOT civil time, which is 1 hr longer per day).

Research results and discussion:

Broccoli Data for 2012 and comparison to 2011
Broccoli as a whole did not do well in 2012. While we had great broccoli in September 2012, the early broccoli yields were not at all good. This was primarily due to disease and pests (flea beetles) in the fields where the early broccoli was grown. The Fall broccoli was grown in a different field. There was little disease and flea beetles, but many deer, which destroyed the later plantings. Figures 1 and 2 show the time to harvest for Everest Broccoli, as well as harvest date vs seeding date.
Figure 3, 4, 5, and 6 compare Broccoli in 2011 and 2012.
See figures below


Corn data for 2012

Corn also had some challenges. The first two plantings froze end of April in some 25 F weather, the later plantings were plagued by weeds. We had crop later in the season, but could not find the tags defining the different plantings for the weeds. Figure 7, 8and 9 compare the data from 2011 and 2013. Figure 10 shows the limited data from 2012. See ‘Figures for SARE project FNE11-718, Corn, 2012.xls’

Why the difference in growing from 2011 to 2012. MAYBE the weed pressure in 2012 held the plants back?


Greenstar Lettuce for 2012
Most all lettuce grew well in 2012. We did loose 2 plantings of Greenstar due to bad germination (the July 11 and July 20th plantings), and end of the year we lost 2-3 plantings due to cold weather. The Greenstar lettuce was planted on the same schedule as 2011, meaning it was roughly weekly, except for new plantings at the end of the year. Figure 11, 12, 15 and 16 show the data from 2012.
Figures 13 and 14 compare Greenstar in 2011 and 2012. The lettuce has good agreement year to year

See ‘Figures for SARE project FNE11-718, Greenstar, 2012.xls’

Vulcan Lettuce for 2012

Most all lettuce grew well in 2012. We did loose 2 plantings of Vulcan due to bad germination (the July 11 and July 20th plantings), and end of the year we lost the last 5 plantings due to cold weather. The Vulcan lettuce was planted on a very different schedule than 2011, we took the results from 2011 and forecast when plantings SHOULD be planted for harvest on a weekly schedule. Figures 17 and 18 show the data from 2012.
Figures 19, 20, and 21 compare Vulcan in 2011 and 2012.
See ‘Figures for SARE project FNE11-718, Vulcan, 2012.xls’

Research conclusions:

The data suggests that the GDD*HD (Growing Degree Days * Day Light Hours) is as follows

• Everest Broccoli, 34,000 to 38,000 GDDf*HD (40 F base), from Seeding.

• Mystique Corn, 27,000 to 30,000 GDDf*HD (50F base) ), from Seeding

• Greenstar Lettuce, 29,000 GDDf*HD (40 F base), from Seeding.

• Vulcan Lettuce, about 29,000 GDDf*HD (40 F base), from Seeding.

So, this data suggests that if one had a greenhouse with lighting and heat so that Light and Temperature were controlled, And if the Light was on 16 hours per day, and the temperature was a constant 75F, that Vulcan Lettuce should grow from seed to a full head in 50 days (assuming a 40 F base). Similarly, if to save fuel, the greenhouse was at 65F, the same lettuce should take 70 days to grow to full size.

An EXCEL spreadsheet has been created to forecast planting dates from seeding dates

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

Results were published by Becky Sideman for inclusion in the UNH Vegetable newsletter.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

Future Recommendations

Remaining Questions, end of year 2 (2012)
At the time of writing this report, several detailed questions remain. However, most of these are beyond the scope of the proposed project, and all were identified and listed in the 2012 final report.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.