Estimating Final Pumpkin Size During the Growing Season by Joel Holland
Orginally published in the N.E.P.G.A. Newsletter - June, 1993
As the 1992 season progressed, I became interested in the possibility of estimating the final size of my growing pumpkins using the data I had collected over the last two years. During 1990 and 1991 I had kept careful records or the size of all of my best pumpkins in various stages of growth using the "Over the Top + Circumference Method." As many growers know, this is a method for measuring pumpkins and squash which involves taking three measurements with a flexible tape. The first is "Over the Top Long" (O.T.L.). It is taken from the ground at the stem end over the centerline of the pumpkin to the ground at the blossom end. The second is "Over the Top Wide" (O.T.W.). It is taken from the ground at one side of the pumpkin over the highest part of the specimen to the ground at the opposite side. The circumference is taken around the fruit at approximately stem/blossom level in a plane parallel to the ground. These three measurements are totaled and the sum is useful in predicting the weight of individual specimens. (See article by Leonard Stellpflug, W.P.C. News Journal June, 1991 for detailed information on the "Over the Top Method.")
When analyzing the data for my pumpkins grown over the previous two years, I was surprised at how closely their size at a given age compared, when expressed as a percentage of their ultimate harvest size. After 40 days from pollination, although there was considerable variation in the actual size of individual specimens, they were all very close to having reached 77% of their harvest size. After 60 days from pollination, my previous pumpkins were all very close to 91% of their harvest size.
I do not think these figures of 77% at 40 days and 91% at 60 days can in any way be construed as an accurate indication of growth rates for areas other than my own. As my pumpkins are grown in a region of limited daytime heating and cool nights, I believe they grow at a somewhat slower rate but over a longer season when compared to specimens grown in warmer regions. I would suspect that in warmer areas, the growth attained at 40 and 60 days would be a higher percentage of harvest size. Some growers may even achieve full harvest size in around 60 days. I do believe, however, if you keep careful records on the growth of your pumpkins, you can develop over time, a system for estimating the ultimate size of current season specimens, through analyzing your own historical data.
The validity of the estimate will rely on the accuracy of the data, and should become more reliable as more data is recorded over additional seasons. There will always be variations due to weather and individual seed genetics, but I think it is interesting, as well as fun, to learn as much as possible about the growth characteristics of the specimens we raise in our own gardens.
The formula I used when attempting to estimate the eventual size of my 1992 827lb. World Record Pumpkin at 40 and 60 days was as follows:
40 day total (272") is to 77% as
Harvest Total (x) is to 1OO%
Step 1) 100 divided by 77 = 1.2987012
Step 2) 1.2987012 times 272" = 353.25" (estimated harvest total)
As shown, my 40 day calculation produced an estimated harvest size of 353.25". After 96 days the actual harvest size was 360". I was pleased the estimate was within 2% of the actual size. At 60 days the calculations were repeated inserting the 60 day total and the percentage of 91%. The estimated size was again within 2% of the actual harvest size. Next season I intend to start as early as 30 days after pollination to further test the validity of estimating final specimen size through analyzing my own historical data.
Editors Note: For newcomers to the NEPGA, guest writer Joel Holland of
Puyallup Washington was the All-time record holder for Atlantic Giant pumpkins, having grown an 827 pounder in 1992.