A Soil Study on
Atlantic Giant Pumpkins

by Don Chambers


Soil is the basis and foundation of all plant growth. Focusing on soil preparation for the Giant Pumpkin plant is first in setting the stage for the sport/hobby of Pumpkin growth. A soil study focusing on pumpkins grown over 1200 lbs. and separated into 100 lb. increments up to the most recent World Record Pumpkin is conducted in this study. Balancing soil available uptake to the plants and soil balance is the goal of this study. These results are available here for further study and knowledge regarding soil test results and why we obtain them. These records are available for anyone wanting to do further studies on this subject. It is time to share the results and have others make their own conclusions and hypotheses based on this available information. Thus far it doesn’t appear that a soil test to this extent has been performed on just AGs alone. Sound scientific study is the key to breaking the One-Ton barrier and beyond. The purpose of this study is to discover what soil stats separate record pumpkins from non-record status.

Hypothesis #1:

Potassium is needed in higher quantities and base percent ratio than originally suspected. 3% is often recommended for vegetables but Giant Pumpkins show consistent 8-9% average needed to grow to their potential.

Materials and Methods

A collection of soil test samples were obtained from most record growers over the period of 7 years. The study was conducted by e-mail, snail mail and soil test results completed by top growers. The results were obtained and meticulously charted over the last 7 years. Top questions were also posed re. soil and answered by Top Growers which was included in the study. The numbers available were studied and conclusions made with the assistance of top growers findings through experience and also their comments taken into consideration.

The results and amendments are posted earlier in this volume for consideration. All growers were attempted to be contacted at least three times asking for the results and also posted needing results at least once a year on BP.com general discussion, which is the utmost contact source for Giant Pumpkin growers around the world.

Contribution Stats:

Just pH results submitted- 14 pumpkins/tests
Inability to contact after 3 attempts by e-mail and BP.com -171 pumpkins
No tests done for several years - 4 growers
No soil test available or could not find - 10 growers
No soil test done - 13 growers
Total available complete tests available - 221 pumpkins
Total - 392 pumpkins/tests

Results - Findings of Soil Study

Result: Findings available show that the hypothesis is correct and highly significant. This is not to say that record pumpkins can’t be grown with Potassium variations of base percent but just show that the majority of record pumpkins require more Potassium than originally suspected and very near the 9 % range theorized by the study.

Base Percent Saturation of K%-Mg%-Ca% is averaged and balanced near an easy to remember ratio of 9-20-67 ratio rounded off. (Note that Potassium % is higher than originally suspected, Calcium % is lower than suspected to be needed). These three balance with Nitrogen and it is helpful to keep them balanced, as one goes up, one goes down etc.

Potassium is needed in higher available quantity than other pumpkins and vegetables. I.e. Recommended for vegetables is 3% but these giants average at 8-9% (closer to 9% available Potassium] needed. Ron & Dick Wallace have been on to this and with timing of these applications as mentioned in newsletters.

Ranges show that the AG plant is quite tolerant to large variations of different nutrients/minerals and to low and high fluctuations. The plants do better with balanced soil but not an overabundance just dumped on the patch.

Organic Matter [OM] is averaged out at about 9%. Anything above this not broken down can possibly be linked to Blossom-End Splits [BES], excess ammonium and less available Calcium uptake d/t excess Ammonium nitrogen in competition. Also see writings by Russ Landry “Trip Down Calcium Highway” [Excerpts in the volume under Calcium in Soil Chemistry section]. Note that a consistent average of 10% occurs until the last three World records where OM is 3-7.9%. This means that organic material is broken down sufficiently but a loamy-sandy soil is key. Humates are ready to act and available for growth.

pH a few years ago averaged almost spot on 6.8, updates point to a new pH average of nearly 6.9-7.0. Closer to this pH has shown bigger pumpkins. pH is very important for uptake of what available minerals are possible. The neutral pH seems to be friendly to a balance of what the plant assimilates. Much higher than pH 7 and Zinc is not taken up correctly, lower than 6.8 and certain other nutrients aren’t available.

Nitrogen is best applied by a slower release more organic means such as fish fertilizer or blood meal rather than high percent synthetic means. Timing is very important and recognizing the time frame of N breakdown to time-frame of needs for plant vs. Fruit growth. These organic ferts are best applied about two weeks prior to transplant around a 15 ft. Area of the transplant from back end (transplant area of plot to 15 ft. towards main vine growth and 7½ on either side. A reading of about 30-35 ppm is about average and efficient.

Sulfur has quite the range for growth 0.8-639 ppm. Sulfur helps break down proteins and help + ions of nutrients/minerals to become available. It is underestimated as a need. S is sufficient at 15-25 ppm but better the closer it gets to 50. Pumpkins can tolerate a good bit.

Zinc can be tolerated to at least 74 ppm but 5-10 ppm is sufficient for disease resistance and immunity of the plant. An underestimated mineral.

Manganese is best kept between 25-26 ppm as it is balanced here. Higher or lower can effect pumpkin growth as it competes with other minerals if used at too high of levels. There is a myth that Mn higher than 11 can inhibit growth but this does not prove to be true.

Iron (Fe) is underrated as a mineral and is especially important with Nitrogen at the needed stage of growth. Larry & Gerri Checkon were on target with the Ironite supplement and how iron can aid absorption and assist Nitrogen for early leaf and vine growth. Plants can tolerate quite a range here as well as some other minerals. The range reveals 2.5-281 ppm. It is ideal near 46-47 ppm.

Copper is not needed in large quantity and if it’s at the recommended range , leave it alone. The study shows that Giant pumpkins can tolerate more but is best between 2-2.3 ppm. Boron can be toxic but also is needed to assist Calcium uptake into the plant. Keep it within the recommended range of 1-1.5.

None of the minerals or factors studied show a completely direct positive or negative correlation although some of the most significant factors or correlations have been discussed in this study.


Biases in this study are:

1) That all soil tests were not available, taken or given.

2) Modes were not extrapolated since some pumpkins were grown in the same plots with same values.

3) Spring to Fall testing was conducted and may be subject to change due to weather conditions. Some chemicals such as Nitrogen will leach out of soil with a lot of rain.

4) Amendments added at different times but all growers took samples before amendments were added.

Atlantic Giant Pumpkins is found to tolerate quite a wide range of different mineral values as you can observe by looking at the test results. The largest of the large seem to have more of a balance needed to fare well. The minerals tend to balance each other in the soil. The closer you can get to balancing the recommended ranges the chances are the better you will grow. Balance here means to use some type of guide rather than simply throw large quantities of ferts and amendments all over the patch. This study will hopefully provide a substantial guide to growing the next World Record.

The present study is just dealing with amounts and percentages. Soil types and all other recommendations need to be taken into serious account as well. Soil is just one of the most important foundations of pumpkin growing. Be careful not to just apply an arbitrary amount of amendment but to always follow recommendations to change any soil values. Soil manipulation may take more than one season to fully correct. Hopefully others can make needed deductions and/or continue with this study. Please feel free to use the information in this study in a scientific manner for further study. Other studies may also find this information to be an important link to that other particular study. The information above is freely available to assist or complement in any of those particular present or future studies and the Commonwealth of all growers.

I give permission to use these graphs for further study with credits to Don Chambers – Giant Pumpkin Soil Study