Do you want to know the secret giant pumpkin fertilizer program to grow a 1,000+ pound pumpkin? The answer: there really are no secrets. There is a lot of available good science available however that gives a grower some guidelines to growing their biggest pumpkin ever. But the truth be told, this is an evolving science that continues to get refined with time and more study, because no company funds big studies on giant pumpkins.
So to answer the most asked question when it comes to fertilizing, "What is the best pumpkin fertilizer?" The simple answer is that it is the one the plant needs at the time. Most growers that grow a 1,000 pound pumpkin get soil tests in the spring/fall or both. Some will also get tissue tests done prior to pollination on the plant to see what it is lacking. Those tests and the recommendations that come with them are a guide to the grower on what to add. But they don't give you much in the way of direction for when to add. Because of this I created my fertilization guide in 2015 that I've updated over the years:
That guide gives you the when, but not so much on how much to add. The soil test recommendations will kind of give you that. But only one lab that I know of has ever done any studies on how much a giant pumpkin needs. Western Labs did that I believe in 2008 and it was a pretty well done study utilizing top growers. The recommendations from it can be found here:
I saw Jon Taberna do a presentation of the results of his study and a couple of things that stood out to me from that presentation is Jon's amazement with how the Atlantic Giant Pumpkin plant can adjust and take up what it needs on demand more so than most other crop type plants. Also, how much demand for potassium a giant pumpkin requires.
The most recent larger scale study on Atlantic Giant pumpkin plants was done by Don Chambers in his Giant Pumpkin Soil Study, which I believe concluded last year. Charts below are from his study:
From the study of 221 pumpkins this was the average of nutrients in the soil for plants the produced 1,200+ pound pumpkins:
So, keeping in mind that many soil testing labs haven't done recommendations for amendments for giant pumpkins, the recommended amounts of amendments might be too low based on what this study has found. Those recommendations are based on standard crops, not 1,200+ pound pumpkins.
Also, another thing to keep in mind. Soil type matters. More sandy soil will leach nitrogen and some micro nutrients much faster than others, so sometimes timing of when amendments are to be added and how much will need to be adjusted based on that. Also, the amount of organic matter affects timing. If you have high OM, as that soil warms up during the season, it is going to release ammonia and other nutrients into the soil. Timing and balance are keys in growing a giant pumpkin.
One other thing to remember when it comes to giant pumpkin plants. The soil may be full of nutrients, but what is available to the plant is just the small area around the root hairs. If demand for example is high for potassium during rapid pumpkin growth, then the plant can get deficient, event though the soil may be a too high in potassium. So that is why I recommend spoon feeding during the season small amounts at regular intervals.
Growing a giant pumpkin is a wonderfully complicated process, but by not doing too much or two little you can optimize growth and achieve a personal best giant pumpkin in 2021.